Cheap £5 (AU$8) Multimeter accidental destruction test - Page 1
Forum section: electronics / testgear

author: raymondclark0
author_rank: Newbie
timestamp: May 20, 2013, 10:03:52 am
content: Hey All,This happened at work the other day, though I'd share. One of my colleagues did an accidental destruction test of one of those crappy £5 multimeter, basically he'd accidentally left it in current, then tried to measure the DC bus (~560VDC) of a 22kW AC drive, here is the result.Opened it up and the meter has no fuse at all on the current measuring side, plus it doesn't have any isolation slots.Surprisingly it still powered on, however I think the accuracy might be a bit out, plus it now has 2 decimal places!He probably would have had burns on his hands if it didn't have a rubber sleeve on it, you can see carbon deposits coming from the gap in the case of the meter.

author: amyk
author_rank: Super Contributor
timestamp: May 20, 2013, 10:16:15 am
content: Even if the CAT II 600V rating was honest I don't think it'd be appropriate for measuring that sort of thing.

author: Towger
author_rank: Super Contributor
timestamp: May 20, 2013, 10:19:30 am
content: That battery must have cost more than the meter.Over here H&S and Unions would now be evolved, with the employee calculating how much Combo he/she could get from their employer for providing unsafe equipment.

author: firewalker
author_rank: Super Contributor
timestamp: May 20, 2013, 10:24:13 am
content: They allow you to come close to fatal voltages using a such a DMM?Alexander.

author: raymondclark0
author_rank: Newbie
timestamp: May 20, 2013, 10:29:51 am
content: I know, we buy our own meters, stupid thing is we have a calibrated fluke 179 sitting around the workshop for people to use, I personally wouldn't trust that meter with 230VAC, let alone the DC bus of a drive, the accuracy of that thing even when it was new would probably be pretty crap.One good thing is, it has convinced him to get a better(well slightly less crappy) meter.

author: EEVblog
author_rank: Unknown
timestamp: May 20, 2013, 11:53:54 am
content: I love the smell of burnt fiberglass in the morning

author: G7PSK
author_rank: Super Contributor
timestamp: May 20, 2013, 12:28:50 pm
content: What is the 250ma fuse for then, It looks intact still.

author: scalzomen
author_rank: Contributor
timestamp: May 20, 2013, 12:36:39 pm
content: Quote from: G7PSK on May 20, 2013, 12:28:50 pmIt is used to protect the multimeter when selecting the current capacity not at 10A.

author: raymondclark0
author_rank: Newbie
timestamp: May 20, 2013, 12:41:37 pm
content: Yeah the fuse goes to the combined Voltage and 200mA current jack.

author: Wytnucls
author_rank: Super Contributor
timestamp: May 20, 2013, 01:00:41 pm
content: I have a hard time believing a professional would willfully connect such a meter to a high power circuit.I would wager this was done intentionally to blow up a cheap meter for kicks, on a slow day at the office.Considering the amount of abuse it was subjected to, it seems to have fared rather well.

author: raymondclark0
author_rank: Newbie
timestamp: May 20, 2013, 01:35:22 pm
content: I definitely wasn't done intentionally, by the look on his face!Most of us have proper meters (mainly fluke) that we have purchased ourselves for use during the commissioning of our panels, the person in question is new and primarily a software guy, so he wouldn't spend any money on a multimeter and bought the cheapest one he could find. He did get a lot of stick about having such a crappy meter "Get that one in a Christmas cracker did you?", made all the funnier when he blew it up. I know some people will say its no laughing matter, and at the time it wasn't, but luckily no one was hurt and lessons were learnt. i.e. Don't buy crappy meters!

author: rsjsouza
author_rank: Super Contributor
timestamp: May 20, 2013, 02:04:44 pm
content: Glad the guy is ok... Hopefully you can convince him to either buy a much safer DMM or stick with the one available on your lab...Quote from: raymondclark0 on May 20, 2013, 10:29:51 amIn my opinion that is one of the huge issues with the DMMs available on the market irrespective of price: the accuracy is usually not bad when new, as most of them use the beautifully designed ICL7106. The major drawback is then psychological: this increases the impression that more expensive DMMs are mostly "marketing hokum", as the differences are not clearly evident.That is one of the large reasons why this and a few other forums are very important for awareness, but unfortunately their audience is very limited compared to the occasional user of these DMMs.

author: AndyC_772
author_rank: Super Contributor
timestamp: May 20, 2013, 04:38:37 pm
content: I keep one of those '830' meters in my toolbox. It's at least 15 years old, works fine and accuracy is spot-on.I don't shove its probes in the mains - I have a couple of Flukes for that - but it was my first DMM and I'd be sad to lose it.What happened to the probe leads, is there anything left of those?

author: sorin
author_rank: Frequent Contributor
timestamp: May 20, 2013, 05:03:11 pm
content: Quote from: rsjsouza on May 20, 2013, 02:04:44 pmI agree with you.I had a DMM based on ICL7106 from 10 years until now and the accuracy is better than +-1digit.

author: Bored@Work
author_rank: Super Contributor
timestamp: May 20, 2013, 05:30:10 pm
content: Quote from: raymondclark0 on May 20, 2013, 01:35:22 pmAnd in what kind of lunatic asylum are you actually residing?I am asking, because, non of you idiots, yes,IDIOTS, had the mental capability and the balls to make sure he didn't use it at all? If any of youIDIOTShas an engineering degree, professional responsibility would have required to prohibit the usage instead of making stupid jokes. If non had the balls to prohibit its usage, why did non of youIDIOTShad that one working brain cell once put to good use and involve occupational HSE and get that crap confiscated from him?

author: SeanB
author_rank: Super Contributor
timestamp: May 20, 2013, 05:45:05 pm
content: Got 4/5 of those and the like around, I like them for quick checks on low voltage and continuity checks. Haven't blown them up like that yet, though have killed one or two by connecting wrong voltages while on resistance ranges, they do not like car coil voltages on resistance ranges.

author: raymondclark0
author_rank: Newbie
timestamp: May 20, 2013, 07:15:07 pm
content: QuoteThis is the first year we've actuallyhadmultimeters, we would normally have just touched it to see what voltage it was, the higher the number of seconds to regain sight = voltage, we had a chart made up on the workshop wall and everything.But on a serious note, most voltages we measure are the control circuit voltage 24V DC, if I had seen him attempting to measure the DC bus with that meter, I would have said something, there is no need, the drive software tells you the incoming and DC Bus voltage.Anyway he's an adult, and I'm not in the habit of confiscating tools from colleagues of equal standing.

author: SeanB
author_rank: Super Contributor
timestamp: May 21, 2013, 04:49:32 pm
content: You must know Clifford then...... AKA the voltage tester. Could tell the difference just by touching the wire.

author: LaurenceW
author_rank: Frequent Contributor
timestamp: May 21, 2013, 09:47:52 pm
content: That'll be thelateClifford, I presume?Oh lookout - you've made BoredAtWork start typing inBOLD CAPSagain.

author: TheRevva
author_rank: Regular Contributor
timestamp: May 21, 2013, 10:17:51 pm
content: Quote from: raymondclark0 on May 20, 2013, 07:15:07 pmCLASSIC!!!I'm willing to bet that that staff turnover was rather rapid?It must be rather rough having to give out a 'long service award' to the guy who only started last Wednesday?Do you have a spare set of 'Cat 1' probes? (These are when you stick feline paws into a mains socket. If the cat survives, it probably wasn't a live socket)This definitely brought a smile to my face (or perhaps that was just a side effect from grabbing the ultor off the 36" CRT tube?)

author: Lightages
author_rank: Unknown
timestamp: May 21, 2013, 11:02:11 pm
content: The thing is, the method of testing live circuit in a power house sometimes was not that far off. I worked in a steel factory and the electricians, the old ones, would spit on their hand and then slide their hands down a line of contactors very quickly and those that sparked were live. When I saw this the first time, I always avoided working with those guys. Needles to say there weren't many old electricians that didn't have calluses across their whole hand. There weren't many old electricians as well.

author: vk6zgo
author_rank: Super Contributor
timestamp: May 22, 2013, 02:54:23 am
content: Interestingly,despite all the hysteria posted about this possibility on this & other sites,the meter fared quite well.It didn't "explode like a grenade",in fact the case plus sleeve contained everything well.And this event wasn't because of the thing failing when used correctly.It was hung across a 600V line,whilst still set to a current range!When the only "CAT" rating was how many mice the Station cat could catch,Radio transmitter Techs usedAVO "8s" & the like to read high voltages all the time.An AVO 8 on its 2500V range could sit there & read your wimpy 600V line all day & not flinch.The three main things to remember when measuring high energy supply voltages are:(1)Check that the meter is configured to read volts (test leads in the correct sockets,etc) ,& is on the appropriate voltage range!(1a)Check that the meter is configured to read volts (test leads in the correct sockets,etc) ,& is on the appropriate voltage range!(1b)Check that the meter is configured to read volts (test leads in the correct sockets,etc) ,& is on the appropriate voltage range!OCD has a bad press,but it is just good practice in these circumstances.(2) If it is at all possible,clip the probes in place,so you don't have to hold them--even better,if you can position them with the circuit deactivated.(3) Unless you absolutely have to,don't hold the meter,place it on the ground,or some other convenient surface---the AVOs were so damn heavy,we were usually happy to do this!

author: ivan747
author_rank: Super Contributor
timestamp: May 22, 2013, 09:12:15 pm
content: Quote from: rsjsouza on May 20, 2013, 02:04:44 pmMy thoughts exactly. I made a multimeter tutorial on an electronics forum in spanish. The reception was mixed. Some people still argue their $3 multimeter is as good as the brand-name ones because it has kept its accuracy during a test they did 1 year later. I bet 10 years later that multimeter will be buried 10m underground at a disposal centre. The Fluke one will be working just as new, same accuracy.

author: andrewkirkby
author_rank: Contributor
timestamp: May 23, 2013, 01:26:35 am
content: Nice! I think I've avoided this by getting myself a decent multimeter. I did tear apart my cheapy ones before though to find much the same inside.Scary stuff! Not so much letting the magic smoke out but the magic smoke was having a smoke party!

author: amyk
author_rank: Super Contributor
timestamp: May 23, 2013, 10:57:19 am
content: Quote from: rsjsouza on May 20, 2013, 02:04:44 pmAccuracy and safety are orthogonal. A 3458A would've not fared well under the same conditions either.

author: raymondclark0
author_rank: Newbie
timestamp: May 23, 2013, 02:59:23 pm
content: QuoteI'm not so sure, the Agilentwould probablywill have proper input protection like HRC fuses and HV Slots in the board preventing any damage beyond the fuse. I was kind of wanting to try this with my fluke under controlled conditions to see if it would hold up OK, as I'm sure it would, (it does say min fuse interrupt rating 17,000A on the back), but I didn't want to take the risk of damaging it. (maybe if I was ridiculously rich I would)

author: Monkeh
author_rank: Super Contributor
timestamp: May 24, 2013, 01:35:02 am
content: Quote from: vk6zgo on May 22, 2013, 02:54:23 amAn Avo won't read accurately unless laid on a level surface anyway.

author: c4757p
author_rank: Super Contributor
timestamp: May 24, 2013, 02:05:52 am
content: Really? My Heathkit meter reads fine at all angles, even upside down, as long as the meter movement is properly balanced. (A ridiculous pain in the ass to do, unfortunately, if it's out of balance...)

author: Monkeh
author_rank: Super Contributor
timestamp: May 24, 2013, 02:08:51 am
content: Quote from: c4757p on May 24, 2013, 02:05:52 amAvo's are very, very sensitive. They do not like being used at angles, nor do they like shocks without the movement being dampened (which was not available as a specific knob setting until later models).They're amazingly accurate for analog meters when properly balanced and used, though.

author: c4757p
author_rank: Super Contributor
timestamp: May 24, 2013, 02:19:01 am
content: Interesting. When I balanced my Heathkit, I put tiny spots of hot glue on the weights to keep them from moving around, and that seems to have held it. It's been around a year, and I'm sure it's been bumped around quite a bit through two complete workbench migrations. Everything on my bench went through accuracy checks after all that abuse, and it all checked out just fine!Of course, Avos are traditional analog meters IIRC, powered from the measurement being made. The Heathkit buffers the input with a triode differential amp (it has 10M input impedance just like a DMM), so it's able to use a stiff movement with a higher current requirement.