- Joined Dec 8, 2019
I'm just trying to get a second opinion on the motor above for an old 30's or 40's-ish Burke 126A miniature mill that I recently obtained. I *think* It's a brush-riding type permanent repulsion-induction motor - but with an unusual electric reversing capability. It's a configuration I've never seen or heard mention of before.
The electric reverse feature hasn't been spoken of anywhere on the internet to my knowledge. It's not shown in any of my modern textbooks or in my period correct copy of Audel's Handy Book of Practical Electricity. It's been my observation that surviving examples of repulsion-induction motors are designed exclusively to be reversed by shifting the shorting brushes back and forth across either 'hard' or 'soft' neutral, thereby changing the relative positions of the armature poles in relation to the stator during startup.
But this one is reversed by switching two of the four (unmarked ;D ) leads in the termination box. From my experiments it appears that one pair of leads is for the main stator winding, while the other (connected in series with the aforementioned) seems to be some sort of compensating winding - if I have my terminology correct?
There's sometimes a clicking sound that comes from the motor when it reaches full speed, and again once it slows down to a certain point. I can't tell if it's coming from a centrifugal shorting necklace buried somewhere on the shaft side of the rotor (repulsion start, induction run?) or just something making a markedly similar noise in the gear head. Sometimes I think it might even just be my imagination. I can't really tell if there is a squirrel cage cast into the armature either - as would be the case with a permanent repulsion-induction motor. The running speed is uncharacteristically stable for a series brush motor (It barely changes when I put load on and take it off), and it exhibits the god-awful power factor that is mentioned in descriptions of repulsion motors (1100VA, 310W running unloaded). It basically sits at 100% or 110% FLA all the time, dependent on the direction of rotation. It runs at the exact same speed in both directions and there is no sparking on the brushes once it's up to speed.
Am I on the right track thinking this is a novel little RSIR/RI motor with electric reverse, or is there something I'm missing?