# Motor question

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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 ?

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I am not a expert on motors or even reasonably knowledgeable about motors. But it seems to me that if the field and armature are in series and the voltage is close to being the same for the field and armature then it should be fine for 220 volts . And you should be able to check whether the voltages are roughly equal with 110 or 220 applied. And if you apply 110 volts with the field and armature in series, it should be obvious that the speed is controllable by varying the voltage.

Dan

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It may not be a universal motor but rather an 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.

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I think that is a very poor assumption. There are series-wound motors and they're very different animals, in that the high armature current also flows through the field. In a shunt-wound motor a much smaller current flows through the field. In a shunt wound the field current is independent of the load and the armature current varies with load.

If you try it, be sure to get a video for us ðŸ˜Š

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A series wound motor has no "speed" contril - it ha torque control and it has infinite torge at zero RPM, going to zero torque at infinite RPM - in theory. When the counter EMF reaches the supply voltage the torque is zero. There is no speed "regulation" - it slows sown with load - USELESS for a machine tool.

A shuint motor has very strong speed regulation To control series motor speed requires a feedback loop to control the voltage in response to speed (inverse to load)

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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.

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OK , this verifies something I thought I remembered from when I was a boy about series motors . I was considering using this motor to power a

5" jointer/planer partly because it's size would anchor the base with it's mass . The last thing I need is a runaway jointer ... so if I do use it I'll be leaving it hooked shunt and on 110V .
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You may be right , I'll have to check it out and see if the commutator pulls back or , more likely , the brush assembly pulls away from it . I used this monster for a short time on my Logan/PowrKraft lathe , but never paid much attention to what was going on inside the end bell .

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Unloaded series-connected universal motors have no upper speed limit, at least in theory.

A runaway is likely to overspeed the jointer knife assembly, which may proceed to burst from centrifugal force - this would be dangerous to man and machine.

Joe Gwinn

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I'd bet on it being an old repilsion start induction motor. Any tag on it? Is it a Leyland or a Century by chance? Have you put a tach on it?

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