Hello,
I am replacing power supply capacitors on one of my amps. I bought fresh ones, same value and voltage, and I am wondering how one measures really BIG capacitors. I guess there's no available capacitance tester able to cope with 0.15F so, out of curiosity I'd like to know if reliable measurement method is available to DIYers.
Thanks
I am replacing power supply capacitors on one of my amps. I bought fresh ones, same value and voltage, and I am wondering how one measures really BIG capacitors. I guess there's no available capacitance tester able to cope with 0.15F so, out of curiosity I'd like to know if reliable measurement method is available to DIYers.
Thanks
Meanwhile I came across this : https://electronics.stackexchange.c...-large-capacitance-e-g-super-ultra-capacitors
Why would you feel the Need to Know?
I have a handful of 5 uf supercaps 2.7 v. And Yess they are clearly marked.
I assumed their face values. Never even occurred to measure them.
Plus they work 'fine'.
I have a handful of 5 uf supercaps 2.7 v. And Yess they are clearly marked.
I assumed their face values. Never even occurred to measure them.
Plus they work 'fine'.
Because a smart previous owner took the sleeves off, thus no marking anymore.
I'm pretty confident with the fresh ones (Fisher & Tausch is a reputable brand) but I would have liked to know if the old ones were off specs or not since they are old.
This one goes to 200,000µF...
https://www.keysight.com/ca/en/product/U1701B/handheld-capacitance-meter.html
https://www.keysight.com/ca/en/product/U1701B/handheld-capacitance-meter.html
Don't forget that multi-Farad capacitors have high leakage currents! Thus for good measurement accuracy, make sure your test apparatus applies > 10x the capacitor leakage current. If your test apparatus is a frequency measurement on an RC oscillator, for example, choose R < (Vsupply / 4) / (15 * LeakageCurrent)
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Not very scientific, but I wanted to check some cheep 4f caps from amazon, so I charged up a 1f car cap from a battery ( 1.5v if I remember correctly ), checked the voltage and if it remained stable, then discharged it through a didy little motor ( out of a CD rom I think ) and counted how many seconds the motor ran for, then repeated with the 4f caps. The motor ran for longer, so even if they were less than specified, they still had more than enough for a 5 watt pam amp.
Take a 9 V battery, a 1 kohm resistor and any multimeter. Measure the battery's voltage. Measure the capacitor's voltage to ensure it is empty.
Connect the battery via the resistor to the capacitor, so it gets charged. Measure the voltage every ten seconds during five minutes. Then wait for an hour, capacitor still connected to the battery via 1 kohm. Then discharge it via the 1 kohm resistor, again measure the voltage every ten seconds.
If the voltage reaches 1 - e-1 ~= 0.6321 times its final value after about 150 seconds during charging, then the capacitor is 150 000 uF.
If it takes much longer, but during discharging the voltage drops to 0.3679 times the original value in about 150 s, then the capacitor is 150 000 uF, but it has a leakage issue that can be fixed by slow charging (reforming the dielectric).
Connect the battery via the resistor to the capacitor, so it gets charged. Measure the voltage every ten seconds during five minutes. Then wait for an hour, capacitor still connected to the battery via 1 kohm. Then discharge it via the 1 kohm resistor, again measure the voltage every ten seconds.
If the voltage reaches 1 - e-1 ~= 0.6321 times its final value after about 150 seconds during charging, then the capacitor is 150 000 uF.
If it takes much longer, but during discharging the voltage drops to 0.3679 times the original value in about 150 s, then the capacitor is 150 000 uF, but it has a leakage issue that can be fixed by slow charging (reforming the dielectric).
I'd use a constant current source of known current to charge the cap and then note how much the voltage rises in so much time and then compute the capacitance from that.
The 1 kohm I recommended in post #11 is a bit on the high side. You can use a somewhat lower resistor, for example 330 ohm, 0.5 W. The test then gets less sensitive to leakage and the times scale proportionally to the resistance, so that 150 seconds becomes about 50 seconds. With too low resistors, you have to worry about the internal resistance of the battery (which can also be a lab supply) and reading off the voltage becomes difficult.
Yes, the theory behind this is called the RC time constant which can be found in basic electrical/electronic textbooks.
For me isn't of interest the values for LF, ESR and capacity with measurement currents/frequencies from usual measurement equipment. I want to have measurement conditions corresponding to those in a high power amplifier, i. e. real live conditions.
I am sure that this will have undesirable effects such as voltage-, current- and frequency-dependent ESR, which otherwise remain hidden and therefore undetected.
Therefore the question:
Which methods and which measuring devices are used by manufacturers such as FTcap, Rubycon, Sic Safco, Cornell Dubilier, Nichicon or Nippon Chemicon for their big electrolytic capacitors with screw terminals and high ripple currents ?
Thanks for some hints.
P.S.: super caps (extrem high capacities) for battery/accu replacement like that one under
https://cdn-reichelt.de/documents/datenblatt/B300/VEC6R0504QG.pdf
are not of interest for me.
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HP made an instrument to check caps up to 1 F in the distant past- HP4282A https://nscainc.com/wp-content/uploads/pdf/A_4282A.pdf it allows you to charge the cap to operatic voltage and check for C and Dissapation (reciprocal of to ESR). Its rare and long obsolete but there are current instruments that are similar. For those big caps if you have the C and the ESR at the ripple frequency and you know the current in your application you really have all you need to know to predict ripple voltage, sag and heat buildup. The physical size will limit the inductance to something higher than you want but you are fighting mother nature. . .
I have an HP 4282A and if you were local we could check the caps.
I have an HP 4282A and if you were local we could check the caps.
good advice - thank you therefore.
some additional URL's:
https://www.amplifier.cd/Test_Equipment/Hewlett_Packard/HP_meter/HP4282A.htm
https://dabbledoo.weebly.com/hp-4282a-repair.html
Bedienungsanleitung und Service-Manual:
https://nscainc.com/wp-content/uploads/pdf/A_4282A.pdf