Smoke from a cheap meter - Page 1
Forum section: electronics / general

author: tom66
author_rank: Super Contributor
timestamp: February 21, 2011, 02:19:37 pm
content: Bought these dirt cheap (£2 each) multimeters as throwaway meters which I could use to measure some things that might damage my more expensive BK 2709B. Little did I know I'd be throwing one away after just a week of use. I'm not sure what made it go (I think I overloaded the current range - it has no fuse), but it still kind of works (shows various random readings), it just doesn't read anything sensible. I'm thinking I can give it a fitting funeral, any ideas?

author: Unknown
author_rank: Unknown
timestamp: February 21, 2011, 03:12:04 pm
content: Quote from: tom66 on February 21, 2011, 02:19:37 pmJust keep in mind that using cheap meters for dangerous jobs may injure or kill you. Those safety features that make good meters more expensive are there for a reason. Using cheap meters for risky jobs is wrong, I would only use them on low-voltage, current-limited circuits (eg. batteries with a high output impedance, or lab supplies), and leave the dangerous stuff to quality meters that have a better chance of protecting the user.

author: tom66
author_rank: Super Contributor
timestamp: February 21, 2011, 03:25:33 pm
content: Quote from: alm on February 21, 2011, 03:12:04 pmPurpose of these was for measuring low voltage and relatively high current (less than 5A) stuff. Given how close the 10A current shunt is to the 1000V input, I wouldn't trust it for measuring a 9V battery.

author: apex
author_rank: Regular Contributor
timestamp: February 21, 2011, 03:29:55 pm
content: Well, but they're cheap!If you keep enough distance, you can use them.Just watch the blog with Dave and Doug Ford blowing up some multimeters.It is indeed true that more expensive multimeters have more safety features, but it just saves you a scratch from that distance and then it's dead.Cheap mutlimeters are a good idea.They might burn, they might disintegrate themselves, everything better than a 10k$ multimeter just going bang!You could look for a multimeter with fast HRC fuses.That could do the job too, but HRC fuses are expensive, too!apex

author: Unknown
author_rank: Unknown
timestamp: February 21, 2011, 03:59:14 pm
content: Quote from: apex on February 21, 2011, 03:29:55 pmFalse economy.Quote from: apex on February 21, 2011, 03:29:55 pmSure, not every circuit has enough energy to be dangerous. A CR2032 battery is unlikely to be able to deliver any significant current for example, or a lab supply set to a low current/voltage limit. 9V batteries can deliver more power. Car batteries even more.Quote from: apex on February 21, 2011, 03:29:55 pmActually they tend to survive most minor abuses (like measuring mains on the ohms setting), which would blow up cheap meters. Catching fire is also a cool failure mode of cheap meters, as long as it's not in your home. The high energy pulse in that video is not the only way a meter can die. For example, with a steady 30A, the meter is unlikely to blow up, but will probably overheat (if unfused) and possibly catch fire.Quote from: apex on February 21, 2011, 03:29:55 pmIf you sell them.Quote from: apex on February 21, 2011, 03:29:55 pmYou don't exactly need to spend $10k to get a fairly safe meter (even the $50 ones Dave reviewed were better than this, and certainly the $100 ones). And everything is better than $10k going bang? Really? How much is your house worth? How much is your life worth? How much is someone else's life worth?

author: Waifian
author_rank: Regular Contributor
timestamp: February 21, 2011, 04:04:45 pm
content: Good thing you didn't get hurt. Looks like the hole in the back may have made it to a hand if it was being held.

author: tom66
author_rank: Super Contributor
timestamp: February 21, 2011, 04:11:43 pm
content: Aside from the safety issues of cheap meters, I'm still looking for a way to give it a fitting funeral. My meter is reading random numbers. I put some low power resistors inside it and blew them up (100W into 0.25W resistors), next to the ADC/LCD driver IC, the epoxy melted slightly but it's still working!I do like cheap meters for this low power stuff. The meter was smoking quite a bit before the hole in the back formed, I actually left it on more as a curiosity, as I knew it was pretty dead past that point.

author: FreeThinker
author_rank: Frequent Contributor
timestamp: February 21, 2011, 04:28:34 pm
content: Tom66 Where did you get those meters from? There are a couple of people I don't like very much who I'm would like to have one.

author: tom66
author_rank: Super Contributor
timestamp: February 21, 2011, 04:29:20 pm
content: Quote from: FreeThinker on February 21, 2011, 04:28:34 pmeBay.

author: Unknown
author_rank: Unknown
timestamp: February 21, 2011, 04:44:17 pm
content: Lol, Quality Certificate sticker, PASSED!You learnt your lesson now, you are still here, and I also hope you will spread the news about dirt cheap multimeters, it seems people still use them. Maybe an international awareness campaign is needed to stop people from buying these pieces of junk.

author: tom66
author_rank: Super Contributor
timestamp: February 21, 2011, 04:51:52 pm
content: Quote from: Alex on February 21, 2011, 04:44:17 pmGuys, I knew about cheap meters BEFORE I bought these. I have owned many cheap meters before. Primarily it was intended for somewhat dangerous stuff, and I was also planning to use this for measuring two quantities - my BK 2709B can measure volts or amps, but not both. They are actually pretty accurate; I compared them. The cheapie read 35.88V, the BK read 35.96V, tried it on most ranges, within 1% accuracy for all DC volts, tended towards the low side of measurements. I blew it up purely because of stupidity.

author: Zad
author_rank: Super Contributor
timestamp: February 21, 2011, 05:06:46 pm
content: I don't have any problem using cheapo meters for measuring comparatively low voltages or currents either. I even get paranoid holding my Flukes when I'm measuring mains, so I don't think I'd be within a metre or 2 of a cheap meter. Strictly low energy stuff. I wonder how much current actually went through that.Anyway, do you have a mate with a 7.5 tonne truck or something a bit heavier that could be persuaded to squash it? Drop from a stupidly high bridge onto somewhere safe?

author: tom66
author_rank: Super Contributor
timestamp: February 21, 2011, 05:48:09 pm
content: Quote from: Zad on February 21, 2011, 05:06:46 pmI want to watch it squirm, since it almost bloody killed me! (joke, just imitating Dave.) I tried submerging it under water, and it still works! I have a 35V power supply, any bets on what it will go up to?

author: tom66
author_rank: Super Contributor
timestamp: February 21, 2011, 06:00:27 pm
content: It died at 30Vbut nothing else happened, display just went blank, didn't even get warm. Time to start probing 35V against parts of the chip! I suspect it's the ICL706, which would rate it at 15V.

author: saturation
author_rank: Super Contributor
timestamp: February 21, 2011, 06:36:07 pm
content: These are great photos, and thanks for sharing. It shows again, what 'extra's you get when you get a reputable meter, and what happens with a cheap meter.I've 2 suggestions, you can salvage the DMM for parts, the LCD looks to still be good, or you can mail the whole thing to your equivalent government product safety bureau to have them investigate whether this type of DMM should be sold in your country.

author: Bored@Work
author_rank: Super Contributor
timestamp: February 21, 2011, 06:38:13 pm
content: Quote from: tom66 on February 21, 2011, 04:51:52 pmYou are a slow learner, aren't you?

author: tom66
author_rank: Super Contributor
timestamp: February 21, 2011, 07:14:21 pm
content: Quote from: BoredAtWork on February 21, 2011, 06:38:13 pmWhat? I fully understood the risk of using such a meter. I was just somewhat surprised when it failed so quickly. I had an old cheapie very similar to this one for about 2 years before I dropped it and it broke, entirely my fault.

author: Neilm
author_rank: Super Contributor
timestamp: February 21, 2011, 07:59:48 pm
content: As I work for a company producing measurement equipment and work with someone who sits on the IEC61010 commitee I would report it. OK you may have bought it on EBay but the seller may still have broken the law and the next person who buys one of these metermight not understand the dangers.YoursNeil

author: tom66
author_rank: Super Contributor
timestamp: February 22, 2011, 01:13:33 am
content: Quote from: Neilm on February 21, 2011, 07:59:48 pmIt's not CAT rated or anything like that, so I don't think there's an actual case for saying it was even trying to be safe in the first place.

author: Polossatik
author_rank: Frequent Contributor
timestamp: February 23, 2011, 02:04:00 pm
content: what to do with it?hum...turn it into roadkill? Might be fun with a slow motion camera watching it going *pats*Put a little buzzer or siren in it that goes off on a few positions besides on that gives dancing numbers, put it somewhere in a public space with a "do not turn" sign - people like to do what they are told not to do and watch them jump back if it goes "beep"Use it as lotto/random number generator - take pictures with 3 sec interval or so and process that using python (need to add an arduino or lego somewhere so you get on hack a day)buy a few of those and make a geek outfit with lots of beeps and wires and then try to pass a TSA checkpointI'm sure i can find more after a couple of beers, but i'm still at work now

author: saturation
author_rank: Super Contributor
timestamp: February 23, 2011, 02:51:52 pm
content: I don't recall the details, but there is a minimum required by any product for safety as required by the EU and IEC to be sold as a testing device, CAT rating isn't necessary. It must have a CE stamp on it to be sold in EU, and that means conformance with the IEC directive.Quote from: tom66 on February 22, 2011, 01:13:33 am

author: Unknown
author_rank: Unknown
timestamp: February 23, 2011, 03:25:02 pm
content: Make sure its the proper CE mark with the right spacing between C and E. The Chinese CE mark products with fake CE marks where the C, if it was a full circle, would overlap with the E. This is not the case with the official CE mark. lol, go check your kitchen scale nowAnyway, I don't even need to touch a multimeter not to mention looking for certifications to figure out if its a $5 POS or something more decent. I also find high current measurements a good test for 'qualifying' quality as it puts a lot of stress on sensitive parts (PC traces, protection, shunt etc).

author: Mechatrommer
author_rank: Super Contributor
timestamp: February 23, 2011, 03:44:05 pm
content: i also have this dead cheapy dmm somewhere. for years i cant figure out the best way to make funeral for it, so i just keep it.

author: Unknown
author_rank: Unknown
timestamp: February 23, 2011, 03:55:50 pm
content: Quote from: saturation on February 23, 2011, 02:51:52 pmOnly if it falls under one of the new approach directives (which I believe includes DMMs), otherwise it's prohibited.Quote from: saturation on February 23, 2011, 02:51:52 pmThat means that the manufacturer/importer certifies that it's in compliance with whatever the requirements of the directive are, not that this was actually verified. They (distributor/importer/authorized representative/manufacturer, whoever has the deepest pockets) are probably liable if this turns out to be false, however.

author: ziq8tsi
author_rank: Regular Contributor
timestamp: February 23, 2011, 07:17:33 pm
content: Haoyue/huayi, one of the big OEMs for these ultra-cheap manual ranging CoB meters, claim to be designing their new models in accordance with the CE requirements, rather than just sticking the logo on anyway:http://www.digimeter.com/views.asp?hw_id=377The differences include removal of the transistor test socket, addition of a fuse on the 10A range, and the elimination of any suggestion of capabilities above 500V.I suspect they are still made of flimsy brittle plastic and accompanied by probes that can pull off their cables exposing bare wire...

author: Neilm
author_rank: Super Contributor
timestamp: February 23, 2011, 07:36:32 pm
content: Quote from: alm on February 23, 2011, 03:55:50 pmAll multimeters fall under the remit of IEC61010 - "Safety requirements for electrical equipment for measurement, control, and laboratory use".Quote from: alm on February 23, 2011, 03:55:50 pmThe responsibility for ensuring compliance rests on the company that first places the device on the market in the EU. That company is then liable for any false declarations. Sometimes importers will take a manufacturers declaration but this is dangerous. When I had a job approving instruments for importation, I insisted on not only seeing the full safety report and checklist (as required by the IEC) but also performing a few series of tests (checking creepage / clearance, surge tests ect). On more than one occasion I found a manufacturer had produced a product with a certificate of test that did not pass, or whose report had glaring ommisions. One of the best (worst) was one that had a check list with every entry marked Not Applicable.I dread to think how many importers take the fact it has a report and certificate and place it on the market without doing any independent checks.Neil