Thread: Burnt out motor

I'm hoping it's the capacitor

+1 for hoping it is the capacitor.

Does the motor have one cap (Cap start) or two caps (Cap start, Cap run)? If its a single cap and the motor was running at normal speed when the problem occurred, the start winding and cap should have been switched out of circuit, so it would be unlikely to be the cap. If single cap and the motor was loaded to below abt 80% normal speed, the cap and start winding could have been switched back into circuit to attempt to boost speed, and the issue could be either the cap or start winding.

If cap start cap run (2 caps) it could be windings or run cap if it was running at normal speed, or either cap or either winding if loaded down enough to engage the start cap.

Basically motor has a run winding, a start winding, one or two caps, and a centrifugal switch. When power is applied, the run winding is energised, and the start winding is energised via the start cap and centrifugal switch. The start winding and cap create a second magnetic field phase shifted from that of the run winding, which establishes the direction of rotation and gives the motor a boost to get it up to speed. Once it gets to abt 80% rated speed, the centrifugal switch opens and isolates the start winding and cap, so they are not in circuit until the motor slows below the switch threshold, where the switch will engage and reconnect the start winding and cap.

The run winding is designed to handle the rated power at the duty cycle of the motor, but the start winding is designed to handle the starting current (up to 6 x rated current) for abt 30 seconds max. Anything that keeps it energised longer is likely to burn out the start winding.

With cap start cap run motors (2 caps) a second lower value capacitor energises the start winding at lower current levels whenever the motor is powered and the centrifugal switch has opened. This assists the run winding and helps increase running torque, and the start winding is capable of carrying the current long term, but still has a very short term rating for the start current.

Thanks for some more insight Malb, it has a start and run capacitor according to the manual, but been too busy to even look at it. Could be a few days away yet too. I had been cutting for a while, not on start up, when it just started smoking and stopped.

Got by yesterday by using the little 9" travelling bandsaw, cutting 2" wood/resin casts, new blade and kept the feed rate down though.

I couldn't get to the capacitors without removing the motor anyway due to access issues, but found I could remove the motor with pulley attached by unbolting the tensioning plate and manoeuvring the assembly out the back.

On removing the first capacity cover I found this

17496239_1619043964776474_89711061_n.jpg

The other capacity looked fine and hopefully the motor is too. Picked up a new capacitor and will fit it tomorrow hopefully and retest it.

Whilst contemplating my options if the motor was burnt out, the only motor I found with a 60mm shaft protrusion and around the 1420rpm was a 3HP (the lower HP motors were ~40mm), that has a larger 28mm shaft but with new suitable pulley delivered was only ~$250. I started thinking upgrading from 1.5hp to 3hp may not be such a bad idea after all. I could fix this one still but keep it as a spare

That old capacitor doesn't look at all healthy.
Hopefully you should be back in business relatively cheaply.

Alan...

Originally Posted by Uncle Al

That old capacitor doesn't look at all healthy.

Yep, spewing crap out both ends, contacts burnt off, wires burnt back to main connections, big hole at one end, and stink boy does it stink

I picked up one from my local tool supplier for $52, he said it was expensive because it was a good one, not the cheap Chinese types. As soon as I got home I looked on Ebay, same type and brand for $35 delivered, but at least I don't have to wait for deliver.

The tool shop didn't have the plastic end cover thingies. Are they necessary, I was thinking of just wrapping in electrical tape?

Well I installed the capacitor and alls good. Did a heap of cutting, big burl chunks/cast burls blocks/Bluegum log, never missed a beat.