[Milsurplus] AN/GRR-5 Power Supply Questions

[Jim Whartenby]

Never heard of this problem with electrolytic capacitors.  I know that
over temperature is a cap killer but never heard that reduced working
voltage will also cause failure.

I have NOS Boxed Cornell Dubilier electrolytics that clearly state the
working voltage range is from 10 to 350 VDCW.  Pictures available!

Regards,
Jim

--- Neil Barnett <neilba at clear.net.nz> wrote:

> >    4. C101, C110 and C111 are 1,200 mfd/15 WVDC caps used as
> filters.
> > Can I use 2,200 mfd/50 WVDC? How about 1,000 mfd/50 WVDC?
> 
> I presume these are electrolytics, in a 12-13.8 VDC system.
> Unlike ceramic and polyester capacitors, where it is permissible
> (and even desirable) to use units of high voltage rating so as to
> avoid breakdown of the dielectric, electrolytic capacitors must
> not be run at less than about two-thirds of their rated working
> voltage.
> 
> If you attempt to use 50 WVDC electrolytics in a 12-13.8 VDC
> system, they will fail to attain their full rated capacitance during
> operation, thus reducing their effectiveness as filter elements.
> Additionally, I'm sure research has shown that such operation
> leads in the long term to the total failure to form any capacitance,
> i.e. a cumulative deterioration in the ability to "form" the correct
> dielectric.
> 
> My advice is to forget the 50 WVDC units.  Try to find units of
> the correct capacitance in the now-standard 16V rating (should
> not be too difficult!).  Use more capacitance, rather than less, if
> you can't get an exact match, for example 1,500 mfd/16 WVDC.
> 
> 73 de Neil ZL1ANM
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