Adjustable Buck Voltage Regulator  - AliExpress - Exiciting finds - Page 1
Forum section: electronics / projects

author: ez24
author_rank: Super Contributor
timestamp: May 03, 2015, 08:09:52 pm
content: HiI just have to share my exciting finds today. I found AliExpress today on this forum and found thisbuck regulator:http://www.aliexpress.com/item/Wholesale-1pcs-DC-Step-Down-Converter-DC-4-0-38V-to-1-25V-36V-5A-75W/32285636716.htmlScroll down and you will find a treasure : specs and documentation (readable)Boy did I have to get a couple of these, and heat sink, standoffs, documentationwow 2 finds todaySure glad to see ebay competitionWasn't that hard to sign up and order - one password for Ali and one for payment (no paypal) - same as fleabayEdit: Another exciting find - I can print out the complete ad with the specs. Ebay cuts the ad and details off. With ebay I have to copy and paste into Notepad to print the details outEdit: Another exciting find - AliEpress allows product reviews like Amazon

author: Canobi
author_rank: Regular Contributor
timestamp: May 04, 2015, 12:01:30 am
content: I've used Aliexpress myself a couple times and was happy with what I got. Another one I use is Deal Xtreme. I got some relatively good quality scope leads just recently for very little, shipping is also free on most items, though it's less component oriented than Aliexpress.

author: wraper
author_rank: Unknown
timestamp: May 04, 2015, 12:23:20 am
content: Just don't expect it running at full rated power.

author: splin
author_rank: Frequent Contributor
timestamp: May 05, 2015, 09:44:24 pm
content: Quote from: ez24 on May 03, 2015, 08:09:52 pm“Danger, Will Robinson!”Those 50V 220uF filter capacitors (in the heavily annotated picture) have a 650mA ripple current spec:http://www.mouser.in/ProductDetail/Lelon/VZH-221M1HTR-1010/?qs=sXzuR3ywNuc25mceIPLw6w%3d%3d(That says 553mA but the datasheet shows 650mA). With a 5A output current there's a *very* good chance that the input capactitor is going to explode and possibly take somebodies eye out - ask me how I know (it wasn't this particular convertor and it missed my eye btw)!This shows the equations for calculating the input and output capacitor ripple currents:http://rohmfs.rohm.com/en/products/databook/applinote/ic/power/switching_regulator/capacitor_calculation_appli-e.pdfLook at the equation on page 3. You would probably find it a bit tricky to determine the inductor ripple current but its not a very significant term anyway. Assuming the inductor ripple current is 1/3 the 5A output current; with an output of 5V and input voltages between 6 and 36V the peak input ripple current is2.52Aat Vin = 2 * Vout and a minimum of 1.39A at Vin = 36V.If you have a low impedance power source and *very* short, low inductance connecting leads then you may be OK as most of that ripple current will come from the source rather than the filter capacitor, but how are you going to measure it to be sure?Bear in mind that the filter capacitor has a specified impedance of 120m ohms at 100kHz so the total source impedance of your power source and the connections and the PCB traces from the input connector to the switching mosfet needs to be less than approx 120 milli-ohms * .65A/2.52A milli-ohms , or < 31 milli ohms to keep the capacitor's ripple current below 650mA.At a switching frequency of 300kHz the reactance of an inductor consisting of a single 8mm diameter loop of wire will exceed that, never mind the wire resistance. The convertor's switching freqency could even be 500kHz or higher making the problem worse.I would replace the input capacitor, at least, with something with a much higher ripple current rating such as:http://www.digikey.com/product-detail/en/EKZN500ELL681MK25S/565-4071-ND/4843881An aluminium-polymer capacitor is much smaller for the same rating but more expensive:http://www.mouser.in/ProductDetail/Nichicon/RNU1H470MDN1PH/?qs=sGAEpiMZZMs9%2fSpGH%2fyc7JYN24Rot9XpwJjNTEwdkxU%3dNow you know why those switching convertors are so cheap - they cost reduce them to the bare minimum and then carry on removing essential parts!Note that ripple current ratings vary enormously with capacitor type and size so you need to check the exact specs.Alternatively, you could leave the existing capacitor and connect a suitable capacitor as close as possible to the input connections, but beware the inductance again from the leads and PCB traces.The ripple current is much less in the output capacitor and probably won't be a problem, but worth trying to estimate from the Rohm link.In the mean time, either limit the current output to not much more than 1A, or a tin-hat and safety vizor might be a good idea!

author: Yansi
author_rank: Super Contributor
timestamp: May 05, 2015, 09:51:06 pm
content: lol, 220uF basic aluminium cap for 5 amps, what a joke!Might be interesting to consider polymer caps, but I've never used those nor I know much about theirs typical specs. But I smell that ripple current vs. capacitnce should be much better than standard aluminium do have.

author: ez24
author_rank: Super Contributor
timestamp: May 05, 2015, 11:10:12 pm
content: Some good info - thanks splinWill have to study all that information.I would never expect to get full rating from Chinese modules. I will test them and put up the test results, starting at 70% and work down. I hoped to get a good 2a from this.

author: paulie
author_rank: Frequent Contributor
timestamp: May 06, 2015, 12:38:57 am
content: LOL. I was wondering how long it was going to take for the china haters and fear mongers to chime in.Out of millions (several thousand personally) of similar type out there I doubt even one has taken any eye out or exploded due to ripple spec. It's true that these do not perform as advertised, even with the heatsink warned about in most listings, but no problem running an amp or two. Now let's bring up the "huge ripple" which might not actually interfere with most applications but might just be detectable with a scope with enough sensitivity. Or what about "fake" chips? That subject's always good for some healthy hand wringing.Listening to problems brought up by units "properly" designed here from both hobbyists and professionals, IMO the Chinese seem to have a much better handle on these than crybaby western experts.I'm positive running with scissors has taken a bigger toll on eyesight and don't forget those wolves under the bed.

author: splin
author_rank: Frequent Contributor
timestamp: May 06, 2015, 02:40:33 am
content: Quote from: paulie on May 06, 2015, 12:38:57 am*Mine* didExplode - that is - fortunately I wasn't looking at it at the time. Hardly surprising when the input capacitor's ripple current was nearly 5 times the specified limit - that's 25 x the heating power - how is it not going to explode???QuoteNo, as I said in my last post, 'don't run it much beyond an amp' - because at approximately 1.2A the ripple current is still in spec! At 5A its way beyond the limit which is what I was warning about. The vast majority won't explode because they won't be running at maximum 'rated' current and at the most stressful input/output ratio, as it turns out mine was when testing it.I'm not a China hater - I love the fact that we can get these things dirt cheap - but you have to be aware of the dangers and their limits. I bought a Chinese hot air station recently; it came with a 3 pin mains adapter which, through terrible design, didn't make contact with the earth pin. I might well have become a 'China hater', for a little while at least, if I'd got 240 of our finest National Grid's volts across my chest! And before you say it, that was a definite possibility because the live, very thinly, single insulated wire feeding power to the heater was trapped hard up against an earthed connection in the air wand. I bought it cheaply not expecting it to be safe, and it wasn't but I could remedy that.QuoteI've no doubt that Western safety standards are set very high - un-necesessarily and expensively so in many cases - but I think you've got a very odd perspective. My friend got severe chemical burns from a Chinese made leather sofa. Does that make us cry-babies because the products were banned?QuoteBut that's 2.5A RMS of ripple current in the input capacitor - you wouldn't need a super-sensitive scope to detect it, an unloved finger and a burns specialist should do just fine.(Because it looks like a bandaged thumb!).It won't have any significant impact on the output voltage ripple so you're application will work just fine until the big bang and the amps go on strike or go elsewhere.

author: paulie
author_rank: Frequent Contributor
timestamp: May 06, 2015, 04:10:10 am
content: Quote from: splin on May 05, 2015, 09:44:24 pmWell that kinda says it all!. And don't forget the black helis.Seriously though, as part of the day job handling large numbers of these, both "proper" from "official" channels and cheapies from The Evil Empire, there has been no big difference in failure rates. I've encouraged clients to return defects for analysis (AKA fix and drop in my parts box). Out of several dozen very few faults involving those caps and those related to solder joints or mechanical damage. No puffies or explosions. Dead silicon far more common. So from my perspective these are a great deal at 1/5th to 1/10th the cost.Anyway your repeated mention of 5a does not sound like direct experience with these particular units. They simply will not supply that and in fact long before 3a simply shut down. Then you "assume" 2.5a ripple which makes comments even less credible. So it don't look like we are even on the same wavelength here.Feel free to throw money out there for the Real Thing. Personally I hate playing the sucker.

author: ez24
author_rank: Super Contributor
timestamp: May 06, 2015, 05:42:24 am
content: thanks allLots of info on ripple - I sure have to study thisI will test these to 2 amp and hope I get that

author: kjs
author_rank: Regular Contributor
timestamp: May 06, 2015, 09:29:02 am
content: If you use Chinese parts you have to be aware how the fairy tales (= Chinese for specifications) are made. If the switching transistor has a maximum current limit of 5A it's a 5A power supply. If the capacitor is marked with 40V maximum input voltage is 40V. There's no such thing as design margin or any concern about reliability or lifetime.Don't get me wrong, we use LM2596 modules as we can't even buy the IC for the $0.54 we pay for the entire module but we have completely characterized the stuff and use them at limits which are far away from what they specify. All modules go through regular final test and whatever isn't as it should be is returned and replaced for free. Much cheaper and as it isn't a part which adds value it doesn't even matter whether the LM2596 are genuine or XL……. marked with TI/National/ON logo.

author: Fungus
author_rank: Super Contributor
timestamp: May 06, 2015, 10:03:10 am
content: Quote from: kjs on May 06, 2015, 09:29:02 amYep. I've had some of those voltage converters running for years. Just run them well below claimed spec, keep an eye on the temperatures, be happy that you paid a quarter of the price!

author: paulie
author_rank: Frequent Contributor
timestamp: May 06, 2015, 01:38:56 pm
content: Quote from: kjs on May 06, 2015, 09:29:02 amI agree 100% on that. I prefer the term "bare faced liars" as more descriptive.Fortunately Ebay buyer protection saves the day. Out of literally thousands of transactions last few years there are couple hundred cases opened. Actually it rarely gets to that because a quick message to seller almost always results in instant refund. They know what they did and just don't care because few bother to complain. They simply write off guys like me as cost of doing business.Quote from: kjs on May 06, 2015, 09:29:02 amWe'll have to agree to disagree on this one. Transistor is actually a minor part of the system. In fact I'd put it a few down on the list below things like inductor and, yes that's right, caps. Splins warning about finger fatality is close to true, not the caps though. For a few rare applications I do have to tack on another cap for noise suppression but it's the coil that gets real hot real quick near limits. That toroid in OPs module is one reason it actually puts out close to 3a instead of 2a for the half buck version that has no pots or display and cheaper inductor.So in my world a max current limit of 5a is a 2-3a supply.ps. Generally for personal use I prefer the buck/boost (SEPIC) versions since there are no concerns at all regarding input or output voltage. A few cents more but worth it to make life easy. The new XL6009 buck/boost are even better with another amp over the old LM2596 and cheaper still.

author: Fungus
author_rank: Super Contributor
timestamp: May 06, 2015, 02:06:59 pm
content: All this is true ofanyelectronic component. Nothing should be run at the "absolute maximum rating" listed in the datasheet.Even if it's something like a MOSFET bought from the most reliable supplier in the world, the "absolute maximum rating" isn't a working value, it's a theoretical limit for the part either under ideal conditions (which don't exist) or for very short bursts of time.If you want to switch a 5A current using a MOSFET then buy a MOSFET rated for 30A. If you want a 5A power supply that will run 24/7 then buy a 12-15A power supply. That's the reality no matter where it's manufactured (unless you work at NASA/military and pay a fortune for mil-spec power supplies).

author: macboy
author_rank: Super Contributor
timestamp: May 06, 2015, 03:57:39 pm
content: Quote from: Fungus on May 06, 2015, 10:03:10 amIf you are running a "5 Amp" module at 1 Amp to avoid self-destruction, did you really get a bargain on that 5 A module, or did you overpay for a poorly made 1 A module?

author: Fungus
author_rank: Super Contributor
timestamp: May 06, 2015, 04:06:09 pm
content: Quote from: macboy on May 06, 2015, 03:57:39 pmI got a decent price on a reasonably well made 2A module.(If it's putting out enough amps for the purpose and it doesn't burn my fingers then it's probably going to last as long as anything you're overpaying for).

author: ez24
author_rank: Super Contributor
timestamp: May 06, 2015, 06:37:11 pm
content: Quotewhat is this ?? (SEPIC) Do you have any links to the devices you use?I think some of the modules I ordered have the XL chip because I could see "X", I will not know until I get them.Searching ebay for SEPIC I came up with this interesting one:- high sales- current set with jumpers (I like this)- BUT I do not know how to set the voltage (shows my ignorance)[url=http://www.ebay.com/itm/150-1500mA-Buck-Regulator-LED-Driver-for-1-50W-High-Power-LED-/161026417634?pt=LH_DefaultDomain_0&hash=item257dec23e2]http://www.ebay.com/itm/150-1500mA-Buck-Regulator-LED-Driver-for-1-50W-High-Power-LED-/161026417634?pt=LH_DefaultDomain_0&hash=item257dec23e2here is another one:[url=http://www.ebay.com/itm/LM2577-Auto-Step-Up-Step-Down-Power-Supply-Module-Solar-Power-Panel-DC-DC-SEPIC-/330809583178?pt=LH_DefaultDomain_0&hash=item4d05c9a64a]http://www.ebay.com/itm/LM2577-Auto-Step-Up-Step-Down-Power-Supply-Module-Solar-Power-Panel-DC-DC-SEPIC-/330809583178?pt=LH_DefaultDomain_0&hash=item4d05c9a64a- this does not have current limitAND basically how is this different (other than specs) than the one I found (mine has current limit)Now I wish I could find one with- current limit with jumpers- voltage limit with pot- LED- large coil- new chip- heat sink(ha ha probably no such animal)FYI I once lived in Taiwan and went into a company that made audio amps. I asked how much power it had and they said anything I wanted. In other words I could have had a 5000 watt amp that put out 1 watt.

author: kjs
author_rank: Regular Contributor
timestamp: May 06, 2015, 07:11:34 pm
content: SEPIC stands for "Single-ended primary-inductor converter". It can convert up and down. This means your output voltage can be higher or lower than the input voltage.Example (LM2577 based, just a random link):http://www.ebay.com/itm/DC-DC-adjustable-auto-step-down-up-power-supply-module-solar-power-panel-LM2577-/111185749981?pt=LH_DefaultDomain_0&hash=item19e32fe7ddQuote from: blueskull on May 06, 2015, 06:46:38 pmI am still searching for one example which isn't over-rated....... And yes, if you operate them at the "specified" limits the inductor can blow up as well as the capacitors. Even when they don't blow up their lifetime is very limited. We measured the temperatures of the LM2596 modules (C and L) at room. 145C when operated to the fairy tale limits. Just use them to what the components are designed for and ignore the fairy tale and they are fine.

author: Fungus
author_rank: Super Contributor
timestamp: May 06, 2015, 07:40:01 pm
content: One of these arrived yesterday, it seems to work well and it's not too badly made (has nicely rounded corners and 'feet'):http://www.ebay.com/itm/391036308181It can display output volts and amps and has a settable current limit (short the output terminals, dial the limit current). Very handy for seeing how much power a circuit is using. Yes it's only 10mA resolution but that's good enough for a lot of jobs.The main chip is an MP2307 buck converter rated for 3A continuous output.$8.60 for a "poor man's bench power supply"? Bargain!

author: Rick Law
author_rank: Super Contributor
timestamp: May 06, 2015, 10:00:50 pm
content: Quote from: Fungus on May 06, 2015, 07:40:01 pmI would not call that a bargain. As said, you can't run that 3A sustained for long. You need to give yourself some headroom.I have been using a few similar ones as my "bench supply" for around a year. They are fairly high noise and generally below spec (ie: give yourself head room). If noise is not an issue, they are not too bad but this one is not a bargain.The only thing that distinguish this one from the $3-$5 (5Amp) alternatives is the build in LED display.This is an analog control unitusing 3296 Trimpot. Trimpot is not designed for frequent adjustments. Looking up specs from Bourns, their relatively high quality3296 trimpots are designed for 100 turns. Once you use it a while (50+ times) the wiper begin to wear out. It will start to get difficult to adjust with the jitter. So, you better get good at trimpot replacement. On one of mine, I replaced the trimpot so many times the copper trace was beginning to lift (got impatient, pull too hard before solder fully melt).I switched over to using the B3603 digitally controlled. It can do close to 2A without external cooling. I did a "mini review" on it here:https://www.eevblog.com/forum/reviews/b3603-dcdc-buck-converter-mini-review-and-how-the-set-key-could-be-fatal/There are some inaccuracy there, but it give you a general feel of that machine. I've learned a lot more since I wrote that. The learning since then pointed me to at least oneembarrassing fact: The unit I reviewed actually had a problem and I didn't even know it at the time!The noise I screen printed is about 1/3 more than it should. I have since repaired my unit. My own inexperience for sure, but that is the process of learning. I plan to update that review but I haven't got around to do it yet.Those corrections are documented in that thread, so if you found that a potential buy, read the whole thread. You get a feel of how the unit works and the unit's strength and weakness far better than if you just read the review.

author: ez24
author_rank: Super Contributor
timestamp: May 07, 2015, 01:12:04 am
content: [url=http://www.ebay.com/itm/391036308181]http://www.ebay.com/itm/391036308181I had not seen this one - it has an inductor that looks half way between the small one and large oneso I ordered a couple of these to testthanks

author: kjs
author_rank: Regular Contributor
timestamp: May 07, 2015, 01:19:02 am
content: They replaced a half way decent pot-core with a lousy axial one to save on cost. Will radiate nicely on the switching frequency.

author: ez24
author_rank: Super Contributor
timestamp: May 07, 2015, 01:20:42 am
content: https://www.eevblog.com/forum/reviews/b3603-dcdc-buck-converter-mini-review-and-how-the-set-key-could-be-fatal/thanks I have been looking for a review like thisthe comment on the pot (100 turns) was a shocker - I did not see this comingback to the drawing boardthanks

author: ez24
author_rank: Super Contributor
timestamp: May 07, 2015, 01:25:42 am
content: Quotepot-core ??axial one ??are you talking about the inductor"Will radiate nicely" is this good or bad ?thanks

author: ez24
author_rank: Super Contributor
timestamp: May 07, 2015, 01:51:02 am
content: Quotethanks I understand now BUT one more stupid questionare we talking about the inductor, it is the only thing I can think of because I think "pot core" means pot metal and the inductor is the only thing I can think of unless it is the caps. I do not think you are talking about the ICs.Will I be able to test EMI using a scope by just holding the probes over the thing (once I find out what the thing is ha ha)thanks

author: kjs
author_rank: Regular Contributor
timestamp: May 07, 2015, 02:03:10 am
content: yes, we are talking of the replacement of a $0.10 inductor with a $0.03 inductor.... Efficiency will be lower too as these axial inductor "don't keep the power inside"....You won't be able to measure radiation with a scope. You can do a crude thing and put a length of wire into it to use as an antenna but to do it right you need a bunch of expensive equipment including the right antenna.To solve the potentiometer issue: Bourns makes really good multi-turn potentiometers with much longer lifetime. They are bulky and you have to install them in a panel but they are precise and good. Made in Mexico but you can find them cheapest on alislow. I paid less than $4.50 including the dial (and free shipping) which I would highly recommend to buy as they come with the ancient 6.35mm diameter shaft. Difficult to get knobs for them.....(Bourns model 3590, 1,000,000 shaft revolutions)EDIT: price went down:http://www.aliexpress.com/item/10K-Ohm-3590S-2-103L-Potentiometer-With-10-Turn-Counting-Dial-Knob/32338241354.html

author: paulie
author_rank: Frequent Contributor
timestamp: May 07, 2015, 02:13:43 am
content: Do NOT forget those wolves under the bed. You could lose an... ummmm... uh... ANKLE!

author: Rick Law
author_rank: Super Contributor
timestamp: May 07, 2015, 03:25:45 am
content: Quote from: ez24 on May 07, 2015, 01:20:42 amre: "the comment on the pot (100 turns) was a shocker - I did not see this comingThose trimpots are made for infrequent adjustment - like setting it to exactly 5.00V, and then it will sit at that position for months or years until the equipment requires service (recalibration). They are not really intended for frequent changes as volts for a variable voltage power supply would.When I used those boards as PSU and when the solder pad starts to come loose, Isubstituted the 3296 trimpot with a pair of knob-turn variable potentiometer. A 10K+500ohm to replace the original 10K 3296 trimpot. The 10K would be the coarse, and the 500ohm as fine adjustment. It was so much easier and quicker to change voltage with the pair of knob-tunners and no need for a screw driver.

author: Fungus
author_rank: Super Contributor
timestamp: May 08, 2015, 10:01:51 am
content: Quote from: Rick Law on May 06, 2015, 10:00:50 pmAs said, I wouldn't ever run eBay stuff at maximum rating.I probably won't go over an amp or so with the stuff I do. I was mainly interested in the amps display and the current-limiting protection for development work.Quote from: Rick Law on May 06, 2015, 10:00:50 pmWhoah! I didn't know that. If I ever do replace it I'd replace it with something with a proper knob so it would only be once.Still, at these prices it's perfectly feasible to have two or three of these set to common voltages (one for 3.3V, one for 5V, etc.)Quote from: Rick Law on May 06, 2015, 10:00:50 pmThanks for the info.Edit: I looked up the pots on my board, they're these:http://en.bochen-gs.com/products_detail/&productId=81.htmlMechanical endurance: 200 cycles

author: Fungus
author_rank: Super Contributor
timestamp: May 08, 2015, 10:12:59 am
content: Quote from: Rick Law on May 07, 2015, 03:25:45 amI'd probably put in a regular multi-turn Bourns pot. They have rotational life measured in the millions.I might even have a couple of 10K units hidden in a drawer somewhere....hmmm...thinks...Almost any old pot would do for the current-limit adjuster, it doesn't need to be very accurate.

author: paulie
author_rank: Frequent Contributor
timestamp: May 08, 2015, 08:58:51 pm
content: That shaft in my Pocket Power Pack is attached directly to the "limited" trimpot on one of those cheepie buck/boost modules and has been tweaked thousands of times over the last couple years with no sign of wear. So IMO, unless you are involved with Mars Rover or heart/lung machine, the concerns from nervous nellies are misplaced.ps. It has a knob on it now so gets twiddled even more often.

author: Rick Law
author_rank: Super Contributor
timestamp: May 08, 2015, 10:18:13 pm
content: Quote from: paulie on May 08, 2015, 08:58:51 pmGo check... their latest datasheet PDF, improved to 200 cycles compare to the last time I checked. Still just 200, not thousands.http://www.bourns.com/pdfs/3296.pdfThis "nervous nellies" consider their datasheet an authoritative source.

author: paulie
author_rank: Frequent Contributor
timestamp: May 08, 2015, 11:23:42 pm
content: It's a choice. One can live in La-La (pdf) land or the real world. For hobby purpose I prefer the latter. Get a lot more done, have more fun to boot, and for pennies on the dollar. YMMVps. FYI at 15 for a dollar I guarantee the 25 turn ones in these chinese converters are not Bourns. Very unlikely they even have a datasheet. So maybe the lesson here is "There's one bourn every minute...". LOL.

author: kjs
author_rank: Regular Contributor
timestamp: May 09, 2015, 12:36:54 am
content: Quote from: paulie on May 08, 2015, 11:23:42 pmAt least the ones I removed from mine were labelled with Bourns but that doesn't mean that they were actually made for/by Bourns....

author: Rick Law
author_rank: Super Contributor
timestamp: May 09, 2015, 12:42:07 am
content: Quote from: paulie on May 08, 2015, 11:23:42 pmAre you suggesting you do not look at datasheets at all?If so, you must have a different hobby than I do.

author: kjs
author_rank: Regular Contributor
timestamp: May 09, 2015, 05:22:47 am
content: Quote from: Rick Law on May 09, 2015, 12:42:07 amThere are hobbyist who are happy when it just works. The rules for a real commercial design or a good hobby solution are different.

author: paulie
author_rank: Frequent Contributor
timestamp: May 09, 2015, 03:13:45 pm
content: I disagree. the rules are exactly the same, just more demanding in some cases. I have produced several designs that reached market. It been a while but a couple still being produced. Only one of those actually required datasheet level compliance. As I hinted earlier there are some applications (military, medical, etc) that need extreme care, other just need to work with some small degree of confidence. Also mentioned that not all parts even have datasheets like with the one discussed here.Quote from: Rick Law on May 09, 2015, 12:42:07 amI've spend quite a lot of time. However often just for entertainment purpose. Many datasheets are rife with errors and often flat wrong, sometimes comically so."There are lies, damned lies, statistics... and datasheets."You are free to spend 99% of your life squinting at specs. I choose a more balanced approach which in some cases involves no involvement at all, other times a little, rarely a lot. I'm not a big fan of simulations either. Can't count the times they worked but app failed. Or the other way around. I'm more real world oriented.

author: Rick Law
author_rank: Super Contributor
timestamp: May 09, 2015, 08:36:07 pm
content: Quote from: paulie on May 09, 2015, 03:13:45 pmWell, your attitude and mine on this matter differ. How interesting.For me (I am a hobbyst), datasheet is the basis from which I judge. For quality products, I expect it to be typically 1 or 2 standard deviation on the "plus" side favoring durability or reliability. For Cheap stuff, I expect it is 1 or 2 typically also, but on the "negative side" favoring cost.If the trimpot is 200 cycles, expecting 400 would be way outside the bell curve's 1 or 2 standard deviation. I called it turns, but cycle really is turning all the way one way then all the way back. Rarely would we turn from 0-100%, it would be back and forward around say 5V; back and forth around that spot at least a couple of times to get it close to on-the-dot.I also expect the better manufacturers to be more consistent. If the first one fails at say 250 turns, I would expect the other one from the same manufacturer to last around 250.

author: kjs
author_rank: Regular Contributor
timestamp: May 09, 2015, 08:52:10 pm
content: Rick, unfortunately the way paulie designs is getting more and more standard and is also what gives most Chinese designs such a bad reputation. With the super short warranty time in the US (90days) most of that stuff won't come back......Walmart tried to sell stuff designed like that in Germany when they bought a chain there (Wertkauf) and learned the hard way that it will bite you. With the long warranty by law they got most of their crap back and made tremendous losses that way.

author: SeanB
author_rank: Super Contributor
timestamp: May 10, 2015, 07:38:52 am
content: Here a 1 year warranty is mandatory. I had an electric kettle that lasted 5 years that way, though it was in reality one repair ( the first time) and then after that 6 new kettles, as they typically failed within a year, so went back under warranty. New unit, new purchase slip, keep the box and a copy of the thermal paper ( so it will be readable after more than 3 weeks) receipt and rinse and repeat. The 6th one lasted 12 months 2 weeks. Not a bad life for a $10 kettle.If I go to Makro ( now owned by Walmart) I don't even need the slip, as the computer system will tell me when I bought it, it goes back over 10 years.....

author: Fungus
author_rank: Super Contributor
timestamp: May 10, 2015, 10:27:37 am
content: Quote from: paulie on May 08, 2015, 11:23:42 pmReally? Is that why mine were stamped "bochen" and I could provide a link to the specs (above)?Quote from: kjs on May 09, 2015, 05:22:47 amOh, no. NotTHATthread again...

author: paulie
author_rank: Frequent Contributor
timestamp: May 10, 2015, 04:39:34 pm
content: Quote from: Fungus on May 10, 2015, 10:27:37 amOk, the ones on the converter in my hand are not labeled Bochen (very similar to Bourne logo) but the bargain bag parts are so I stand corrected. I suspect data was just copied from a Bourne spec and 100 changed to 200. So moral of the story is if you have great faith in chinese spec sheets then these 15/$1 pots last twice as long as the $2 each Bourne brand.There are genuine Bourne kicking around here and I can tell the difference right away. It's the lash or play or hysteresis or whatever you call it. Expensive ones take one or half a turn when reversing direction while the cheapies sometimes do nothing for 5-6 turns. Actually resistance typically even increases for a couple turns before starting to decrease as intended.ps. This is how they behave when new and the same after 5-10 stop to stop (1.2v to 40v on my power pack) per day average for couple years. I have a half dozen of these units but admittedly only one gets exercised like this. Maybe the resistance changes more than specified 3% over time but that's not an issue for me. I'm convinced getting thousands of cycles out of these.

author: Fungus
author_rank: Super Contributor
timestamp: May 12, 2015, 05:19:52 am
content: Quote from: paulie on May 10, 2015, 04:39:34 pmHow do they work inside? Has anybody done a teardown of a bourns-style trimmer pot?(I don't have a spare/useless one lying around that I can attack with a pair of side cutters).Quote from: paulie on May 10, 2015, 04:39:34 pmI can easily imagine that the track is made of very soft stuff to ensure a good contact.Still, 200 doesn't seem like very much. It seems unlikely they'd be completely broken after only 200 turns.

author: Rick Law
author_rank: Super Contributor
timestamp: May 12, 2015, 06:23:08 am
content: Quote from: paulie on May 10, 2015, 04:39:34 pmWhile not questioning if it is true, an anecdote is just an anecdote. I know someone who work at an arcade and win the lottery at 45. It doesn't mean others should plan on getting a job at an arcade at 44 so as to retire on lottery winning.If I am doing the same change 5 to 10 times per day, by the end of the first week and knowing there is another couple of years ahead -- of doing the same mind numbing thing 5 to 10 times a day:I would have solder in a 2p3t switch and 3 trimpots (on a daughter board) and make the 3 pots switch-selectPot A=set to 1.2V, Pot B=set to 40V, Pot C=random, whatever that pot C is set to be at the time.Then again, we all value our time differently. As a hobbyist, I have the luxury of doing things my way and spend my time only on what I consider fun. As an employee, I have to spend time on what my boss values. Whatever he/she values more, that is what I do more of.Quote from: Fungus on May 12, 2015, 05:19:52 amIf the manufacturer said 200 turns in the datasheet, and you like to push it, that is your prerogative.It would not turn into ashes on the 201st turn, it will justnot be able to do what it is suppose to as well as it didand gets worst as time proceed. My experience is it gets jittery (such as while steady turn up the voltage with the trimpot, it goes from 5.01V to 5.20V then back to 5.10V all while in turning in the same direction, and some setting I used to be able to get, the pot doesn't seem to stop there anymore). Thermo stress can cause it to go wild perhaps due to contact no longer secure.The trimpot is just a 25 cents part and cheaper in bulk. So why introduce such uncertainty. Get some in stock, and just grab a solder iron and replace the darn thing when it begin to jitter or shows signs of failure. After replacing trimpots may be half a dozen times, it becomes a very easy 2 minute job.It is however your prerogative if you choose to deal with difficulties in adjustment over difficulties in replacement.

author: bktemp
author_rank: Super Contributor
timestamp: May 12, 2015, 06:38:01 am
content: Quote from: Fungus on May 12, 2015, 05:19:52 amYes. I don't know if it was a genuine Bourns one, but the construction looks good.The wiper consists of many springy contacts connected in parallel to assure a good contact.

author: Fungus
author_rank: Super Contributor
timestamp: May 12, 2015, 07:36:58 am
content: Quote from: bktemp on May 12, 2015, 06:38:01 amThat's a cool design (and not what I imagined at all...)

author: Fungus
author_rank: Super Contributor
timestamp: May 12, 2015, 07:52:26 am
content: Quote from: Rick Law on May 12, 2015, 06:23:08 amI'd put in something that's going to last longer if I was getting the soldering iron out too often.

author: kjs
author_rank: Regular Contributor
timestamp: May 12, 2015, 08:27:23 am
content: Quote from: Fungus on May 12, 2015, 07:52:26 am+1. I have a power supply I build in my youth with a Bourns 10-gang pot (the BIG round ones with 6.35mm shaft). It still adjusts perfectly without playing kangaroo. If a power supply jumps to much it may even destroy some sensitive circuits when the voltage exceeds the maximum limit. For calibration these small screwdriver actuated ones are fine but not for something which gets adjusted on a regular basis.

author: Rick Law
author_rank: Super Contributor
timestamp: May 12, 2015, 07:46:15 pm
content: Quote from: kjs on May 12, 2015, 08:27:23 am"If a power supply jumps to much it may even destroy some sensitive circuits when the voltage exceeds the maximum limit."That is exactly what originally drove me to look into life expectancy of those trimpots. I went look for datasheets and I was shocked -I was expecting thousands but found 100when I looked about a year ago. Yeah, it is 200 now, but still not what I thought it would/should be.Eventually, I too changed to use shaft-potentiometer on my day-to-day use PSU.Funny I should be raving about datasheet. At least a couple of times, I continued to use vented-capacitor. I was waiting on replacement, but knowingly soldering back on a vented capacitor was I think worst then just keeping over-worn pots in service.Call me a hypocrite, I deserve it.