electrolyte capacitor - guideline about maximum current

[Grossel]

Hi.

I think about making a test rig for electrolyte capacitors. Before I consider if this is something that is worth doing, I want to know how much current I can apply to a capacitor over some minutes to be able to determine that the cap is in working order.
This is if you guys actually have an answer for that for a typically electrolyte cap to find in current supply applications. If not I may consider to either not build such a test rig, or just collect a number of capacitors and do a manual test to see how much I can stress the caps before they fails.

Problem is - I don't want to do this kind of extreme destructive test at home, where I run the risk of getting bad toxic smoke in house. So therefore it is way more easier to just ask straight out, how much a typical capacitor can be stressed before the internal power loss becomes a problem.

So I know the number of possible values of maximum voltage, capacitance, physical size, etc all plays a role here and make a near infinitive number of types. So I hope being given some general guidelines.

I have not yet decided for test method, an oscilloscope is for sure included. I think a simple one-diode rectifier after a transformer would be the absolute simplest way of testing, but for smaller capacitors it won't be a good testing method in my mind.

 

[dknguyen]

Best bet would just be to find some datasheets for standard sizes from two or three manufacturers and use those as representative values.

 

[alec_t]

One useful test would be to measure the ESR (equivalent series resistance) of the caps, since high ESR results in internal heating and is a common cause of cap failure. So build an ESR meter. Designs are plentiful online.

 

[Nigel Goodwin]

As others have mentioned, the absolute main fault (99%+ of cases) of electrolytic capacitors is high ESR.

A simple, and cheap, Chinese component tester (using an AVR processor) will test them for you simply and easily.

 

[dr pepper]

An interesting way to visualize esr on a 'scope is to apply a bipolar square wave to it via a current limiting resistor, and look at the trace, an ideal cap would flat line, esr shows itself as a squarewave, the amplitude of which is proportional to esr.
Switching resistors enables you to change the current drive.
Another thing that can happen with caps is leakage, I have a cheap lashup using a neon, a cap and a resistor, the neon flashes at the rate of leakage, this is more usefull for vintage equipment repairs, I htink the circuit is copied right out of a piece of vintage test gear, besides a leaky cap is probably high esr anyway.

 

[Grossel]

Thank you very much for your ideas. I'll have that in mind.

 

[Colin]

The one thing that everyone has failed to mention is this:
It is the most important factor in determining the life of a capacitor.
Basically it is called ripple current but to keep it simple it is the change in voltage and the time it takes to make the change.
This is what heats up an electrolytic capacitor and you will find some 35v capacitors are smaller than 25v capacitors. This is just an example. The reason is the ripple current is smaller.
Electro's in a voltage doubling arrangement are fully filled and fully emptied on each cycle and these have a very short life.
All the talk about ESR is totally tangential as it is the circuit that determines the life and the ripple capability of the electro.