Re: Power supply question - reforming caps
Posted by
beer@s...
on 2002-04-24 14:25:11 UTC
On 24 Apr, CAD_CAM_EDM_DRO@yahoogroups.com wrote:
chemical reaction that occurred in storage to reverse itself.
In your case, remove the 100k resistor from the negative lead of the
cap. Leave it connected to the positive lead. ( 100k happens to be a
nice size to use as bleed resistor as well as a forming resistor )
Now, locate a source of DC roughly equal to the DC voltage rating of
the cap. Somewhat lower is OK, higher is not.
Connect the negative lead of this DC voltage source to the negative lead
of the cap. Connect the positive lead of the DC voltage source to the
free end of the 100k resistor.
DC + ---- 100k resistor --- cap +
DC - ------------------------cap -
Turn the power on and leave it that way for a day or two.
Measure the voltage across the power supply and across the across the
now charged cap.
Note: the now CHARGED cap.
They should be close. If the cap were prefect, they'd be exactly the
same. But large old caps often have some leakage. If the voltages are
within a few percent, you're laughing.
If they're not, remove the 100k resistor and replace it with a 1k
resistor. Use the same power supply and plug it in again for about an
hour.
Measure the voltage again. A few percent difference, fine. More than
that, one worries about the cap. Electrolytic caps DO fail, with age,
with use, with misuse, with no use.
If the cap passes muster, reconnect the 100k bleeder resistor.
It goes without saying that if any appreciable voltages are involved,
extreme caution is required.
Alan
--
Alan Rothenbush | The Spartans do not ask the number of the
Academic Computing Services | enemy, only where they are.
Simon Fraser University |
Burnaby, B.C., Canada | Agix of Sparta
> Hi Alan,The idea here is to initially feed the current in SLOWLY to allow some
>
> Can you expand on this a little ?
>
> > I still, with any cap old or new
> > over 10,000 uf or so, connect it
> > to a power supply with a
> > 100k - 1meg or so series resistor.
> > Lets it reform slowly and gives
> > me an idea of leakage.
>
> I saw a post recently about a gentleman who procured multiple caps
> and then reformed? recovered ? them by a similar action.
>
> I have a 68K cap from some old Telco equipment. 100k ohm to bleed off
> the stored energy when not in use.
chemical reaction that occurred in storage to reverse itself.
In your case, remove the 100k resistor from the negative lead of the
cap. Leave it connected to the positive lead. ( 100k happens to be a
nice size to use as bleed resistor as well as a forming resistor )
Now, locate a source of DC roughly equal to the DC voltage rating of
the cap. Somewhat lower is OK, higher is not.
Connect the negative lead of this DC voltage source to the negative lead
of the cap. Connect the positive lead of the DC voltage source to the
free end of the 100k resistor.
DC + ---- 100k resistor --- cap +
DC - ------------------------cap -
Turn the power on and leave it that way for a day or two.
Measure the voltage across the power supply and across the across the
now charged cap.
Note: the now CHARGED cap.
They should be close. If the cap were prefect, they'd be exactly the
same. But large old caps often have some leakage. If the voltages are
within a few percent, you're laughing.
If they're not, remove the 100k resistor and replace it with a 1k
resistor. Use the same power supply and plug it in again for about an
hour.
Measure the voltage again. A few percent difference, fine. More than
that, one worries about the cap. Electrolytic caps DO fail, with age,
with use, with misuse, with no use.
If the cap passes muster, reconnect the 100k bleeder resistor.
It goes without saying that if any appreciable voltages are involved,
extreme caution is required.
Alan
--
Alan Rothenbush | The Spartans do not ask the number of the
Academic Computing Services | enemy, only where they are.
Simon Fraser University |
Burnaby, B.C., Canada | Agix of Sparta