Crappy multimeters :(

[Marks256]

[long story]

I have been without a multimeter for about a year now, as i blew out my old one. What happened was, i was playing around with my radioshack learning lab thingy, and got curious how a transformer worked. Not being satisfied with the built-in transformer on the learning lab, i went outside and took a transformer off an old industrial air conditioner (about the size of two 3.5" hard drives stack on each other, not sure about number of turns, but there was a crap load).

After having a 9vdc battery hooked up to the wires on it, and having nothing happen, i remembered that i read somewhere that transformers used AC, not DC. So, with the same 9vdc battery (which was about half dead at this point), i connected up a DPDT switch so that it would create AC when flipped.

As i flipped the switch, i was probably creating 9vac @ maybe 3hz to 4hz. Again, being curious, i connected my not-so-expensive ($10 at jameco) multimeter up to the other side of the transformer... All i remember was the last reading the multimeter reported was somewhere around 250VAC... Wow... I thought that was pretty cool, except for the fact that it FRIED MY DAMN MULTIMETER!!!!!!

It didn't blow the fuse, it just fried everything BUT the fuse.
[/long story]

Anyways, point of the (long, sorry... ) story is, i am in need of a good multimeter. Not too expensive, but not cheap. Maybe $20-$50. The more features the better, also. I like gadgets...

 

[Andy1845c]

240v fried a multimeter?

I don't have my Jameco catalog here at work, but it seems like 50 bucks should buy you a decent one from them. They are alot cheaper nowadays then they used to be.

 

[mneary]

It's been a long time since I needed a really good multimeter. I have half a dozen of various $5 to $10 that I keep everywhere. One in the glovebox, one in my backpack, one in each of about 3 toolboxes, and the best one on my bench. There should be another here at work, but I don't see it off hand; maybe a co-worker has it.

On ebay, you can get a pack of 4 for about $20. If you want to add capacitance, a single unit starts at about $30.

If you have $50, then you can get the 4 cheap and one better one, that I mentioned.

 

[Marks256]

I wouldn't mind spending a bit more than $50, but i would also like to be able to get some other things while i am at the order... Jameco is offering free shipping on orders of $99 or more, and i intend to stock my shelves...

 

[bananasiong]

You mean you connected the 9 V battery to the secondary winding of the transformer, and measured on the primary and you got 250 V by turning the switch on and off?
Most multimeter can handle more than 240 Vac isn't it?

 

[Marks256]

Yep. I had it setup so when the DPDT switch was moved, it would oscillate between +/- and -/+. It worked, a bit too well...

 

[Nicksan]

Ive got a Fluke 110, its a great meter, but it wasnt cheap

 

[Leftyretro]

Yep. I had it setup so when the DPDT switch was moved, it would oscillate between +/- and -/+. It worked, a bit too well...

Well you were not generating sine waves but rather just square waves and the transients created along with the transformer's turn ratio I'm sure created quite the spikes. Even my Fluke 87 has a maximum voltage specification and fuses are not effective against fast events like you were generating. So bottom line, do invest in the best DVM you can afford but also learn it's limitations and specifications if you wish to protect your investments.

Don't feel too bad, if you cruse E-bay for quality used HP test gear (costing tens of thousands new) you will find many units that have burned out front ends due to human error and we are not talking just beginner hobbyist here.

Good luck and remember every failure carries a lesson and adds to your experience.

Lefty

 

[Hank Fletcher]

I bought the following at a local store about a year ago, but noticed that it was also being sold by Electronic Goldmine. Works great, really easy to change the battery (although I haven't had to yet), and like their ad says, lots of features for a low-cost meter.
https://www.goldmine-elec-products.com/prodinfo.asp?number=G12941

***hmm... I just took a closer look at my meter and the one from Electronic Goldmine. Mine's a Velleman DVM850BL, which looks almost exactly like the one in the photo. I've had good luck contacting EG to get them to clarify product details, so you might want to give them a ring first to make sure the meter's exactly what you're expecting.

 

[Gayan Soyza]

The cheap Digital Multi Meters OHM scale & AMPERE range readings are worst of all.

In OHM scale X1, X10, X100 ranges are not accurate
In AMPERE scale 20A range is quite good.Other ranges

But the VOLTAGE reading is quite good in all ranges.

 

[pc88]

I've been eying the EX330 - $50 at Jameco and a little less at Mouser.
Being able to measure frequency and small currents are useful for (battery
powered) uC work. If you also need true RMS you can get the EX430 for $30
more.

Also, I find it useful to have a few cheap meters lying around, especially if I'm
worried about frying my good one. I once tried to measure the voltage
across the terminals of a neon sign power supply - well, because I was
curious. Only after I saw arcing and glowing components inside the meter
did it dawn on me that I probably exceeded the meter's operating limits.
This was confirmed when I tried it on more pedestrian voltages and found it
was pretty much fried. I wound up throwing it out, but I should have saved it
because the enclosure would have been handy for a project that used test
leads.

For a pretty good deal on a cheap meter, I just noticed that kitsusa is currently
running a special:

**broken link removed**

Actually, the most useful function a DMM can have (IMHO) is an audible
continuity test - why can't you find a $5 meter with this feature? And the second
most useful function is the transistor hFE test (can never remember which way
different transistors go in). The one feature I'm still looking for in a DMM is a diode
test that will show the voltage drop for white (and other higher voltage) LEDs - that
would be really nice to have.

ok, enough rambling...

 

[Hero999]

The average waveform was 250V but the peak was probably much higher, 2kV is probably not unreasonable.

I don't think you would have had 9V at the input for long, that battery probably dropped to 3V as soon as it was connected but the initial HV pulse was probably enough to kill the meter.

 

[chemelec]

[long story]

I have been without a multimeter for about a year now, as i blew out my old one. What happened was, i was playing around with my radioshack learning lab thingy, and got curious how a transformer worked. Not being satisfied with the built-in transformer on the learning lab, i went outside and took a transformer off an old industrial air conditioner (about the size of two 3.5" hard drives stack on each other, not sure about number of turns, but there was a crap load).

After having a 9vdc battery hooked up to the wires on it, and having nothing happen, i remembered that i read somewhere that transformers used AC, not DC. So, with the same 9vdc battery (which was about half dead at this point), i connected up a DPDT switch so that it would create AC when flipped.

As i flipped the switch, i was probably creating 9vac @ maybe 3hz to 4hz. Again, being curious, i connected my not-so-expensive ($10 at jameco) multimeter up to the other side of the transformer... All i remember was the last reading the multimeter reported was somewhere around 250VAC... Wow... I thought that was pretty cool, except for the fact that it FRIED MY DAMN MULTIMETER!!!!!!

It didn't blow the fuse, it just fried everything BUT the fuse.
[/long story]

Anyways, point of the (long, sorry... ) story is, i am in need of a good multimeter. Not too expensive, but not cheap. Maybe $20-$50. The more features the better, also. I like gadgets...

The FUSE in these meters ONLY Protects the Current Ranges. Not the Voltage Ranges.

And before you do any measurement like this you should understand what your measuring and how to propery measure it.
In This Case, A multimeter is not the proper way.
The Update Time on them is Too Slow to get a True Reading. That 250 Volts Could have been MUCH HIGHER.

You probably blew up the meter with a high voltage spike.
Even a Good meter can be distroyed by what you did.

 

[Speakerguy]

Fluke 177 at home, Fluke 179 at work.

Buy 'em once, buy 'em for life.

And throwing the switch on a transformer could definitely produce a meter-killing voltage spike without it registering it. The spike might have lasted less than a microsecond, and multimeters don't have that kind of bandwidth.

 

[Marks256]

The FUSE in these meters ONLY Protects the Current Ranges. Not the Voltage Ranges.

And before you do any measurement like this you should understand what your measuring and how to propery measure it.
In This Case, A multimeter is not the proper way.
The Update Time on them is Too Slow to get a True Reading. That 250 Volts Could have been MUCH HIGHER.

You probably blew up the meter with a high voltage spike.
Even a Good meter can be distroyed by what you did.

Ok, go back in time one and a half years, and THEN tell me that.