checing capacitors

I think it would be nice to have a dedicated capacitor checker to verify ev erything.

I have a one of the mega328 Chinese component checkers and compared to a Se ncore LC75, it's pretty close on capacitor values as long as the capacitors don't have any leakage. If there's any leakage, the values are skewed. Th e other odd thing is that the 328 will return different results depending o n what combination of terminals 1, 2, or 3 are used, which is odd.

Compared to the Sencore and an EDS88A ESR meter, the 328 component tester i s good enough to trust with ESR.

The 328 is pretty good with resistances as long as it's over an ohm. Anyth ing under an ohm is a waste of time. For low value resistors, I use one of my Fluke DMMs.

The 328 component tester is also not very accurate on inductances. For indu ctance, I use the Sencore LC75.

1, 2, or 3 are used, which is odd.

I did not think to start with to check the leakage. At 500 volts it is a lot less than .1 Ma. I don't usually worry about resistors under 1 ohm for a value. If they read short they are ok and if open then bad. If I wanted an accurate ohm measurment under around 1 ohm I would use the voltage and current test and calculate.

I have thought about a quality capacitor checker, but do not do that much that I need to do more than get into the ball park with them.

Generally:

a) Capacitors that leak will read *higher* than face-value. b) Unless otherwise marked, film caps are +/- 20%. c) Unless otherwise marked, an electrolytic cap is -20/+100%. d) Testing capacitors at operating voltage is best. e) Failing that, *start* with an ESR meter, then measure capacitance.

There are many ways for a capacitor to test 'funny' depending on their nature and the nature of the test instrument. Be sure you understand how the instrument tests before taking the results as necessarily valid.

I keep a Fluke multi-meter with capacitance testing, a Sencore LCR meter, and a PEAK ESR meter. And, a vintage, but fully functional Heath cap checker good up to 450 VDC.

Peter Wieck Melrose Park, PA

y everything.

a Sencore LC75, it's pretty close on capacitor values as long as the capaci tors don't have any leakage. If there's any leakage, the values are skewed . The other odd thing is that the 328 will return different results dependi ng on what combination of terminals

er is good enough to trust with ESR.

nything under an ohm is a waste of time. For low value resistors, I use on e of my Fluke DMMs.

inductance, I use the Sencore LC75.

I don't usually worry about resistors under 1

I work on a lot of current regulated power supplies where the source pin of a driver mosfet is grounded through a low value resistor of fractional ohm s and tight tolerance. The voltage drop across it (or several in parallel a rrangement for to get a value between standard values). A tenth of an ohm is the difference between a tightly regulated supply and a runaway.

Then the component tester is good enough for what you need. They read valu e and they read ESR. They can't do leakage though. On rare occasions I've found caps that read fine for value and ESR, but those values change after charging them to their rated voltage.

There's more than one way to read capacitance value. Each method's results are affected differently by ESR & leakage.

NT

Test old high-voltage capacitors (other than silver mica which are probably OK) for leakage at the operating voltage:

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** You misunderstand the purpose of such checkers- which is to test the C value or ESR vale of a GOOD cap. In order for them to work, the cap must NOT be faulty.

The C value of a leaky cap will be way off and the ESR value of a shorted cap tells you nothing.

So do an ohm meter test FIRST !!

..... Phil

I see what you are telling me. The way many of the capacitor checkers work a leaky capacitor will throw them way off. I just had not even thougt that out very well.

Of course the shorted one is no use to even check that on the capacitor checker. The China checkers will probalby tell me that I have a resistor of zero to very low ohms.

C value or ESR vale of a GOOD cap. In order for them to work, the cap must NOT be faulty.

ed cap tells you nothing.

that is the usual result

So it's told you the cap is faulty and what's wrong with it. Sounds useful to me.

I much prefer these cheap testers to the old Heathkit. The China special gi ves a quick reading of C (which is indeed affected by C faults), ESR & Vlos s. High R caps show up with high ESR, leaky caps show up with high Vloss, a nd some caps show up with C loss. The one big limitation is it only tests a t 5v, but so far I've found it still picks up caps that fall over at higher voltages, ie their 5v performance isn't ok either.

NT