"Chuck Harris" wrote in message
...

That would be fine if you are looking to get doused with electrolyte.
A better test would be to measure the capacitance as they sit.
Then reform them with a 1.5K resistor in series with the supply.
Then retake the measurements.


I have a Heathkit IT-28 capacitor checker. I'll use that to run up the
voltage on the caps. The eye tube indication should keep me from
overstressing the caps. I hope we can handle it!

I'm really curious about the magnitude of the capacitance change with
voltage, so I've decided to let the 25V caps cook at 15V for another
data point. I've checked caps before and after running them up to their
rated voltage, even some 50 year old ones, and I've never noticed a big
difference in either capacitance or ESR. Well, this time I'm going to
pay attention!

I have blown caps with the Heathkit cap checker, but never from
overheating. I have turned the voltage control up way too high, and
arced them internally.



If the cap isn't drawing current during the reform, it means the
maker got the electrolyte formulation right, you probably won't see
much change in measured characteristics.


Does that mean that the manufacturers learned how to make a stable,
predictable electrolytic capacitor? If they can do that much, why can't
they manage to make them with precision?

How long would it take a right electrolyte capacitor to "unform"?

Just when did the manufacturers get the electrolyte formula right?


If the cap is drawing
heavy current during the reform, you should see greater differences
in the reformed cap vs the "NOS" cap. ESR should go down, capacitance
should go down, and so should leakage current.

-Chuck, WA3UQV


I've numbered up all 11 of my 25+ year-old Ducatis and checked them for
capacitance and ESR. I'm sure nearly all of these things have no voltage
applied since I bought them at Olson Electronics for a penny apiece,
back around 1978.

I've got them paralled with clip leads and I'm letting them form to 15V
on the Heathkit. We'll see what we get tomorrow night.

Before I powered up all the caps, I selected one of the old Ducatis and
ran it up to 25V, just to see what would happen. It took about a minute
to come to a low leakage point.

Befo 99ufd 0.22 ohm ESR

After: 100 ufd 0.20 ohm ESR

It's worth mentioning that the Heathkit cap checker marks off the
capacitance every 10ufd in that part of the scale. So most of these
numbers are estimates. But in this case, the distinction is real. The
indicator moved from the edge of the 100 ufd line to right in the
middle. However, I don't know if the distinction is important. It
might just be a temperature effect. The ESR is down 10% but I can't
make much from that either, especially since it's the last digit.

Frank Dresser