I have a Startrite 352 bandsaw and the (separate) starter is buggered - it blows the tripswitch when plugged in to the 3-phase supply. I'm having trouble finding out what capacity of starter to buy to replace it - anyone have any ideas?
Thanks very much - I have a suitable meter so will start from there.Ideally you'll need a decent continuity meter.....
If the thing pops the breaker immediately, the first thing that I would eliminate would be the coil/no-volt switch section - everything else is isolated at this point. That should be easy to disconnect. After that you will have just three incoming cables and three out to the motor. Check the coil rating. If it is single phase, three will be a neutral wire - if not and it is 400 V, it will connect across two phases.
I would expect that motor to be star-wound. As a general rule and assuming a Direct-on-Line induction motor starting in the unloaded state, (such as on a band-saw), starter overload ratings were typically selected around 115% full load current (FLC).
However, assuming sufficient tolerance in your circuit breakers, take the starting current into consideration. The starting current is often too rapid to record without specialised gear, but it will, in basic terms, be a function of the motor resistance and the impedance of your supply. If you see a rating on the motor plate stating locked-rotor current (LRC) it will be a notional stall condition.... probably in the area of a start-up draw.
Its worst starting condition will be from cold - motors that have a residual running temperature in the windings draw less at start. It'll all be over in about 10-20 electrical periods.
Hope that this helps....... try to eleimiante one thing at a time. If you disconnect anything DRAW IT OUT on a piece of paper! Good luck.