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 Capacitor replacement oil filled AC caps.

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trainman2



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PostSubject: Capacitor replacement oil filled AC caps.   Sat Oct 16, 2010 4:00 pm

In the power supply of the Sprague TO-16 there are 3 oil filled 1md 220 vac caps. Can I replace these with regular poly caps? One is leaking, so I'd rather replace them all.


Tony


Last edited by trainman2 on Sun Oct 17, 2010 6:45 am; edited 1 time in total
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glasdave

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PostSubject: Re: Capacitor replacement oil filled AC caps.   Sun Oct 17, 2010 4:06 am

Oil filled caps are pretty durable, I would just replace the leaking one and call it good.
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burnt fingers



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PostSubject: Re: Capacitor replacement oil filled AC caps.   Sun Oct 17, 2010 6:32 am

By now oil caps are quite suspect as proven by all the leaky ones in WW2 equipment. As with any cap quality varied all over the place so either shotgun or use another cap tester to evaluate.

The last radio I worked on even had some prior repairs using Vitamin Q caps which were even showing lots of leakage on a Triplett 630.

Nothing is sacred any longer.

Carl
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trainman2



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PostSubject: Re: Capacitor replacement oil filled AC caps.   Sun Oct 17, 2010 6:44 am

Ok, but can I use regular poly film caps to replace these? what is the equivalent dc voltage rating to use for a capacitor rated 220v AC?

Tony
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pixellany



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PostSubject: Re: Capacitor replacement oil filled AC caps.   Sun Oct 17, 2010 7:03 am

trainman2 wrote:
Ok, but can I use regular poly film caps to replace these? what is the equivalent dc voltage rating to use for a capacitor rated 220v AC?

Tony

I've never seen such a conversion specifically for capacitors, but the MINIMUM would be the peak AC voltage:

220v RMS = 311v peak
I'd use a rating of at least 450volts. My source (Just Radios) has metallized polyester caps up to 2mf @ 630volts
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Wcirco

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PostSubject: Re: Capacitor replacement oil filled AC caps.   Sun Oct 17, 2010 7:12 am

Dont touch that oil, its bad stuff. PCBs and such. Shocked
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trainman2



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PostSubject: Re: Capacitor replacement oil filled AC caps.   Sun Oct 17, 2010 7:49 am

sO, WAS THE OIL USED AS THE DIELCRIC, OR WAS IT ADDED TO COOL THE CAPACITOR?

sO i AM GOING TO ASSUME i CAN USE A NON OIL FILLED REGULAR POLY FILM CAP TO REPLACE AC OIL FILLED CAPACITORS IN AN AC POWER SUPPLY.
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pixellany



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PostSubject: Re: Capacitor replacement oil filled AC caps.   Sun Oct 17, 2010 8:16 am

Can you post a schematic? After all this discussion, some of us may not know exactly how these caps a being used.
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radiotechnician



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PostSubject: Re: Capacitor replacement oil filled AC caps.   Sun Oct 17, 2010 8:51 am

Oil filled capacitors were used to provide a metal housing hermetically sealed to exclude moisture and air, hence the oi. The oil transferred heat from the capacitor assembly to the case but was not the dielectric. The dielectric material is either a porous material (eg paper) saturated in oil. PCBs were used because they were flameproof.
The old cans weep oil through bushings.

Any capacitor you want to use can be substituted as long as it is non-polarized and has an
equivalent time duty rating, The VDC rating should be the same. The non polarized aspect is because cans have no polarity mark. The line or outside foil marking on radio capacitors is not a polarity mark in non-electrolytic units.

You cannot make ANY assumptions when it comes to converting a DC rated capacitor to AC.
The reason is, simply, AC components bear testing certifications based on being tested on AC.
Find a capacitor rated for AC. Suggestion: generic ceiling fan capacitors. http://www.nteinc.com/capacitor_web/pdf/cfc.pdf

If you change the style or type of a capacitor, you carry all consequeces.


de
VE7ASO
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Alan Douglas



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PostSubject: Re: Capacitor replacement oil filled AC caps.   Sun Oct 17, 2010 10:03 am

AC-rated capacitors have an amperage specification, since they carry substantial current. The metallized electrodes in some DC capacitors are too thin to handle much current. However, it's unlikely that this Sprague has any motors inside, and the AC-rated caps may simply have been easier to get than DC-rated ones. You'll have to look at the schematic to see what the actual working voltage is. You can't go wrong with 630V caps though.
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Rich, W3HWJ



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PostSubject: Re: Capacitor replacement oil filled AC caps.   Sun Oct 17, 2010 10:52 am

The oil transferred heat from the capacitor assembly to the case but was not the dielectric. The dielectric material is either a porous material (eg paper) saturated in oil.[b]

Since oil is between the capacitor plates, it is a dielectric. The paper is really more of a separator to ensure the foils don't come in contact. Special oils were used, most containing PCB, selected for their dielectric and hi voltage characteristics.

Rich

http://www.gepower.com/prod_serv/products/capacitors/en/downloads/pcb_msds_pcb.pdf

http://www.gepower.com/prod_serv/products/capacitors/en/downloads/pcb_msds_pcb.pdf
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pixellany



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PostSubject: Re: Capacitor replacement oil filled AC caps.   Sun Oct 17, 2010 2:49 pm

The dielectric is whatever is between the plates, n'est-ce pas? In this case, it sounds like it's probably a combination of paper, oil, and maybe a few air bubbles. I'm not sure which one is the weak link.
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burnt fingers



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PostSubject: Re: Capacitor replacement oil filled AC caps.   Sun Oct 17, 2010 7:20 pm

I believe it was Curt who stated that the receiving type bathtub caps did not contain PCB's. In any case nobody is going to be hurt by handling a leaking cap, just dont go licking it.

In the TO-16 the caps are specified as 1uf @ 600V paper so the 630V poly is your ideal choice. Either the ones in there are replacements or all they could grab as the impending WW2 was already limiting availability of many items.

Carl
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trainman2



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PostSubject: Re: Capacitor replacement oil filled AC caps.   Sun Oct 17, 2010 11:32 pm

The caps in the unit are original. Maybe like ALan said, the AC rated caps were cheaper.
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burnt fingers



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PostSubject: Re: Capacitor replacement oil filled AC caps.   Mon Oct 18, 2010 7:57 am

Note who's name is on the tester and on the caps; I dont think they were having to play the price game. Then look at the years it was built and reread my prior post.
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Fred Scoles



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PostSubject: Re: Capacitor replacement oil filled AC caps.   Mon Oct 18, 2010 9:13 am

A real danger with older oil-filled AC capacitors is if they overheat and smoke or burn, which can release very toxic combustion chemical derivatives into the room. We had the capacitors in a 1960's Sola wall-mounted AC regulator burn in an enclosed room, which required over five years to finally pass air quality standards in that room. The combusion products of various PCB's are well documented.
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radiorich



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PostSubject: Re: Capacitor replacement oil filled AC caps.   Mon Oct 18, 2010 10:32 am

Hello trainman2
you can go to grainger and buy some oil filled motor caps to replace your old ones

Rich


Last edited by radiorich on Mon Oct 18, 2010 10:02 pm; edited 1 time in total
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smeezekitty

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PostSubject: Re: Capacitor replacement oil filled AC caps.   Mon Oct 18, 2010 10:52 am

Fred Scoles wrote:
A real danger with older oil-filled AC capacitors is if they overheat and smoke or burn, which can release very toxic combustion chemical derivatives into the room. We had the capacitors in a 1960's Sola wall-mounted AC regulator burn in an enclosed room, which required over five years to finally pass air quality standards in that room. The combusion products of various PCB's are well documented.
Heres a helpful tip: Consider loosening the standards.
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easyrider8



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PostSubject: Re: Capacitor replacement oil filled AC caps.   Mon Oct 18, 2010 2:33 pm

Tony

Just replace then with film caps 630vdc, if you need any let me know

Dave
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trainman2



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PostSubject: Re: Capacitor replacement oil filled AC caps.   Tue Oct 19, 2010 10:54 am

Thanks Dave, I have caps. Too bad, all the old caps are Spague's. Restuffing the paper caps. Bought new Spague Atoms (TVA Series) for electrolytics.
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OZ132HOME



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PostSubject: Re: Capacitor replacement oil filled AC caps.   Wed Oct 20, 2010 10:08 am

glasdave wrote:
Oil filled caps are pretty durable, I would just replace the leaking one and call it good.
Me too.
Good oil filled caps seem to go on and on...
I actually had one on test on 240 VAC for over a year with no sign of leakage.
I had a post on this test in the "Old" forum...
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pixellany



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PostSubject: Re: Capacitor replacement oil filled AC caps.   Wed Oct 20, 2010 10:58 am

smeezekitty wrote:

Heres a helpful tip: Consider loosening the standards.
In my book, that does not qualify as "helpful".....

First, I think you will find quite a few people that LIKE having air quality standards.

More importantly, your statement is not at all useful in the context of the discussion in this thread.
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trainman2



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PostSubject: Re: Capacitor replacement oil filled AC caps.   Wed Oct 20, 2010 10:59 am

They're getting replaced because all 3 are the same brand, capacitance and age. If one is leaking oil , I'm sure the rest will leak soon.
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smeezekitty

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PostSubject: Re: Capacitor replacement oil filled AC caps.   Wed Oct 20, 2010 11:03 am

pixellany wrote:
smeezekitty wrote:

Heres a helpful tip: Consider loosening the standards.
In my book, that does not qualify as "helpful".....

First, I think you will find quite a few people that LIKE having air quality standards.

More importantly, your statement is not at all useful in the context of the discussion in this thread.
Yes, But it sure shouldn't take 5 years.
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glasdave

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PostSubject: Re: Capacitor replacement oil filled AC caps.   Wed Oct 20, 2010 11:20 am

?
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