Re: A Tale of Two Condensers

[jim-moffatt]

I use a low voltage digital multimeter that tests capacitance value and leakage resistance but not ESR. I also have observed real time condenser failures in running motors. I will try to ad my thoughts.

First as an outboarder and not a tester Fan/collector I have found that the low voltage tests for value and leakage usually are all thats needed. Most all of my failed condensers have both high capacitance value and leakage below several megohms. The ESR is an important parameter however and values exceeding the coil primary resistance (usually around 0.7 ohms) may degrade performance. So take your pick of how much you want to get into advanced testing equipment. I have gotten along well with just the multimeter.

Now my capacitor failure experiences are all similar. The "about to fail" condenser tests a little poor on leakage but intiallly works wel and the motor runs fine. But then with as little as an hours use it begins to cause high speed missing after running at high speed. if you slow the motor down there are no misfires. But in another 30 min or so the misfire begins at lower RPMs and the motor is totally unusable. When you take the condenser out it tests very high for capacitance value and extremely poor on leakage ( below 2 megohms). This has happened on two motors before I became a believer in always replacing capacitors with a new (not NOS) one.

I agree with most all of legendres statements except that since the spark occurs when the points are open, the primary circuit is an LRC circuit not a RC one. The R comes from the primary coil resistance the capacitor ESR and the leakage resistance of the capacitor. The L is the primary winding inductance and the C is the capacitance of the capacitor. Since any resistance produces a loss all of the 3 resistance values diminish the spark intensity, hopefully not enough to prevent the motor from running