Proper way to test electrolytics?

[sawdust]

I just picked up a bunch of used Mallory electrolytics and need to test them. I have a Fluke 8020 DVM. I took a known good cap (22ufd/450v) and with my DVM on 20m scale, positive lead to positive on cap; neg to neg. The resistance slowly goes up to over a million ohms after about a minute or two. It does the same thing on several of the used caps. Is this a reliable method or should I just go buy a cap meter, probably should anyway just to have one.

Dave

[FYL]

Is this a reliable method or should I just go buy a cap meter, probably should anyway just to have one.

Basic cap meters only measure capacitance. Midrange models also allow for ESR/DF measurements. High end versions add leakage tests.
A full cap qualification should include all three tests.

Electrolytics should be reformed first, by applying a rising voltage under very low current up to nominal V, something most affordable modern cap testers don't allow.

Get a vintage cap tester/analyzer such as the Heath IT-28...

[kagliostro]

Hi  :)

I find out this link

http://www.ilriparatore.it/pagine/trucchi/fugas.htm

I'm not sure is a circuit to test also electrolytics but seems a simple and interesting way to test capacitors

as the link is in italian I try to translate for you

The cables in order to connect the condenser must be short.
The condenser must totally be taken apart from the circuit for being tried
does not have to be touched with the hand during the test, because this can produce one erroneous indication.

In the moment that is connected, a lightning bolt is produced in the light bulb to Neon, during loads with the condenser (a greater ability, will make a lightning bolt longer), in order to see if the condenser is in good state, the light must be extinguished totally.
If it remains ignited, the condenser is in loss.
This test can control escapes than 100 more Mega ohms

Attention:
Short cut  always the condensers, after to have tried it.
It can remain loaded with an elevated tension, and can give one not pleasant discharge manipulating it, in special way if draft of members of one sure ability.

Materials:

T1 - Transformer adapted to the net (120 or 220V) and secondary of 230 or 250V x 2 (Can use some with only one secondary 230 or 250V, in this case, logically, a bridge of four diode for rectifier)
D1 and D2 - Diode 1N4007
R1 - 470 ohm 1/2W
R2 - 220 k ohm 1/2W
C1 and C2 - electrolitic  capacitors 4.7uF 350V
Neon - Light bulb to Neon (little spy 220V)

hope is a useful link

Kagliostro

[Nigel]

I just picked up a bunch of used Mallory electrolytics and need to test them. I have a Fluke 8020 DVM. I took a known good cap (22ufd/450v) and with my DVM on 20m scale, positive lead to positive on cap; neg to neg. The resistance slowly goes up to over a million ohms after about a minute or two. It does the same thing on several of the used caps. Is this a reliable method or should I just go buy a cap meter, probably should anyway just to have one.

Dave

I wouldnt even touch old capacitors.
New ones are so cheap now.
Why risk your precious amp with possibly dodgy components ?