[Timothy Daniels]

I've got 30 large electrolytic capacitors (like soup cans)
to sell (12,000 and 8,300 µfd, working voltage 100dc,
purchased as new surplus), and they've been sitting is a
cabinet for 20 years. Is there a simple way to test them
to see if they're still good? Any suggestions on where a
guy could sell a third of a farad of electrolytic capacitance?

*TimDaniels*

[GregS[_3_]]

In article , "Timothy Daniels" wrote:
I've got 30 large electrolytic capacitors (like soup cans)
to sell (12,000 and 8,300 µfd, working voltage 100dc,
purchased as new surplus), and they've been sitting is a
cabinet for 20 years. Is there a simple way to test them
to see if they're still good? Any suggestions on where a
guy could sell a third of a farad of electrolytic capacitance?

*TimDaniels*

They are probably OK. They may need to be charged slowly
up to 100 vdc or higher to make sure. I have some over 40 years old.

Nothing simple for sure.


Measure the ESR.
Charge up to 100 volts and measure the discharge curve.
You can also see if they will hold a charge.

I think the key here is size, for those wanting a paticular mechanical
size replacement. Whats the brand and type ?

greg

[Timothy Daniels]

"GregS" wrote:
"Timothy Daniels" wrote:
I've got 30 large electrolytic capacitors (like soup cans)
to sell (12,000 and 8,300 µfd, working voltage 100dc,
purchased as new surplus), and they've been sitting is a
cabinet for 20 years. Is there a simple way to test them
to see if they're still good? Any suggestions on where a
guy could sell a third of a farad of electrolytic capacitance?

*TimDaniels*

They are probably OK. They may need to be charged slowly
up to 100 vdc or higher to make sure. I have some over 40 years old.

Nothing simple for sure.


Measure the ESR.
Charge up to 100 volts and measure the discharge curve.
You can also see if they will hold a charge.

I think the key here is size, for those wanting a paticular mechanical
size replacement. Whats the brand and type ?

greg


Yeah, the problem has always been that I don't have a variable
voltage power supply to "form" them and no 'scope to watch their
discharge rate. The 12,000µfd caps were made by GE with nos.
92F308ALA, and the 8,300µfd caps were made by Mallory with
nos. CG832U100G1.

*TimDaniels*

[Eeyore]

Timothy Daniels wrote:

I've got 30 large electrolytic capacitors (like soup cans)
to sell (12,000 and 8,300 µfd, working voltage 100dc,
purchased as new surplus), and they've been sitting is a
cabinet for 20 years. Is there a simple way to test them
to see if they're still good?

Yes. But possibly pointless. See below.


Any suggestions on where a
guy could sell a third of a farad of electrolytic capacitance?

Cap sizes have shrunk so much, you'll only sell these on ebay as NOS for
repairs.

Graham

[Eeyore]

Timothy Daniels wrote:

Yeah, the problem has always been that I don't have a variable
voltage power supply to "form" them

Just use a suitable series R to limit disastrous currents and bangs.

Graham

[Timothy Daniels]

"Eeyore" wrote:


Timothy Daniels wrote:

Yeah, the problem has always been that I don't have a variable
voltage power supply to "form" them

Just use a suitable series R to limit disastrous currents and bangs.

Graham


OK. I take it that "forming" doesn't have to be done
gradually, i.e. over a period of... 5 to 10 seconds, say.
What's a safe current?

*TimDaniels*

[Timothy Daniels]

"Eeyore" wrote:

Timothy Daniels wrote:

I've got 30 large electrolytic capacitors (like soup cans)
to sell (12,000 and 8,300 µfd, working voltage 100dc,
purchased as new surplus), and they've been sitting is a
cabinet for 20 years. Is there a simple way to test them
to see if they're still good?

Yes. But possibly pointless. See below.


Any suggestions on where a
guy could sell a third of a farad of electrolytic capacitance?

Cap sizes have shrunk so much, you'll only sell these on ebay
as NOS for repairs.

Graham


Is that "New Old Stock"? Maybe I'll have them checked out
on Antique Road Show! :-) Hey! *Someone* out there likes
the looks of huge capacitors and heavy transformers. Or is it
just me?

*TimDaniels*

*TimDaniels*

[Eeyore]

Timothy Daniels wrote:

"Eeyore" wrote:
Timothy Daniels wrote:

Yeah, the problem has always been that I don't have a variable
voltage power supply to "form" them

Just use a suitable series R to limit disastrous currents and bangs.

OK. I take it that "forming" doesn't have to be done
gradually, i.e. over a period of... 5 to 10 seconds, say.
What's a safe current?

5 to 10 seconds on a variac wouldn't be wise on caps that old anyway IMHO.
You might as well connect them straight.

Say allow 5W ? dissipation. At 100V that's 50mA. 2 k ohms. If the
voltage rises very slowly, there's a lot of re-forming going on.

Graham

[Timothy Daniels]

"Eeyore" wrote:
Timothy Daniels wrote:
"Eeyore" wrote:
Timothy Daniels wrote:

Yeah, the problem has always been that I don't have a variable
voltage power supply to "form" them

Just use a suitable series R to limit disastrous currents and bangs.

OK. I take it that "forming" doesn't have to be done
gradually, i.e. over a period of... 5 to 10 seconds, say.
What's a safe current?

5 to 10 seconds on a variac wouldn't be wise on caps that old anyway IMHO.
You might as well connect them straight.

Say allow 5W ? dissipation. At 100V that's 50mA. 2 k ohms. If the
voltage rises very slowly, there's a lot of re-forming going on.

Graham

Thanks, Graham. I may take these to a local university, perhaps as
a donation. When you need this much capacitance, it's hell to have to
search on the Web.

*TimDaniels*