[Prev][Next][Index][Thread]
Sync motor mod, 4 flats ?
Hi once again list members,
I have a question for all you induction motor experts,
I have a 240V, 50Hz, 1/8th HP, 1420 RPM, capacitor run
induction motor from a clothes drier machine. I figured that
since this is a 4 pole motor, it requires 4 flats to be
ground on the rotor. (This procedure introduces saliency
into the rotor and causes it to lock into the rotating field
of the stator. The motor will then run at synchronous speed,
in this case 1500 RPM.)
My problem is that I removed the rotor and initially ground
only 2 flats 180 degrees apart, because it was hard work.
I tried powering up the motor, and found that it instantly
locked to the line frequency when the shaft was viewed with
a stroboscope. I even took a rag and tried loading the
motor by hand, and could not cause a pole slip to occur !
I could only manage to cause a phase lag of maybe 10 degrees
at most.
I measured the line current at 600mA, and left the motor
running for a few minutes without any problems. From start-
up it was found to lock into one of four shaft orientations
(90 degrees apart) as expected. So my question is should I
remove the rotor again and grind the other 2 slots or should
I leave it with only 2 slots ?
It seems to work OK, gives plenty of torque, and does not
overheat, so I am tempted to leave it with 2 slots, but
I know the theory says there should be 4. I don't want to
take off too much metal, and end up with a motor which
draws too much current. I am worried that I am overlooking
something because I cannot see how it can properly lock into
the 4 pole stator field with only 2 slots.
If you have any experience in this field, (no pun intended,)
your advice would be very much appreciated.
PS. For those interested in this modification procedure it
is explained in many many posts in the Tesla List Archives,
but I could not find an answer to this puzzler.
- Richie
- Grinding iron laminations
in sunny Newcastle.