Repulsion Motor

[flandrax]

I am wondering if there is anyone out there that knows about an old repulsion motors?

Having problems with pulling a little more than 2.5x nameplate amps at no load.

I know and realize that the motor speed can reach a very high rate with no load, but this is a siren so trying figure this out without going deaf.

Rough nameplate(Hard to Read)
10 Hp
3200 RPM
56 Amps
220 Volts

Can get the motor to pull around 62 to 38 amps at 110 volts with some ajustment to the brush holder, but at 220 volts
it is way out of the park.


I would greatly appreciate any thoughts or information.

 

[rasevskii]

Try taking it apart, that is, remove the siren impeller, and run the motor by itself on the bench. If that cannot be made to work at reasonable current and various brusholder positions
then you might just have a bad winding. Stator, rotor, or both. Megger them at say 100V. Maybe it has been sitting for years, idle. Tired. New model possibly indicated...A museum piece...

rasevskii

 

[flandrax]

There is the catch. The stator and armature were both burned up so we rewound them.

It is more of a sentimental piece, but an opperational one.

 

[rasevskii]

I think the brushholder position determines not only the torque, but also the rotation direction, in other words at a certain neutral position it will not rotate at all, but only draw bags of amps. By offsetting from this position it will turn one way or the other, at some optimum position from that will be the maximum torque, or speed in this case. Use a 110V variac to supply it if you have one, at reduced voltage for testing.

Is this a Century motor? That was a repulsion-induction motor. Today a valuable item. There is in that case a centrifugal switch that lifts the brushes when up to speed, then it runs as an induction motor.

Only old sods know these things...

rasevskii

 

[jraef]

It's more likely a Repulsion-start / Induction-run motor, that's what was commonly used in sirens. In those motors, the commutator is shorted just before the brushes are moved away from the rotor once it gets to 3/4 speed. If the shorting mechanism fails to make contact, the motor will draw excessive current even under low load or unloaded conditions. So just because your brushes move out of the way, doesn't mean the commutator is shorted. Moving the brushes is just done to prevent excessive wear, the mechanism by which it runs as an induction motor involves the shorting of the commutator.


"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
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[waross]

My memory of repulsion/induction motors is tracking well with jraef's.
The mechanism that shorts the commutator also lifts the brushes. You may have neglected to reinstall the shorting bracelet or it may be dirty or corroded and not properly shorting the commutator. There may be mechanical damage. As I remember the brushes were movable but not adjustable. They were turned all the way to one stop for forward rotation and all the way to the other stop for reverse rotation.

The stator and armature were both burned up so we rewound them.

I have seen these old work horses subjected to such abuse for extended periods of time that I have to ask;
Did the building burn down around it? Accidentally sent to the burning pit? Yes I'm joking a little, but any one who has seen the abuse that these motors will accept may ask the same.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[ScottyUK]

I have some notes on many antiquated motor types in an old book - much older than me - which I could scan when I get back in to work. I'm off this week so not much I can do right now, but let me know and I'll see what I can dig out.


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If we learn from our mistakes I'm getting a great education!

 

[flandrax]

I really appreciate all the replies.

It is strickly a repulsion motor.

NO shortcircuiting device. It never had one. It's not brush lifting either.

I guess when I say it was burn up.... I mean they let all the smoke out. Winding was melted, but not to the point as to where it may have melted any mechanical means of shorting the comm. out or lifting the brushes. The comm. was/is not phisically able to have a mechanical short-circuiting bracelet.

I have worked on several repulsion start/ induction run motors and is true that most brush holders do not shift very far on those types of motors, but the brush holder on this motor will rotate 360 degrees. It's not a series motor, there is no voltage applied to armature.... It's all induced.

I feel pretty confident about the data in the stator.
Is there any way that maybe too many, or not enough turns/ coil pitch off/ comm. pitch off, that would cause an excessive amount of amps at it's rated voltage???? Or would it strickly be a data problem in the stator???