Thread: Motor question
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David Billington[_2_] David Billington[_2_] is offline
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Default Motor question

On 23/01/2021 14:31, David Billington wrote:
On 23/01/2021 01:52, Snag wrote:
Â* It's an old motor , 3/4 hp . And it's a universal motor , with a
flat disc commutator and brushes that can be rotated to reverse motor
rotation . I was looking at it today and saw on the tag that it can
be operated on 110 or 220 volts ... Currently it's wired with the
armature and field windings in parallel , I believe that's called
shunt . I was operating it on 110 volts on my lathe (until I got a
smaller unit , this thing is huge) . I have a project that I might
use it on , but I'd like to go 220V . Am I correct in assuming that
hooking the windings in series will convert it to 220 ? Since this
motor is a universal motor , is it speed controllable by varying the
voltage ?


It may not be a universal motor but rather an repulsion motor
https://en.wikipedia.org/wiki/Repulsion_motor , possibly a repulsion
start induction run variant. I have a 1hp one on a compressor and the
commutator segments move once up to speed to take them out of the
circuit and like yours the brush position can be changed to alter the
starting torque and direction.

If this is a repulsion motor then there is no connection of the brushes
to the mains they simply serve to short the rotor. That would seem to
leave the need for 2 field windings for dual voltage operation them
being wired in parallel for 110V operation and in series for 220V. In my
repulsion start induction run motor the action of the commutator segment
moving when the motor runs up to speed is quite obvious with the brush
access cover removed. Access to some images would help to comment further.