High voltage capacitor needed & questions

post pics of the caps and any markings on them.

I would expect Miller to have the parts available, at least unless the welder is an antique. It's a big part of why I bought a Miller instead of an off-shore el-cheapo. That being said, in order to find a suitable replacement from other sources, you need to know the characteristics of the capacitor you are trying to replace. And it is more than just the capacitance and voltage. Many types of capacitors don't take kindly to being charged backward and, if you put AC across them, they'll literally explode. Even if they have enough of a DC charge on them that they never see a reverse polarity, if they have a significant effective series resistance (ESR), they'll get hot and blow if there is a substantial AC signal riding on the DC. And this just scratches the surface...

Jerry

You'll need to know working voltage and capacitance. Then google on "transmitting mica". High voltage mica caps are routinely used in radio transmitters. Yes, they can be paralleled to get the required capacitance. If size, performance and cost are the measures of "better", I doubt if there's a better cap for this app than mica.

high voltage mica caps aren't hard to find, I have a 30,000 VAC mica cap sitting here at this moment - it's about 8 inches X 6 inches X 12 inches, with a 8 inch insulator on top, the case is one terminal, the other is on top of the insulator.

I suspect your TIG welder needs a lower voltage.

Mica has particular dielectric benefits in certain frequency bands - and oil dripping out is not a real problem, jsut remove the cap, refill with oil and seal it again. use mineral oil if you can't find capacitor oil.

" They are mica capacitors. Can types other than mica be

Just make sure it's oil in there, not PCB. What vintage is the machine?

regards,

John

Oh oh....Now Erics place is a Hazmat site. PCBs...Run Erick Run!!1

Call and ask for Dennis. Tell him Gunner refered you. Id be surprised if he didnt have some good used ones kicking around

Gunner

"Pax Americana is a philosophy. Hardly an empire. Making sure other people play nice and dont kill each other (and us) off in job lots is hardly empire building, particularly when you give them self determination under "play nice" rules.

Think of it as having your older brother knock the shit out of you for torturing the cat." Gunner

Capacitor oil kinda sounds like skyhooks and file grease. I'm sure it's not. I'll look for it and try to see why the things are leaking. Will oil loss make the capacitance lower? Eric

The machine was built in the early seventies. Were PCBs used then? I think they were. If they are leaking PCBs then wouldn't the best fix be just re-filling with non PCB oil and sealing them? I could take them to the county as hazmat but then they would have to deal with them. ERS

Mmmmmmmmmmmm! IMO, nothing beats PCB's spread on a ritz cracker :-)

Pics and part numbers.

I deal with high voltage capacitors and would love to help, but you need to provide info on the part itself.

No. The oil is to prevent flashover within the case, and to cool the mica, which does the heavy lifting. Flashover within a capacitor in a welder may destroy the capacitor, so I'd make sure there is enough oil in the capacitor case.

Joe Gwinn

I thought I'd already posted a message concerning pics in the dropbox. I will be taking pics tomorrow and posting them in the dropbox. In the meantime here's the info on the capacitor: GAMO TYPE MICA CAP Miller Electric P/N 31-602 And from the manual: Capacitor, mica .002 uf 6000 volt The capacitors themselves have places on them for Amps, Volts, MFD, but these spaces are blank. I hope the info above will help. Thanks, eric

The oil has been leaking for a long time. I thought it was something else. If flashover occurs will it act like a short? And would this prevent any high frequency at all? I ask because the high frequency is weak and always has been. But it is there. The spark gaps work. But every Goldstar machine I've used has been the same. Maybe they all have defective caps. On Lincoln machines you could see purple sparks emanating from the tip of the tungsten and dissipating into the air. But Miller Goldstar machines I've used never would do that. Eric

I recently sold a 5,000 V, 2 uF capacitor, rectifier and transformer for $32. It was a part of a military radar test set.

i

Here is a site with hv mica caps. I would use this one: CFT) 224M356 .001 µF (dual) 10 kv 1-1/8" x 1-7/8" 9.00

IF it is a dual cap you can parallel it to get the .002 uf that you need. The cap is rated at 10 kv which is just the voltage rating. A higher rating will work the same.

John

The physical case sounds really large for such a capacitor, especially a mica one.

Induction heater polypropylene caps might be an acceptable replacement.

Does anybody know what frequenecy these welders operate at, and possible RMS current levels these caps see?

Size alone and that these are mica says you're going to need a AC rated, probably RF duty cap. No bathtub cap or filter cap will work.

It the cap does not have "no PCBs" printed on it than it can be assumed to contain PCBs which means you've got a bit of a problem on your hands if it leaked.

Pete C.

The following might be of use:

Pete C.

You could also assume it's full of gold, but that's wrong too.