[McDaniel8402]

I'm still scratching my chin on this. I burned up a perfectly good multimeter tonight while trying to read the frequency output from an old Miller DialArc HF welding machine. With the machine set to weld AC without the high frequency switch turned on, i read a nice, steady 60 HZ output, as would be expected. I turned on the high freq and tried to read the output with my meter, and fried the meter faster than i could yell "oh sh*T!!". Have no idea what happened. The meter was set correctly. Open circuit voltage should have been about 90 volts. I'm not sure what the frequency would have/should have been. Ticked me off to fry a perfectly good meter. Now i've expanded my "wonder what the output frequency is?" question to include "wonder why that little exercise just fried my meter?". Any guesses?

Edit: I know this isn't related to wiring, per se. I am a pretty experienced electrician. I am licensed. I'm not a dummy. Please don't bash me to badly if the answer to this question is obvious.

 

[backstay]

Years ago my partner put his fluke meter(77) on a circuit that was chattering. It was a MG set. Smoked the thing instantly. Something about hi freq that the digital didn't like. Why? No clue, I didn't use mine to see if it was a one time deal.

 

[BT Electric]

I killed a Fluke meter troubleshooting an MG set many years ago. Ruins your day. I am not sure why they don't like the high frequency though.

 

[Rollie73]

I've heard this as well about the very high frequncies and DMM's. Something about the frequency screwing with the display board in them.....I can't remember what it was I had heard and I still like my meters so I've never tested it to find out.:no:

 

[wendon]

Have you every used a welder with a High Freq on it? On the one I used, if you just ran the high freq box, you got a literal spark arcing between the rod and the work. Probably what went on inside your meter!

 

[8V71]

What wendon said. It's a very high voltage (thousands) generated with the aid of a spark gap inside of the machine.

 

[McDaniel8402]

I did some further digging, called Miller welding company, and learned a thing or two. As mentioned by Wendon and 8V71, it was high voltage that killed the meter, not high frequency. According to the Miller tech, there should be about 10kV across the open circuited contacts when the HF switch is turned on. Information i could have used YESTERDAY!! lol. Live and learn. I found a decent excerpt that explains a little more here. http://books.google.com/books?id=qF...ark-gap oscillator in welding machine&f=false

 

[nrp3]

Its ok. We've all done it. Left tdr hooked up to piece of uf I was trying to find fault and fried it when I hooked the fault locator to it. Putting new battery in other fault locator that had unusual colors for battery leads and fried the board. We all have our moments.

 

[Mshea]

Thanks for the information. I never considered that HF would also be HV. Are there no warnings on the HF equipment?

 

[Meadow]

Could the high frequency effect the reverse recover rate on the internal diodes?


Either that high open circuit voltage. Its like sticking a multi meter in an HID socket.

 

[McDaniel8402]

Thanks for the information. I never considered that HF would also be HV. Are there no warnings on the HF equipment?

If I had realized what the arc-starter was, it would have been a red flag to me that high voltage would be likely, but it never even occurred to me. There are no warnings on the welder to warn of the high voltage present when the HF switch is turned on. I'm just glad it happened to a cheapo Craftsman meter and not one of my Flukes.

Definitely add it to my list of silly stuff to not do again!