Old Airco Welder becoming Safety Hazard

[sbmarcom248]

Hello Everyone.

I am a college student, and I bought an ancient (Circa 1965) Airco welder a few years back. I have used it a lot for TIG and stick, and it has worked very well for me. Unfortunately, in the last few weeks I've been getting shocked by the ground clamp when I have the machine on DCEP and DCEN. I checked the voltages and here's what I got

45v from Work clamp to ground --> 45v from ground to stinger on DCEP
-45V from work clamp to ground --> -45V from ground to stinger on DCEN
0V from work clamp to ground on AC

I double checked by wiring from the wall and everything checks out. I have attached some pictures of my setup and a circuit diagram for everyone to look at. If you know of any possible causes for this and remedies please let me know. The machine still welds beautifully and I just did a big aluminum fabrication project on AC tig where didn't shock me at all. DC is the issue.

I would really hate to sell this machine for scrap, I learned to weld on it and have made some cool stuff. But if it is a safety hazard I'm not willing to get electrocuted to save a 60 year old machine.

[Kelvin]

I have a similar welder (Miller 330AB/P) that behaves similarly (never checked it on AC, though). I think I get maybe 15VDC from the leads to ground.

I'm just careful to wear gloves and boots (or rubber-soled shoes) when using it. Probably not what you wanted to hear, but...

[sbmarcom248]

I just went out and double checked the voltages, and on the DCEP setting there is 220V AC across the leads in addition to the 45V DC. No wonder I'm getting such nasty shocks.

[jmm03]

SB, you may want to check your transformer connections, also where the main line comes into the machine. Does the machine have a good equipment ground connection coming from your main service?

[Kelvin]

I just went out and double checked the voltages, and on the DCEP setting there is 220V AC across the leads in addition to the 45V DC. No wonder I'm getting such nasty shocks.

Ouch. 220VAC no bueno!

You sure it wasn't 240VAC? You're gonna get our resident "it's 240V, not 220V" cops on yer butt!

[sbmarcom248]

Yeah the ground is fine, I checked the resistance from the plug to the panel this morning and it was 1 ohm. I'll pull the machine away from the wall and check my main connections. And yes it was probably 240v, the multimeter was fluctuating a lot but it was around 120V from each terminal to ground.

[danielplace]

Yeah the ground is fine, I checked the resistance from the plug to the panel this morning and it was 1 ohm. I'll pull the machine away from the wall and check my main connections. And yes it was probably 240v, the multimeter was fluctuating a lot but it was around 120V from each terminal to ground.

Could that be telling you the ground isn't great. No load but meter and voltages wandering around could be hint something is up. Or not.

Have he panel and meter/main checked first just to be sure grounding is all good.

Regardless the voltages your getting sound like a good way to get hurt. Gotta keep at it until it's fixed or quit using that thing.

[sbmarcom248]

Well everyone, I found the issue. The balancing resistor switch had fallen down and was just barely touching the frame. This was sending power to the ground clamp. I riveted the switch back on the frame and now it is acting just like it should. If you look right below the top contact on the switch you can see a little black mark where it must have been arcing.

I really appreciate the responses, I'm glad it was such an easy fix.

[jmm03]

enough leakage to ground to shock you but not enough to trip the breaker... good that you are going to check your ground system.

[sbmarcom248]

enough leakage to ground to shock you but not enough to trip the breaker... good that you are going to check your ground system.

The machine is on a 100 amp breaker so no surprise there. I went through the circuit pretty closely this morning and everything is on the up and up with the grounds.

[SweetMK]

The machine is on a 100 amp breaker so no surprise there. I went through the circuit pretty closely this morning and everything is on the up and up with the grounds.

That is amazing,, was the switch previously held by pop rivets? or did you upgrade from some previous fastening method??

My BIL's welding machine used to shock us when we were teens learning how to weld..
We found that if we poured a 5 gallon bucket of water on the ground rod outside the shop,, we would get shocked "less"...
TEENS!! What we would not do for fun,,

In our case, the ground wire that was attached at the pole had come loose,,
With the twist of a screwdriver, a 10 year problem was fixed,, I think it was only 3/4 of a turn,,,