Author Topic: Cheap multimeters... what is so bad?  (Read 33184 times)

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Offline vk6zgo

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Re: Cheap multimeters... what is so bad?
« Reply #25 on: July 13, 2013, 02:57:52 am »

Early DMMs like the Beckman didn't explode or melt,either!


They weren't built to the lowest price.
I also said "I never heard of any of the little Sanwa El Cheapo analogs exploding,although there were thousands of them around!
These "pocket" Sanwas were definitely built down to a price,& were the instrument of choice for many hobbyists.

Quote

It is not good practice to handhold a meter when measuring Mains if you can help it,just in case you are silly enough to leave it on a current or resistance range.

Interestingly,both the meters blown up in Lightage's videos were sitting there propped up on their bale arm in the correct manner.
There is no indication in either video as to what range they were set to.
Has anyone a video of a DMM blowing up when set to the correct range to read 240V AC?

All that said,newbies these days do seem to have a fixation with Mains supplies.
Perhaps the danger is in letting people who know nothing, & don't really want to learn, loose on mains voltages.
Of course they were set up - no one I know would want to hold them while they explode like that.
You've misunderstood me.
I said that standing a DMM up on its bale arm instead of holding it is the correct method when measuring the Mains!


When I did these sorts of tests, we had the test item in a separate room and remotely energised it. I would note that I have seen a video with a dummy holding the test leads and the meter stood up on the side.

When the connection was made, the meter exploded and the voltage rise as the short cleared caused a secondary arc flash between the probes. The dummy caught fire. This was based on an actual accident - the worker who took the role of the dummy had 3rd degree burns from the waist up.

IEC 61010 states the manufacturer should test for forseeable misuse - connecting to a rated supply with the meter in current mode rather than voltage mode is forseeable.

Neil
 

Offline Robomeds

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Re: Cheap multimeters... what is so bad?
« Reply #26 on: July 13, 2013, 03:49:06 am »
I think cheap meters can be a good value and I have recommended them to others but with specific caveats.  Not long ago one of my sibs was asking about testing a small heating device (don't remember the details but probably 200W, AC powered).  It had quit working and he needed something to do basic continuity checks.  I told him the cheap Harbor Freight meters (830B meter) would be sufficient for that task.  I also told him to never use it on anything more than a 110 wall outlet and it would probably be best to never even use it on that.  He's smart enough to understand that a wall outlet can dump a lot more power than a battery toy.  In the case of what he was looking at the circuit was dead when he was testing it.  We decided the thermal fuse had blown.  That was enough to decide not to repair the thing.  Meter did it's job.

Basically the 830Bs are a cheap and junky as the meters get.  My take is those are OK as "emergency", low power tools.  The sort of thing that might help you find a short or open circuit from time to time.  When I was younger and working with RC cars even an 830B would have served my needs.  I actually used a pocket Radio Shack meter for about a decade with no issues.  Nothing fancy but even perhaps 2 decades later it agrees with my Fluke 87 with in the meter's tolerance (1.3222 vs 1.323).  Many of the cheap meters have lose tolerance ranges but I've rarely run into one that didn't hit the specs unless it was really messed up. 

The build quality can be an issue.  I think some of the junk meters can last a long time if you treat them well.  They will also die a quick death if you use them every day and with little care. 

I certainly see the differences in safety.  I would feel safe working on basically any 12V circuit in say a car with a meter with even cheap fuses so long as all inputs are fused.  A 12V battery has plenty of amp potential but I just don't see a 500V or 5000V spike coming out of my car battery.  So long as the voltage can't be high why worry about a better than glass fuse?

If someone talks about measuring things in their house wiring I will tell them to get a decent meter or as often as not, don't touch it.

All that said, I really do appreciate a good meter.  Many of the little differences do add up and I got a deal of a Fluke.  I don't think it has done much I couldn't have done with cheaper meters but I sure do like using it!
 

Offline don.r

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Re: Cheap multimeters... what is so bad?
« Reply #27 on: July 13, 2013, 04:04:41 pm »
Its all about confidence. Confidence in safety, confidence in accuracy, confidence over time. How much you are willing to pay for this confidence is an individual decision. Personally, I think the UT136B is the "best" meter under $25. I have confidence that the meter will give me decent readings in a safe manner. I wouldn't go measuring any high voltage circuits with it, however. I'm not so confident about the probes that came with the meter either.
 

Offline Spunky

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Re: Cheap multimeters... what is so bad?
« Reply #28 on: July 15, 2013, 12:27:56 am »
Interesting thread. I have cheap meters, and good ones. I use them each for what they're good for. Cat4 meters (Fluke, Metrel, etc) with fused leads for electrical installations, but then I've been using a chinese VC99 today for repairs on PCBs. It's fine for that, and perfectly safe on an isolated ELV circuit or for automotive work. It's actually nice to use, it has all the ranges I need and nice big digits.

You should see what my dad used to have as a mains tester, a light bulb with 2 wires soldered to it. Now that's not recommended  ;)
 

Offline Phaedrus

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Re: Cheap multimeters... what is so bad?
« Reply #29 on: July 15, 2013, 03:53:50 pm »
Harbor Freight 830B at home, Fluke 85 V at the lab. At home I rarely do anything higher-voltage than measuring 18650s for charge. In the lab I work on prototype power supplies that may or may not contain faults that could cause a sudden voltage spike or other dangerous situation. Or at the old lab when I needed to occasionally check the 400V 3-phase for faults because our AC source was hiccuping.

Although to be honest I'm more worried about the PSUs themselves killing me than the meter. Ever seen a pair of 420V 480uF electrolytic caps blow up? I have. And smelled it. Those were Rubycons too! :wtf:


Anyway, the point is that a cheap meter is fine for low-voltage applications, but if you're going to be working with high voltage or any type of unpredictable system, I highly recommend a quality meter.
« Last Edit: July 15, 2013, 06:16:25 pm by Phaedrus »
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Offline mzacharias

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Re: Cheap multimeters... what is so bad?
« Reply #30 on: July 15, 2013, 06:15:34 pm »
Harbor Freight 830B at home, Fluke 85 V at the lab.

If you really have an "85-V" I'd give you some serious money for it.

Guessing you meant "87V" ? The 85's didn't make it past the III series.
 

Offline Phaedrus

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Re: Cheap multimeters... what is so bad?
« Reply #31 on: July 15, 2013, 06:24:01 pm »
Prolly misread it, I'll check it next time I'm at the lab. I didn't spec any of this equipment, this was all picked out by the previous engineers. So I don't really remember the part #s.
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Offline mzacharias

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Re: Cheap multimeters... what is so bad?
« Reply #32 on: July 15, 2013, 06:44:20 pm »
No need. I was just yanking you around. Couldn't help myself. But yeah - they go straight from 83 to 87 in the "V" series.

Have a great day!

 :-+
 

Offline Phaedrus

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Re: Cheap multimeters... what is so bad?
« Reply #33 on: July 15, 2013, 06:57:30 pm »
Well now I want to know what's actually on my bench, so... :p


But yeah, I would not test a 400V 3-phase line with anything less than a Fluke or similar quality instrument with full safety ratings. I would not trust the Harbor Freight with my life in that instance. It might work. But it might not. I *know* the Fluke will work.
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Offline elliott

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Re: Cheap multimeters... what is so bad?
« Reply #34 on: July 15, 2013, 10:15:50 pm »
I always keep a few of the Harbor Freight meters on hand, every once in a while they have a coupon for a free one with any purchase. You could buy a candy bar and get a multimeter. I've actually wondered if it is worth the cost of replacing the batteries in them when I forget and leave them on.

Since both of my bench power supplies have analog meters, I keep a Harbor Freight meter connected to each one for a voltage measurement. Of course, I always verify the readings against a good meter before I start using one.

My main meters don't get much love on here either though, Extech EX530s, I bought one a few years ago and it has been a great meter. I started having problems with the main input jack though and Extech just sent me another one under warranty, told me to just dispose of the other one. Of course, I kept it and use it for current measurements only now since those jacks are just fine. The main jack is just a little oversized from years of use and various leads of questionable quality, I could probably fix it if I removed the plastic around it and just crimped it down a little. They molded the jacks into that model for water proofing, so there is no way to actually replace them.
 

Offline Phaedrus

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Re: Cheap multimeters... what is so bad?
« Reply #35 on: July 15, 2013, 10:51:08 pm »
Speaking of Extech, our Extech 380820 just bit the dust an hour ago after the power supply we were testing failed (internal short between +12V and ground). The power analyzer appears totally dead. We checked the fuse and it's fine. Something in the analyzer has failed internally. Joy.
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Offline marshallh

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Re: Cheap multimeters... what is so bad?
« Reply #36 on: July 16, 2013, 04:11:44 am »
Put a new 9v into my cheapo Velleman DVM830L (rebranded under many other names)



I had the back open so I felt the chunk blow out. Didn't reverse battery polarity, it showed properply for about 5 seconds, then showed low battery and then POP.


Good thing I have a Fluke 87 now.
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Offline Lightages

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Re: Cheap multimeters... what is so bad?
« Reply #37 on: July 16, 2013, 05:30:12 am »
Thanks for that image marshallh. It shows that it is not just safety we are talking about, it is reliability and measurement confidence too.
 

Online rsjsouza

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Re: Cheap multimeters... what is so bad?
« Reply #38 on: July 16, 2013, 04:13:46 pm »
Put a new 9v into my cheapo Velleman DVM830L (rebranded under many other names)
Maybe that explains the catastrophic failure: according to Velleman's webpage, this DMM is powered by two AAAs...  :-DD

(yeah, I know there are zillions of hardware revisions... Just pulling your leg)
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winluk

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Cheap multimeters... what is so bad?
« Reply #39 on: July 16, 2013, 04:48:18 pm »
Have you divided by zero by any chance? :)
 


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