? on old electrolytic caps

In ESR, low is good. But 0 ohms could be shorted. It's easy to check for a short other ways.

Check some cap data sheets for max or typical ESRs. Really big aluminum caps, or polymer aluminums, can be milliohms.

Practice, practice, practice. Try all the electrolytics you have on hand, try some in-curcuit (assuming the unit tests in-circuit), buy some new ones and see. Try to get a feel.

Keep bringing home junk from the garbage that will likely have bad caps, like LCD monitors. Once you find some bulging capacitors, which are bound to be bad, test those and see.

This will give you a feel for what's good and what's bad.

Michael

"Dave"

The reading should be tens or hundreds of thousands of ohms.

The lower the ESR reading, the better.

Make sure to post the details of your LCR meter - cos not all work the same.

.... Phil

"John Larkin"

FYI: by "ohm meter" I meant an analogue one, ie a moving coil multimeter. In any case, a shorted electro would show up on a DMM quite reliably.

The OP is asking the impossible cos verifying some old electro is still OK requires a bank of tests, meters and PSUs.

Where possible, after doing an ESR test, I just switch old equipment on and watch out for smoke.

Anecdote:

-----------

I had a new in box power amplifier for repair some years back that insisted on blowing its AC fuse at switch on. However, I found it could be brought up gradually using a Variac, pulling a large AC current if done too fast.

Made in Germany it used a pair chassis mount, 30mF, 100V Siemens electros in the PSU - the kind with 5mm bolts on top.

Both were getting damn hot and even after an hour the Variac was set not much beyond half mains voltage - so I stopped torturing them.

Turned out, the amplifier had been left in storage for about 2 years and the electros had depolarised something fierce.

... Phil

Actually ESR should be one tenth of Xc or less.

This a candidate for "Meaningless Post of the Year" ?

Or is it too dumb ...........

.... Phil

Could you please clarify that a bit? I am only an inbred from Maine and I did quite get that one.

Jamie

Well I screwed that up royally. Damn send button.

Greetings Jamie, Though I am only a basics electronics kind of guy I do sorta know this. ESR is Equivalent Series Resistance and plain old resistance is resistance to the flow of DC. So an ohm meter will measure the resistance to DC, which should be high. The ESR is not measured with DC, but with AC. And AC should be able to go through the cap easily while it should block DC. I think I got that right. Eric

You know if "Leakage" resistance was put in the statement, I may have understood that.:)

Jamie

Rick

"Jasen Bleats"

Baaaaaaaaaaaaaaaahhhhhhhhhhhhhh

Plop.

.... Phil

If you take an electronic device, even something simple like a battery there are still losses inside the device from the wiring, connections and other electrochemical stuff going on inside the device.

Those internal losses are what's called ESR. For instance, if you short out a AAA battery you will get less current than if you short out a D cell, even though both can in theory output 1.5V. The D cell has beefier internal construction and offers a lower internal resistance, so more current can be drawn from it.

The tricky part is a battery, (or capacitor or anything really) is not a plain resistor, so you can't measure this "equivalent" value with an ohm meter, but if you could, the result would be the ESR.

In capacitors, you generally want the lowest possible ESR. A cap with a high ESR is old, failing, cheap or just junk, and it can potentially heat up during use, just like a resistor. Heat makes electrolytic capacitors dry up, which increased the ESR, which make them heat up more, until they explore or just stop being capacitors.

On Tue, 17 Jun 2014 16:50:40 -0500, "Dave" wrote as underneath :

This might be helpful to you - its a link to the Peak ESR meter instruction manual which has a chart on page 9 uF/voltage/ESR approx expected in average conditions.