Since they have a large value, you can do a basic capacitance check by charging them and then discharging them over a large resistor. The capacitance is the time that the voltage needs to drop by a factor of e ~= 2.7182818284 divided by the resistance. Make sure to take into account the input resistance of the meter.
Buy yourself a cheap capacitor-meter including a basic esr function.
It will be a good investment anyway.
If a modern cap is in good condition, it can work in practically any role
OMOE,
is the small transformer in your second photo mains powered ??
IF so, please do not use simple alligator clips to apply mains voltage to the transformer !!!!
Safety first - mains voltage can be lethal. Please use proper wiring and insulation.
is the small transformer in your second photo mains powered ??
IF so, please do not use simple alligator clips to apply mains voltage to the transformer !!!!
Safety first - mains voltage can be lethal. Please use proper wiring and insulation.
Yes, I saw this one recommended by somebody here and I ordered it.
LCR-T4 Mega328 Transistor Tester Diode Triode Capacitance ESR Meter With Shell | eBay
It should arrive soon. I don't know how good it is but for the price... 🙂 Probably not good for checking ESR.
Yes aboos I should be more careful Thank you
Malcel I don't understand your formula. We take the voltage we charge the cap (say 40v.) and divide by 2.7182818284 ? Then the time it takes to discharge to 14.71 volts divide by the resistance we use to discharge the cap ? gives us the capacitance ? I think I make a mess of that formula. 🙂
That's correct, no mess at all 😉 But as your capacitors are rated for 35 V, it makes more sense to charge them to 35 V and wait until the voltage has dropped to 12.88 V.
Last edited:
In my case, that would take a long time.
The 15,000uF / 63v caps were charged to 50v directly from my bench supply (no series resistors involved) in March of this year, then set aside on a shelf.
Yesterday, I read them at about 29 to 31 volts and holding.
I just momentarily "touch them" with a Fluke meter to get a reading to avoid loading them down.
Wow. What is your life expectancy?
Gee, I may be smarter that my dogs think I am. 🙂
I will try it. It will be a shorter time for me. What is the unit of mesurement for the time? Minutes, hours?
Cool.
Ok, they are showing their age, in my book they are "usable" but I´d consider 35V **surge** voltage, and effective "rated" voltage 25V under any condition, and maybe 30V IF Mains voltage is stable. (which depends on where you live).
I consider that "reforming" 🙂 but still too close to rated 35V , I´d revise my safe voltage up to 28/30V , still NOT 35V.
Hey, not bad for FREE caps!!!
I´d call that reforming more than charging, see above.
Well, 16 hours is a lot, specially for presumed leaky caps.
I´d wait 15 minutes after disconnecting charging supply.
I think I mentioned itearlies as a way to check cap polarity.
No matter what the forward voltage capability, reverse voltage is "a few" volts ... just what you found.
Also the reason why reverse charged caps tend to explode. 😱
Repeat tests with shorter discharge times, in any case that tends to confirm my "safe up to 25V" rating, but repeat test as suggested.
.
Repeat test but waiting more realistiv 15 minutes or so.
Both charging and discharging.
Not applicable, as the discussion OMOE and I had was about measuring capacitance by discharging the capacitor with a resistor of a known value and measuring the time constant.
In any case, I also have the experience that the leakage of electrolytic capacitors is usually decades below the specified worst-case value unless they haven't been charged for a very long time. Still, from March to August is really good!
Seconds. The time depends on what parallel resistor you use. With 10 000 uF and 10 kohm, it will be about 100 seconds, long enough to measure reasonably accurately with a watch and a digital multimeter. Digital multimeters usually have an input resistance of 1 Mohm or 10 Mohm, so large enough to neglect compared to 10 kohm.
Just finish re-test 6 of them took at random.
I was surprise they charge to 35v. in less than a minute.
It could be because I've charge them individually this time or after yesterday workout at 40v., they are reformed or partially reformed.
After 15 min. they are all at 32.6 or 32.7 volts
Since it seams consistent, I didn't check more capacitor.
I will wait to see how much time they take to go down to 12.88v. to check the capacitance... just to see. 🙂
Just check again after 30 min. 32.0.or 32.1v.
Yes I discharge them with the same resistor 3k64 ohms and I count the time.
Between 47 and 52 secondes for the same 6 caps I had with the previous test.
The result must be in Farad. (47 sec. = 0.01291)
That means they are between about 12,000 and 14,000 micro farads.
right??
Between 47 and 52 secondes for the same 6 caps I had with the previous test.
The result must be in Farad. (47 sec. = 0.01291)
That means they are between about 12,000 and 14,000 micro farads.
right??
You mean they don't charge fast enough?
3k64 X (what is the c ?) and X by second
I realize the capacitance test could be more accurate regarding to the time with a bigger resistance because it's discharging fast with 3k64 and one sec. more or less seems to do a big difference.
Oh I think I got it
Resistance * capacitance = time to charge to 23.3v. (35/3*2=23.3) It should take 43.7 sec.
I've try on one : 36.9 sec.
Resistance * capacitance = time to charge to 23.3v. (35/3*2=23.3) It should take 43.7 sec.
I've try on one : 36.9 sec.
c is the value of the capacitor in farads.
r is resistor value.
0.013F * 3k64=47 secs to 2/3 voltage.
Last edited:
Well it's fun to learn new stuff but I took enough of your time... for now. 🙂
The projects I have in mind for now is with LM3886 with 24-0-24 Dc because I got all the parts for it. May be later a Pass ACA 0-20 or 24 DC. So I'm confident I can use those capacitors with small amplifiers like that.
Thank you very much everybody for your time and patience, it's very kind of you.
Have a good day/night.
François
The projects I have in mind for now is with LM3886 with 24-0-24 Dc because I got all the parts for it. May be later a Pass ACA 0-20 or 24 DC. So I'm confident I can use those capacitors with small amplifiers like that.
Thank you very much everybody for your time and patience, it's very kind of you.
Have a good day/night.
François