Electrolytic ESR

J

John

Guest
I have a faulty switched mode psu. I've tested the ESR of the electrolytics
and one of them may be faulty. I have not used a cap ESR meter until now so
am not sure if the reading I am getting is indicating a good or a suspect
cap. The cap in question is a 500 Volt 33 uF and the ESR measured out of
circuit is one ohm. measuring frequency is one hundred kHz. I've read
that high voltage electrolytics have a higher ESR than low voltage ones.
Does the 1 ohm figure sound ok or suspect for this cap ? I don't have a
similar valued cap to make a comparison test.

Thanks
 
I would suggest this: Compare the reading to another cap at 33 uF that
you know is good. Remove the cap and check it with an ohm meter to make
sure that it is not DC shorted. An analog ohm meter is the best to
check caps for shorts. The ohm meter should give a reading, and then
drop off. It should eventually reach infinite. A digital meter should
go up to a very high value of reading, but if it is pulse sampling, it
may never reach infinite. Most of the higher cost digital meters use
pure DC for ohm readings. You want to know if the cap is shorted in this
case.

The idea is that in theory you want a low reading on the ESR meter, and
an infinite reading on an ohm meter. The cap would have to be removed
from the circuit to use the ohm meter test. Then again, for the low
cost of a cap, I would consider to replace it, if there was any suspect
of it being defective.

--

Greetings,

Jerry Greenberg GLG Technologies GLG
==============================================
WebPage http://www.zoom-one.com
Electronics http://www.zoom-one.com/electron.htm
Instruments http://www.zoom-one.com/glgtech.htm
==============================================
"John" <abuse@global.freeserve.co.uk> wrote in message
news:bf97bb$rme$1@news7.svr.pol.co.uk...
I have a faulty switched mode psu. I've tested the ESR of the
electrolytics
and one of them may be faulty. I have not used a cap ESR meter until
now so
am not sure if the reading I am getting is indicating a good or a
suspect
cap. The cap in question is a 500 Volt 33 uF and the ESR measured out
of
circuit is one ohm. measuring frequency is one hundred kHz. I've read
that high voltage electrolytics have a higher ESR than low voltage ones.
Does the 1 ohm figure sound ok or suspect for this cap ? I don't have a
similar valued cap to make a comparison test.

Thanks
 
The cap value measures in tolerance on a capacitance meter.

Analogue multimeter check is fine. (needle drops back fine)


"Jerry G." <jerryg@total.net> wrote in message
news:bf97re$phj$1@news.eusc.inter.net...
I would suggest this: Compare the reading to another cap at 33 uF that
you know is good. Remove the cap and check it with an ohm meter to make
sure that it is not DC shorted. An analog ohm meter is the best to
check caps for shorts. The ohm meter should give a reading, and then
drop off. It should eventually reach infinite. A digital meter should
go up to a very high value of reading, but if it is pulse sampling, it
may never reach infinite. Most of the higher cost digital meters use
pure DC for ohm readings. You want to know if the cap is shorted in this
case.

The idea is that in theory you want a low reading on the ESR meter, and
an infinite reading on an ohm meter. The cap would have to be removed
from the circuit to use the ohm meter test. Then again, for the low
cost of a cap, I would consider to replace it, if there was any suspect
of it being defective.

--

Greetings,

Jerry Greenberg GLG Technologies GLG
==============================================
WebPage http://www.zoom-one.com
Electronics http://www.zoom-one.com/electron.htm
Instruments http://www.zoom-one.com/glgtech.htm
==============================================
"John" <abuse@global.freeserve.co.uk> wrote in message
news:bf97bb$rme$1@news7.svr.pol.co.uk...
I have a faulty switched mode psu. I've tested the ESR of the
electrolytics
and one of them may be faulty. I have not used a cap ESR meter until
now so
am not sure if the reading I am getting is indicating a good or a
suspect
cap. The cap in question is a 500 Volt 33 uF and the ESR measured out
of
circuit is one ohm. measuring frequency is one hundred kHz. I've read
that high voltage electrolytics have a higher ESR than low voltage ones.
Does the 1 ohm figure sound ok or suspect for this cap ? I don't have a
similar valued cap to make a comparison test.

Thanks
Click to expand...
 
Thanks for the info. The ESR meter is the one described in Poptronics
(formerly Popular Electronics) magazine a few years ago (with the
corrections to the circuit diagram applied). As soon as I built the tester
I grabbed about 20 electrolytics and tested them all. I was surprised that
even old used one's tested good with ESR less than 0.5 ohm. (The only ones
that read higher are low value caps were the capacitive reactance would be
high at 100 kHz as you would expect) I calibrated the meter using low value
carbon resistors. Its just that I heard that high voltage caps have a
higher ESR than lower voltage ones of the same capacitance value. I guess I
will have to get a new 500 Volt 33 uF cap and compare the reading to the
suspect one.

In passing, are any of your cap meters the Poptronics design ? I find that
if you short the probes and zero set the meter then measure a cap the
reading is beyond the end of the scale indicating even lower resistance than
shorted. (there is no DC blocking cap in the Poptronics design....So, I
put a 0.68 uF in series with the probe lead, that fixes the problem. Now
when I short the probes and zero the meter then measure a cap the meter
never deflects to greater than full scale. I believe the readings are now
good based on calibration with the resistors and also when measuring low
value caps and calculating the capacitive reactance value. The meter reads
the correct ohms value.




"Sofie" <sofie@olypen.com> wrote in message
news:vhgdkppopp6qce@corp.supernews.com...
John:
The advice in the Jerry G. reply post is exactly correct.
I have on my benches several different brands of ESR meters and all of
them
come up with different readings. Since you did not tell us what kind of
ESR meter you have we can only speculate.
No matter what brand of ESR meter you have, until you get accustom to the
readings it produces with a variety of electrolytic values you would be
very
wise to grab a few or a bag full of new electrolytics and make comparisons
and maybe make a note or two regarding the typical readings you obtain
with
random new electrolytics. Of course you need to compare the same value
electrolytics..... different capacitance values will of course produce
different "normal" readings.
You will find that there can be a variation in the readings even with new
"same value" electrolytics from the same source but you will soon be able
to
determine what is normal and what is not.
--
Best Regards,
Daniel Sofie
Electronics Supply & Repair
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

.
"Jerry G." <jerryg@total.net> wrote in message
I would suggest this: Compare the reading to another cap at 33 uF that
you know is good.
Click to expand...
 
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