I'm using a Fluke 115. I was trying to test my 22000uF 35V capacitors for the power supply and I'm just wanting to get some input. It was just saying OL, so I went to the manual and it says 1 - 9999uF. I have only measured capacitors for the ACA and the moreplay I built so they were pretty low.
Am I reading this upper limit of the Fluke 115 correctly?
Am I reading this upper limit of the Fluke 115 correctly?
rayma beat me to it! Almost any capacitor in series which is a balance between enough to bring the total down below the max reading but still giving a value which can be accurately extracted.
I didn't know you could read a cap with a multimeter. OK, 1000pFd, but not soup-cans. There can't be enough juice in a meter to soak a cap to capacity? (I admit that 9999uFd is impressive.)
It takes a minute and a buck to check a big cap. R and C. Charge from a battery then disconnect. "Time Constant". Watch for when the cap voltage falls 63%; rather when it falls to 37% of initial voltage. For handy 9V cell that's like 3.33V. Time that.
Since you think you know the cap value, pre-compute the time. 22,000uFd * 1,000 Ohms is 22,000,000 microSeconds or 22 Seconds. Does the voltage decay to about 3.33V at about 22 Seconds? Faster or slower tells you stuff also.
(the 'ground' is not necessary except my simulator won't work without a zero-point.)
It takes a minute and a buck to check a big cap. R and C. Charge from a battery then disconnect. "Time Constant". Watch for when the cap voltage falls 63%; rather when it falls to 37% of initial voltage. For handy 9V cell that's like 3.33V. Time that.
Since you think you know the cap value, pre-compute the time. 22,000uFd * 1,000 Ohms is 22,000,000 microSeconds or 22 Seconds. Does the voltage decay to about 3.33V at about 22 Seconds? Faster or slower tells you stuff also.
(the 'ground' is not necessary except my simulator won't work without a zero-point.)
Yeah, just after I'd designed and built a C-meter to work with my trusty Avometer I bought one of those new DMM thingys. It will read up to 10mF. But I still use my cap meter with an Avo because on the 100pF range it will read down to 1pF. If you keep your fingers away that is. Mind you, my Avo won't give you a frequency reading...
And you are assuming that testing a cap means measuring its capacitance. That is one small part. ESR is a more informative measure, only some meters do that. But at least in tube amps, leakage is way more important. A 450v cap might "test" just fine at 10v, but may leak like a screen door over say 200v. Your meter tests caps with only a volt or two.
Yes, a very helpful instrument indeed. But it literally eats batteries, and it's proprietary (rather long DC plug of small diameter) AC adapter is $$$. And there are other sources than A****n.
Best regards!
@Enzo
I do not know who you were replying to but I was not addressing a complete capacitor characterisation. The OP was concerned about measuring the value of the capacitor. That was all I was addressing, you have correctly pointed out that other factors are important.
I do not think that in this context 450V capacitors were relevant (22mF @ 450V?) but ESR, ESL and leakage/ BV are important but not what was raised as a question.
I do not know who you were replying to but I was not addressing a complete capacitor characterisation. The OP was concerned about measuring the value of the capacitor. That was all I was addressing, you have correctly pointed out that other factors are important.
I do not think that in this context 450V capacitors were relevant (22mF @ 450V?) but ESR, ESL and leakage/ BV are important but not what was raised as a question.
@ JMFahey
Depends on who is paying? (Many on here will be using their own time of course, but in a work environment a quick reading from a meter might be better value for money if not so much fun.) A point I am concerned about is how the meter tests a capacitance, That may be unknown ( I don't know what method my DMM uses; others may know how theirs works) and an important point you allude to. If you have made your own meter and taken the trouble to calibrate it then I think it is not "blindly" relying on it to take a measurement. Must hook the DMM up to the scope one day to find out.
Depends on who is paying? (Many on here will be using their own time of course, but in a work environment a quick reading from a meter might be better value for money if not so much fun.) A point I am concerned about is how the meter tests a capacitance, That may be unknown ( I don't know what method my DMM uses; others may know how theirs works) and an important point you allude to. If you have made your own meter and taken the trouble to calibrate it then I think it is not "blindly" relying on it to take a measurement. Must hook the DMM up to the scope one day to find out.
Available everywhere cheap meters typically measure reactance by applying a square wave (way cheaper to generate than a true sinewave) to capacitor and measure voltage available at the other end, across a load.
A somewhat better one is to use it as a charge pump, they apply very narrow peaks,again rectify what appears at the other end and charge a second capacitor, voltage is proportional to capacitance.
That said, they assume a perfect capacitor.
If it´s lossy, extra current (bad) is taken as extra capacitance (good), that´s why many mistakenly claim that "old capacitors increase in capacitance" which is nonsense, but they argue: "hey!!! I measured it!!!"
It´s actually measurement error.
Also errors appear at very large and very low values:
There´s where "going back to basics" shines, and I am not only talking capacitance here, but many other parameters.
I can easily measure magnetic flux in a very narrow speaker gap where no probe fits and Hall effect sensors are WAY above their limits, by simply sweeping a voice coil through it and integrating results.
The way Maxwell did, go figure, there´s no more hardcore back to basics than that. 😉
Of course, instead of a mechanical ballistic galvanometer like he could have used, I integrate current using an Op Amp and a capacitor.
My method can be used to calibrate a $2000 magnetometer, go figure.
By the same token, and just as an example, I can measure bullet speed (I am a shooter/reloader) using a pendulum, same way as Leonardo used 500 years ago when designing muskets and cannon.
Not so small detail: I live in Argentina, where ordering stuff from US is slow and expensive, and as they say: "Necessity is the Mother of Invention" so MANY times it was faster (let alone cheaper) building some device than ordering the modern replacement.
IF in US, yes, I would probably order from Amazon and get it next day.
By the way, not only in Argentina: you´ll often see Forum members from, say, India, South Africa, Eastern Europe (and Russia), Brazil or Australia posting very clever and "unusual" solutions to everyday problems.
A somewhat better one is to use it as a charge pump, they apply very narrow peaks,again rectify what appears at the other end and charge a second capacitor, voltage is proportional to capacitance.
That said, they assume a perfect capacitor.
If it´s lossy, extra current (bad) is taken as extra capacitance (good), that´s why many mistakenly claim that "old capacitors increase in capacitance" which is nonsense, but they argue: "hey!!! I measured it!!!"
It´s actually measurement error.
Also errors appear at very large and very low values:
- small (a few pF) capacitors: parasitic capacitance messes up results.
- large (thousands of uF) ones take "too long to charge" or "pass way too much current" depending on kludge used.
There´s where "going back to basics" shines, and I am not only talking capacitance here, but many other parameters.
I can easily measure magnetic flux in a very narrow speaker gap where no probe fits and Hall effect sensors are WAY above their limits, by simply sweeping a voice coil through it and integrating results.
The way Maxwell did, go figure, there´s no more hardcore back to basics than that. 😉
Of course, instead of a mechanical ballistic galvanometer like he could have used, I integrate current using an Op Amp and a capacitor.
My method can be used to calibrate a $2000 magnetometer, go figure.
By the same token, and just as an example, I can measure bullet speed (I am a shooter/reloader) using a pendulum, same way as Leonardo used 500 years ago when designing muskets and cannon.
Not so small detail: I live in Argentina, where ordering stuff from US is slow and expensive, and as they say: "Necessity is the Mother of Invention" so MANY times it was faster (let alone cheaper) building some device than ordering the modern replacement.
IF in US, yes, I would probably order from Amazon and get it next day.
By the way, not only in Argentina: you´ll often see Forum members from, say, India, South Africa, Eastern Europe (and Russia), Brazil or Australia posting very clever and "unusual" solutions to everyday problems.
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This sounds interesting, especially in case I have an alnico magnet musical instruments speaker of unknown history in front of me! Perhaps you may want to elaborate on this, maybe in another thread?
Best regards!
Ok, I´ll have to make some drawings to explain it better, "words are not enough" he he.
You´ll need a proper sized voice coil that fits, to be used as the pickup .... literally.
Only it is a "calibrated" pickup.
But be ready to be disappointed, "old guitar speakers" typically have lost a lot, and will need recharging; do you have access to a Magnetizer?
Alnico is relatively "easy", compared to ferrite , but still needs a magnetizer, even if not that powerful.
Just curious, what speaker are we talking about?
You´ll need a proper sized voice coil that fits, to be used as the pickup .... literally.
Only it is a "calibrated" pickup.
But be ready to be disappointed, "old guitar speakers" typically have lost a lot, and will need recharging; do you have access to a Magnetizer?
Alnico is relatively "easy", compared to ferrite , but still needs a magnetizer, even if not that powerful.
Just curious, what speaker are we talking about?
I was addressing the OP and the question of testing caps in general. Time after time after time I see someone write in saying they know a cap is good because they tested it. While the OP's immediate concern was his 22,000uf cap, I cannot assume he wants test gear only for the one cap. And I also cannot assume he was the only person reading the thread with interest.
A 450v 22,000uf cap does seem unlikely, but in my pro audio world, I see tube amps every day, and a 22uf 450v is extremely common. Leakage at voltage is indeed a lot less likely on the 35v rails of a typical solid state amp. But if you want a piece of test gear not limited, these other factors are worth keeping in mind. And in general, if I suspect a cap, its value is usually not atop the list of concerns.