? on old electrolytic caps

I have an LCR meter which shows the ESR for electrolytic caps, but I have no idea how to interpret this number. How do you know if a cap is shorted or boardering on that status? I mean, if it gives me a reading of zero Ohms, that's obvious, but what if a small (4.7uF), medium voltage (35V) cap comes up with a reading of, say, 3 Ohms? Is that too low, like I expect, or should it be considered acceptable? I just don't know what a good cap would likely register, and have been surprised in the past when a brand new cap registered a lower ESR than the one I thought was bad. Where can I find info on the subject? Any ideas are welcome.

Thanks...

Dave

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

3 ohms for the 4.7u sounds perhaps a little high, but might be OK; maybe it was old and getting dry. A new one could well be lower.

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

--
John Larkin         Highland Technology, Inc 

jlarkin att highlandtechnology dott com 
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Reply to
John Larkin

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

Reply to
Michael Black

"Dave"

** Make and model please.
** As with any measurement, you must know what to expect or it is meaningless to you.
** Use an ohm meter.

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

** You are way off the game.

The lower the ESR reading, the better.

** Even in old equipment, most electros are still fine so take note of the readings you get and make a list with varying values and voltages and the corresponding ESR.

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

.... Phil

Reply to
Phil Allison

"John Larkin"

** Quite so.

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

Reply to
Phil Allison

Actually ESR should be one tenth of Xc or less.

Reply to
jurb6006

** Huh ????

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

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

.... Phil

Reply to
Phil Allison

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The ESR (Equivalent Series Resistance) of a capacitor is the 
resistance (_not_ the reactance) it presents to charge trying to 
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Reply to
John Fields

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

Jamie

Reply to
Maynard A. Philbrook Jr.

Well I screwed that up royally. Damn send button.

Reply to
jurb6006

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

Reply to
etpm

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

Jamie

Reply to
Maynard A. Philbrook Jr.

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If you did "quite get" it, why is clarification necessary? 

John Fields
Reply to
John Fields

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Doesn't Ohm's law work in Maine? 

John Fields
Reply to
John Fields

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For reference

Rick

Reply to
Rick

"Jasen Bleats"

** Now that is the "Dumbest Post of the Year"

Baaaaaaaaaaaaaaaahhhhhhhhhhhhhh

Plop.

.... Phil

Reply to
Phil Allison

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.

Reply to
Cydrome Leader

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Right. 

They turn into explorers. ;) 
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Reply to
John Fields

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.

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C+

Reply to
Charlie+

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That's a keeper! Thanks. :-)
Reply to
John Fields

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