Frank Dresser wrote:

OK, I'll grab some of those old Ducatis and check 'em. I'm
sure they haven't seen a polorizing voltage in at least 25
years, because that's when I bought them as surplus.

Then I'll run 'em up to their rated voltage for 24 hours and
recheck.

I'll see how much extra voltage they take and hold them at
that voltage for another 24 hours.

Just for curiosity, I'll also check the ESR at each step
with my Dick Smith meter.

I know none of this is lab quality procedure, but if there's
any gross changes, I think I'll catch 'em.

Frank Dresser



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.

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. 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

Hi,

Thats very much true with older caps up to about 1970. But later model
caps don't exhibit this 'memory'.

I'd make that "1950."

There have been alot of improvements in the electrolytes, and now the
caps last virtually forever. But the oxide thickness still determines
the tolerance, and as such it still changes with temperature, age and
voltage. Just not as much as it used to.

Funny, I've measured a dozen caps before and after reforming, new
old stock from 1946 to 1997. Other than the 1946 one, which dropped
from 17 to 12.1 µF, all the others *increased* their capacitance. That
includes ones from 1947, 1962, and 1967.

73, Alan

Hi,

Thats very much true with older caps up to about 1970. But later model
caps don't exhibit this 'memory'.

I'd make that "1950."

There have been alot of improvements in the electrolytes, and now the
caps last virtually forever. But the oxide thickness still determines
the tolerance, and as such it still changes with temperature, age and
voltage. Just not as much as it used to.

Funny, I've measured a dozen caps before and after reforming, new
old stock from 1946 to 1997. Other than the 1946 one, which dropped
from 17 to 12.1 µF, all the others *increased* their capacitance. That
includes ones from 1947, 1962, and 1967.

73, Alan

"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

"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

"Frank Dresser" wrote in message
...

.. 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.

Oops! I meant polarizing voltage. I've already checked them for
capacitance and ESR, but that's AC.

Frank Dresser

"Frank Dresser" wrote in message
...

.. 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.

Oops! I meant polarizing voltage. I've already checked them for
capacitance and ESR, but that's AC.

Frank Dresser

"Chuck Harris" wrote in message
...

Here's the numbers from the cap tests. The format is cap number, ESR
in ohms, capacitance in ufd.

Column 1, out of the drawer after sitting unused for maybe 25 years.

Coulmn 2, after 24 hours with 15V applied.

1 .19, 100 .18, 105
2 .22, 100 .20, 100
3 .21, 105 .20, 100
4 .20, 110 .19, 105
5 .21, 115 .20, 105
6 .21, 109 .20, 102
7 .24, 103 .22, 098
8 .23, 098 .21, 098
9 .16, 112 .16, 112
10 .21, 100 .20, 100
11 .22, 099 .21, 098


I don't notice any big changes. Capacitance and ESR may be down a bit.
Or it may be a temperature effect. I've now got them all sitting at
their rated voltage of 25V.

Frank Dresser

"Chuck Harris" wrote in message
...

Here's the numbers from the cap tests. The format is cap number, ESR
in ohms, capacitance in ufd.

Column 1, out of the drawer after sitting unused for maybe 25 years.

Coulmn 2, after 24 hours with 15V applied.

1 .19, 100 .18, 105
2 .22, 100 .20, 100
3 .21, 105 .20, 100
4 .20, 110 .19, 105
5 .21, 115 .20, 105
6 .21, 109 .20, 102
7 .24, 103 .22, 098
8 .23, 098 .21, 098
9 .16, 112 .16, 112
10 .21, 100 .20, 100
11 .22, 099 .21, 098


I don't notice any big changes. Capacitance and ESR may be down a bit.
Or it may be a temperature effect. I've now got them all sitting at
their rated voltage of 25V.

Frank Dresser

Here's the numbers from the cap tests. The format is cap number, ESR
in ohms, capacitance in ufd.

Column 1, out of the drawer after sitting unused for maybe 25 years.

Coulmn 2, after 24 hours with 15V applied.

Column 3, after 24 hours with 25V applied.

1 .19, 100 .18, 105 .19, 100
2 .22, 100 .20, 100 .22, 100
3 .21, 105 .20, 100 .22, 105
4 .20, 110 .19, 105 .21, 110
5 .21, 115 .20, 105 .22, 115
6 .21, 109 .20, 102 .22, 100
7 .24, 103 .22, 098 .25, 100
8 .23, 098 .21, 098 .24, 098
9 .16, 112 .16, 112 .18, 112
10 .21, 100 .20, 100 .22, 100
11 .22, 099 .21, 098 .23, 098



Still nothing I'd call a significant change. Also, it's worth noting
that the ESR meter zero point is another source of small errors.

They're at 30V right now.

Frank Dresser