How do you test big filter caps?

[mikay786]

So as of so far for big caps pretty have just been checking them for visual signs.

Basically with my multimeter I can only test smaller caps, with big caps I cant get a reading even after leaving it attached for a while. Is this due to not having enough juice to charge cap?

Do you need special equipment to test larger caps? Ive got a ESR meter like this ebay transistor / esr tester (https://www.badcaps.net/forum/showpo...6&postcount=50)

but the pitch is a bit small but could solder leads to it but again I'm sure ive tried before and same issue not getting a reading on larger filter caps.

Caps I'm wanting to test are 63v 10000uf Samsung SMS caps.

[stj]

Re: How do you test big filter caps?

the esr meter should handle 10,000uF
just make sure the bitches are fully discharged just before you test them - big caps can slowly self-charge.

[vinceroger69]

Re: How do you test big filter caps?

my cheap ebay transistor / esr tester test filter caps just fine ive never had any issues with testing them etc i have more trouble finding the data sheets for the correct esr reading.

[mikay786]

Re: How do you test big filter caps?

Cool will try the esr meter, yea I made a discharge tool using a cheap probe with crock clip on one end and probe in other, cutting it in half and soldering in a big encapsulated 5w resister in between and heat shrinking it.

Does the job nicely, about 25-30 to fully discharge big caps. Surprising though even with under 1 volt left in a big cap I shorted it with a screw driver and still got a spark. So now keeping it on longer and then shorting to make doubly sure.

[stj]

Re: How do you test big filter caps?

it's the ripple current that gives the spark.

[vinceroger69]

Re: How do you test big filter caps?

I should make a discharge tool can i use a 5w 100k cement resitor as i have some spare.

[momaka]

Re: How do you test big filter caps?

it's the ripple current that gives the spark.

Actually, from what I've read before, it has more to do with the energy stored in the cap, which is
0.5 x capacity x voltage^2
with capacity in Farads and voltage in volts.

And the ESR matters a lot too, of course - two times lower ESR can often double the current at short-circuit.

I usually discharge my high voltage caps (up to 450V) with a 4.7 KOhm 5W resistor for a few seconds. If the cap has only a few volts left on it, I short-circuit it with a screw driver.

big caps can slowly self-charge.

Indeed.
Which is why I always try to keep mine fully charged when in storage - that way, it becomes a habit of discharging them first. And believe me, I thought myself that habit the hard way - those HV caps will bite if not careful!

[stj]

Re: How do you test big filter caps?

crt's are the best caps.
hmm - gives me an idea, next time i have one exposed i'll try to put it on the component tester!!