Thread: Blown Motor?

Originally Posted by triden

Hi, i have a 1 1/3 HP motor i want to use for a disk sander. The problem is that when it runs it seems to hunt, and one of the brushes has a lot of sparks coming from it. Is the motor shot? Any ideas?:confused:
Thanks

What do you mean by "hunts" and the sparks are probably due to the the bare copper in the worn graphite bush being in direct contact with the armature windings.

Shedhand, by the motor hunting i mean that when it starts, it runs fine for about five seconds, and then slows down and speeds up randomly. Asfor the brushes, one brush is ok. it just has a faint hint of sparks but the other one looks like a roman candle. Both brushes are about 30 mm long so i dont think that they are worn. There is no smell from the motor.
Cheers

Originally Posted by triden

Shedhand, by the motor hunting i mean that when it starts, it runs fine for about five seconds, and then slows down and speeds up randomly. Asfor the brushes, one brush is ok. it just has a faint hint of sparks but the other one looks like a roman candle. Both brushes are about 30 mm long so i dont think that they are worn. There is no smell from the motor.
Cheers

Hmm. I'm not really qualified on electrical stuff just really simple stuff. Why don't you post the question in the Electrical forum under Home Renovtions. Sure to get a better response.
Cheers

These are obvious but . . . . . are the springs which hold the brushes in OK, ie not collapsed or missing. This would explain the poor contact with the commutator and the roman candle effect. Are the brushes sitting neatly?

maybe the burnt brush is not sliding freely in the brush holder.
If it doesn't sand it down with a bit of 120 wet & dry so it does slide freely.

If it already slides freely and the springs etc are ok it sounds like the arcing has already caused "flying shorts" in the armature.

Consider this a cheap fix. Get new brushes (forget rather they look good or not they obviously are acting up.) Most guys try to strain the last bit of life from brushes when in fact you are damaging the commentator and the wiring with faulty brushes. Brushes are the cheapest repair going. Get new brushes and clean the contact area, If possible remove the head taking care about the contact wires and where they are attached to the brush holders. Check the contact wire, will (should be ) attached via a spring wrapped around the brush holder. Clean, reassemble, reattach the contact wires to the brush holders, install the new brushes and springs and run for awhile to seat the brushes. Should see a great difference.

My guess is that the contact wire and connection spring is at fault creating a faulty connection, Comes and goes , etc.

Originally Posted by Hickory

Consider this a cheap fix. Get new brushes (forget rather they look good or not they obviously are acting up.) Most guys try to strain the last bit of life from brushes when in fact you are damaging the commentator and the wiring with faulty brushes. Brushes are the cheapest repair going. Get new brushes and clean the contact area, If possible remove the head taking care about the contact wires and where they are attached to the brush holders. Check the contact wire, will (should be ) attached via a spring wrapped around the brush holder. Clean, reassemble, reattach the contact wires to the brush holders, install the new brushes and springs and run for awhile to seat the brushes. Should see a great difference.

My guess is that the contact wire and connection spring is at fault creating a faulty connection, Comes and goes , etc.

Only add is to clean the commutator grooves , try an old hacksaw blade ground to suit the thickness of the groove

Gday Triden
As already suggested, it sounds like a brush and/or spring problem. try using the end of a ball-point pen (A plastic one and NOT a pencil) or a skinny stick and gently push the brush in. This will seat it more firmly on the com and if the sparks decrease, you'll be on the right track
Be careful! Use only something that's insulating or you'll know about it! :eek:

I'm curious though. A motor 1 1/3 HP is a pretty big motor to have brushes and a commutator. They exist, but are not very common apart from crane motors. Can you give any more details from the name plate, such as : Manufacturer name, Voltage, Date, Type of winding?
Where did you get it from and was it running somewhere previous to this, or has it sat for a while?

Thanks for all the replies. I will give them all a try and if none work will take it to the doctor. The only markings i can make out on the case are 240V-50Hz-1800W. I found it dumped out side a building site. Again thanks for your help

Originally Posted by triden

. . . . I found it dumped out side a building site. Again thanks for your help

Maybe that explains why it is behaving so badly?

Originally Posted by Ashore

Only add is to clean the commutator grooves , try an old hacksaw blade ground to suit the thickness of the groove

I just got in from the garage and after doing Ashores suggestion the motor runs a lot smoother. There is still some sparking that seems excessive to me. I will get some brushes and see what happens.
Cheers