Thread: (Nearly) Dead Dusty

If its tripping the circuit then you have a leakage back to earth or a short to negative. I would take off any covers and give the motor a good blow out and see if that works. If you have a build up of dust in the wrong place that would give you the trouble (IMHO).An electrician was given a cut off saw doing the same thing so it was "dumped". All he had to do to get it to go was blow the metal dust out of it and .....it worked fine.

At 2 Hp, I am guessing 240V single phase, but a small 3 phase unit is a possibilty.

If single phase, the likely issues are bearing failure due to dust intrusion, large chips jamming between the impellor and housing, dust build up between rotating and stationary elements of the motor,or a fault in the starting winding system.

Remove the power plug from the socket and the dust hose entry adaptor from the impellor housing. This will give you access to the blower impellor and a nut or bolt to attach it to the motor spindle. Depending on available clearance, either spin the impellor directly, or connect a socket and extension to the bolt/nut and spin the motor that way. If the motor spins freely either way the bearings should be OK, if hard to turn, either the bearings are failing, there is significant dust buildup in the motor or there are big chips stuck between the impellor and housing. Depending on ability and resources, you could try to strip the unit down to locate and fix the problem, or send the unit out for repair.

If you can spin the impellor and motor shaft freely with the above test, but it is slow starting and tripping breakers, the problem will most likely be in the starter system.
Single phase motors have two groups of windings, Run windings that are energised whenever the unit is powered up, and Start windings which are normally energised until the motor gets to about 70% of its rated speed.

A single phase motor normally will not start if only the the Run winding is energised, the shaft will generally rock a small amount in either direction. This occurs because there is nothing to tell the motor hich way to run. In this situation the motor can often be flick started with a quick flick in the required direction, but this is not an option for a dusty.

The start winding is typically connected in series with a Starting capacitor and a centrifugal switch. The capacitor acts with the winding to temporarily introduce a second power phase to the motor, giving it a kick in the right direction. However the windings are arranged so that the current passing through the Start winding is significantly more than that through the Run winding. The centrifugal switch connects the Start winding and capacitor while while the motor is stationary or running slowly, and then disconnects it once the motor is approaching rated speed.

In your case, I suspect that either the centrifugal switch contacts are burnt and limiting the current in the start winding, or the start capacitor is failing with similar results. Both will prolong the start period, and make tripping the breaker more likely.

There are different control curves for different classes of breaker. Normally a breaker will carry it's rated current indefinitly, but trip with a moderately higher current in a couple of seconds, or trip with extreme currents (e.g. short circuit) instantaneously. Although a motor can draw significantly more than its rated current while starting, this is for an extremely short time and will not trip a breaker or cause excessive heating in in the supply wiring.

If the breaker trips instantaneously, there will be a short circuit in the motor/wiring somewhere. If it can hold for a second or two while the motor tries to start, this indicates that the start winding, capacitor and centrifugal switch system is faulty, allowing starting currents to flow at lower levels but much longer duration, causing the breaker trip.

If the unit is 3 phase, it does not have the starter winding, cap and switch as outlined above, but 3 groups of windings. In that case the issue would be a supply failure for one phase, or a fault in the switch gear.

Thanks chambezio and malb for your consideration. Yes, it is a 2HP single phase motor.

Tomorrow morning I'll give the motor a good clean and see if it starts any quicker. I did manage to get it to start after a short delay this afternoon (after manually spinning and checking to see if anything was fouling the impellor). While doing this I noticed the 6 inch hose leading from the impellor to the dust bag had perished - so I'm crossing my fingers the motor has been showered with dust and a good blow out will fix it.

If not, I'll get someone to look at the start winding, capacitor and centrifugal switch system.

Thanks again for your help,

homesy135

Follow-up post to let others with similar electric motor issues know that my motor is fixed.

I took my crook motor to my closest electric motor repairer who replaced the capacitor (on the spot) for $40. Much cheaper than a new dust extractor.

I'm happy I took the time to get it assessed and repaired and that the motor didn't end up as land-fill or scrapped for the metal.

Thanks again to those who responded to my initial query.

Regards,

magpie135