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How did this motor get rewound?

Matt Matt

Cast Iron
Joined
Jul 11, 2014
Location
Oshawa
I picked up what I believe to be in 1930's to 1940s drill press. I do believe it was out of the Niagara Falls region based on the widow info I bought it from.

The original manufactures tag States it to be:
7.0/3.5 A
110/220 V ,
Single phase,
1/2 Hp,
25 cycle.
1425 RPM
This is a two pole motor.

The new motor tag states that it is
11.0/5.5 A
110/220 V
Single phase
1/2 Hp
60 cycle
1725 RPM
This is now a four pole motor.

Is it that easy to just change A two pole motor to a four pole motor?
The second tag or the conversion tag states it was converted to 60 cycles by HEPC. Through some research this stands for Hydro electric power company. I do believe the rewind was done internally as the HEPC was a government venture.

The other part and I'm a little confused at is the amps on the rewind tag for a half horse power motor. Don't they seem to be a little bit high for a single phase motor?
 

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Changing the motor poles is as easy as rewinding to put 4 poles in the slots that held two before. There are plenty of details, of course, especially with a single phase unit that has to fit another winding in there with the main one..

The rotor does not care, as long as it has enough bars, and it should.

The current is a bit higher than the NEC current, maybe 10-15%. Some of that may be due to the (possibly) thicker sheets in the stator iron, etc.
 
Is it that easy to just change A two pole motor to a four pole motor?
Likely, yes, for very many AC induction motors. If there were an even multiple of two winding sections aka coil groups (e.g., 4, 8, 12) in the original stator, converting two-pole to four-pole is basically just a matter of how you interconnect the individual sections with each other and the supply leads. I can't speak to that particular motor, but it's not unusual to have dozens of winding sections in a stator, so an even multiple is pretty likely.

Since that's a dual-voltage motor, the original stator actually would have needed a 4-multiple of two winding sections (e.g., 8, 16, 24), as the dual-voltage windings dedicate pairs of winding sections to be wired in either series or parallel to accomodate the two supply voltage options, and each pair counts as "one" from a pole-counting perspective.

I'm a little confused at is the amps on the rewind tag for a half horse power motor. Don't they seem to be a little bit high for a single phase motor?
By 12%, yes. I believe the NEC-based standard nameplate ratings for 1/2HP single phase dual voltage motors are 9.8A/4.9A. I've read that two-pole motors take less magnetizing current than four-poles (not my area of expertise) but that doesn't seem like the cause of such a large different in nameplate currents. It's also entirely possible that the original two-pole stator design draws higher current as it was intended for lower speed and higher torque (to yield same HP rating). I.e., the winding wire size might be larger than optimal for a four-pole winding. The result of the rewiring may not have been very efficient. The folks at HEPC might also have been more conservative (cautious) in their nameplate ratings than the OEM, too.
 
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