Re: "Forming capacitors" - means what?


Miroslav Pokorni
 

The gradual voltage increase seems just to extend time of the process and
does not seem to buy anything effective. Checking temperature is probably
good thing, but you have to be checking very often and be a damn fast gun to
react to any increase.

It seems to me to be much more effective to have a current source that would
limit current to, say 10 mA, and ram full rated voltage to the cap. If cap
shorts, 10 mA at 450V is below 5W, not enough to destroy anything, and if
cap reforms current will drop. That is how caps are made, in first place,
then reforming can be done in same way.

Current source is quite a simple thing, a power FET on a moderate heat sink,
an opamp and a voltage reference of any kind would do the job.

Regards

Miroslav Pokorni

----- Original Message -----
From: "Mark Gulbrandsen" <cinerama84106@yahoo.com>
To: <TekScopes@yahoogroups.com>
Sent: Sunday, June 22, 2003 8:30 AM
Subject: [TekScopes] Re: "Forming capacitors" - means what?


I use an EICO 1030 variable high voltage bench supply to re-form
caps. This not only has adjustable DC voltage output of up to 400
volts but it also has a ma meter on the front panel as well for
monitoring leakage. This unit has been valualable to reform
capacitors,and I agree on the temperature idea..... A warm capacitor
is definately a leaking capacitor. It does take about 48 hours to
properly reform a cap!! I start out at 100 volts(for a 450 volt cap),
50 volts(for a 350 volt cap) then dial it up by about 50 volts every
4 hours or so. When its at the max cap voltage I let it run another
24 hours checking the caps temperature frequently t be sure its not
too hot. Sometimes they will get a tad bit warm, but eventually the
caps temp goes back down to room temperature. Never had one leak or
explode on me this way.
Mark

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