I've just acquired a 6 x 4" bandsaw – been in a few fights but basically sound enough apart from a few details, one of which is the motor. It's an AEG, frame size 80 but with no data plate. Having looked in the terminal box I've decided it is a 3 phase, and has a capacitor wired in – I think this is called a Steinmetz connection.

I've measured the resistance of the windings at 12.3 ohms, and when it's running the voltages across the windings are 242v L to N, 201v and 156v. That seems a bit too unbalanced to me, so I'm not surprised that it gets a bit warm – I cut some 50mm round bar this evening, and I thought it best to switch off after one cut and leave it to cool off. Also, the motor seems to lack a sense of direction or needs a kick start to get it spinning, so maybe the capacitor is on the way out.

So, the question is, what size capacitor? My thoughts are that the motor is probably 750watts based on the frame size. This points me to a capacitor of around 50 mF (micro far ads, can't do a mu on this tablet) based on the rule of thumb of 70% of the wattage rating. I have no capacitance meter and in any case if it's failing I'll get a suspect reading. Anyone got any better ideas (maybe based on the winding resistances and voltage readings?)

Edited By Steve Pavey on 25/09/2016 20:40:06

There are six connections coming from within the motor to the terminal block. Although I haven't taken the motor apart I can't hear a centrifugal switch. The terminal posts are marked u1 v1 w1 u2 v2 and w2. If it is a 3 phase motor then it is connected in delta, with the capacitor connected across a different set of windings to the L and N connections. There are no markings on the capacitor – it's had a hard life, a couple of paint jobs and a few dents.