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Miller Goldstar high voltage capacitors needed & questions

I posted this to RCM too: Last week Ernie Leimkuhler held a mig welding tutorial at Grant's place ( Thanks again Grant and Ernie!). Ernie told me that the high voltage caps in the high frequency circuit go bad and it is hard to find replacements for them. I had noticed that something was dripping on the floor underneath the Miller Goldstar welder. I searched without success for the source of the drips. Then yesterday I found the source while wiring in an extra relay and receptacle. The relay connects the receptacle to 115 volts which then powers up the water cooler for tig welding. The source is the high voltage capacitors. Some kind of oily substance is coming out of them and dripping down the red phenolic mounting board. Ernie was right, these caps are hard to find. In fact, using google tonight to find these caps was fruitless. They are mica capacitors. Can types other than mica be used? And can they be paralleled to increase the value? Is there a better type than mica? And finally, does anybody here have some to sell? Thanks, Eric R Snow

Reply to
Eric R Snow
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What is the spec on these capacitors? Digikey has 179 mica capacitors.

i
Reply to
Ignoramus24693

Caps can be paralleled to increase capacitance value, or put in series to increase voltage value. Parallel, the values simply add. Series, they add like resistors in parallel (2 in series is 1/2 the capacitance of each, 3 is 1/3). Types vary in behavior, but several of the plastic film types (polypropylene, for instance), if you can get them in high enough voltage and capacitance for your application (specifics would help, I don't know what values you need) can (IIRC) generally be used in place of the mica types where you need a non-polarized capacitor.

Depending on age of machine, you might want to be careful able dripping capacitor oil, which was commonly loaded with PCBs for many years.

Reply to
Ecnerwal

Call American Equipment Service in Kent, or Precision welding repair in Seattle, and ask them. I suspect there are some newer ones that can be used in their place.

Reply to
Ernie Leimkuhler

Are you sure they are Mica and they drip oil ? or is the oil from something else. Mica isn't normally oil filled. Paper caps are. Mica is used for very high voltage and for very precise values - stable.

I suspect there is a misunderstanding somewhere. Maybe it is a boosted voltage type.

Where is it used ? - how is it used ? I bet it is just an oil filled cap.

Part number ? I have tons of old stuff and docs here - let me know maybe I can help. Photo posted somewhere might be the ticket.

Martin Martin Eastburn @ home at Lions' Lair with our computer lionslair at consolidated dot net NRA LOH, NRA Life NRA Second Amendment Task Force Charter Founder

Ecnerwal wrote:

Reply to
Martin H. Eastburn

Martin, They are mica electrolitics and have electrolite in them. They were commonly used in older tube type transmitters as part of the matching network between the anttena and the final. They are not only high voltage but need a high power rating also. As part of a tank circuit they will dissapte quite a lot of energy. Most I have seen are in the .02pf, 15KV, 5KW range for ratings. Since it is a non critical circuit frequency wise anything close should work fine.

Glenn

Reply to
sleykin

Glen -

I have a bunch of Mica caps and they are small squares to large 2" on a side. I have never heard of a Mica cap in oil. Just another step I suspect.

I think you typo below - 0.02pf that is femto I think you intended to say is .02uf which is pf.

I know all about that - was a Professor in EE - and have bin in industry at senior levels for more than 25 years.

I had just gotten one like you speak - in a microwave that I scrapped out. It was a 1980 model that delivered microwaves since then. An early 700 watt.

Now we have a high tech 1000 watt with a switcher supply - my wife can carry it!

The largest power stuff used transmitter tubes that the repair men take off a cover, climb inside, replace the special filament and make it out (in leaded suits naturally) to draw down a vac over many days. - Oh the coolant pool was a pretty blue :-)

Martin Martin Eastburn @ home at Lions' Lair with our computer lionslair at consolidated dot net NRA LOH, NRA Life NRA Second Amendment Task Force Charter Founder

sleyk> Martin,

Reply to
Martin H. Eastburn

Reply to
Phil

Martin, It wasn't a typo .. it was a brain fart :) It should have been .002 uF. These mica caps are about 2" tall X 1" wide by about 3" long. I have been a nav comm tech for over 30 years and they were a suprise to me too when I first encountered them in the HF unit on my welder. The bad part about it is they want about $100 each for them and mine uses 3. The electrolite is more like hot melt glue .. sort of an amber tar. I checked mine with an old magik eye cap tester and they check good but the tester only goes up to 500V so they may be breaking down at higher voltages. I have been inside the tubes you speak of .. real earth shakers :)

Reply to
Glenn

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