I have a 18VDC motor that I replaced the comm. on. I tried it with a 12 VDC supply but it stalled and nearly took out the P.S. It is a 3-coil, 3-comm.segment, 2-pole PM Motor. Any ideas? I do not have a winding diagram. Any ideas appreciated.

 

The traditional test after replacing a com is to test it with a simple device called a 'growler' it essentially induces a voltage into the armature and the voltage at the com bars are measured for equal voltage out on all pairs.
Sounds like you may have a short.
Max.

 

The traditional test after replacing a com is to test it with a simple device called a 'growler' it essentially induces a voltage into the armature and the voltage at the com bars are measured for equal voltage out on all pairs.
Sounds like you may have a short.
Max.

Thanks.
This is a small motor 18VDC for a weed-eater, so can't afford to buy a growler. Looking for some simple way to check what is wrong i.e. short etc.

 

Thanks.
This is a small motor 18VDC for a weed-eater, so can't afford to buy a growler. Looking for some simple way to check what is wrong i.e. short etc.

 

Did you ensure the correct armature connections were made, you may have to lift off the soldered ends on the com and do some testing.
Max.

 

Did you ensure the correct armature connections were made, you may have to lift off the soldered ends on the com and do some testing.
Max.

It is a new 3-seg. comm. I got from China, so assumed it was OK, but will try out your idea. So, after removing the connections to the comm. what testing do you suggest?
Thanks

 

Check for shorts between segments and check the coil continuity and separation from each other.
How many segments and is it oriented right?
Max.

 

Check for shorts between segments and check the coil continuity and separation from each other.
How many segments and is it oriented right?
Max.

3 segments, 3 coils - not sure about orientation and separation, kindly suggest how to check.
Thanks

 

Should be very simple to test separation of the coils, also the com segments, but have never oriented a 2 pole motor, something may be found with a search.
I will consult my motor rewinding manual and see if it confirms it.
Max.

 

Should be very simple to test separation of the coils, also the com segments, but have never oriented a 2 pole motor, something may be found with a search.
I will consult my motor rewinding manual and see if it confirms it.
Max.

Thanks. Look forward to your guidance. beatsal

 

I assume you have three commutator coils?
On the connections to each com segment, ensure that the start of end of one winding connects to the start of the next and so on, if you inadvertently connect two ends or starts it will cause what you saw, also check for shorts to GND.
Back feed the motor and see if it generates first after completion.
Max.

 

I assume you have three commutator coils?
On the connections to each com segment, ensure that the start of end of one winding connects to the start of the next and so on, if you inadvertently connect two ends or starts it will cause what you saw, also check for shorts to GND.
Back feed the motor and see if it generates first after completion.
Max.

Thanks. Yes, I have 3 coils and 3 comm. segments.
I assume when you say "ensure that the start of end of one winding", you mean end of one winding connects to start of next. Not sure about "backfeed the motor"

 

I assume when you say "ensure that the start of end of one winding", you mean end of one winding connects to start of next. Not sure about "backfeed the motor"

Yes.
Backfeed the motor is to drive its shaft with another source, motor etc, electric drill for e.g..
Max.

 

Yes, I have 3 coils and 3 comm. segments.

Never heard of one like that. Usually if there would be three coils in the armature there would be six commutator segments wouldn't/shouldn't there be? So each coil could make a north and south pole. Since there also should be two magnets for the field N and S, and also two brushes.

 

Normally DC armature coils are connected with a pair of connections, the end of one coil and the start of the other.
Max.

 

Normally DC armature coils are connected with a pair of connections, the end of one coil and the start of the other.
Max.

I understand that, but only three segments on the commutator?

 

An odd number of armature coils is not uncommon, these 3 seg are usually used in small toy motor applications.
Three segment example.

Max.

 

Better explanation of a 3 coil 3 section com.
Max.

 

Thanks learn something every day here. I still have a motor I built as a kid, but it only has two poles and two segments.

 

Yes.
Backfeed the motor is to drive its shaft with another source, motor etc, electric drill for e.g..
Max.

I backfed the motor with a drill, got 0.4V @ 1000RPM. Motor still won't start, gives a kick when 18V applied but nothing else. Tried to check if start connected to finish for the 3 coils but very hard to see. Any way of checking what's wrong?