- checing capacitors - 5 Updates
| Ralph Mowery <rmowery28146@earthlink.net>: May 28 03:55PM -0400 Today I received one of the roughly $ 20 component testers. Checking it out and comparing capacitors I notices a big difference in a couple of them I was using a Fluke 87, a LCR meter from China, an older component tester and the new component tester. The first capacitor was a Sprague .06 uF 600V. Two China testers showed near the value. Within the 10% tollorence, The LCR tester showed it to be .08 and the Fluke as .1 uF. This is a new,but very old capacitor. Next capacitor was a 20 year old no name of .068 of 50 V made with the Poly something dielectric. All meters were with in less than 10 %. Ok here. Same results with a newer one of .01 uF . Next came a Silver mica. It is .01 at 600 V. Fluke shows up at .0150, LCR at .0120. Two component testers were close and in spec. What gives with some capacitors checking like they should and some being way off, not just 10 % or so ? I ran the tests several times on each capacitor to see if maybe the leads were not making good contact and any other similar thing I may have missed like having my fingers across the leads. Ralph ku4pt |
| John-Del <ohger1s@gmail.com>: May 28 01:24PM -0700 On Thursday, May 28, 2020 at 3:55:50 PM UTC-4, Ralph Mowery wrote: > other similar thing I may have missed like having my fingers across the > leads. > Ralph ku4pt I think it would be nice to have a dedicated capacitor checker to verify everything. I have a one of the mega328 Chinese component checkers and compared to a Sencore 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. The other odd thing is that the 328 will return different results depending on 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 is good enough to trust with ESR. The 328 is pretty good with resistances as long as it's over an ohm. Anything 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 inductance, I use the Sencore LC75. |
| Ralph Mowery <rmowery28146@earthlink.net>: May 28 06:53PM -0400 In article <a68bc438-0423-4e6f-b6fd-6f239204722b@googlegroups.com>, ohger1s@gmail.com says... > I think it would be nice to have a dedicated capacitor checker to verify everything. > I have a one of the mega328 Chinese component checkers and compared to a Sencore 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. The other odd thing is that the 328 will return different results depending on 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 is good enough to trust with ESR. > The 328 is pretty good with resistances as long as it's over an ohm. Anything 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 inductance, I use the Sencore LC75. 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. |
| "pfjw@aol.com" <peterwieck33@gmail.com>: May 29 04:07AM -0700 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 |
| John-Del <ohger1s@gmail.com>: May 29 09:39AM -0700 On Thursday, May 28, 2020 at 6:53:12 PM UTC-4, Ralph Mowery wrote: > > Compared to the Sencore and an EDS88A ESR meter, the 328 component tester is good enough to trust with ESR. > > The 328 is pretty good with resistances as long as it's over an ohm. Anything 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 inductance, I use the Sencore LC75. 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 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 ohms and tight tolerance. The voltage drop across it (or several in parallel arrangement for to get a value between standard values). A tenth of an ohm is the difference between a tightly regulated supply and a runaway. > 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. Then the component tester is good enough for what you need. They read value 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. |
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