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Old 30th April 2004, 10:27 AM   #1
Wagener is offline Wagener  South Africa
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Default testing second hand filter caps

I am having a bit of trouble locating filter caps at a reasonable price.

A new 10,000 uF 63V cap costs R110

I can get two second hand phillips 10, 000uF 63V caps for R100

I don't know how to test them thoroughly though.

Will 63V caps work with in psu which supplies +58Vdc and -58Vdc?
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Old 30th April 2004, 10:33 AM   #2
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I would not apply 58 volts to old capacitors that are rated for 63 volts. I'd try to find a couple of caps rated at 75 or 100 volts.
If you decide to try these 63 volt caps, reform them thru high-value resistors (47k) before you attempt to apply full voltage without the current limiting resistors.
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Old 30th April 2004, 11:53 PM   #3
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Default Re: testing second hand filter caps

Quote:
Originally posted by Wagener
I am having a bit of trouble locating filter caps at a reasonable price.

A new 10,000 uF 63V cap costs R110

I can get two second hand phillips 10, 000uF 63V caps for R100

I don't know how to test them thoroughly though.

Will 63V caps work with in psu which supplies +58Vdc and -58Vdc?
There is no firm rule on this. Anything over 10 years is suspect, 20 years highly suspect (assuming you can read the date code on the cap). Of course if they are leaking or dented, be very wary.
I've seen 30 year old electrolytic caps that worked just fine, and fairly new ones that failed. I tend to look at the manufacturer and the quality of the cap. Computer grade and high temp (105C) caps tend to last forever, while consumer caps from cheap makers fail withing a few years.

Phillips is a good brand. If the caps seem to have low leakage on a DVM ("resistance" slowly rising to infinite), reform them by supplying a trickle of current to them overnight, as the previous poster suggested. They will probably be fine if they are not extremely old.
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Old 1st May 2004, 12:37 AM   #4
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Quote:
Originally posted by Wagener
A new 10,000 uF 63V cap costs R110
I can get two second hand phillips 10, 000uF 63V caps for R100
If a used cap cost already half of what one retails new, I wouldn`t bother to buy used ones - especially when You don`t know how old they are!

I usually don`t buy even "new" surplus caps for much more than 10% of the normal retail price.

I don`t buy anything much older than 5 years.


Quote:
Originally posted by Wagener
Will 63V caps work with in psu which supplies +58Vdc and -58Vdc?
I assume this is for an unregulated power supply.
If so, IMO caps rated for 63V are very marginal for unregulated +/-58VDC power supply.
Taken into account that there may be line supply voltage fluctuations, I`d consider about a minimun of +20% of the intended DC-supply voltage as safety margin for those caps.
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Old 2nd May 2004, 03:14 PM   #5
Wagener is offline Wagener  South Africa
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So what if I buy them new? Can I then use 63V? My options are 63V and 100V and the 100V is very expensive
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