Reply To: Motors and thermal protection


Sven-Olof, I was wondering the same. I’m definitely going to evaluate the cap because, with just a little investigation, I see that Mike is pointing me in a good direction to diagnose the drill press. I’ve thought a little about mechanism, and what comes to mind is this, but it is me guessing. If the cap is failing in the sense of allowing a leakage current, i.e., if it could pass DC, then I would expect the effect of the capacitor would be to produce a current that is the sum of a portion with a 90 degree phase shift (as all good capacitors do) plus an AC current with zero degree shift. The purpose of the cap is to shift the phase in one of the motor windings, so what you’d end up with is a bit of in-phase current where you only want 90-degree shifted current, and the result is a motor that is fighting itself, in effect. In short, the “DC current” is really an AC current, in phase, and arising from the failing cap’s ability to leak DC current….even though there’s no DC current. Wild guess on my part.

I have a bit of work to do, but then will test the capacitor.