Cheap DMMs.

[milkyspit]

The Harbor Freight DMMs have achieved some popularity around CPF because they sometimes go on sale for $2.99. The problem is that their normal price is $9.99, plus for those of us who don't live near a Harbor Freight store, their shipping is a complete ripoff.

Well, by accident I just noticed an alternative! It's at MPJA, a surplus electronics supplier that I've ordered from several times in the past. From the photo, it looks like they might even be selling the SAME model of el cheapo DMM, only it's grey instead of yellow. The regular price appears to be $3.95, so these are available for cheap all the time. (At least until they run out!) Take a look over here.

 

[UK Owl]

I have one similar to this (as well as a Fluke 87 for serious work), and I have found this type of DMM is OK for electronics work when only dealing with small voltages and currents and where a slightly lesser accuracy is required, but I would not recommend using one on higher voltages i.e. mains.

 

[Floating Spots]

Especially when you screw up in current mode.
Had one somewhat similar to these that was lent to a friend's kid for a science project.
The kid essentially tried to measure current out of the wall
Meter smoked and sparked, leads melted, kid was unharmed.
There was no fuse on the current shunt.

 

[JSWrightOC]

I was testing the current consumption of an overhead light fixture once with my DMM once by connecting it across the switch terminals. (This is on a 120VAC 60Hz ciruit) One probe slipped (it just HAD to be the load side!) and it shorted out against the ground terminal. There was a flash from the arc and then another flash, which was the wire burning open at the handle end of the red test lead, all before I could even pull it away from the terminal. I was unharmed, the meter was unharmed (even though it was unfused) but the test leads were quite warm from the sudden high current. I disassembled the leads to examine them and there were melted spots in the copper strands all along their lengths, with a nice air gap where the positive lead was soldered to the test probe in the handle. The insulation was undamaged. The 15A circuit breaker did not trip, either.

 

[Brlux]

I Have destroyed 2 rather high quality meeters ($75+) By accidently having it on current mode instead of voltage mode when checking the voltage on a 120V circuit. /ubbthreads/images/graemlins/broke.gif Bolth of which were fused and the fuses did blow but not without taking out the main IC. /ubbthreads/images/graemlins/frown.gif Those V&A can get confusing to me when I am excited. Well after the last time I went out and purchased several cheeper ones for general use incase I do a repeat. I save the Fluke 83 for special situations where I need greater accuracy and I am taking the time to double check everything.

 

[Doug Owen]

[ QUOTE ]
eyetechds said:
I Have destroyed 2 rather high quality meeters ($75+) By accidently having it on current mode instead of voltage mode when checking the voltage on a 120V circuit. /ubbthreads/images/graemlins/broke.gif Bolth of which were fused and the fuses did blow but not without taking out the main IC. /ubbthreads/images/graemlins/frown.gif Those V&A can get confusing to me when I am excited. Well after the last time I went out and purchased several cheeper ones for general use incase I do a repeat. I save the Fluke 83 for special situations where I need greater accuracy and I am taking the time to double check everything.

[/ QUOTE ]

While I've yet to send one to DMM heaven this way, I've dealt with a *pile* of DMMs the students had their way with over the years. What eyetechds just said. A dead meter often goes with the fuse it contains. Worse yet, a partially dead one. Sometimes things just get cooked a mite (like the shunt resistors) so a range or two is off, but it's otherwise "OK" after the new fuse. Sometimes it's more subtle. Bad karma for sure. If you have a 'fuse accident' you really should check carefully.

Mind it's not that I'm all that careful, and for sure not for lack of trying, that I've never blown a meter hooking it up too quickly when in current mode, a lifelong habit of never leaving it in current mode is responsible. Not only do I tend to be deliberate (think about what I expect to find before measuring), but a 'red light' of sorts goes off when I make current measurements. It only seems to go off when things are 'safe' again. Like I said, the way I was taught. No fuses back then.....

Yet another argument in favor of the 'cheap' meter.

Doug Owen

 

[Brock]

Another reason I like the Fluke 87, it beeps at you if your in voltage and you have the probes in the amperage holes. Without that I would have blown many fuses for sure.

I was over at my brothers and he was using the meter to check some wiring while I was doing another outlet and I hear the "beep beep beep" and I turn and start to say, "The beeping means... SNAP... Oh never mind." /ubbthreads/images/graemlins/wink.gif

 

[JSWrightOC]

"The beeping means... SNAP... Oh never mind."
Did he pop anything? /ubbthreads/images/graemlins/ooo.gif

I have a Tektronix TX-3 and although it doesn't do quite
what the Fluke 87 does, it will beep at you several times and show on the display "CHECK PROBE" when you change it from current to some other setting.

I believe this meter is fused at 15A, and rated at 10A continuous, 15A for 15 seconds. (slow-blow fuse perhaps?)

Whenever I am dealing with high-energy circuits (AC mains, battery packs, computer power supplies, etc.), I always check the lead connections.

 

[Brock]

Just just blew the little 8 buck fuse inside the meter. I know the fuses for the Fluke's are pricy, but if that's what it takes to save the meter I am all for it.

 

[JSWrightOC]

SNAP!!!

There goes 8 bucks!

Better than the cost of the meter, I agree.

 

[PlayboyJoeShmoe]

Interesting stuff!

I have an old radio shack DMM that slowly lost functions until all it will still do is DCV. I killed the DCA fuction last, when I tried to get flash amps off of a 14.4V battery pack (DOH!).

I have a decent UEI meter in my truck.

I have been considering a new cheap DMM for home use. I guess I will for sure!

 

[Cougar_Allen]

The current jack on the Harbor Freight is prominently marked: "10A max unfused"

 

[Techmedic]

Cheap Meters:
If your meter has three inputs, get another lead of a different colour, eg blue (or a junk lead and wrap blue tape around the end!) and place it into the current measurement. Make sure that it is insulated on the end to avoid touching stuff. A simple visual cue to not using the current lead.

Expensive Meters:
Look at the display and inputs and listen to the beep-beep before using it, and NEVER loan it out.

Develop good bench practices to put the leads into the voltage jacks when done.

I own a number of meters and I always grab the cheapest meter first, moving up to my fluke 83 for more accurate readings and troubleshooting of complex items.

Take your time, even when playing with flashlight stuff!