# Is there any equipment to measure dv/dt of capacitor?

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Is there any equipment to measure dv/dt of capacitor?

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Bwahahahahahahaha! ROTFLMAO!

...Jim Thompson

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|  James E.Thompson, P.E.                           |    mens     |
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What are you trying to do?

-- Joe Legris

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MMmmmm......... Interesting !

Why / what do you want to know?

Graham

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It's called an ammeter ....

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"GSiu"

** The dv/dt rating ( aka pulse current rating) of a capacitor is usually quoted in the specifications.

It is not a simple measurement ( like capacitance value) but a performance rating which maker is confident the parts he supplies can meet on a long term basis.

If you want to determine the maximum " dv/dt " being experienced by a cap - monitor the current flowing through the cap with a scope and series sense resistor and use the formula:

dv/dt = I / C

Eg:

10 amp current spikes flowing through a 100nF cap = 100 volts /uS

...... Phil

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Need a equipment to measure dv/dt of capacitor - for QC purpose and engineering test. Capacitor from USA and China claim have the same dv/dt, but the price level is not the same. If there is equipment to measure those China made film capacitors, then can purchase lower cost capacitors from China.

Kind Rgds, GSiu

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You would probably have to do some sort of highly accelerated liftime test. HALT.

Take samples from each manufacturer nad make measurements on the parameters the manufacturers use to define failure.

Ovenise them to their highest operating temperature, use the same for both samples. Apply a square wave bipolar current drive to achieve the maximum specified dV/dT. Adjust the frequency to drive the capacitor voltage to the rated value.

Run the test for 'some' time (up to a week) and then take the same measurements again.

If there is no significant change then double the dV/dT, double the frequency to maintain the same peak voltage, and run the test again. Use 'new' capacitors each time. Keep increasing the dV/dT and iterate until something significant starts to go wrong.

At some point you will be able to characterise things so you can specify the parameters for your own version of a HALT test for film capacitors. Once you have those parameters use them on a sample of capacitors from each manufacturer and compare performance.

DNA

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"Genome" "GSiu"

** If there are significant doubts about the credibility of published specs, quality control, consistency and reliability of the Chinese caps then DO NOT buy them.

Only a *complete fool* imagines such things are ascertained by a testing a few samples with any sort machine.

Seems you qualify.

...... Phil

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If the capacitors being offered offer a cost saving that exceeds the cost of verifying the quoted performance figures then test them. Assuming that performance cannot be verified by other means. If continued confidence cannot be gauranteed and the savings are still available then make the testing an ongoing process. In volume manufacture the results can be significant.

Obviously since you have only designed two things in your life and only one of them worked and only one of them was built you would not have been worth the 4 cents that might have been saved.

Then how did the manufacturers verify the figures they give in the first place. Are you suggesting that they just guessed and published them. You don't think they might have tested some samples do you. You don't suppose they have an ongoing quality control method where they sample and test things to ensure that what they are producing is what they claim it to be.

Well, thank you very much. I'm glad I pass the Phil Allison test for being a

*complete fool*. Incidentally are there any published methods and procedures that you use to Qualify the award of such a title?

Ah yes, that would be the Phil who had the job before and now everything is broken and needs fixing. You mean you didn't sack him, he just sort of blew up and didn't turn up for work one day.

DNA

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"Genome ASD" "GSiu"

** Obviously you cannot read, let alone think.

The OP doubts the published specs so has no faith in the maker = DON' T BUY THEM.

The potential financial harm if the caps do prove to have a high failure rate in service is ENORMOUS.

** That remark was aimed at the OP.

BTW:

Psychotic piles of sub human garbage like "Genome" can go f*ck a dead donkey.

...... Phil

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A current probe for an oscilloscope. as i=c.dv/dt is it for a snubber ?

Colin.

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Perhaps these are for mains use, or you might not be so concerned about this particular characteristic. Are there any safety agency approvals on the parts? You might want to validate them and check what tests were performed. They use large lots for such tests (hundreds of pieces and long-term accelerated testing at high temperature).

Exceeding the maximum dv/dt can just burn off little bits of metallization and won't necessarily show itself immediately in an obvious way.

Chances are if the construction and matererials are similar, the max dv/dt characteristics will be similar.

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Some capacitors have this parameter specified, such as the types intended for flyback tuning in CRT displays. Possibly the most revealing test is to incorporate the cap into a high power LC circuit and asses its performance when the slope of the waveform approximates to the dv/dt spec on the datasheet.

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How's Genome's not washing marathon going? - maybe the dead donkey smells better!

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Some capacitors may well have a specification for MAXIMUM RATED dv/dt before dielectric failure; but the OP didn't ask that... unless, of course, he has no clue ;-)

...Jim Thompson

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|  James E.Thompson, P.E.                           |    mens     |
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Got a bit sweaty during the hot weather type stuff and had to resort to Canestan to clear up the red halo around my arsehole.

There are a few crotch pores building up plugs but nothing worth harvesting for a chew yet.

DNA

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"Jim Thompson" wrote in message news: snipped-for-privacy@4ax.com...

You're just trying to make excuses for going BwaaaHaaHaaHaa.....

DNA

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;-)

...Jim Thompson

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|  James E.Thompson, P.E.                           |    mens     |