If you check out eBay, Amazon, or the other kinda-shady online retailers out there, you’ll quickly find you can buy a CAT III (600V) rated multimeter for under $50. If you think about it, this is incredible. There’s a lot of engineering that needs to go into a meter that is able to measure junction boxes, and factories in China are pushing these things out for an amazing price.
Over on the EEVBlog, these meters are being pushed to the limits. Last month, [joeqsmith] started a thread testing the theory that these cheap meters can handle extremely high voltages. A proper CAT III test requires a surge of electrons with a 6kV peak and a 2 ohm source. With a bunch of caps, bailing wire, JB Weld and zip ties, anyone can test if these meters are rated at what they say they are. Get a few people on the EEVBlog sending [joeqsmith] some cheapo meters, and you can have some real fun figuring out how these meters stack up.
The real experiments began with [joe smith]’s low energy surge generator, a beast of a machine that can be measured with an even beastlier high voltage scope probe. This is a machine that will send a voltage spike through anything to short out traces on poorly designed multimeters.
How did the cheapo meters fare? Not well, for the most part. There was, however, one exception: the Fluke 101. This is Fluke’s My First Multimeter, stuffed into a pocketable package. This meter is able to survive 12kV pulses when all but two of the other brands of meters would fail at 3kV.
What’s the secret to Fluke’s success? You only need to look at what the Fluke 101 can’t do. Fluke’s budget meter doesn’t measure current. If you ever look inside a meter, you’ll usually find two fuses, one for measuring Amps and the other for all the other functions on the scope. There’s quite a bit of engineering that goes into the current measurement of a meter, and when it goes wrong you have a bomb on your hands. Fluke engineers rather intelligently dropped current measurement from this budget meter, allowing them to save that much on their BOM.
There’s an impressive amount of data collected by [joeqsmith] and the other contributors in this thread, but don’t use this to decide on your next budget meter; This is more of an interesting discovery of how to make a product that meets specs: just cut out what can’t be done with the given budget.
china is in a market crash right now….man down..man down..
I just posted this on the “Joining Sheet Metal together” story but this one is much ore suited. I am teaching myself electrical engineering not long started bought myself a multimeter along with lots of other little tools and components. Well I thought I would try and fix a laptop charger I had sitting around. I pulled out my trusty new multimeter and thought I can do this! So I opened up to power brick and started shoving the multimeter probes here there and everywhere. Then Bang!! a big Blue flash a deathening ring in my ears I Have never jumped so much in my life. I was walking back and fourth for a few minutes thinking about how stupid I was for just putting the probes on any componant without thinking. I live in UK so we have 240v mains I could have been toast.
Since then I have a massive respect for electricity. I should have stuck with low voltage stuff until I had a basic understanding. Part of my problem was I thought multimeter’s where “perfectly safe” to use which I am sure they are when used properly.
I am pretty glad I havent got one of these crazy exploding multimeter’s.
When I was starting out I use to use a cheap £5 Chinese multimeter. It did the trick for all the low voltage stuff but when it came to fixing the main supply for a monitor I decided to shell out for a fluke 17b. I have not regretted that decision since, the thing is an absolute tank for the price (the 15b is even cheaper). It handled mains voltages without a hitch. I’m not so sure I would still be here to write this had I used the £5 meter to fix the power supply.
Mine is a cheap multimeter from china basicly a Mastech MAS830L clone, I have opened up and checked it is earthed and fused, I am gonna stick with it for now however If I need to do anything high voltage I will be upgrading. My problem is I am just getting into this so I am spending a small fortune buying all first time tools and equipment. I am glad that the multimeter I use is not on their dogdy meter list but even so I know now not to risk it.
Thereby confirming that sometimes the right tool is the economical choice, and that knowing the limits of the tools is critical to safety. Even the right tool, used incorrectly, can be dangerous, but used properly is much less likely to be a risk than the wrong tool. A good tool, used incorrectly, can be just as dangerous as a bad tool. Any tool, even the correct one, used in ignorance or under inappropriate circumstances, can kill. Using low voltage leads and meter to test a line when the transformer has a fault to the HV side, for example. Or, a ground fault through a line-connected test instrument (had this one a while back… Didn’t float scope with an iso transformer and didn’t know that the device under test had reversed hot and neutral)
I totally get what you are saying here, When working with dangerous tools or utilities you need to prepare for the worst because even using the right tool you need to expect the unexpected. I have a question though why did I trip a circuit breaker when I made the short circuit? I would have thought the multimeter would have blown a fuse first Is that correct? Does that show a defect with my multimeter or is that what is supposed to happen when you mess up?
Depends entirely on how the short was made. If the meter was on a voltage range, and the meter was designed and operating properly, then the short was not through the meter, but was at the probe tip, and the same as putting a paper clip across. It is also possible the the short was at the meter (probe leads in circuit), in which case the options become more numerous, but, unless you were on a fused range of the meter, which is generally the low current ranges, the circuit breaker did its job admirably. Many less expensive meters fuse only low current ranges, if even those. The highest current ranges and all non-current ranges are generally be unfused.
Best bet is a meter: Used Fluke 8000A bench meter can be had for $5 or so (last one I bought) at tag sales and flea markets, in good working condition. New leads are inexpensive. They are a rugged, reliable, and safe meter. I got my first as a hand-me-down in about 1980-ish when the 3-3/4 and 4-1/2 digit models became available.
“Exploding”
Here’s a cheap radioshack multimeter that accidentally got connected to a 6kV 15kJ capacitor bank. The case was literally blown off and the leads were vaporized.
https://imgur.com/FtkCmLC
Looks like my last meter which took a hit from something in a car surging. Probably the same model. I was considering replacing the one they gave me, also a Radio Shack meter with the Ampro he was testing in these videos. Looks like a good choice of replacement considering I recently seen that specific model of Ampro at Harbor Freight for around what I paid for my crappy Radio Shack meter.
Lesson I learned wasn’t one of meter choice as much as using clamps instead of probes where possible. If ya fry a clamp your out a couple dollars but if you fry your hand, good luck.
Yeah, if you do that you’re gonna have a bad time. I don’t think the protection components even in Fluke meters are rated for anywhere near that amount of fault energy.
Fuses are only used on current ranges, voltage ranges have much higher input impedances and can’t pass the high currents required to do explosive damage. Most DMMs have 2 fuses because most DMMs have 2 current ranges
The fuses and input impedance make no difference in this case. If the voltage is high enough, and if what you are measuring can source enough current, you will get arc-over in the traces in the meter and end up with an exploding meter. See the entry from [Jeremy] above.
What is the point of a meter without current measurement? How am I supposed to test remaining amps in alkaline batteries :-)
my first meter “oopsy” was with a trusty, brand new Sanwa analog meter, I was checking out a 240V power outlet in a friends bathroom.
When I arrived I said “Hi” to her neighbour who was working on his motorcycle trailer, arc welding and grinding away.
So I’m checking the power outlet on the 500V setting, I could see there was 240V present, but the switch looked to be not closing properly everytime.
I could hear the arc welder doing its thing, then there was a big blue flash and bang from my meter.
The 500V resistor was slagged, big mutha wire wound one as well.
the electrician who came to replace the bathroom power outlet said he has seen this kind of thing happen before, the back EMF from the arc collapsing can send huge pulses back through the grid.
As for “quite a bit of engineering” going into current measurement, most of those cheap meters have a big wire shunt.
I’ve caught a few friends with those meters on the 10A setting leaving them in circuit, pulling nearly 10A.
They get REALLY hot!
It might say 10A on the meter, but I’d not want to try that for any length of time.
Reading the small print (usually on the front face of the meter) usually tells the user the 10A rating is for “10s max in 1 minute period”
So, let me get this right. The comparison is Others against Fluke. The Others group has current measurement and thus fails for a variety of reasons related to current measurement. The other has no current measurement and does not fail.
Can we all say apples and oranges? It makes no sense to “evaluate” dissimilar items and declare winners and losers.
Nope.
The person who did this test didn’t test the other meters in current mode except at the very beginning of the test. At higher voltages only the other ranges were tested.
The test was fair, it was apples to apples. Fluke won by a huge margin.
If Flukes could kill / you’d be lying on the floor / you’d be begging me please, please / don’t hurt me no more…
Your mission, should you choose to accept it…
This multimeter will self-destruct in five seconds. Good luck, Jim.
What’s the point of all this???
Fact #1
For low voltage stuff, any crap meter will do the job. And since even good old bench meters have more resolution than those overpriced Fluke handhelds, I’d rather buy one of these.
Fact #2
With enough voltage and current any DMM will blow up, no matter whether it’s a holy fluke or any china crap.
Fact #3
If you mount (duct tape) a probe (one stick) and your DVM+probe (other stick) onto long isolator (e.g. Teflon or polyamide) sticks and thereby keep the probe wires and the meter a long distance away from you, it doesn’t matter that much, if it blows up. That is how the professionals (or anyone who works with high voltage and takes safety seriously) do it. I’d much rather measure high power stuff with a cheap china meter on a 2 meter stick than holding a fluke and the probes in my hand. For the real stuff, you need an external voltage dividers, so you need isolator sticks anyway.
Ok. So without your multimeter how do you know the transformer has failed and that CMOS circuit isn’t at 240V? Oh yes; because it explodes.
Buy a decent meter, look after it. Simple.
Where’s the video?
I think a huge point being missed here is that none of the meters listed are rated for anywhere near that kind of energy, and the main reason? THE TEST LEADS, YOU IDIOT. The test leads are not even rated to go that high on most meters. So why would you subject your meter to a voltage higher than the test leads were even rated for, and will probably break down and remind you, not so kindly that you are probably stupid for doing whatever it was in the first place?
I mean I won’t even use top name brand CAT III test leads on 480VAC nor will I hold the freaking meter in my hand just because shit happens… I hang the stuff safely, then step away and hit the breaker, and when nothing says “BOOM”, I’ll take a look. But I ain’t touching the damn thing until the power is off!
You SHOULD use a hand held voltage divider, not like the P6013, which is made for oscilloscopes but rather one that is made to work with DMMs and make sure the ground lead is properly grounded or you risk being that path, which is bad, bad news….
Using a cheap hand held DMM for more than typical CMOS level voltages is like changing your sparkplugs in your car with a ball peen hammer… IT’S THE WRONG FUCKING TOOL…..
Don’t be stupid and use cheap ass meters for serious work, please. I mean if your life means anything at all to you. And if you are going to test anything higher than typical household voltage, use an industrial strength meter, and anything higher than it (or even is close) to it’s top end rating, use a voltage divider designed to be used at said voltage with said DMM.
If you don’t have the money or time for your own safety and protecting your own life, then maybe you shouldn’t be playing with things like this….
But again, I see it all day long on HaD, people who would rather not spend money wisely, but would rather do shit for cheap and then end up spending money on dumb stuff.
“So why would you subject your meter to a voltage higher than the test leads were even rated for,”
– Because 1000V Cat III/IV rating includes 8kV and 12kV from 2 ohm transient insulation, and if they claim those categories, they must safely handle those transients.
IIRC, they don’t have to survive those transients, but they do have to avoid those voltages reaching the user holding the meter (tested by wrapping the whole meter in foil connected to ground).
This includes the cables that are correspondingly rated.
Okay, looking into it, they also have to survive the transients, they just don’t need to be capable of measuring them