Scooter Dc motor windings

[Brozum]

I have a 24 volt 350 watt scooter motor that need rewound. The specs say 3000 rpm no load. Does anyone know how many turns are on each coil?

 

[Lucien Nunes]

The number of turns needed to get a certain speed at a certain voltage depends on the flux constant of the motor, which will vary from one model to another although not widely. Is there no intact coil that you can unwind? Sometimes you can get a very good approximation by weighing a coil cut out of the armature in pieces, measuring the mean length of a turn and the gauge of the wire.

I would be surprised if it is cost-effective to rewind, as new motors are probably made for a fraction of the value of the time you spend doing it. If you can find a source.

 

[Brozum]

The number of turns needed to get a certain speed at a certain voltage depends on the flux constant of the motor, which will vary from one model to another although not widely. Is there no intact coil that you can unwind? Sometimes you can get a very good approximation by weighing a coil cut out of the armature in pieces, measuring the mean length of a turn and the gauge of the wire.

I would be surprised if it is cost-effective to rewind, as new motors are probably made for a fraction of the value of the time you spend doing it. If you can find a source.

I'm looking to increase to output torque and decrease the speed a bit for what it's being used for

 

[Lucien Nunes]

I assume this is a permanent-magnet motor?]

Decreasing the speed is easy - put more turns on the armature. In theory this will also increase the torque but it might not be possible to use that increase because of thermal limitations.

Torque is proportional to armature volume, flux density and amp-turns. You can't change either of the first two. You can put more turns on but if the slots are already full of wire you would have to use thinner wire. This gives you a double-whammy of increased resistance - more turns and more resistance per turn - and hence increased heat dissipation. For intermittent duty it might be acceptable.

There is a practical limit to the torque available from any particular size of PM motor, which stems from the economically achievable flux density and the resistivity of copper. Historically, this has meant that as new magnet materials have been developed, more torque has been available for a given size. Conversely, it means that if you want to increase the torque from a given size of motor without compromising thermal performance, efficiency and speed regulation, you need stronger magnets.