The Ford Barn

JoeCB · 08-21-2023, 10:24 AM

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There is more to testing "caps" than measuring the capacitance. And I hope that someone with more electronic knowledge than I chimes in with more details. I have much experience with capacitors in small engine magneto applications. One can do a rudimentary test using a VOM ( volt Ohm Meter), but a cap that tests "good" may well fail in actual use because in use the cap is subject to a relatively high voltage surge ( in magneto application several hundred volts). I don't know the size of the surge in a battery ignition application, but I guess that it's considerably greater than battery voltage. If the insulation within the cap is weak that cap will fail in actual use.
Only way to be sure is to test on an instrument that subjects the cap to a high voltage, like a Mertronic or Stevens ignition tester.
Joe B
PS, as a side note, it is curious that . 22 micro farad (or there about !) is a common size for many many engine applications, small 4 cycles, outboards and Model A's

08-21-2023, 10:24 AM	#6
JoeCB Senior Member Join Date: Nov 2018 Location: Farmington MI Posts: 389	Re: Condensors Sponsored Links (Register now to hide all advertisements) There is more to testing "caps" than measuring the capacitance. And I hope that someone with more electronic knowledge than I chimes in with more details. I have much experience with capacitors in small engine magneto applications. One can do a rudimentary test using a VOM ( volt Ohm Meter), but a cap that tests "good" may well fail in actual use because in use the cap is subject to a relatively high voltage surge ( in magneto application several hundred volts). I don't know the size of the surge in a battery ignition application, but I guess that it's considerably greater than battery voltage. If the insulation within the cap is weak that cap will fail in actual use. Only way to be sure is to test on an instrument that subjects the cap to a high voltage, like a Mertronic or Stevens ignition tester. Joe B PS, as a side note, it is curious that . 22 micro farad (or there about !) is a common size for many many engine applications, small 4 cycles, outboards and Model A's