EEVblog Electronics Community Forum
General => General Technical Chat => Topic started by: PirateKitty on September 11, 2020, 11:15:57 am
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Heya,
I just found bags of electrolytic caps in my basement storage from 1990's. Mostly 1000uF and 470uF. close to 1000 total.
I think I bought them from Jamco back then. A bag of a 1000 a piece.
They test fine on 2 component testers I have and show an ESR of only 0.050 Ohms!
I went to measure them for leakage with my DMM. On Ohms setting, I read 4 Meg Ohms for 1000uF and 40 Meg Ohms for 470uF! :scared:
Aren't these caps supposed to have high enough resistance, that they shouldn't register with regular DMMs? My DMM croaks after 60 Meg Ohms and shows Over Range.
Are these caps good now after 25+ years. Would caps from 90's be considered old and leaky?
Just wondering if they're worth hanging on to...?!
Cheers.
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It depends what is your plan with them... Also make and model have a great influence on shelf time too. As a rule of thumb a virgin capacitor especially sitting on the shelf a lot, need formatting before serious usage. Charge and discharge the capacitor to rated voltage (or 80% of it) at Irated/10 a few times.
During this the chemistry is shaked up a bit and you can perform charachterization of the specs, eg. the leaking test.
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Hi
Use a bench power supply set for about 90% of rated voltage of the capacitors. put say a 1K resistor in series with the capacitor and monitor the voltage drop across the 1K resistor with your DMM.
Over time (hours) voltage across 1K will drop to a very low level and the capacitor will reform. If you are checking an batch of identical capacitors they should all drop in the same time to approximately the same
low voltage across the 1K resistor.
George G6HIG Dover UK
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Hey thanks for the quick reply.
That explains why the few I put across my bench power supply and turn it on and off a few times, brought them back!
I thought I discovered something new! :-DD
Now I know it was the capacitor reconditioning people talk about.
Some went bad. Dropped from 4 Meg to 380K, but they still read fine on the 2 component testers. Still with 50 Milli Ohm ESRs!
But I'm throwing those out. The ones that jump from 4 Meg to infinity after reconditioning, I'll keep.
I think I'll build a leakage tester and test them all. Thanks again.
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I came to a crud version of this solution by accident.
Thanks to you, I can now expect and quantify their behavior.
Do you know of a circuit I can build, to automate this reconditioning process?
Cheers.
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I came to a crud version of this solution by accident.
Thanks to you, I can now expect and quantify their behavior.
Do you know of a circuit I can build, to automate this reconditioning process?
Cheers.
An HP 4350A High Capacitance Meter is an excellent device for reforming and testing electrolytic capacitors. It includes an adjustable internal bias supply up to 100V and a wide range leakage current meter to monitor leakage current during the process of reforming. It also includes a capacitance meter and loss factor meter for capacitance measurements in the range 1uF to 300mF so it is useful for really large capacitors that the average LCR meter can't handle.
Unfortunately these are quite rare these days so you may have to hunt around a bit for one. Don't go for the 4350B as this doesn't have the leakage current function.
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Even harder to come by is cash!
I've already whipped together an indicator, that is build around 2 GP transistors.
Simple circuit and cost nothing for me to build. :-+
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I use a Heathkit Condenser Checker
Tests at higher voltages, 25 to 450 Volts, has leakage test.
Capacitance reading on mine is not very accurate ( probably needs recal) but the cheap electronic meters give you a cap value
Good for testing old tube radio stuff.
If you find one, they are really cheap, maybe $ 5-10.
I reform old caps in radios that have been sitting for a long time starting with maybe 50% of 120 V line voltage, then up it, usually works.