Source for resistor kits - Page 1
Forum section: electronics / general

author: (In)Sanity
author_rank: Regular Contributor
timestamp: January 17, 2013, 12:58:30 am
content: Does anyone happen to know a good source for relatively inexpensive, but relatively good metal film resistor kits ? I'm tired of the stuff coming out of China, it's either fake (Carbon film) or just really poor quality. There must be someone that's selling resistor kits that cover the full range for reasonable prices and still have decent quality?I had finally tapped in to a batch of resistors I got from sure electronics years ago only to find they were all fake. Not only were they fake they had a 540 ppm temperature coefficient on the 100k resistors I tested. They are of course also negative coefficient just like a carbon film.If needed I'll just start ordering resistors from the major distributors one value at a time. I'm just not finding they have the types of kits I really want in metal film. Too granular.Thanks,Jeff

author: robrenz
author_rank: Super Contributor
timestamp: January 17, 2013, 01:47:13 am
content: Jameco has some nice reasonable quality resistor kitsHERE.

author: AlphZeta
author_rank: Regular Contributor
timestamp: January 17, 2013, 01:55:19 am
content: Dipmicro has some metal film ones (kits) as well (http://dipmicro.com/store/SET-RF405). I ordered from them a few times and their service is pretty good and shipping is fast and relatively inexpensive.

author: Nirios
author_rank: Regular Contributor
timestamp: January 17, 2013, 02:07:11 am
content: Amazon has a decent kit. 1/4 watt 1% metal film in individually labeled bags. No issues with the one I ordered, I would get them again if I needed more.http://www.amazon.com/Joe-Knows-Electronics-Value-Resistor/dp/B003UC4FSS/ref=sr_1_2?ie=UTF8&qid=1358388036&sr=8-2

author: (In)Sanity
author_rank: Regular Contributor
timestamp: January 17, 2013, 03:15:57 am
content: Quote from: Nirios on January 17, 2013, 02:07:11 amI was looking at those a little while ago. I assume when heated the resistance increases ? It's a quick way to find out if they are most likely real and a sure way to know if they are fake. The ones I had naturally decreased in resistance when heated. I tossed them back in their bag and they can sit until I use some of them for stuff like pull-up resistors or such.I'm not sure why anyone would include zero ohms and actually include it as a count. That's a bit questionable practice.I'm looking at the other links as well.Thanks,Jeff

author: Nirios
author_rank: Regular Contributor
timestamp: January 17, 2013, 06:38:28 pm
content: Quote from: (In)Sanity on January 17, 2013, 03:15:57 amI actually never tested them. I do have a meter and a hot air reflow gun. What test would you like to see? I'm now curious to see how they perform.

author: ftransform
author_rank: Frequent Contributor
timestamp: January 17, 2013, 06:51:24 pm
content: I have a batch of metal film resistors that have varying temperature coefficents.I have ordered carbon film and metal film resistors (both from our chinese friends).I selected two same value resistors and scraped the epoxy off and I could see a difference between the two resistors, the the spiral on the carbon film one was less reflective then the metal film one.When I performed heating tests on two of my metal film resistors I found that47 ohm resistor -> decreases15k resistor -> increases.Comparing the two devices visually (I do not have a microscope), I'd say the colour and shine of the bands is similar.I do not think temperature testing is a good way to distinguish between carbon and metal film. Remember tempco is specified as +- for these devices.

author: (In)Sanity
author_rank: Regular Contributor
timestamp: January 17, 2013, 07:04:43 pm
content: Interesting, more clarification on this issue would be great from someone with the knowledge to do so. I think carbon is always negative..but I could be wrong.Jeff

author: ftransform
author_rank: Frequent Contributor
timestamp: January 17, 2013, 07:13:06 pm
content: Here is a photograph I took (excuse the lack of lighting) between a supposed carbon film and supposed metal film resistor.http://image.bayimg.com/71b0b4fe2f0a029ec69bd522d3cbffe2204c2113.jpgThe resistor on top is a 47ohm 5% tolerance carbon film resistor, measuring about 50 ohms and the other one is a 1% metal film measuring about 47 ohms.It is difficult to catch the difference on camera but the difference in reflectivity is easily visible through a magnifying glass and bright light. I am not a resistor expert so take this with a grain of salt.Perhaps a reaction with mineral acid can confirm the band material.

author: (In)Sanity
author_rank: Regular Contributor
timestamp: January 17, 2013, 07:17:30 pm
content: Pretty much the same findings I've found with regard to the color of the film.Also I just found this, not sure how accurate it is.http://hyperphysics.phy-astr.gsu.edu/hbase/tables/rstiv.htmlThe interesting part is it lists carbon as negative.Thanks,Jeff

author: ftransform
author_rank: Frequent Contributor
timestamp: January 17, 2013, 07:20:18 pm
content: Yea, both resistors in that picture drop when they are heated with a lighter.

author: (In)Sanity
author_rank: Regular Contributor
timestamp: January 17, 2013, 07:29:06 pm
content: It would be interesting to know if you have any in that batch that increase ? Without torching your resistor collection of course. Just a little bit of heat will tell you.I've not found any in my collection of fake metal film that go up instead of down when heated.Jeff

author: ftransform
author_rank: Frequent Contributor
timestamp: January 17, 2013, 07:55:21 pm
content: Quote from: (In)Sanity on January 17, 2013, 07:29:06 pmI might some time later in the day when I feel a burst of energy. That really is alot of work so I'm hoping someone else on the forum will have some insight that will prevent me from having to do it. I would need to test 1, 10 , 100, 1000, 10000, 100000, 1MHow did you know that your metal films are fake?I'm gonna go out on a hunch here and say that the low values will have a negative tc and the higher values will have a positive tc.http://www.electro-tech-online.com/general-electronics-chat/39279-metal-film-temperature-coefficient.html

author: (In)Sanity
author_rank: Regular Contributor
timestamp: January 17, 2013, 08:08:01 pm
content: Based on the info in that forum I would say, if you have one that goes up when heated your entire batch is good. It's what I've also seen. If you can't find a single one that goes up then their is a good chance they are really remarked carbons.Jeff

author: kcs
author_rank: Regular Contributor
timestamp: January 17, 2013, 08:55:02 pm
content: Interesting topic. I was about to orderthis kit.

author: ftransform
author_rank: Frequent Contributor
timestamp: January 17, 2013, 09:03:32 pm
content: Quote from: (In)Sanity on January 17, 2013, 08:08:01 pmso they can somehow shine up carbon ?Why not just scratch it off and look?

author: (In)Sanity
author_rank: Regular Contributor
timestamp: January 17, 2013, 11:46:53 pm
content: Quote from: ftransform on January 17, 2013, 09:03:32 pmFrom what I've seen so far the metal film and carbon film do look a bit different once you scrape off the enamel. I doubt they would bother to disguise it beyond just being blue and the extra band. The only reason I can see against the scratch method is if you want to figure out a larger grouping of them, or perhaps loose resistors or maybe even those you pulled from another device.For me it's not really the cost of the resistors, it's just getting what you paid for. How do I know that if I pay $50 for a kit that I'm getting quality vs the $20 kit. I need to improve my small environmental chamber to better plot the temperature coefficient of various parts. Having a 6 1/2 digit mete certainly has come in handy. I can tell if a resistor goes positive or negative often just be waving my hand at it. Touch it and it's really obvious. I think I forgot that many people don't have those extra digits.Jeff

author: ftransform
author_rank: Frequent Contributor
timestamp: January 18, 2013, 01:05:28 am
content: Quote from: (In)Sanity on January 17, 2013, 11:46:53 pmI really don't think they will mix in fake resistors. They are in a tape and making a special machine to "cut" the tapes would be expensive and their not done by hand because those leads are thin and you would see the imperfections from human hands + the cost of labor would not be worth it as resistors are cheap. I also noticed that the epoxy on the carbon ones is slightly different then the epoxy on the metal film ones.I would not trust high precision low tempco resistors from ebay but I think for general purpose it is fine. IMO that kind of kit will be good enough for development purposes, once you get the prototype going then order better more expensive parts from digikey. Resistors are cheap enough that you should never need to recycle them..Having cheap parts on hand is really useful too, because then you can build your circuit with two different kinds of parts and see how well it performs. Maybe you will discover that your circuit performs adequately using the cheapest of parts, and you can get a better feel of what to expect if you want to mass produce your product cheaply. Exactly why I bought carbon film resistors in addition to metal film resistors.The thought of having an assortment is super awesome resistors is nice but thats rich people shit.

author: (In)Sanity
author_rank: Regular Contributor
timestamp: January 18, 2013, 02:08:23 am
content: Sadly what I found was the Radio Shack 500 resistor assortment I have out performs the fake metal films from China. Using a make shift environmental chamber based on a peltier cooler/heater I started graphing the temperature coefficient of various resistors I had. I had some metal films that were around 40-50 ppm/C and shockingly some Chinese surface mount resistors that were < 10 ppm/C with repeated tests. The Radio Shack assortment came in around 340-350ppm/C and the fake Chinese metal films came in about 540 ppm/C. So all that being said for basic day to day development I'm better off going down to RS and buying their kit. For actual production I'm far better off using SMD components, which is what I normally do anyway. The tolerance on all of them was within spec.I don't have a good enough assortment of quality resistors lying around for doing any type of precision work. It's the temperature coefficient that kills me. I have some resistor on the way from Amazon that I'll report back on.It would be nice to have a verified list of suppliers to purchase from.Jeff

author: Psi
author_rank: Super Contributor
timestamp: January 18, 2013, 03:49:30 am
content: Anyone tried ordering 100 of every value from digikey?

author: (In)Sanity
author_rank: Regular Contributor
timestamp: January 18, 2013, 04:08:45 am
content: Quote from: Psi on January 18, 2013, 03:49:30 amI thought about doing just that. Perhaps even just the E48 range, although the E96 range would be nice.385 values to cover the E48 range. So figure $2-$4 per 100 for decent resistors. That's $770 - $1540 for 38,500 resistors. That's a lot of resistors and a lot of money. Perhaps ten each would be a bit more realistic. Actually thinking about this it's no wonder the Chinese makes fake ones. They can sell hundreds of their fake kits for one of the real kits sold.Jeff

author: ftransform
author_rank: Frequent Contributor
timestamp: January 18, 2013, 05:58:31 pm
content: I still don't understand what you mean by fake. Do you mean poor performance or disguised carbon film resistors?As a relative test I compared two 11k resistors:1) Chinese metal film2) Digikeyhttp://www.digikey.com/product-detail/en/MFR-25FBF-11K0/11.0KXBK-ND/13227Their initial values after stabilization in a 2 ohm measurement on a 6.5 digit meter were within 2 ohms of each other.Anyway, I nulled out the meter and performed a finger pinch heating test, being careful not to touch the leads. I held them for a while (it took lets say 20+ seconds to stabilize).The digikey one, listed at +- 100ppm, stabilized at ~ +1.6 ohms.The ebay one, listed as 100ppm (i think?), stabilized at ~ -3 ohms.I don't know how hot my hand makes em but they are similar size and I was holding it similarly. When I released my fingers the resistors went back to null (as good as they will get in a slightly drafty room) and the results were fairly repeatable (lets say to 0.2 ohms).So it seems that worst case, assuming the digikey resistor is in spec, the chinese one has -200ppm temperature coefficent.I'd imagine that the digikey resistor is slightly better then its spec, (as dave jones demonstrated that the tolerance of resistors listed as 1% was more like 0.5 percent) then I don't think the chinese ones are too bad.Perhaps I will try pressing them against a light bulb in a styrofoam box or something. Getting a stable thermal environment seems like a complete motherfucker.

author: bjorg
author_rank: Newbie
timestamp: January 18, 2013, 07:46:23 pm
content: http://www.digikey.com/product-search/en/kits/passive-kits-resistors/2490615

author: (In)Sanity
author_rank: Regular Contributor
timestamp: January 18, 2013, 08:41:02 pm
content: What I have are remarked carbon films with a temperature coefficient of around 540 ppm/C for a 100k resistor. They have steel leads and are generally low quality. I have some Radio Shack carbon films that measured around 350 ppm/C for the same value resistor. So not only are my Chinese resistors "Fake" metal film aka disguised, remarked, etc. They are also very low quality for even a carbon film.Jeff

author: ftransform
author_rank: Frequent Contributor
timestamp: January 18, 2013, 08:57:58 pm
content: Quote from: (In)Sanity on January 18, 2013, 08:41:02 pmDamn, well if you can use those in your design reliably then you will be a chinamaster.

author: (In)Sanity
author_rank: Regular Contributor
timestamp: January 18, 2013, 09:29:26 pm
content: Surprisingly all the "Fake" metal film resistors I have were well within the 1% tolerance. All that really means is that they were hand sorted. I have zero doubt they are in fact remarked carbons. The company I purchases them from later on even said they had accidentally got a lot of counterfeit metal film resistors. I of course just now found this one some time later. Next batch I get in I'll check them right away.Jeff

author: ftransform
author_rank: Frequent Contributor
timestamp: January 18, 2013, 09:37:13 pm
content: Quote from: (In)Sanity on January 18, 2013, 09:29:26 pmHow did they hand sort them? I think that would be a serious operation requiring many many people...I'm surprised that's even profitable considering the prices they are. Did someone really hire 50 workers to get a 3$ profit in his pocket?I would have thought the costs of organizing such a operation would exceed the money made.I mean maybe if they sold a fake shipment of vishay dales that go for 2 dollars a piece but counter fitting to save pennies on pennies? god damn.

author: (In)Sanity
author_rank: Regular Contributor
timestamp: January 18, 2013, 09:39:57 pm
content: Quote from: ftransform on January 18, 2013, 09:37:13 pmHow much does 50 workers cost in China ?

author: ftransform
author_rank: Frequent Contributor
timestamp: January 18, 2013, 09:47:56 pm
content: Quote from: (In)Sanity on January 18, 2013, 09:39:57 pmHey btw, could you get a 11 kohm resistor for which you measure the tempco and try my finger pinch test?I'm going to build some kind of crude thermal chamber later (I even have a mercury thermometer, stryrofoam shipping box and halogen light bulb) but I'd like to know how much the resistance changes so I can get some kind of crude relative measurement.I set it up so the resistor is oriented horizontally and then pinch it with my thumb and pointer finger, being careful not to touch the leads. I assume you are not a vampire.I do this in a 23 degree C room with closed door, window and no large fan running.ima get some exercise and build the test chamber.

author: M. András
author_rank: Super Contributor
timestamp: January 18, 2013, 09:53:45 pm
content: a bucket of rice?

author: (In)Sanity
author_rank: Regular Contributor
timestamp: January 18, 2013, 10:56:17 pm
content: Quote from: ftransform on January 18, 2013, 09:47:56 pmLooks like all I have in that batch are 10k, 12k, 13k,15k, 16k, 18k ..etc..etc. How about a 10k ?Jeff

author: ftransform
author_rank: Frequent Contributor
timestamp: January 18, 2013, 10:58:07 pm
content: Quote from: (In)Sanity on January 18, 2013, 10:56:17 pmthats fine I have those tooCan you describe your temperature coefficient tester? I think that this styrofoam box will be pretty good but I'd love to hear better ideas.The box is 5 by 4 by 3 inches roughly. Do you think I should include a little fan in along with the halogen bulb in order to mix to atmosphere or is it better to let a thermal gradient develop?

author: (In)Sanity
author_rank: Regular Contributor
timestamp: January 18, 2013, 11:09:31 pm
content: Quote from: ftransform on January 18, 2013, 10:58:07 pmLOL, I'll have to put it back together. It was a crude but effective device consisting of a peltier cooler attached with HS compound to the top of a side mounted Pentium 4 heat sink / fan. Copper bottom. I made a jig out of cardboard to act as a table sitting around the peltier. On top of the pelt I attached a standard aluminum block. To enclose it I use the heavy plastic case that came with my GoPro Hero. It acts like a pastry dish / display.For temp control I used a type K thermocouple an op-amp and a few resistors to feed in to a PIC micro. The PIC's only job was to just cycle the peltier on and off via a Power FET in an attempt to regulated temperature. I monitored all of this with another probe on one of my DMM's. Overall it worked pretty well for a throw together. All you really need is a comparator and a thermistor. Just be sure if you use a FET you switch it on all the way..or HS the crap out of it...but you know all this.So think pastry dish with a peltier in the middle..just reverse the leads for heating.Jeff

author: ftransform
author_rank: Frequent Contributor
timestamp: January 18, 2013, 11:17:13 pm
content: Quote from: (In)Sanity on January 18, 2013, 11:09:31 pmI'm hoping that after the lightbulbs been on for half an hour the temperature will stabilize and that will be that. I really don't want to rewire my rtd and rig up a control system.so yay or nay on the fan?

author: (In)Sanity
author_rank: Regular Contributor
timestamp: January 18, 2013, 11:33:43 pm
content: Ok, the first 10k I found in the pile reads ~10.16200k @ 71.0F (21.66C). The finger test resulted in 10.109xxk before it appeared to stop falling. It's not easy to keep a stable reading that way. Also toss some HST over the leads to keep you from touching them. No need to actually shrink it. Ohh and I used 4 wire Kelvin clip setup. Not sure how scientific this isJeff

author: (In)Sanity
author_rank: Regular Contributor
timestamp: January 18, 2013, 11:35:47 pm
content: Quote from: ftransform on January 18, 2013, 11:17:13 pmI only used a fan for the peltier "Hot" side, or the cool side if I reversed it. It was pretty isolated from the chamber with the exception of maybe some air currents under the dome.

author: ftransform
author_rank: Frequent Contributor
timestamp: January 18, 2013, 11:37:53 pm
content: kong bong cheapie start value : 9.99580 kohmdigikey resistor start value: 9.98350 kohmat a temperature of 73 degree Flightbulb is ~0.5 amps @ 7.5 voltsexperiment start time is 6:37pmtime till stryofoam meltdown eta unknown9.9823 ohms at 102 degree F, digikey final value

author: ftransform
author_rank: Frequent Contributor
timestamp: January 18, 2013, 11:39:00 pm
content: Quote from: (In)Sanity on January 18, 2013, 11:33:43 pmthis type of procedure may qualify as alchemy

author: ftransform
author_rank: Frequent Contributor
timestamp: January 19, 2013, 01:08:37 am
content: kong bong cheapie start value : 9.99580 kohmdigikey resistor start value: 9.98350 kohmat a temperature of 73 degree Flightbulb is ~0.5 amps @ 7.5 voltsexperiment start time is 6:37pmtime till stryofoam meltdown eta unknown9.9823 kohms at 102 degree F, digikey final value10.00425 k at 104 degree F, Chinese final value.assuming linearity (is this appropriate)?digikey change = 1.2 ohms over 29F change, 16.11C increase, meaning 0.074 ohms per degree Cchinese change = 4.625 ohms over 31F change, 17.22 increase, meaning 0.268 ohms per degree C,

author: ftransform
author_rank: Frequent Contributor
timestamp: January 19, 2013, 01:39:18 am
content: So correct me if I am wrong but my final calculations indicate that theChinese resistor PPM is roughly 50 and the digikey resistor PPM is -7I think that's pretty good for ebay parts? Are my calculations wrong?I used this formula:http://hod.koaspeer.com/website/koafaq.nsf/740ef94ac62ac8a685256324006d4a58/8567aa3e0f8f98e5852568d4004a6710?OpenDocumentThat seems too good to be true, considering that they are sold as 100ppm.When my test chamber cools down I will do a test on a carbon film one of similar value.

author: (In)Sanity
author_rank: Regular Contributor
timestamp: January 19, 2013, 02:02:51 am
content: Sorry I was forced to eat Chinese food and drink beer. Checking your numbers now.Jeff

author: JuiceKing
author_rank: Regular Contributor
timestamp: January 19, 2013, 02:11:45 am
content: I have the 1/4W 1% metal film "Joe Knows Electronics" resistor set and found it very convenient for projects. I want to defend Joe. Could Joe be the Lance Armstrong of hobby electronics?I compared tempco of a 220R resistor from Joe vs. an expensive 205R 1/4W 1% metal film resistor manufactured by Yageo. They are pretty close values.I connected both to 20,000-count Fluke meters in min-max mode with similar clips and simultaneously blasted them with a heat gun for about 10 seconds.Joe: 217.0R -> 219.3R (1.06%)Yageo: 203.3R -> 203.6R (0.15%)Say it ain't so, Joe!

author: (In)Sanity
author_rank: Regular Contributor
timestamp: January 19, 2013, 02:33:00 am
content: Quote from: ftransform on January 19, 2013, 01:39:18 amUsing the formula you provided your numbers are correct. 49.04 ppm/C for the Chinese parts and -7.46 ppm for the Digikey parts.7ppm of 10k would be 0.07 ohms.49.04 ppm of 10k would be 0.4904 ohmsGood page for sanity checking.http://www.rapidtables.com/convert/number/PPM_to_Percent.htmI think my formula might be off, it would however not change the ratio I'm seeing between the Radio Shack carbons and the counterfeit metal films, or perhaps I should just call them the deceptive metal films.I'm going to do some more testing using your provided formula.Jeff

author: ftransform
author_rank: Frequent Contributor
timestamp: January 19, 2013, 03:00:12 am
content: 9983.95 ohms @ 74 degree F - carbon film ebay chinese experiment begin.23.33 ckeep in mind that my temperature measurement is crude, as this mercury thermometer is graded with 2F marks, but I don't think the numbers are too bad. It is a calibrated one, and it read the correct reading in a ice bath swirl. It is graded from -20 to 120F.

author: (In)Sanity
author_rank: Regular Contributor
timestamp: January 19, 2013, 03:15:23 am
content: I just did a 70F to 60F test on the same 10k Chinerfeit and used your formula. I ended up with 252ppm/C. So while lower then my readings with my formula it still shows the vast quality difference between the ones you have vs the ones I have.Jeff

author: ftransform
author_rank: Frequent Contributor
timestamp: January 19, 2013, 03:40:09 am
content: Quote from: ftransform on January 19, 2013, 03:00:12 amOK it seems to have stabilized pretty good at 9937.55 ohms @ 106F.Using the formula I got a -260ish ppm/degree C.I don't think the resistors you got are TOO terrible. I wonder what the rolls royce of carbon film resistor is.

author: (In)Sanity
author_rank: Regular Contributor
timestamp: January 19, 2013, 03:48:45 am
content: Quote from: ftransform on January 19, 2013, 03:40:09 amI need to re-test the Radio Shack brand resistors next. Of course I just dumped about 1000 sorted resistors all over the floorAfter that I'm going to test some Chinese 10 turn pot's. Should be interesting.

author: ftransform
author_rank: Frequent Contributor
timestamp: January 19, 2013, 04:01:03 am
content: omg yes i have BONENS, BAORES and maybe even a BOCHEN multi turn trimpot!!!!!!!I also have hong kong panasonic single turn trimpots!

author: (In)Sanity
author_rank: Regular Contributor
timestamp: January 19, 2013, 04:24:54 am
content: Ok still messing with the same 10k Chinese counterfeit.Tested from 50F to 126F I end up with ~350ppm / C +- 2 ppm.Radio Shack 10k carbon I tested from 55F to 126F and got ~ 289ppm / C

author: ftransform
author_rank: Frequent Contributor
timestamp: January 19, 2013, 06:19:27 am
content: Hmm I must try my tests with a wider temperature range. Unfortunately this thermometer only goes to 120F, so I need to make a solid RTD circuit. Maybe I will finally do something with these peltier coolers that I have had sitting around for a year.cold and hot tcr is used as a piecewise approximation I guess. they dont like polynomials for resistorshttp://www.token.com.tw/pdf/resistor-ppm/resistor_ppm_terminology_glossary.pdfthat elaborates on some standards.

author: (In)Sanity
author_rank: Regular Contributor
timestamp: January 19, 2013, 06:33:24 am
content: Quote from: ftransform on January 19, 2013, 06:19:27 amI don't agree with that test range at all. Real world gear is often subjected to much higher and sometimes lower temperatures. A typical power amp or power supply, LCD display, Plasma TV..etc.etc. I think you'll find over 100F in many of these items. I've also found going above a certain point doesn't impact the measurement. I've tested up to 130F so far and didn't see any change in the ppm's.On another note I just tested a thick film 180k Chinese 805 size SMD resistor, and it scored in @ 19.6 ppm over 56F to 126F. I have thousands of them, so at least I have something to build with.Also from what I understand the higher the resistance the higher the ppm will be.If you put a positive tempco resistor in series or parallel with a negative tempco resistor do you end up with a more stable resistance ? In theory you should. Pretty sure that's the principles of basic temperature compensation where your offsetting drift in silicon with an opposite drift.Jeff

author: ftransform
author_rank: Frequent Contributor
timestamp: January 19, 2013, 06:45:11 am
content: Quote from: (In)Sanity on January 19, 2013, 06:33:24 amI know that tempco matching technique is used for voltage references. In some circuits they will match them for greater stability over a temperature range. I have not heard it done with resistors but i'll be it is. I think that 75 C is reasonable, consider the electrolytic capacitor, which would be rather unhappy at those temperatures. You would need to use 130 C electrolytic, and even then the product would experience a short life span.I want graphs for every resistor I use now lol.

author: SeanB
author_rank: Super Contributor
timestamp: January 19, 2013, 06:56:50 am
content: TC varies from batch to batch, so will need selection into matched pairs for use.

author: (In)Sanity
author_rank: Regular Contributor
timestamp: January 19, 2013, 07:21:16 am
content: Quote from: ftransform on January 19, 2013, 06:45:11 amOk, I didn't put two and two together. 75C yes, I thought you were in Fahrenheit. BIG difference.Tested my first 10k 10 turn pot, Chinese made "Baoter 3296". I ran it from 55F to 126F and it came in at 64.98 ppm / C. Not as bad as I was expecting. Assuming I don't fall asleep I'll test some more. This is a time consuming process due to the soak periods needed.

author: SeanB
author_rank: Super Contributor
timestamp: January 19, 2013, 07:58:44 am
content: Check linearity, or at least mid position resistance where it will be at it's worst. Just two extra resistance measurements and will be interesting.

author: ftransform
author_rank: Frequent Contributor
timestamp: January 19, 2013, 08:46:49 am
content: this "panasonic" trimpot is disappointing -732 ppm when it the divider is set to 500ohm - 1500ohm, from 19c to 46cDid you use loctite on yours before heating it?http://industrial.panasonic.com/www-data/pdf/AOH0000/AOH0000CE2.pdfthat's what they claim it is.UNLESS I made a typo and wrote 2 instead of 1. In that case the tempco would be -18.I'm letting it cool down to room temperature again to see whats going on.

author: (In)Sanity
author_rank: Regular Contributor
timestamp: January 19, 2013, 04:52:29 pm
content: Quote from: ftransform on January 19, 2013, 08:46:49 amActually so far I've only tested the end to end resistance and temp co only. Today I'll test some divisions. I wanted a baseline to see just how much the mechanical wiper impacts the overall stability. I tested end to end a 1k 10 turn trim pot from the same manufacturer and obtained 110 ppm/C. I may test divisions on this one first.Jeff

author: (In)Sanity
author_rank: Regular Contributor
timestamp: January 19, 2013, 09:48:40 pm
content: Ok, so I did a test of the 1k 10 turn put at the half value center tap vs end to end.End to end was 110 ppm and half value was136 ppm.I also just got a set of 600 "Metal film" resistors in from Amazon. The scrape test is not all that encouraging. The direction of the temperature coefficient is positive..which is good.I'll report back on the temp co.Jeff

author: (In)Sanity
author_rank: Regular Contributor
timestamp: January 19, 2013, 11:20:22 pm
content: Sorry about all the back to back posts.So which two of these are carbon film ?I you guessed the middle one and the bottom one you would be right. The others are metal film. The middle one was marketed and sold as being metal film. The second to the bottom one looks identical to the middle one with the exception that it appears to be real metal film. Both are not very good quality using metal leads for example. The second to the bottom is coming in around 240~ ish ppm/C temperature coefficient.

author: ftransform
author_rank: Frequent Contributor
timestamp: January 19, 2013, 11:26:06 pm
content: I think you need more light in your pictures it is very difficult to tell. Cameras suck at this, you really need a bright bulb real close to it imo.I remeasured that panasonic trimpot, it turns out that it is -250ppm. The value did however drift by 1 ohm after it warmed up again. I wonder if loctite would prevent this.

author: (In)Sanity
author_rank: Regular Contributor
timestamp: January 19, 2013, 11:56:42 pm
content: I actually used a Canon 60D, but I used the built in flash and didn't use manual settings. I have a canon speedlite flash of good quality that I could use. I'll see what I can do.Jeff

author: (In)Sanity
author_rank: Regular Contributor
timestamp: January 20, 2013, 12:21:18 am
content: Is this photo any better at telling the difference ?

author: nanofrog
author_rank: Super Contributor
timestamp: January 20, 2013, 04:46:19 am
content: Quote from: (In)Sanity on January 20, 2013, 12:21:18 amPretty hard to tell from just scraping it IMHO.For example, take a look at a cross section photo of this carbon film resistor (http://en.wikipedia.org/wiki/File:Carbon-resistor-TR212-1.jpg). It's a dull grey, not black as one might expect.

author: (In)Sanity
author_rank: Regular Contributor
timestamp: January 20, 2013, 05:55:27 am
content: Quote from: nanofrog on January 20, 2013, 04:46:19 amAt this point I agree. I actually found some low value resistors in my original questionable batch of resistors that when scrapped without a doubt look like metal. No grey at all and they are shinny. But then I have the one in the photo that looks more carbon then metal. They test out as very poor quality and that's what counts.In the end I would suggest to anyone to test the resistors in a fashion that makes you happy. If your using them for pullup (or down) resistors with logic circuits..who cares. If your using them as a voltage dropper with LED's...who cares. If your going to build a precision op-amp circuit stop what your doing and order from a respectable company with proven parts. You get what you pay for, but sometimes it's good enough.Jeff

author: ftransform
author_rank: Frequent Contributor
timestamp: January 20, 2013, 07:22:07 am
content: Did you use any kind of advanced control for the peltier or was it the most simple implementation of on/off? How good does it hold the temperature inside a small chamber that way?I'd love to do curves from 10-75C but the temperature regulation part is a bit intimidating. I had PI control in mind but the software part of the project kind of discourages me. On/off in responce to my RTD can I can do, but all the control system stuff is a bit daunting.

author: (In)Sanity
author_rank: Regular Contributor
timestamp: January 20, 2013, 07:33:59 am
content: Quote from: ftransform on January 20, 2013, 07:22:07 amI had a simple control system my first go around, I had taken it all apart (breadboard) so this time I opted to just use constant current and let it hit the top and bottom of cooling and limited heating. For cooling I was pushing about 60 watts, for heating 10 watts. Once it hit it's limits it was very stable. I added some foam to the chamber to reduce the volume more. I'll toss together another controlled setup in the future. Too many things to do.Jeff

author: ftransform
author_rank: Frequent Contributor
timestamp: January 20, 2013, 01:32:42 pm
content: Quote from: (In)Sanity on January 20, 2013, 07:33:59 amVolume reduction is a good simple idea that I am ashamed not to have thought of. I noticed that a good stable max point is reached with a lightbulb, I suppose that a peltier cooler is no different.Have you ever found a graph of resistance vs temperature for a normal (carbon/metal/wire) resistor? It's surprisingly difficult to find, all I seem to run into is graphs of thermistors and "increased tcr" types. I want to see how linear the change in resistance of a regular resistor is from experimental values. Eventually I will make my own once I get to this project but I am curious now.

author: (In)Sanity
author_rank: Regular Contributor
timestamp: January 20, 2013, 05:22:18 pm
content: Quote from: ftransform on January 20, 2013, 01:32:42 pmDo a search for "temperature coefficient resistor" in Google Images.

author: (In)Sanity
author_rank: Regular Contributor
timestamp: January 20, 2013, 05:28:50 pm
content: Just stumbled on this article.http://www.eetimes.com/electronics-news/4199812/Strengths-and-weaknesses-of-common-resistor-typesI also think it's important to note based on this article and others I've now found that it would appear you don't want to test below 25C to get your PPM reading. It almost appears as if it's two different responses.

author: M. András
author_rank: Super Contributor
timestamp: June 17, 2013, 08:01:21 pm
content: bought a resistor kit for testing purposes, well its advertised as metal film but most likely carbon film they have a nice negativ tempco. tested around 10 different value all of them dropped on the readings using my fluke 289 and soldering iron for more quicker and wider response from the resistorshttp://www.ebay.com/itm/300863774703?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649.wondering what the seller will say about this

author: (In)Sanity
author_rank: Regular Contributor
timestamp: June 18, 2013, 04:49:28 am
content: I tossed a bunch that I got off ebay. I ended up with a few batches off Amazon that appear far better in quality. Still you get what you pay for, so while they are better they are still not really good. I do have some SMD resistors that I got from ebay that have proven to have very nice temp-co's. A soldering iron test is going to tell you the direction, but it's not going to give you a very good test of stability. I guess it might work as a course reference against a known higher quality resistor.Jeff

author: M. András
author_rank: Super Contributor
timestamp: June 18, 2013, 03:14:17 pm
content: gonna buy anyway some good quality yageo 1%metal films 0.6watts from a local electornics store i wanted to use these as throw away test they stock the whole e24 range so i jump in with 100 each, unfortunatly they dont stock the whole range in smd