Multimeter cheapie fried - Page 1
Forum section: electronics / beginners

author: godmodder
author_rank: Newbie
timestamp: September 05, 2020, 02:39:36 pm
content: Hi,I just fried my cheapie multimeter by measuring mains in continuity mode. I know: it's stupid. But it's a mistake I just keep making when switching between measurements. Luckily, it was a real cheap meter. But I would like to get a better one in the future.I do think it's strange for it to fail like this though. The fuse and the board look just fine, but the display won't show anything.So now I would like to ask: do you have a method / workflow to prevent this kind of thing from happening? Are there multimeters that have a protection for this? Maybe all these cheapies just suck and better multimeters have prevention mechanisms?

author: Doctorandus_P
author_rank: Super Contributor
timestamp: September 05, 2020, 04:56:27 pm
content: Any decent (by definition) DMM will survive mains voltage on it's input terminals when in "continuity" mode, or in almost any other setting of the dial.The only exception is the Amps input terminals. It is a bad Idea to try to measure how much amps a mains socket can deliver.Usually the fuse blows if you try this.The best way to pevent this is to buy a DMM that beeps at you when the banana plug is in the amp socket, while the dial is not in a current measurement mode.This has saved me a few times (and the DMM's I was using.My weirdest failure yet was ... 30+ years ago, when I was still a young brat.The DMM I had then was an unfused el cheapo and I did try to measure amps out of a mains socket.Lot's of sparks and noise, scared the hell out of me.After that the DMM did not work properly anymore, even thou it sometimes gave somewhat plausible readings.Or, at least I thought so.I put the meter aside as I found it logical it would not survive such an abuse.Some time later, I examine the meter a bit closer and discovered that the test leads had melted. After replacing them the meter still worked OK-ish in most settings.

author: ledtester
author_rank: Super Contributor
timestamp: September 05, 2020, 05:04:42 pm
content: There are meters which will prevent you from measuring voltage in current mode which is almost guaranteed to blow your meter's fuse. Some high-end ones can detect which sockets your probes are plugged into. Others will block off certain sockets depending on which setting you have the meter in like with this one:https://lygte-info.dk/review/DMMHoldPeak%20HP-770D%20UK.htmlBut I'm not sure either of these will prevent you from attempting a continuity measurement on the mains lines.I think the best approach is not use cheap meters on mains voltages.You can use non-contact voltage detectors to determine which of your mains wires are hot (live). (Always check that your NCV tester is working by using it on a known live wire.)I did once use a multimeter on mains wires to check for continuity, but I made sure the power was off at the electrical panel and verified that none of the wires were live. And the meter I used was a Fluke.

author: joeqsmith
author_rank: Super Contributor
timestamp: September 05, 2020, 05:37:05 pm
content: Quote from: godmodder on September 05, 2020, 02:39:36 pmMany meters I looked at can survive what you describe. It's not uncommon to discover other ways to damage them beyond the case that you describe.https://docs.google.com/spreadsheets/d/1cXzYpIoyVm9QJUju4KXqM22CEQZP3_xwWvDyeVwxTy4/edit#gid=400910915

author: godmodder
author_rank: Newbie
timestamp: September 05, 2020, 07:11:50 pm
content: Thanks for all the replies! I should have known better than measure mains with this shitty brick. The build quality was just awful and I might have underestimated how much I was risking my life using that thingThe screen is also attached in a really weird manner, with the contact points on the PCB resting on some soft mushy strip coming from the screen, but because the PCB is bent a little there might be bad connections perhaps.I'll see if I can repair this thing for low-voltage measurements. For mains, I have just ordered a Brymen 235. Exciting

author: wizard69
author_rank: Super Contributor
timestamp: September 06, 2020, 02:06:08 am
content: If you have a future where you expect to be testing mains voltage it might make sense to have a separate meter just for that. First off it is hoped that by reaching for a different meter you will in effect do a context switch and heighten your awareness of the safety issues in general. It is extremely easy to make a mistake of the type where you do something that has no lethality on a low voltage system but could be deadly at high voltages.The second thing is that there are meters optimized for the types of work an electrician might be doing as opposed to what an electronics tech might be doing. Often the current range on these sorts of meters is a clamp-on or other type of inductive pickup, such that your test leads are never turned into a current probe. Such a meter may other protections built in.The reality is people do make the sort of mistake you have made and isn't an unknown threat to hardware and sometimes personnel. It is probably safe to say that the majority of people on this forum have had a meter on the wrong scale/range. So don't feel bad that you have done so, do however be extra careful with anything mains related. If you are careful you can be asking questions 20 years from now.