On 2010-06-08, Robert Swinney wrote:
Too large a filter cap -- excessive surge current -- blown rectifier, or worse. Iggy, these things
are well covered in Eng. design handbooks.


Bob, would not the transformer limit current?

i

"Ignoramus8975" wrote in message
...
On 2010-06-08, Ned Simmons wrote:
On Tue, 08 Jun 2010 08:27:46 -0500, Ignoramus8975
wrote:

On 2010-06-08, Karl Townsend wrote:

"Ignoramus14096" wrote in message
...
I found a DC power supply among the stuff that I had. This is a Syncor
PP-1659A/G military power supply called "battery charger". It is a
multitap
transformer and a rectifier. Goes up to 150 volts and up to 20 amps.

I fixed up whatever physical damage it had (missing banana plug) and
now it seems to work well, except that on some settings it does not
seem to have good contact. Probably needs some multitap contacts
cleaned.

Anyway, I can set it to, say, 76 volts DC and just user it? Do I need
to put in any capacitors, since this is a pretty bare rectifier?

i

Iggy, electrolytic caps are really cheap. just add some. This web site has
an explanation of how big a unit to get.
http://www.kpsec.freeuk.com/powersup.htm




I got two 10,000 uF capacitors from digikey, 100v max, 18000 hours
life. When charging the caps niitially, would the diodes be stressed?

Oversize the diodes; large rectifier bridges are dirt cheap. I've buit
many supplies for AMC and Copley servo amps with just a transformer,
rectifier bridge and cap and never had a problem. Oh, and don't forget
a bleed resistor for the cap.


After a bit of thinking, I began to realize that the whole setup is
limited by the transformer, and so, putting lathe caps on output would
not be likely to ruin the existing diodes. I will try turning it off
and on a few times. If the diodes fail I will oversize them.