Electrolytic capacitor esr reading question

[pentoad]

Some new electrolytic caps: 33uf 450v ESR reading 2.8 ohms and 8uf 450v ESR 4.8 ohms - although the ESR table only goes up to 250v, are those reading far too high and therefore they most probably defective?

[Nuvistor]

Reform them and check them again.

[pentoad]

Originally Posted by Nuvistor

Reform them and check them again.

Do those readings indicate defective caps to you?

[trobbins]

Depends what meter you are using and the test frequency. Some meters measure just impedance. ESR is also very temperature dependant.

[Diabolical Artificer]

You say "new", how new? I've pulled out new caps from my stash that have been there a year or so and had to reform them, yet other "new" 20 year old caps have tested low ESR and low leakage.

Andy.

[pentoad]

Originally Posted by trobbins

Depends what meter you are using and the test frequency. Some meters measure just impedance. ESR is also very temperature dependant.

The meter is an MESR - 100

Originally Posted by Diabolical Artificer

You say "new", how new? I've pulled out new caps from my stash that have been there a year or so and had to reform them, yet other "new" 20 year old caps have tested low ESR and low leakage.

Arrived today

[dave cox]

I would say they are very likely OK.

The ability to withstand full rated voltage is another thing altogether
Always proceed with caution at those kind of voltages!

dc

[Nuvistor]

I have never owned an ESR meter, I have just reformed caps if they have been in stock a long time, note long time could be on suppliers shelf.
This is some discussions on esr with tables but is fraught with uncertainties.
https://www.eevblog.com/forum/beginn...trolytic-caps/

[Richard]

Hi

Using a Peak ESR60.

All caps tested are NOS, various ages.

Rifa 33uF 450V, bought from RS about 4 years ago
34.9uF 0.12 Ohm
34.34uF 0.10 Ohm
35.00uF 0.10 Ohm

Rifa 10uF 450V, bought from RS about 4 years ago
11.98uF 0.75 Ohm

Dubilier 8uF 500V. I have had at least 20 years. Date code 7006. 1970?
8.51uF 0.08 Ohm

I will connect them all to my HV supply and reform them, and see if anything changes.

[Richard]

Hi

After connecting them all in parallel (I know, naughty, could go bang) to HV supply, set to 450V via a 10K resistor for 30 mins, voltage on caps rose to 450V after 1 min or so.

Rifa 33uF - all now measure just over 35uF, ESR 0.16 Ohm
Rifa 10uF - now measures 12.16uF, ESR 0.63 Ohm
Dubilier 8uF - now measures 8.36uF, ESR 0.11 Ohm



Richard

[pentoad]

This what the supplier has said:

"These are not a low ESR capacitor and as such will have an ESR of over 5 ohms. These capacitors where made less than a year ago so they are not old stock. I hope this has reassured you that these capacitors are OK and perfectly fine to use"

Has the technology of modern electrolytics changed so much that ESR readings are no longer useful indicator in this instance, if so when did things change or does that mean not caps are made equal?

[Sideband]

Low ESR caps have been around for many years. They are usually rated at 105 degrees ...some are even higher. Most 'standard' electrolytics are rated at 85 degrees C and are for general purpose use in non-critical circuits (like decoupling). Low ESR caps are specifically designed to operate at higher frequencies and temperatures as found in switch mode power supplies and these are the ones that must be replaced with similar low ESR types. The ones you have would not be suitable for a switch mode power supply.

In short...no, not all electrolytics are made equal.

[pentoad]

But they are not intended for a switch mode supply -
my question is: would an ESR 5 ohms in a conventional circuit result in failure

[PsychMan]

I wouldn’t be concerned about those esr values unless I’d specifically bought low esr caps. I checked a few random cheap electrolytics in my stocks recently on a component analyser and saw similar esr levels.

[PsychMan]

Originally Posted by pentoad

But they are not intended for a switch mode supply -
my question is: would an ESR 5 ohms in a conventional circuit result in failure

No. Some applications, particular switch mode power supplies are fussy about esr, for most uses it won’t matter, and if it did it wouldn’t amount to “failure”. Not in my opinion anyway

Best regards
Adam

[lesmw0sec]

I agree. The only time I have closely looked into ESR was when selecting a cap for an electric detonator, where the discharge capabillty at high current was clearly important.

[trobbins]

Like battery impedance testing, the test should be about the relative value - has it changed with usage, life - it is an indicator of end of service life. A spot measurement is only of use if you have same-same comparisons.

I'd suggest that even mains rectified first filter applications can be an issue for ESR, especially if the ripple current is up near the cap limit.

[Station X]

The voltage rating of the capacitors suggests they're intended for use in the PSU section of a valve radio, record player or W.H.Y.

I've never bothered to check the ESR of capacitors, original or replacements, used for this purpose. I just check the leakage using a reformer and the capacitance using a capacitance meter. The latter test is in case the cap is open circuit. How long the cap takes to discharge through a DMM on volts range is another guide to its condition.

[pentoad]

Originally Posted by Station X

The voltage rating of the capacitors suggests they're intended for use in the PSU section of a valve radio, record player or W.H.Y.

I've never bothered to check the ESR of capacitors, original or replacements, used for this purpose. I just check the leakage using a reformer and the capacitance using a capacitance meter. The latter test is in case the cap is open circuit. How long the cap takes to discharge through a DMM on volts range is another guide to its condition.

Many do rely on ESR meters to test caps in circuits.
I would of thought that someone in this forum would be able to tell me if an ESR reading of 5ohms on an 8uf 450v is excessive or not, or indicated a fault.
Earlier on in this thread somebody had tested a 8uf with a reading of 0.1 which is what I would have expected.
The caps in question (mine) is from a reputable make and and should have a leakage value of 3uA

[ajgriff]

Originally Posted by pentoad

I would of thought that someone in this forum would be able to tell me if an ESR reading of 5ohms on an 8uf 450v is excessive or not, or indicated a fault.

I suspect you won't get a definitive answer here or anywhere else because there are so many dependencies. However, I'll stick my neck out and say that 5Ω doesn't indicate a fault in a bog standard aluminium electrolytic with the parameters you've quoted.

Alan