Resistor Sizes Vary Greatly? - Page 1
Forum section: electronics / beginners

author: Wil_Bloodworth
author_rank: Regular Contributor
timestamp: November 15, 2023, 12:57:28 am
content: Hello!I purchased some components from DigiKey. Some are surprisingly small versus others that have the same power rating; 1W in this case.How can the resistors in the middle, which are clearly listed as 1W resistors on the bag, handle the same amount of power as the resistors on the left and the right?Is it just because these larger resistors have a much higher resistance or am I missing something else?Thank you,- Wil

author: wraper
author_rank: Unknown
timestamp: November 15, 2023, 01:13:03 am
content: Small resistor is of compact type that withstands very high temperature to allow high power dissipation at small size. As of large ones I dunno why you bought them at all. They are high voltage resistors rated for 10kV.

author: Wil_Bloodworth
author_rank: Regular Contributor
timestamp: November 15, 2023, 01:55:56 am
content: Yeah, I didn't know what I was ordering.- Wil

author: Zero999
author_rank: Super Contributor
timestamp: November 15, 2023, 12:02:17 pm
content: More specifically, the middle resistor is made from a ceramic material, which is why it can withstand high temperatures.Note that, the middle resistor is probably rated to a much higher temperature, than most PCB materials and indeed other components. If it's mounted too close to the PCB, or an electrolytic capacitor, it will burn them. Either de-rate it, or use long leads and ceramic stand-offs to ensure it's a safe distance from the PCB and other components, so it doens't desolder iself, or burn anything.

author: Wil_Bloodworth
author_rank: Regular Contributor
timestamp: November 15, 2023, 03:53:47 pm
content: Thanks. I don't work with anything that has a PCB in it so I don't think that will be a problem (for now).- Wil

author: Siwastaja
author_rank: Super Contributor
timestamp: November 15, 2023, 05:13:53 pm
content: This discussion reappears every now and then, and some people have hard time believing the differences are real. But yeah, basically dissipating same amount of heat in smaller area must mean the surface temperature is higher. This must mean that the materials used by the manufacturer must handle this higher temperature.There are other factors too, for example surface emissivitycouldbe different, heat generation could be more even throughout the whole resistor so less hotspotting and thus better use of the available size without exceeding the material limit somewhere, but it's hard to say how significant these factors are in resistor design.

author: TimFox
author_rank: Super Contributor
timestamp: November 15, 2023, 05:56:52 pm
content: In my youth (say, before 1970) in the US, most general purpose resistors were Allen-Bradley carbon composition (or competitors), and we all learned the package sizes for 1/4, 1/2, 1, and 2 W (and the rare 1/8 W).Those resistors are now rare, but lead-bending gauges have kept the package dimensions as choices.As discussed above, there are many technical details in the manufacturer's datasheets to guide the designer's choice of actual power rating for his circuit.An interesting example: the military rating on an RN65 metal-film resistor (0.562 inch body length) is 1/2 W.The commercially-rated similar Vishay resistor CMF65 (same body size) is 1 W, but the datasheet has cautions about resistance changes caused by high power operation.The older A-B 1 W carbon resistor is also 0.562 inch body length.When in doubt, unless you arereallycramped for space, derating the power on a resistor is a good idea.

author: radiolistener
author_rank: Super Contributor
timestamp: November 15, 2023, 06:18:16 pm
content: it's hard to understand actual size from photo, but it looks that small one is 0.125 W.0.25 W resistors a little bit bolder.Here is comparison of size for different power:

author: Wil_Bloodworth
author_rank: Regular Contributor
timestamp: November 15, 2023, 06:20:30 pm
content: That is the point of the post... that small resistor is actually a 1W resistor (or at least it is listed as such) just like the two larger ones.- Wil

author: radiolistener
author_rank: Super Contributor
timestamp: November 15, 2023, 06:28:13 pm
content: Quote from: Wil_Bloodworth on November 15, 2023, 06:20:30 pmthis is Chinese 1 W1 W resistor cannot be the same size as 0.125 W, just because it dissipate 1 W power and needs large enough surface area to radiate it, so it cannot be small. If it has not enough surface area to dissipate heat it will be overheated, melted or damage other components around it.

author: Wil_Bloodworth
author_rank: Regular Contributor
timestamp: November 15, 2023, 06:39:26 pm
content: These resistors came from, as you can see, DigiKey so they are "reputable"... and they are saying they are 1W resistors... which is the entire point of me posting here.Your quote, "1 W resistor cannot be the same size as 0.125 W"... is the entire point of my question.- Wil

author: Siwastaja
author_rank: Super Contributor
timestamp: November 15, 2023, 06:39:42 pm
content: As always, just ignore radiolistener. He's probably on everybody's ignore list here.Normal design cautions apply, as with all datasheet ratings; gotta understand what the datasheet parameters exactly mean. Thermal design is non-trivial and that applies even to older resistors with smaller power density. The better understanding you have, the closer you can calculate; you can always add fudge factors (i.e. derating) to hide uncertainties (parameters you don't know, lack of your understanding, incapability of purchasing expensive thermal modelling software etc.)Heat damage done to surroundings is a very real issue even with larger resistors, it can't be ignored, and small components of course invite you to miniaturize your design, too, increasing the power density of the whole, which is the risky part, not using the small resistor itself.

author: wraper
author_rank: Unknown
timestamp: November 15, 2023, 07:17:05 pm
content: Quote from: radiolistener on November 15, 2023, 06:18:16 pmFYI Soviet resistors came in different sizes for the same power rating.

author: floobydust
author_rank: Super Contributor
timestamp: November 15, 2023, 07:29:05 pm
content: It's getting worse - there are many "mini" or "supermini" resistors being offered by resistor manufacturers nowadays that are typically 1/2 to 1/4 the size of what I am used to.Last night I went to buy "1/4W" through-hole resistors for breadboarding, the 6-7mm wide parts I've used for decades.I found "Metal Film Resistors - Through Hole .4watt 1% 1/8watt body size"That is the 1/8W body size MBA0204 rated "standard mode" (0.25W) part max. is 125°C, "power mode" (0.4W) is 155°C.Going upsize to theMBB0207"standard mode" (0.4W) part max. is 125°C, "power mode" (0.6W) is 155°C. It's the size I'm expecting. At 1/4W it's temp rise is 35°C and old school would run it at 1/8W for temp rise 15°C.Part of the new game and what has changed is:-Higher temp materials (but who cares, nobody runs them that hot anyway) giving inflated power dissipation numbers that must compete with other spec stretchers.-Thinner/thicker leads, and copper verses steel construction can give misleading graphs-Specs that are for forced-air cooling use, in a fan-cooled (i.e. power supply) enclosureSo my old "1/4W" parts are rated 0.6W nowadays.Most manufacturers are not giving thermal resistance or temperature rise data for their parts.I commend Vishay for doing this, and curse Yageo for their game of omitting the spec and claiming a 1/4W sized part is "1W" FFS.I did get a response from Vishay forthis threadabout the test jig used for the temp rise test. They (i.e. "0.4W") are the absolute max surface temperature (say 155°C) in 70°C ambient in the jig, 56 day run?. But I did not get it all figured out yet because many tests/specs are "common knowledge" in the resistor industry but never taught, to withstand the flames from people.Dave could do a better investigation to help with the traps in choosing resistors.SMT resistors are other whole set of traps, I just read how 0603's have a lower thermal resistance than 0805's due to their aspect ratio. Who'd have thought?

author: coppice
author_rank: Super Contributor
timestamp: November 15, 2023, 07:39:49 pm
content: Quote from: wraper on November 15, 2023, 01:13:03 amWell you need about 2kV to get 1W out of a 3.9M resistor.

author: wraper
author_rank: Unknown
timestamp: November 15, 2023, 07:50:47 pm
content: Quote from: coppice on November 15, 2023, 07:39:49 pm10KV is still a pulse voltage rating even if RMS voltage is limited by resistance. Any resistor series have max voltage rating even if it's actually must be lower for particular resistance to be within max heat dissipation.

author: Gyro
author_rank: Super Contributor
timestamp: November 15, 2023, 09:24:31 pm
content: Call me cynical, but that middle resistor looks like a bog standard 1/4W 5% carbon film resistor that DigiKey have screwed up the data entry on.

author: wraper
author_rank: Unknown
timestamp: November 15, 2023, 09:30:24 pm
content: Quote from: Gyro on November 15, 2023, 09:24:31 pmIt neither looks 1/4W, nor carbon film. Also if you actually check the datasheet, yes it's this small.

author: radiolistener
author_rank: Super Contributor
timestamp: November 15, 2023, 10:43:14 pm
content: Quote from: Wil_Bloodworth on November 15, 2023, 06:39:26 pmTwo of them are VISHAY, yes this is reputable.But the rest one which we're talking about is marked as "Manufacturer: YAGEO"Are you sure that this is reputable manufacturer?

author: coppice
author_rank: Super Contributor
timestamp: November 15, 2023, 11:00:30 pm
content: Quote from: radiolistener on November 15, 2023, 10:43:14 pmYAGEO are the third largest passives maker in the world.

author: wraper
author_rank: Unknown
timestamp: November 15, 2023, 11:07:50 pm
content: Quote from: radiolistener on November 15, 2023, 10:43:14 pmI'm pretty sure that Yageo is the largest passive component manufacturer in the world.

author: wraper
author_rank: Unknown
timestamp: November 15, 2023, 11:13:01 pm
content: Quote from: coppice on November 15, 2023, 11:00:30 pmI guess you took it from Wikipedia. From what I've seen they are third in MLCC and inductors, first in resistors and tantalum capacitors, quite large at electrolytic and some other components. Overall at least by a total number of components produced should first too.

author: coppice
author_rank: Super Contributor
timestamp: November 15, 2023, 11:44:35 pm
content: Quote from: wraper on November 15, 2023, 11:13:01 pmYeah, I knew they were huge, but I got that figure of third place from Wikipedia. 10 years ago it looked like Vishay would completely dominate passives, and simple semiconductors like small diodes. Now its looking like, through internal growth and acquisitions like KEMET, YAGEO is king.

author: floobydust
author_rank: Super Contributor
timestamp: November 16, 2023, 12:49:37 am
content: Yageo should be called scam-eo. The only reason they are selling well is noobs believing their fake specs - they don't give thermal resistance. When you withhold specs, same thing as lying.OP'sFMP seriesa usually 6.3mm 1/4w sized part- is rated 1W?! yet the usual 155°C max. rating.Anyone care to explain how they get the 1W I'm all ears. TheMFR-25same size but 1/4W rated P70.It's total bullshit, where is the magical unicorn cooling fan?

author: wraper
author_rank: Unknown
timestamp: November 16, 2023, 01:07:23 am
content: As I see it, it's ambient temperature spec, not actual resistor temperature.

author: floobydust
author_rank: Super Contributor
timestamp: November 16, 2023, 01:31:51 am
content: Which temp am I misunderstanding? Yageo hides important details I think.Vishay's similar part (1/4W body size yet rated 1W like the Yageo FMP100)PR01includes good data but still a little smoky."Applied maximum film temperature, θFmax.: 250°C" but derate graph ends at 200°C.Looks like you have to have it raised above the PC board 15 or 20mm? that hot degrades the solder.Cu or FeCu lead options, Cu does run a bit cooler. Thermal resistance 135K/W.

author: Zero999
author_rank: Super Contributor
timestamp: November 16, 2023, 08:28:19 am
content: Quote from: Gyro on November 15, 2023, 09:24:31 pmIt's difficult to tell from the picture, but it appears to have a matt finish, which means it most likely has a ceramic case. If it were an ordinary carbon film resistor, it would have a more shiny finish, indicative of an epoxy laquer.

author: mikerj
author_rank: Super Contributor
timestamp: November 16, 2023, 10:19:06 am
content: Quote from: floobydust on November 16, 2023, 12:49:37 amPower dissipating devices have both maximum power and maximum temperature limits. Depending on the application you typically hit one of these limits before the other and it's up to you to as the designer to ensure neither limit is exceeded. Even without forced air cooling, the power dissipation limit of a resistor will be highly dependant on it's environment and mounting, something with lots of space for convection and lots of PCB area to dissipate heat is going to be able to work at a higher power than a resistor packed into a tight space with other components close by.There is no magic here, just a misunderstanding of device specs.

author: Gyro
author_rank: Super Contributor
timestamp: November 16, 2023, 10:21:51 am
content: Quote from: Zero999 on November 16, 2023, 08:28:19 amYes you're right. Now I look closer it does appear to be a matt cement finish. I still wonder if it's actually worth having a 1W body that small though. Unless the rating is only used for intermittent dissipation peaks, it's going to cause greater thermal wear and tear on the FR4 substrate and solder pads, or the hassle of standing it off the board. Also the need to distance other thermally sensitive components like electrolytics will make it's 'effective' [Ed:body sizefootprint] larger than its physical one.

author: Siwastaja
author_rank: Super Contributor
timestamp: November 16, 2023, 11:11:39 am
content: It's interesting to think that there are a few people who think world's largest resistor manufacturer publishes deliberately wrong data and scams their customers, while their actual customers, who buy these parts inbillions, have nothing bad to say about the parts, nor any difficulty designing them in.Think about it, and it's actually pretty close to flat earth tin foil stuff.

author: coppice
author_rank: Super Contributor
timestamp: November 16, 2023, 12:53:40 pm
content: Quote from: floobydust on November 16, 2023, 01:31:51 amEveryone fails to document important details in resistor specs. A huge number of resistors are carrying a pulsed current these days. Just how big can that pulsed current be before you are obeying the overall, say, 1W rating, but causing such intense momentary heating that bad things will happen? I never see that properly defined.

author: Siwastaja
author_rank: Super Contributor
timestamp: November 16, 2023, 01:23:41 pm
content: Quote from: coppice on November 16, 2023, 12:53:40 pmNever? For example, that very resistor posted by OP, see datasheet pages 5-6:https://www.yageo.com/upload/media/product/productsearch/datasheet/lr/YAGEO%20FMP_datasheet_2023v4.pdfOr do you mean this is somehow improper, if yes, what's wrong with it?

author: coppice
author_rank: Super Contributor
timestamp: November 16, 2023, 01:27:31 pm
content: Quote from: Siwastaja on November 16, 2023, 01:23:41 pmI just looked through the data sheet. That one does seem to properly address the concerns of a designer of modern systems. Well done YAGEO.

author: Zero999
author_rank: Super Contributor
timestamp: November 16, 2023, 02:06:06 pm
content: Quote from: Gyro on November 16, 2023, 10:21:51 amWho said anything about FR4? If the resistor is on a ceramic PCB, next to other high temperature rated components it will be fine.

author: Siwastaja
author_rank: Super Contributor
timestamp: November 16, 2023, 03:58:00 pm
content: Quote from: Zero999 on November 16, 2023, 02:06:06 pmYeah, or more commonly, even FR4 comes in different temperature grades, you can easily place the resistor further away from the board surface, you can add cutouts for cooling, or the circuit runs at low enough duty cycle that FR4 does not heat up too far.The first thing transitioning from hobbyist to professional is to stop assuming things and start learning, calculating, modelling. We are not paid for nothing, we are paid for our expertise. $1000 worth of work can go into a design around a $0.05 resistor, that's completely normal.

author: Siwastaja
author_rank: Super Contributor
timestamp: November 16, 2023, 04:00:13 pm
content: Quote from: coppice on November 16, 2023, 01:27:31 pmI rarely have hard time finding such basic information, maybe try looking at the datasheet instead of assuming that it'sneverthere?That being said, omission of important data is not uncommon, and not limited to resistors. Just a decade ago, it was quite normal to omit DC bias characterstics of MLCC capacitors even though it's a key parameter; people had to make assumptions (often wrong) or expensive testing. This is much better now, too.

author: Siwastaja
author_rank: Super Contributor
timestamp: November 16, 2023, 04:04:32 pm
content: Also one wrong assumption seems that higher surface temperature of resistor means higher temperature for the surrounding components. This is only the case if you utilize the smaller size of the resistor to fullest extent possible and squeeze everything tightly together "because you can". On the other hand, if you leave the same amount of room you would use for a larger resistor, then the smaller resistor enables you to place it, within that free space, further away from some heat-sensitive component (e.g., electrolytic capacitor); with a larger resistor, you wouldn't have that luxury, it has to be placed where it fits.

author: coppice
author_rank: Super Contributor
timestamp: November 16, 2023, 04:06:47 pm
content: Quote from: Siwastaja on November 16, 2023, 04:04:32 pmDo you know its standard practice in power products to put a large wet electrolytic next to the highest consuming resistor or transistor in the whole product?

author: Gyro
author_rank: Super Contributor
timestamp: November 16, 2023, 04:24:40 pm
content: Quote from: Zero999 on November 16, 2023, 02:06:06 pmOh please, that's a rather tenuous use case don't you think? Higher cost ceramic substrates are used for specific purposes and normally use SMDs and /or deposited resistors, they're not usually drilled for the benefit of some random through hole resistor. I'm sure lots of us have seen browned areas on, and the occasional detached pad, on boards due to a hot running component. It's usually the first place to look when tackling a fault.

author: Siwastaja
author_rank: Super Contributor
timestamp: November 16, 2023, 04:46:53 pm
content: Quote from: coppice on November 16, 2023, 04:06:47 pmI know it's a tongue-in-cheek comment, but yeah, confirmation bias amplifies this perception - we of course see those failed products where the hottest resistor or transistor is next to the electrolytic capacitor, maybe one which is already stressed close or beyond ripple current limits, - and then 99 out of 100 products that donotdo this go unnoticed!But sometimes this placement is partially unavoidable, after all the very purpose of a capacitor is to offer low-impedance power supply, in particular low-inductance, which requires minimization of distance, especially to a switching transistor. On the other hand, just moving it a fewmillimeterscould be enough to cut the destructive heating. And this is exactly where smaller power resistors help, even if they have higher surface temperature; you have better control where that heat is generated.

author: tggzzz
author_rank: Super Contributor
timestamp: November 16, 2023, 04:53:13 pm
content: Quote from: coppice on November 16, 2023, 12:53:40 pmThe max pulse power vs time rating is sometimes documented.I like to point out to people that my maximum heart rate is anywhere from 220bpm to <1µbpm, depending on the averaging period chosen.

author: schmitt trigger
author_rank: Super Contributor
timestamp: November 16, 2023, 05:01:30 pm
content: Not only that, but many times is less expensive to have four 1/2 W resistors replacing a 2 W resistor.

author: Wil_Bloodworth
author_rank: Regular Contributor
timestamp: November 16, 2023, 05:03:55 pm
content: Why would you want to make that huge mess (with 4 resistors instead of one) for saving a few pennies?- Wil

author: Gyro
author_rank: Super Contributor
timestamp: November 16, 2023, 05:13:25 pm
content: A few pennies saving in BOM cost is huge in a high volume product.

author: Wil_Bloodworth
author_rank: Regular Contributor
timestamp: November 16, 2023, 05:20:19 pm
content: And I would venture to say that ZERO people on this forum are doing anything in volume! Let's not kid ourselves and be real for a minute!- Wil

author: Gyro
author_rank: Super Contributor
timestamp: November 16, 2023, 05:22:37 pm
content: Hey, I've had consumer products in production that shipped 60k units/month. There are a lot of professionals on here. $0.10 saving adds up to a lot when you multiply by all the mark-ups before the customer gets his hands on it!

author: coppice
author_rank: Super Contributor
timestamp: November 16, 2023, 05:33:45 pm
content: Quote from: Wil_Bloodworth on November 16, 2023, 05:20:19 pmFor quite a few of us run rates below a million a year are considered low volume.

author: Siwastaja
author_rank: Super Contributor
timestamp: November 16, 2023, 05:34:05 pm
content: Quote from: Wil_Bloodworth on November 16, 2023, 05:03:55 pmWhy do you think it's a "mess"? There is some elegance in using larger number of parts, when possible; that way, heat is spread over a larger area. Resistors are very good candidates for both series and parallel connections because they share voltage/current well. Sometimes you also can reuse a part which already exists in BOM. But of course it isn't automagically always the right solution, rarely such thing exist in electronic design.Quote from: Wil_Bloodworth on November 16, 2023, 05:20:19 pmWhy would you think so? While hobbyists are well regarded here, this also is the #1 English language professional electronic design forum on the planet. Every professional I have worked with at leastknowsthis place even if they do not post (or admit posting) themselves. I'm 100% certain there are a few contributors here who design stuff that sells in tens if not hundreds of thousands a year, but quite obviously, lead designer of Apple or Asus would not be here.Nevertheless, many design principles are similar even when dealing with one-offs or small batches. Personally, I apply the principle of cost reduction even in small scale customized stuff whenever it does not interfere with other constraints. Surprisingly often the customer still wants that a PCB does not cost more than say 50€ to manufacture (each), even when the NRE costs dominate, and the product which originally was meant to be an experimental batch of 50 is now explored for the possibility to be manufactured in thousands. Well at thousands a few cents of a single BOM line doesn't mean much, but when applied to the whole thinking pattern it makes a difference.

author: tggzzz
author_rank: Super Contributor
timestamp: November 16, 2023, 05:57:12 pm
content: Quote from: Wil_Bloodworth on November 16, 2023, 05:20:19 pmPrepare to be surprisedSome of the people here are very competent; others less so. A very few notoriously less so.By and large the more competent people get pleasure from nudging the less experienced people in the right direction. It doesn't always work, but that's merely a microcosm of real life.

author: wraper
author_rank: Unknown
timestamp: November 16, 2023, 06:11:58 pm
content: Quote from: Wil_Bloodworth on November 16, 2023, 05:20:19 pmDo not kid yourself. There are many senior industry professionals including millionaires on this forum. I wouldn't call myself a large producer but some of the products that I designed and produced are used even by multi billion dollar organizations AFAIK.

author: schmitt trigger
author_rank: Super Contributor
timestamp: November 16, 2023, 06:15:38 pm
content: Quote from: Wil_Bloodworth on November 16, 2023, 05:20:19 pmThe highest volume product I was involved with, that was utilized across the whole vehicle spectrum of one of the Big-3, sold 2 1/2 million units a year.The board even had dual footprints for a relay, to leverage the cost between two different relay manufacturers.

author: floobydust
author_rank: Super Contributor
timestamp: November 16, 2023, 09:27:53 pm
content: Quote from: Siwastaja on November 16, 2023, 11:11:39 amQuote from: coppice on November 16, 2023, 01:27:31 pmPlease provide any numbers for OP and the thread, compared to armchair opinion- What power would you use the FMP100 for? How hot? Have you heard of math?Experts in the beginner's thread kindly give a usable power dissipation, temp rise even for operating the part at 1/2 or 1/3 of rated P70of 1W.OP's Yageo does a scam-eo by not providing heat-rise/thermal resistance data for theirFMPfamily. Sorry Yageo fanboys "world's largest resistor manufacturer" means sweet FA. Is it incompetence or deception that the data is missing?Ohmitedoes the same - no heat rise/thermal resistance for their parts.Perhaps it needs tinfoil fashioned into a heatsink, unless you can provide any numbers. Something engineers like to work with.

author: floobydust
author_rank: Super Contributor
timestamp: November 17, 2023, 03:54:37 am
content: Vishay response about the resistor test jig used:"The resistor is mounted on a PCB (see Fig) which is set up vertically, with the resistor horizontal. Using an infrared camera, a thermal image is made of the resistor, thus defining the hot-spot and solder-spot temperatures."---------------------To me it looks like max convection cooling and a lot of copper too. Not mentioned but the test board I believe is EN 140400 (for SMT is 2.3.3: FR4 100mm x 65mm x 1.4mm, 35μm Cu, pad 2.0mm width).So it's a rosy scenario compared to a horizontal PCB in an enclosure.

author: Siwastaja
author_rank: Super Contributor
timestamp: November 17, 2023, 07:12:51 am
content: Quote from: wraper on November 16, 2023, 06:11:58 pmSame here; I can say I have designed specialty electronics for some of the largest corporations on the planet; and while it sounds fancy, it really isn't and it happens easily! Those multi-billion organizations tend to be quite paralyzed due to sheer size, and outsource a lot of experimental work, through weird and long chains, at end of which some random guy they have never heard about builds something random in a week and gets paid $5000 for the job, and is never heard again. Such projects end up in some drawer, but allows these large corporations to explore ideas which are impossible for them to explore due to their internal bureaucracy.On the other hand, if you build say some interface box (let's say USB-CAN interface) or a programming jig or similar essential tool, chances are it will be sold in tens of thousands and even largest of corporations buy it, or at least their engineers buy them bypassing their purchase departments. Many hobbyists have succeeded in becoming "professional" large producers this way with relatively simple products.

author: Siwastaja
author_rank: Super Contributor
timestamp: November 17, 2023, 07:18:22 am
content: Quote from: floobydust on November 17, 2023, 03:54:37 amThere is nothing "rosy" in it, it's the standard way of rating all components. You as a designer are responsible for understanding what Ta means. It's not the temperature of your house, or temperature of Antarctica. It's the temperatureinsideyour case,aroundthe resistor (what else could it be?), and you are the only one who can calculate/simulate/test/measure the thermal performance of your case. It''s a ridiculous idea that a resistor manufacturer would start guessing how typical boxes work and somehow nudge that number into their ratings. Instead, a responsible manufacturer arranges the measurement so that such application-specific conditions are removed from the equation. Selling a part with pessimistic ratings because a test mimicked blocked airflow in a tight case serves no one's interest.Besides, the amount of copper seems very fair, it is very easy to use more copper than that, for example there seems to be no contiguous ground plane at all, and a 4-layer board would perform significantly better. If they wanted to con you, they would do that.re vertical, understanding convection is basics for a designer. If you opt for a fan-less design, then you need to be pretty damn sure to provide room for air flow with very little pressure drop; if the board is vertical, don't place anything sensitive above the hot part, and remember not to block the air flow from below either, and make sure the product is operated at correct orientation. If the board is horizontal, consider adding cutouts or cooling holes under the resistor; they are usually free-of-cost. All of this works exactly the same even if you use a larger resistor with smaller power density!But I guess you are beyond salvage. You are blinded by the idea of a conspiracy and see clear evidence of there being none as there being one.

author: shapirus
author_rank: Super Contributor
timestamp: November 18, 2023, 10:25:01 am
content: It would be interesting to see what will happen to that small resistor when there is actually 1W of heat generated in it. Will it burn? Will it crack? Will it glow red and keep working? Will it survive, but change color? Will it retain its original resistance after cooling down?Testing this, however, will require a power supply that can provide 68.5V (and then make it lower as the resistor heats up), which is on the less common side.@Wil_Bloodworthdo you have a lower value resistor of the same series? For example, a 150 Ohm resistor will require only 12V to produce 1W of power.

author: wraper
author_rank: Unknown
timestamp: November 18, 2023, 10:48:34 am
content: Quote from: shapirus on November 18, 2023, 10:25:01 amResistor marking may discolor and PCB pads may delaminate over time depending on their size, material, resistor mounting height, cooling. In any case, generally you don't want to run parts at 100% of their power rating, it reduces reliability significantly.

author: shapirus
author_rank: Super Contributor
timestamp: November 18, 2023, 10:54:41 am
content: Quote from: wraper on November 18, 2023, 10:48:34 amIt's so small that running it at 500-700 mW would be just as interesting.

author: Siwastaja
author_rank: Super Contributor
timestamp: November 18, 2023, 06:18:27 pm
content: By all means test it, but I have boring news to you: nothing special happens. Manufacturer tests them at rated power given the test procedure image shown. You can, of course, wrap some paper around this resistor and make the paper discolor or even ignite, or block the convection cooling or thermally insulate the resistor and make it fail, butDiscoloration of the resistor may or may not happen and does not indicate failure because the markings exist for part identification during assembly.If it fails, it's big news. So far, people who talk about resistor power rating conspiracy have produced zero evidence, even when the test is really easy to arrange. Absolutely zero, not even circumstantial. If there is something to it, and anyone proves it, I'm happy to stand corrected and join your camp.Of course, some derating is almost always a good idea. With components for professional designs, manufacturers do not much or any safety margins as that would only fudge the reality; it's a convention that this task is for the designer to do (it could be the other way, too, but this is what the convention is, and it only works when everyone follows the same convention).If you want to criticize an almost con-like manufacturer convention, look at how tantalum capacitor voltage ratings work, and how manufacturers recommend 40% derating in separate documents because the parts are literally rated to some dozenhoursof lifetime, and after that they burst in flames violently! Another commonly used front page specification which carries no practical purpose and exists only to mislead young players are MOSFET ratings at Tj= 25degC.

author: floobydust
author_rank: Super Contributor
timestamp: November 18, 2023, 07:35:28 pm
content: Quote from: shapirus on November 18, 2023, 10:54:41 amNobody here will stick their neck out, give a number or calculation of the usable power dissipation for our old friend the 1/4W body resistor.I get a good laugh out of that, armchair experts galore that can't put out.Soon OP's 1/4W sized part will be rated 2,3,4W... and it ends with something called A LIGHT BULB

author: wraper
author_rank: Unknown
timestamp: November 18, 2023, 07:59:15 pm
content: Quote from: Siwastaja on November 18, 2023, 06:18:27 pmIt's note like that really and the problem is not the lifetime, it's about failure rates. Technically manufacturers don't lie about their voltage rating. If you spot weld or attach them with conductive glue, that voltage rating is fine. However they get damaged during reflow and if they are run at high voltage, instead of gradual self-healing, they can burst in flames. Majority of them will last for a long time but you certainly won't like single digit % failure rates over a short time period.

author: floobydust
author_rank: Super Contributor
timestamp: November 18, 2023, 08:38:56 pm
content: I find component manufacturers give maximum ratings. Was always taught, even 40 years ago to derate parts for long life.Voltage-derating tantalums, power-derating resistors.But nowadays it's a bigger trap because noobs and beginners don't really know this and the numbers are further stretched as competition heats up (pun intended).A tech specified a replacement snubber resistor, original out of stock and into production went one of these "miniature" resistors. I wondered why it was too small. Of course it ran super hot, even though lead-bending was up off the board.I phoned the resistor manufacturer (not Vishay) and flamed them and the product manager told me "um, well these parts are intended for fan-cooled systems". You couldn't say that on the datasheet?! "No because it's evaluated to legacy standards (convection cooling)."

author: shapirus
author_rank: Super Contributor
timestamp: November 18, 2023, 11:10:50 pm
content: Quote from: Siwastaja on November 18, 2023, 06:18:27 pmThis is a prediction that is likely, but not certain, to be proven correct.Quote from: Siwastaja on November 18, 2023, 06:18:27 pmThat's a good point regarding the test procedure. Is it in the resistor's datasheet? Does the datasheet specify test conditions (in particular, forced vs natural air flow, as mentioned in one of the posts above)? The answer is "maybe": it depends. If someone is curious enough to find the datasheet and see what's inside, then the test can be reproduced to see if the resistor can handle the claimed wattage and not only what we subjectively expect a "1W" resistor to be able to handle.Quote from: Siwastaja on November 18, 2023, 06:18:27 pmThis is precisely why a practical experiment sounds interesting to me, especially considering all the prior discussion. And especially because it's the beginners section of the forum.I have some small (in terms of size) resistors with a suspiciously high claimed wattage in my parts box. Today it's too late, but tomorrow, if I don't forget, I will test some of them, if I find suitable values to use with my lab PSU, and see what happens.

author: Siwastaja
author_rank: Super Contributor
timestamp: November 19, 2023, 11:16:02 am
content: Quote from: floobydust on November 18, 2023, 08:38:56 pmYeah. Remember though that derating is not a silver bullet. It's just the cherry on the top; important but only part of the deal. The foundation should be understanding and then calculating/simulating/testing all mechanisms behind those limitations. When you handle that all, you can go pretty close to limits. You add derating to cover for uncertainties; the more uncertainties you have, the more you need to apply derating, but also the less confident you are whether it's truly enough, so you cover by adding even more derating.QuoteYes. But rules of thumb can be tricky. Aluminum electrolytic caps are formed at something like 130-140% rated voltage and actually sustain some overvoltage pretty well, and it's rare to see failures because somebody ran an aluminum elcap exactly at rating (failures go up only when significantly exceeded). Some MLCCs easily withstand +500% overvoltage without any reduction in lifetime. And then there are tantalums, which, as wraper correctly points out, fail in high numbers if used at rated voltage, after the soldering process.

author: wraper
author_rank: Unknown
timestamp: November 19, 2023, 01:05:20 pm
content: Quote from: Siwastaja on November 19, 2023, 11:16:02 amNot true, they withstand 500% but often for not that long. I've seen reports of this feature used by scummy laptop services in Russia. When doing some inexpensive work, like cleaning dust and replacing thermal paste, they also solder multiple low voltage MLCC in parallel to charging connector and then wait for returning customer to claim expensive motherboard repair is needed.

author: Siwastaja
author_rank: Super Contributor
timestamp: November 19, 2023, 02:44:48 pm
content: I saidsome, this means designs that are clearly close or identical to higher rated parts, but for some reason (e.g. supply chain related i.e. demand) rated for lower voltage. I.e., those with suspiciously low ratings for package size.If the part is 25V 1uF 0603 to begin with then it likely cannot take 100V. On the other hand a 6.3V 0.1uF 1206 part could take 63V. My point is, MLCC voltage ratings are quite arbitrary andsometimesthere are huge margins before failure.Soldering a physically large MLCC with excess heat and maybe giving it a mechanical bump would be a great planned obsolescence trick, too. Make it crack, measure to verify it isn't an instant short, and some time later it becomes a short, possibly aided by humidity.

author: shapirus
author_rank: Super Contributor
timestamp: November 19, 2023, 04:13:01 pm
content: Quote from: shapirus on November 18, 2023, 11:10:50 pmSo the closest I had (which I'd say extrapolates well to the one in question) is aHitano MFR-SS("super mini size") 2W metal film resistor. 560 Ohm in my case. 9.0 mm x 3.0 mm.Here's the test setup.I kept it running like this for ~15 min. There was that typical smell of hot resistors, but otherwise, just as predicted by@Siwastaja, nothing special happened. No burning, no discoloration, no resistance change after cooling down. Temperature rise above ambient was higher than specified in the datasheet, but that's most likely due to the fact that the datasheet assumes (without explicitly stating it) that the specified temperature rise is measured when the resistor is soldered in a PCB, which acts as a heat sink, and the resistor's leads are shorter, creating a shorter path for the heat to escape.The 1W resistors of the same series are smaller, 6.0 mm x 2.3 mm, and will probably be comparable to the one that was the starting subject of this topic.

author: Siwastaja
author_rank: Super Contributor
timestamp: November 19, 2023, 05:52:49 pm
content: That's as expected. Such small resistor probably is at thermal equilibrium after just 15 minutes, so any more test time would be to prove absence in resistance shift or slow deterioration. More interesting would be see how it performs after, say, 10000 hours at this power. Since I realize the obvious difficulty testing this, maybe try accelerated aging test at 3W. If it is able to run at +50% of rated power for a few hours (or even 15 minutes), without changing the value or failing, that would give further confidence on the rating.

author: shapirus
author_rank: Super Contributor
timestamp: November 19, 2023, 09:36:22 pm
content: That's an interesting scenario. However, my PSU goes up to only 36 volts, so no luck there: with 560 Ohms it'll be only ~2.3W, which isn't enough, and I don't have lower values of these.Theoretically, though, resistors of this type are made from nichrome film over a ceramic core (so the datasheet says), so I would venture to guess that anything below glowing red isn't going to damage or degrade them (at least in a short run).

author: floobydust
author_rank: Super Contributor
timestamp: November 20, 2023, 06:58:45 pm
content: Checked and found the same beliefs I'm mentioning here in The Art of Electronics:"A word of caution: It is our belief thatone should not place complete reliance on the kind of curves provided by manufacturers" ..."Generally, though, it’s better not to “twist the dragon’s tail”;our advice is to derate resistors by 50%."Paul Horowitz,Physics and EE prof. Emeritus at Harvard.Winfield Hill,Director of the EE Lab at the Rowland Institute at Harvard University.Definitely give them a ring regarding my conspiracy on not blindly trusting manufacturer's datasheetsI think the "50%" resistor power-derate rule was OK many decades ago, it might even go back to the days of point-point wiring with carbon resistors.But nowadays it's not enough, on a PCB and with high temp materials, practical power is much less. Let's say 1/3 of P70looks good to me. Unless fan cooled. IS safety standards max. is 2/3 of rated power to be considered infallible.SMT resistors are also something to look at, best in another thread as they have "hidden EE common knowledge" as I call it traps as well regarding power dissipation.I was just reading about the infinite heatsink test (two copper blocks) while measuring surface temperature and look forward to that spec on a resistor datasheetIt's needed for science, just as power mosfets use the same spec - but EE's need to know practical, achievable values.

author: tggzzz
author_rank: Super Contributor
timestamp: November 20, 2023, 07:15:19 pm
content: Quote from: floobydust on November 20, 2023, 06:58:45 pmIt hasalwaysbeen the case that you need to read and understand whatis notbeing guaranteed/required in a data sheet. No change there.EEs havealwaysneeded to understand the theory of reliability and practical failure mechanisms. No change there.EEs havealwaysneeded to work out how practical components will behave in their circuits. No change there.Data sheets havealwaysstated specifications involving ideal conditions that won't apply in a real circuit. No change there. The legal profession also has to do the same, e.g. to get their client acquitted of charges, or to invent tax avoidance schemes. The physics equivalent is the famous "assume a spherical cow".

author: floobydust
author_rank: Super Contributor
timestamp: November 20, 2023, 07:25:28 pm
content: Withholding measurement data is the same as lying by omission.Nobody here can ballpark OP's yageo scam-eo resistor temperature operating at 1/2 power or anything reasonable.How is this the EE's fault?

author: Siwastaja
author_rank: Super Contributor
timestamp: November 20, 2023, 07:58:52 pm
content: That text you quoted is decades old. Youonce againproved yourself wrong on your claims that new resistors are a conspiracy. How long are you going to keep making yourself a laughing stock? I mean, the credibility you have left is basically zero. Keep wrapping more tinfoil and keep providing zero evidence.Once again, I have zero problems using moden high power density resistors significantly over 50% rated power. Other professionals agree. No proof of otherwise, not a single bad experience by a professional who actually designed this stuff in has been shown. The burden of proof is on who makes the claim, and extraordinary claims require extraordinary evidence.50% derating suggestions hide some assumptions (e.g. PCB orientation, possible blockage of cooling, how close multiple heat-generating parts are close together, etc.). It's a rule to ease thermal design for those who don't have time or energy to think about it. There is no need to follow such practice if you understand thermal design and can simulate or practically measure the performance.Exactly as with all other component types, manufacturer cannot predict how the customer uses the part and tests how it performs in isolation. Just like you can drive faster when there is no other traffic, and thus cars have higher top speeds rated compared to what you actually can drive at.

author: tggzzz
author_rank: Super Contributor
timestamp: November 20, 2023, 09:45:13 pm
content: Quote from: floobydust on November 20, 2023, 07:25:28 pmCaveat emptor is a useful principle.If a component doesn't have a specification for X, then don't use it in an application where X is important. Either use a different component where X is specified, or qualify/test the component.Classic example: MLCC where the voltage decorating curve is not specified.There is no substitute for understanding and for experience.

author: Siwastaja
author_rank: Super Contributor
timestamp: November 21, 2023, 06:19:46 pm
content: Quote from: tggzzz on November 20, 2023, 09:45:13 pmOr work with the manufacturer to get the specifications you need; they know how to qualify/test their parts. Yes, there is cost to this. Basic principle of any business is offering different level services to different customer tiers who pay differently. This applies to components as well. If you are a poor hobbyist or startup, then work through the night and test it yourself. If you are a large business, just the information alone that you are willing to buy in millions will get the manufacturer to offer data just for you.

author: floobydust
author_rank: Super Contributor
timestamp: November 22, 2023, 09:17:26 pm
content: Quote from: Siwastaja on November 20, 2023, 07:58:52 pmCredibility, reputation- I'm not here for that malarkey. In electronics a person is constantly wrong and only has more to learn.Engineers that know it all and have a lot of ego crash and burn in the best ways. This is where you and I differ.You've provided no formulas, calculations, datasheets, app notes, tech papers, URL's towards helping the thread, aside from urine.Piss on me, piss on the thread but at least offer guidance for OP and the beginners here, or GTFO.I see no way toreach outto Yageo to ask why they omit heat rise data for some of their acquired brands. FMP, PNP. So that OP would understand being ripped off.I compared data on 65 different resistor makes/models including temp rise and physical (body) size, lead diameter etc. to see the game.It's the 1/4-sized parts that I have issue with, as well as their deceptive datasheets.Industrial products I design to 60°C ambient so a practical ball park dissipation numberYageo VitrohmPOS seriesthe 1/4W-body rated P701W is 130K/W and +200°C max. (which is more typical for wirewound).Using 130K/W people here can do a little math and get a rosy estimate.

author: Wil_Bloodworth
author_rank: Regular Contributor
timestamp: November 25, 2023, 02:12:53 am
content: I don't know how these can be equivalent. The Chinese ones are even supposed to have a 5% tolerance.- Wil

author: wraper
author_rank: Unknown
timestamp: November 25, 2023, 02:24:14 am
content: Quote from: Wil_Bloodworth on November 25, 2023, 02:12:53 amOf course they are not. Small one is miniature, large one is not regular either but for high energy surges. As already told many times, power rating is not nearly the only thing that matters.

author: Wil_Bloodworth
author_rank: Regular Contributor
timestamp: November 25, 2023, 02:28:38 am
content: Quote from: wraper on November 25, 2023, 02:24:14 amYes, I understand that. I guess what I'm saying is that when I'm ordering resisters from DigiKey or Mouser, unless you just have a history of ordering that specific capacitor, there is no way to know what you're getting. As far as I can see, there was nothing indicating that these were anything other than "normal" when ordering. And you know... size always matters.

author: ArdWar
author_rank: Frequent Contributor
timestamp: November 25, 2023, 02:38:44 am
content: What are you even talking about? Both distributors include size/dimensions in their resistor table/data fields, and all reputable manufacturers provide datasheets for their products. The less common a product dimensions is, the more important its datasheet will be.If you buy resistor without checking the data first or at least checking the corresponding product series then it's in you if you didn't get what you think you'll get.

author: Wil_Bloodworth
author_rank: Regular Contributor
timestamp: November 25, 2023, 02:55:38 am
content: Quote from: ArdWar on November 25, 2023, 02:38:44 amI'm new to electronics so I don't know all that crap. No need to be a jerk.And you guys do realize this was posted in the Beginners section don't you!!!- Wil

author: ArdWar
author_rank: Frequent Contributor
timestamp: November 25, 2023, 03:05:05 am
content: I mean, you're the one claiming "no way to know" and "nothing indicating".Another way to figure out albeit less reliable is when you find non beige/brown/blue axial resistor you're probably dealing with something "not normal"

author: shapirus
author_rank: Super Contributor
timestamp: November 25, 2023, 03:54:05 am
content: test them.

author: Siwastaja
author_rank: Super Contributor
timestamp: November 25, 2023, 07:22:24 am
content: Quote from: Wil_Bloodworth on November 25, 2023, 02:28:38 amThat's a wrong way to buy. Don't buy random parts based on quick parametric search; instead, take your time to look through the datasheet; calculate, simulate, measure, whatever is needed to qualify the part into your design - then buy, and confirm the suitability through prototypes. Then keep buying the same part number, so it doesn't matter where you buy it as long as it's a credible supplier and you don't get fakes.

author: Siwastaja
author_rank: Super Contributor
timestamp: November 25, 2023, 07:27:27 am
content: Quote from: Wil_Bloodworth on November 25, 2023, 02:55:38 amThat's OK. We are just reminding you about the fact that distributors like Digikey really do not exist for hobbyists (although they serve them as well). Component manufacturers make parts for professionals, to be used in production, and write their datasheets for professional design engineers. Hobbyists and beginners start working with many false assumptions and get surprised all the time, and that's fine; we all have been through that phase and I think it wasfun; just remember you are the one who should be learning; don't turn into what floobydust became, a disgruntled hobbyist who decided so start a war against component giants because his own unwillingness to learn.

author: Simon
author_rank: Unknown
timestamp: November 25, 2023, 08:31:30 am
content: Quote from: ArdWar on November 25, 2023, 03:05:05 amGreen is usually an inductor

author: wraper
author_rank: Unknown
timestamp: November 25, 2023, 08:50:24 am
content: Quote from: Simon on November 25, 2023, 08:31:30 amOnly if it's glossy and somewhat different length and diameter proportions.

author: Simon
author_rank: Unknown
timestamp: November 25, 2023, 09:03:02 am
content: Yes typically 0.25W through hole inductors look like resistors but are greed, more than the gloss it's the bigger dip in the middle if I remember rightly, I guess it depends on value as it's probably the slot for windings that may be more or less filled.The big give away is their very low resistance. When I was a kid I took one into my friendly TV repairer who explained why this perfectly healthy looking resistor had a wrong and very low resistance for it's markings.

author: Gyro
author_rank: Super Contributor
timestamp: November 25, 2023, 10:17:28 am
content: Quote from: Simon on November 25, 2023, 08:31:30 amFlameproof resistors are normally Green, or Reddish Brown. The epoxy coating on inductors is shiny.

author: tggzzz
author_rank: Super Contributor
timestamp: November 25, 2023, 04:35:36 pm
content: Quote from: Wil_Bloodworth on November 25, 2023, 02:28:38 amWhen I started professional engineering, I too was "confused" by the variety of capacitors available. So I took the RS catalogue, and made a table showing the advantages and disadvantages of each type of capacitor. You might like to do the same; you will learn a lot.Just wait until you wonder why some 10A fuses are a 5mm*20mm glass envelope, while other 10A fuses are 12mm*150mm and opaque (and marked 200,000A rms), and others are SMD.You might "not have any way to know", but most people find the principal characteristics from the columns in the DigiKey (or Mouser/RS/etc) search results. Then, for the interesting devices, we can even use a more advanced technique:RTFDS, where DS is "Data Sheets"On the bright side: you are a beginner, so ignorance is unsurprisingand curable. None of that applies to some other prolific first posters on this forum.

author: Siwastaja
author_rank: Super Contributor
timestamp: November 25, 2023, 04:44:29 pm
content: Also remember that the distributor information is sometimes just plain wrong. Some engineer there reads thousands of datasheets every day and quickly gathers the numbers. Mistakes happen. Always carefully cross-check part numbers between datasheet and what you are ordering, and carefully read thecorrectdatasheet. At beginning this takes a lot of time but you'll get better at it.

author: coppice
author_rank: Super Contributor
timestamp: November 25, 2023, 06:13:48 pm
content: Quote from: tggzzz on November 25, 2023, 04:35:36 pmThere isn't a single capacitor type out there which doesn't have a mass of quirks. I haven't found anyone who thought this was well covered in their education. Its rather sad. You end up picking up things as you go along, from colleagues, data sheets and other snippets of knowledge, rather than a clear and complete comparison of current technologies.

author: Siwastaja
author_rank: Super Contributor
timestamp: November 25, 2023, 07:21:35 pm
content: Indeed; if you can handle the different types and characteristics of real-world capacitors and inductors, then understanding power ratings and cooling of resistors should be easy-peasy.

author: tggzzz
author_rank: Super Contributor
timestamp: November 25, 2023, 07:26:49 pm
content: Quote from: coppice on November 25, 2023, 06:13:48 pmI wouldn't want itwellcovered in education; there are far more fundamental topics that are more important.That there are differences should benoted, with the details being understood when they become relevant.

author: shapirus
author_rank: Super Contributor
timestamp: November 25, 2023, 08:01:52 pm
content: Quote from: Wil_Bloodworth on November 25, 2023, 02:28:38 amActually, today it's way easier to know that than ever. In the absolute majority of cases you can easily find any information very quickly on the internet. Part specs, typical circuits, questions and answers etc. Well, to be precise, it was easier some time ago, before the search results became flooded with tons of useless AI-generated crap, so today one needs to develop a better skill of filtering useful info from garbage than ever before.Still, today versus the days before the internet became widespread is night and day difference. It was hard to get information back then. You were limited to what you could read in specialized magazines and in literature, not all of which were good at what they tried to do, especially where beginner-level things were concerned. Combined with the lack of, or very high price of equipment back then that one can get ridiculously cheap today, it really made it challenging for hobbyists and enthusiasts, and, above all, for kids. In my case, it was the reason why I quit the EE hobby in my early teens when I hit the barrier imposed by the (un)availability of information, parts, and equipment, and focused on computers instead, which at the time offered much broader opportunities to learn and achieve something. Now I revived this old hobby that I had abandoned, and I find it very satisfying to learn and do something when you have information and tools.Going back to resistors, and other parts for that matter, datasheets are usually readily available in a couple of clicks and there's no difficulty whatsoever in reading them (and learning by understanding the parts that are new to you).

author: coppice
author_rank: Super Contributor
timestamp: November 25, 2023, 08:30:56 pm
content: Quote from: tggzzz on November 25, 2023, 07:26:49 pmI think it justifies an hour or two of lectures. Engineers waste enormous amounts of time coming to terms with the fact that MLCCs aren't even close to being real capacitors, electrolytics have a bunch of funky issues, polarisation and absorption in some types of capacitors can be a problem, etc. Its one of those areas where you don't know what you don't know, so its hard to even formulate questions. If you've been primed then years later, when you have forgotten most of the details, you'll probably still remember that gotchas that lie in wait.

author: tggzzz
author_rank: Super Contributor
timestamp: November 25, 2023, 09:26:29 pm
content: Quote from: coppice on November 25, 2023, 08:30:56 pmI'm in favour of making students realise that.you can't buy a resistor, but can buy something that is a combination of inductor plus capacitor plus resistor. Then do a little analysis to determine where typical poles and zeros will occur.I'm not in favour of getting students to think too deeply about polystyrene caps advantages over teflon capacitors - except where it is critical to experimental apparatus they are using.If you teach the characteristics of MLCC caps, what are you going to omit? What's the half-life of such knowledge? University should teach fundamentals that will last a lifetime. If they understand fundamentals, they will be applicable to whatever they encounter in the future. That won't happen with knowledge of the C-vs-V characteristics of CapCon's current products.

author: Wil_Bloodworth
author_rank: Regular Contributor
timestamp: November 25, 2023, 10:35:25 pm
content: Quote from: tggzzz on November 25, 2023, 09:26:29 pmI'm learning electronics at home in my living room in my spare time by myself without an instructor. Unfortunately, the luxury of a teacher/mentor is not an option.- Wil

author: coppice
author_rank: Super Contributor
timestamp: November 25, 2023, 10:56:15 pm
content: Quote from: tggzzz on November 25, 2023, 09:26:29 pmA well balanced degree course teaches mostly strategic knowledge to keep you useful in the long term, sprinkled with a broadly useful mix of tactical knowledge to make you useful in the short term.Things lots of people struggle with for many hours are excellent candidates for that tactical knowledge area, where they can be made useful in an hour or two.

author: tggzzz
author_rank: Super Contributor
timestamp: November 25, 2023, 11:13:23 pm
content: Quote from: Wil_Bloodworth on November 25, 2023, 10:35:25 pmThat doesn't change the point, of course.I was in your position for a decade or so, before I became old enough to go to university. All I had available was a few magazines from newsagents, a few books from the local library, and my imagination.Data books? No. The nearest was Towers International Transistor Selector.Text books? No. Too expensive and specialised.Instead we learned to scavenge any information we could find, and more over it to extract everything it contained.Now the issue is to quickly determine what to ignore - the polar opposite.I made many mistakes and planned how to make only new mistakes:)

author: tggzzz
author_rank: Super Contributor
timestamp: November 25, 2023, 11:22:09 pm
content: Quote from: coppice on November 25, 2023, 10:56:15 pmI would modify that to say the degree should give you the wisdom to know where your knowledge/experience is inadequate, and then to know how to learn what you need to know next. That learning will take several lifetimesTactical knowledge is fine and useful, but if that's all somebody knows, they will waste time on blind alleys and things which are known to be impossible. That happen especially often with software, of course. Professor Eric Laithwaite at Imperial College used to set exams where one question was easy and sufficient get you a pass mark, one was more challenging and could get you a good degree, and one could not be answered adequately in the time available.He expected his undergraduate engineers to be able to determine which questions to avoid. If they couldn't, they wouldn't make good engineers anyway. I doubt he would be allowed to do that now, more's the pity.

author: coppice
author_rank: Super Contributor
timestamp: November 25, 2023, 11:55:52 pm
content: Quote from: tggzzz on November 25, 2023, 11:22:09 pmYou expect people to gain wisdom out of a degree course? You have extremely high goals. I'm happy if they just acquire a reasonable amount of understanding, and not just how to answer questions like a parrot.

author: tggzzz
author_rank: Super Contributor
timestamp: November 26, 2023, 12:28:10 am
content: Quote from: coppice on November 25, 2023, 11:55:52 pmYes, I do - within the limit I described. If they can't, then they aren't fit to go on to be an engineer.So did Professor Eric Laithwaite at Imperial College.Just because 50% of youth get degrees whereas only 10% of youth got degrees when I was young, doesn't mean the definition of a good degree has changed.I, and a few friends (one a member here), went back to our university on its open day, for our <mumble>th anniversary of graduation. I'm pleased to say that the students we spoke to and the university course they described seems to have exactly the same ethos as when we were there.

author: shapirus
author_rank: Super Contributor
timestamp: November 26, 2023, 12:49:08 am
content: Quote from: tggzzz on November 26, 2023, 12:28:10 amThat's perfectly right, as long as we're talking about engineers, as in, people whose profession is to design things (and be paid for this). Engineers must have respective education, or experience and skills that can effectively serve as its substitution (and are required in addition to education anyway).However, there's a lot of variants, in terms of possessed and required (expected) knowledge and skills between a beginner hobbyist and a professional engineer. And I guess in this topic and in this section of the forum we're more in the context of the former than of the latter.

author: Jwillis
author_rank: Super Contributor
timestamp: November 26, 2023, 12:54:54 am
content: Quote from: Wil_Bloodworth on November 25, 2023, 02:12:53 amThe smaller Chinese one is a Yageo.The tolerances only mean that the true values of the resistor will be within plus or minus the coded values.Both the larger resistor and smaller resistor can have similar characteristics But the test qualifications can be different.The smaller resistor has an IEC (International Electrotechnical Commission) standard bases on those test set out by the IEC.The larger resistor has a Mil (Department of Defence) qualification. Which tend to be far more stringent than the IEC. The construction and dimensions will be based on those tests set out by the department of defence. If you want to dive down that rabbit hole, all the power to you.Body colours of resistors and inductors can be different depending on the manufacturer and series. There is no standard body colour for either. You must read the datatsheet for the component from the manufacturer that produced it.For general purpose, standard metal film , carbon composite and /or ceramic cement will work just fine in most applications. Check that the voltage rating of the resistor is acceptable for the voltages you will be using. Usually the voltage rating of a resistor should be double the operational voltage. As long as the rated voltage is higher than the applied voltage plus any possible spikes in voltage.There is no rule, other than space restrictions, that dictates that a higher power resistor can't replace a lower power resistor.Smaller resistors of the same power rating as larger ones will dissipate heat over a smaller area. So the "Real Feel'' will be hotter on a smaller resistor than an equivalent larger one. This temperature won't effect the resistor in it's self, by may effect components near it. So give small hot resistors they space they need or change it to a larger one.The main requirements when choosing a resistor is the Value, Power, Voltage, Stability(temperature coefficient) and cost.

author: tggzzz
author_rank: Super Contributor
timestamp: November 26, 2023, 11:11:30 am
content: Quote from: shapirus on November 26, 2023, 12:49:08 amI agree, but I will note these points...My comments were in the context of coppice's posts which include (the traditional) "thread drift".My attitude to "technician vs engineer" is the same as "nurse vs doctor": they are complementary, with different advantages, both arenecessary, neither issufficient. Vive la difference!I do strongly object to anybody that thinks nurses are "better" (in some poorly defined way) than doctors. Ditto technicans being better than engineers.The relevance to a beginner is that they may not appreciate the differences - and knowing the differences may help them choose the foundation for the rest of their career.

author: coppice
author_rank: Super Contributor
timestamp: November 26, 2023, 12:40:54 pm
content: Quote from: tggzzz on November 26, 2023, 12:28:10 amWe must be using different dictionaries. You can teach engineering. You can't teach wisdom. Some of the most capable engineering minds have no wisdom at all. We need to make use of their engineering skills, and keep them well away from decision making.Its delusional to think that degrees have not changed. In the UK we used to leave high school at 18 having studied the material in a US bachelor course. Now a UK bachelor degree is no higher in standard than a US degree.When I was at university, UCL had about 7,500 students and was the largest single college in the UK. I think Imperial was about half that size. Now UCL has 43,000 and Imperial 20,000. Together they are not much smaller than the total UK university student population when I studied. Less than 10% of youngsters took A levels, and far more of those went on to things like day release and evening classes than full time study at a university. You really think they have been able to expand universities from taking 3% of state school leavers and a similar number from the public schools and maintain similar standard?

author: tggzzz
author_rank: Super Contributor
timestamp: November 26, 2023, 01:15:40 pm
content: Quote from: coppice on November 26, 2023, 12:40:54 pmYes, we must be.This is as good a definition as any, and it can be taught. "the ability to use your knowledge and experience to make good decisions and judgments"https://dictionary.cambridge.org/dictionary/english/wisdomMost people will learn something from such teachings, but there are always people that can't/won't learn.QuoteI have no idea what you are thinking there; it makes no sense to me.Having engineering skills requires having good judgement (and good taste).It could be argued that technicians have less need for judgement, since they follow pre-defined procedures. I wouldn't make that argument, since a good technician iscapableof doing that and more.

author: coppice
author_rank: Super Contributor
timestamp: November 26, 2023, 01:31:04 pm
content: Quote from: tggzzz on November 26, 2023, 01:15:40 pmYou can't teach good judgement. You can talk through the unintended outcomes of narrowly focussed thinking, that ignored the big picture, and make people better aware of the value of good judgement. Good luck trying to teach it, though. Its a quality of a person's character, like critical thinking. Another area of utterly failed experiments in teaching.

author: Siwastaja
author_rank: Super Contributor
timestamp: November 27, 2023, 04:49:34 pm
content: Quote from: coppice on November 26, 2023, 01:31:04 pmIt's not either-or. If a person is totally incapable of critical thinking, maybe it's too late trying to educate this after kindergarten / few first primary school years, but there surely are people who have mixed traits and it's pretty important to nudge them a bit into the right direction. We should be able todefine our values, and tell people what matters in engineering. We should also give examples, and while at it, use real-world examples because then they double as direct transfer of information. You can't teach every technical detail like that, but if you choose well which details you teach, they work as examples of higher level concepts.

author: coppice
author_rank: Super Contributor
timestamp: November 27, 2023, 05:22:51 pm
content: Quote from: Siwastaja on November 27, 2023, 04:49:34 pmI don't think there is much research about wisdom, but there has been about critical thinking. Obviously its not a black and white ability you either have or lack, but nobody has succeeded in training to improve it. Various weak studies have thought they had found improvements, then people who applied more critical thinking to those studies found the subjects had simply been trained with analytical responses to the particular topics they had been taught. They had gained no generalised ability to analyse. This is really sad. Most things are very much a combination of nature and nurture. You can't turn an idiot into a genius through education, but you can add a few points to their IQ score, and that can be enough to make a considerable difference to their life outcome. There is no sign you can go anything about critical thinking.

author: Bud
author_rank: Super Contributor
timestamp: November 27, 2023, 05:41:38 pm
content: Quote from: coppice on November 26, 2023, 01:31:04 pmI am with coppice on this one. Especially on the "big picture" statement, which requires the mind qualities which many of the perfect tech engineers lack.

author: tggzzz
author_rank: Super Contributor
timestamp: November 27, 2023, 07:25:41 pm
content: Quote from: Bud on November 27, 2023, 05:41:38 pmA perfect engineer never loses sight of the big picture. Engineers know their objective is to drain the swamp, not to kill alligators.If something cannot be taught, then the only alternative is that it must be genetic.Siwastaja's statements are nuanced and, I believe, pretty accurate. Attitudes can be inhaled when young, and can be taught by example when older. Having said that, nobody could have taught me to be a fast runner, nor high jumper, nor...

author: coppice
author_rank: Super Contributor
timestamp: November 27, 2023, 08:14:59 pm
content: Quote from: tggzzz on November 27, 2023, 07:25:41 pmThere goes that dictionary issue again. Your "nuanced and accurate" seems to equate to my "wishful thinking, unsupported by evidence". The inelastic nature of many human traits has always been hard for many people to accept. "You can be anything" is such BS. Most people have to accept reality when a 1.7 metre tall teenager thinks they can be the next Michael Jordan, but ignore it when reality isn't fully rubbed in their face.

author: Siwastaja
author_rank: Super Contributor
timestamp: November 28, 2023, 07:09:16 am
content: Quote from: coppice on November 27, 2023, 08:14:59 pmOf course it is, but nobody suggested that. You are creating a strawman. From personal experience, I can easily remember university teachers and later bosses who really nudged me into the right direction (and I mean attitude and engineering process), and those who just tried to transfer information with not much success. It is natural to human to copy behavior from the surroundings, trying to adapt to the culture. This is why the voting behavior can be easily manipulated by just telling them "how others will vote", so that they will vote for the assumed winner, instead of discussing the values of the parties/representatives and choosing one that matches their values.Similarly, you can tell students to learn to question, let's say, credibility of appnotes (T3sl4c01ls pet peeve), andshow an exampleof a misleading / plain wrong information on an appnote, and explain why and how it is wrong - do it well and the students remember it for the rest of their lives, and some, those capable of it, would be more prone to apply similar thinking to other appnotes.No scientific proof of such behavior? Bummer. Either you didn't look too hard, or it doesn't exist, but absence of proof is not proof of absence. It is sometimes surprising how little we have studied human behavior, or even psychology. You can find much more scientific studies from animals because the tests are so much easier to arrange.

author: tggzzz
author_rank: Super Contributor
timestamp: November 28, 2023, 10:34:58 am
content: Quote from: Siwastaja on November 28, 2023, 07:09:16 amYes indeed.My presumption would be that those that those who are not "capable of it" would never make goodengineers. They might be very productive in other roles, of course.Too often people fall into the trap of "I can't do it therefore it can't be done", or "I can do it therefore you can/should do it".As an illustration of the unspoken "I can't do it therefore it can't be done", I well remember an anecdote in the wonderful book "Most Secret War" (aka "Wizard War") by RV Jones about his experiences in Scientific Intelligence in WW2. Jones was gathering evidence about a new powerful unknown rocket weapon (later known as the V2), and the UK scientific experts said the intelligence should be discounted because it was theoretically impossible. When it became obvious how it was being achieved, those experts said "ah, yes, liquid fuel, didn't think of that".

author: coppice
author_rank: Super Contributor
timestamp: November 28, 2023, 10:58:32 am
content: Quote from: Siwastaja on November 28, 2023, 07:09:16 amHuge numbers of people love the mantra that you can be anything you want. Its pervasive through society these days, even though most people realise its rubbish. As you said, most people will go along with rubbish rather than point it out. When I was young the mantra was more to find your strengths and play to them. The change has been quite destructive.QuoteHave you ever followed some people who don't question things enough and see how they behave over a reasonably long time? Most of them will spend ages struggling over something., eventually figure it out, and say "well, I won't fall for that again". Not too long later they do. The interesting thing is if you point this out they generally cannot see the similarity of the two situations, while the good critical thinkers around them easily can. You can train people to parrot better behaviour in exactly repeating situations, but can you make them do it when the situation is even a little different. Research says no.QuoteThere has been research. Its rather dismal, so people try to play it down.

author: tggzzz
author_rank: Super Contributor
timestamp: November 28, 2023, 11:48:09 am
content: Quote from: coppice on November 28, 2023, 10:58:32 amWhen I was young the zeitgeist was more along the lines of accepting your place in the hierarchy and deferring to those with better breeding.Both are demoralising and destructive when applied without thinking about exceptions - as such thingsalwaysare.

author: coppice
author_rank: Super Contributor
timestamp: November 28, 2023, 12:20:36 pm
content: Quote from: tggzzz on November 28, 2023, 11:48:09 amThat has ebbed and flowed in the UK. When I grew up in the 1960s I expected by adult life to be massively constrained by my working class origins. However, things opened up as Britain realised that to maintain industrial power it needed talent wherever they could get it from. I was easily able to get into a top tier university merely by being in the top 1% of school results. Then Britain gave up being a first world power, and the class base for society became strong again. Where were you on that time line?

author: tggzzz
author_rank: Super Contributor
timestamp: November 28, 2023, 01:38:46 pm
content: Quote from: coppice on November 28, 2023, 12:20:36 pmSimilar.My father was a chemical engineer, so I never conceived that being an engineer wasn't possible. The grammar school vs secondary modern divide was more of an issue.As for me, I got a scholarship to a local public school, but elected to go to the local grammar school. Never had any cause to regret that, was using the darkroom and their scopes in my lunchtime, and reclaiming transistors and passives from a stock of scrap boards in a cupboard. Everybody took maths and English Lang O-levels a year early, and I wasn't the only one with 5 STEM A-levels, too (one was a duplicate of two others).

author: Wil_Bloodworth
author_rank: Regular Contributor
timestamp: November 28, 2023, 02:24:58 pm
content: This topic is about resistor sizes and how size compares to power dissipation. While the topic of education certainly has merit, it does not belong in this topic and this topic has been driven off the rails. Please create a new thread to discuss this further. Thank you!- Wil

author: tggzzz
author_rank: Super Contributor
timestamp: November 28, 2023, 03:52:14 pm
content: Quote from: Wil_Bloodworth on November 28, 2023, 02:24:58 pmThread drift has been happening for the past 40 years, and will continue indefinitely.Let us know if you manage to prevent it.

author: coppice
author_rank: Super Contributor
timestamp: November 28, 2023, 06:11:51 pm
content: Quote from: tggzzz on November 28, 2023, 03:52:14 pmThread drift is a looming threat.

author: Zero999
author_rank: Super Contributor
timestamp: November 29, 2023, 01:53:47 pm
content: Quote from: Wil_Bloodworth on November 28, 2023, 02:24:58 pmA better way to deal with a thread going off-topic is to post something to bring it back on course.Do you have any further questions relating to the the original topic?

author: BILLPOD
author_rank: Frequent Contributor
timestamp: November 29, 2023, 02:49:14 pm
content: Quote from: Wil_Bloodworth on November 28, 2023, 02:24:58 pm