General > General Technical Chat

How to determine the voltage rating of an unknown capacitor?

<< < (9/11) > >>

saturation:
That's a really interesting device.  Rather than just a transistor or any other semiconductor tester, its really a 1kV or 200V current limited supply that you could use for testing anything for its reverse breakdown or voltage limits and a handheld at that.  I don't think anyone else makes such a thing in such a form or cost.

Its very helpful for salvaging parts or overstock and characterizing them.


--- Quote from: Aurora on January 26, 2013, 12:07:17 am ---I bought a Duoyi DY294 Semiconductor analyser a couple of years ago that also claims to provide the breakdown voltage of capacitors. I have never used it for such but suspect it works on the leakage across the dielectric as the voltage is ramped up to 200V  :o I don't like causing a breakdown in a dielectric....it just seems the wrong thing to do somehow. I suppose if the capacitor is sacrificial and not for use it is of little consequence.

I have attached the DY294 manual

A review is here:

http://www.jestineyong.com/review-of-the-dy294-digital-transistor-tester-part-1/

http://www.jestineyong.com/review-of-the-dy294-digital-transistor-tester-part-2/

http://www.jestineyong.com/review-of-the-dy294-digital-transistor-tester-part-3/

For GBP30 delivered, it wasn't a bad buy.

Regards

Fraser


--- End quote ---

JackOfVA:
The high K ceramic dielectric capacitors have complex C versus V behavior, to say the least.

The first plot below demonstrates two behavior characteristics.

First, hysteresis - the capacitance at a particular voltage depends upon the history of the voltage. This is the electric field analog of B-H hysteresis seen in magnetic core inductors. Note that the starting point, just like a B-H curve, does not fall on the hysteresis loop.

Second, the C versus V relationship depends upon the interval between voltage steps. See Bob Pease on "dielectric soakage" for a discussion of this phenomena. A short version of it is that the dipole charge elements in the dielectric do not all orient and reorient at the same speed with respect to voltage changes.  This is modeled by Pease as multiple RC elements in parallel.

The data is taken with an HP4192A impedance meter using the internal bias voltage, with the HP 4192A controlled over the IEEE-488 interface by a program I wrote. Data analyzed and plotted with Origin software.  I intentionally used a Z5U part for these measurements to illustrate how far their behavior diverges from the perfect capacitor we often think of.

To illustrate the dielectric soakage further, I ran the same 0u1 Z5U capacitor through a series of alternating +35V/-35V cycles. The first plot shows the full data run and the second shows an expanded view of a couple of reversal periods.

To show how badly the non-linear capacitor can be in real life, I looked at current through a Y5U at 1000 Hz and compared it with a high quality film cap. Voltage is the upper trace, current through the capacitor is the lower trace. The distortion is obvious just looking at the current waveform.

Finally, it's not just capacitance that can change with applied voltage; so can the dissipation factor. The D versus V plot is older data, taken with a General Radio bridge.



robrenz:
Nice work JackOfVA :-+

Fraser:
Saturation,

I bought the DY294 because it looked useful for all manner of tests and appeared well made for the money. I must be honest and say that I have not used it in anger. It does seem to be a lot of test capability for not a lot of money. I know of no other kit in my lab that will voltage test a capacitor or VDR so easily.

The user manual is pretty appalling and no new versions beyond V3 seem to be available. The ergonomics of the unit are not optimum either....but for GBP30 delivered....its not bad.

Worth having in the test kit inventory ? I think so.

Fraser

(In)Sanity:
Well the graphs provided by JackOfVA certainly add more complexity to this puzzle.   It's starting to sound like their is no simple way to perform these tests.   That's not to say I've given up.   

Thanks,

Jeff

Navigation

[0] Message Index

[#] Next page

[*] Previous page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod