RE: [CAD_CAM_EDM_DRO] Re: Charging Capacitors

Thanks for the info. A little more time on the voltage then as a unit
with all 6 in parallel.. That was 40-50ma per cap if I'm reading the MM
right. Did I mention they are used and 30 yrs old?





_____

From: David Speck [mailto:Dave@...]
Sent: Wednesday, June 07, 2006 1:30 PM
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: Re: [CAD_CAM_EDM_DRO] Re: Charging Capacitors



Larry,

If all 6 caps together are leaking 50 mA at 170 volts, I'd say that is
acceptable. It works out to about 8 watts dissipation over the 6 cans,
which would not cause damaging heating.

If it's 50 mA per cap, then you will have a little more heating, i. e.,
8 watts per cap. probably enough to make them warm to the touch, but
you might get away with it.

I doubt that increasing the reforming voltage to 200 V would make any
significant improvement in their performance.

You will have to check how hot the caps get in actual operation, because

you will have the ripple currents to contend with. Now, with no load on
them, the ripple is negligible, but in use, the caps will charge and
discharge with every peak of the line current, 120 times a second. The
current flowing in and out will cause additional heating which may or
may not be a significant source of additional heat.

I suspect that there may be a runaway phenomenon if the caps get too hot

-- the hotter they get, the more they leak, which just makes them hotter

still, until they fail explosively. Just be careful, and keep the caps
in some sort of protective enclosure so that if one of them lets go,
then the electrolyte doesn't coat more expensive components. It stinks,
and is hard to remove.

Dave

oldpayphones wrote:

> I've been charging (reforming)capacitors since Saturday and I just

have

> a couple of questions. First off I an using a 120V variac and a bridge

> rectifier this is fed through my multimeter set for 0-300MA. I am
> slowly increasing voltage keeping the current limited to between 40-
> 100MA. I have managed to bring the voltage up to full line voltage

over

> a period of about 25-30 hours. This translates to about 170VDC. I

can't

> get the caps to fall below about 50MA of current draw at 170VDC. The
> caps are about the size of a soda can and are 200VDC @ 5400uf. Is this

> a good current draw for this type of cap? Would it be advisable to

find

> a P/S that would deliver the full 200VDC rating for the cap to reform
> at their maximum voltage? Note: The caps (6ea.)will be operated at
> about 120-125VDC when they finally get installed in the PS that I am
> building. I am also building a 10A soft start for them.
>
> Thanks,
> Larry Olson

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