desoldered capacitor is self charging until 0.6 voltage.

[chth96]

I have an 21 inch CRT TV which is not able to power on.
I disassembled 21 inch CRT TV and measured voltage of main filter capacitor(Samhwa HC 400WV 220uF) in the circuit.
It shows 270V on my DMM.

So I discharged this main filter capactior completely and detached circuit board from cathode-ray tube.
Then I desoldered this main filter capacitor from circuit board.
But I noticed that this desoldered large capacitor(Samhwa HC 400WV 220uF) is slowly charged by itself until it reached 0.6V

I measured its ESR value with MESR-100 and it shows 0.1 ohm,judging by ESR value I think that there is no flaw in this capacitor(Samhwa HC 400WV 220uF).

By the way,Does it really no flaw in this capacitor which is self charging until 0.6 voltage?

[momaka]

Yup, dielectric absorption it is indeed.

I find this quite often with large high(er) voltage (typically 50+ Volts) capacitors... and also sometimes on larger capacity capacitors that have a very low leakage current / self-discharge rate.

Latest case of this was when I found a couple of old 42V 4700 uF Panasonic capacitors on a scrap board from a Technics amplifier. Charged them up to 40-ish Volts to reform them, just in case (even though they showed healthy parameters.) After I was done with reforming them and checking their leakage current, I discharged them (safely, though a resistor.) The next day, one had 6.x Volts, and the other almost 9V.

Can I use this large capacitor(Samhwa HC 400WV 220uF) as main filter capacitor in future?

Absolutely.
Though I suggest to be careful where you use it. In particular, you might want to avoid using it in PSUs with APFC, because APFC tends to stress primary caps a lot more and some of these "regular" HV caps can overheat internally.

[stj]

the foil is a coil, it is picking up energy from the sun, tv, cell towers etc.
i have strings of led lights that run forever on this principle!
free energy for some - loses for others!

[petehall347]

i find some capacitors charge back up after discharging them . be careful it can be quite shocking .

[PeteS in CA]

Dielectric absorption

[chth96]

By the way it usually took more than 20 hours to charge by itself until 0.6V.
Then Is it ordinary Dielectric absorption and Can I use this large capacitor(Samhwa HC 400WV 220uF) as main filter capacitor in future?

[momaka]

Yup, dielectric absorption it is indeed.

I find this quite often with large high(er) voltage (typically 50+ Volts) capacitors... and also sometimes on larger capacity capacitors that have a very low leakage current / self-discharge rate.

Latest case of this was when I found a couple of old 42V 4700 uF Panasonic capacitors on a scrap board from a Technics amplifier. Charged them up to 40-ish Volts to reform them, just in case (even though they showed healthy parameters.) After I was done with reforming them and checking their leakage current, I discharged them (safely, though a resistor.) The next day, one had 6.x Volts, and the other almost 9V.

Can I use this large capacitor(Samhwa HC 400WV 220uF) as main filter capacitor in future?

Absolutely.
Though I suggest to be careful where you use it. In particular, you might want to avoid using it in PSUs with APFC, because APFC tends to stress primary caps a lot more and some of these "regular" HV caps can overheat internally.