Changing of 4 poles to 8 poles motor 2

[sonix1680]

Friends, is it possible to convert a motor which is 4 pole to 8 pole motor. How will i do it? i dont have some data coz i was only asked by this. i am very curious about this.. i didnt find answers from books so i posted my question hoping somebody would help.. tnx

 

[motorsdirect]

No...I'm afraid not...Even though it may be possible to rewind the stator...the rotor would then be wrong..Sorry.
If it is three phase you could always run it on a frequency inverter drive..

Jeff

http://www.motors-direct.co.uk

 

[sonix1680]

tnx motordirect!: ) but if it is possible to rewind the motor... it would affect the rotor? regardless if it is squirrel cage or wound type?

 

[nbucska]

It may be cheaper just to buy one and sell the old one...

<nbucska@pcperipherals DOT com> subj: eng-tips
read FAQ240-1032

 

[motorsdirect]

The rotor will normally be of a different design...made for the speed involved...i.e. more bars in a cast rotor or a different angle on the bars.
As Nbucska said...probably better to get a new one!!

Jeff

http://www.motors-direct.co.uk

 

[smms]

Ask the motor supplier, maybe they can help you.
A rewind of the motor from 4 to 8 pole is probably possible, if the number of slots is enough (48, 72, ...).
The cooling is not so good because of the low speed if the van remains. So you have to decrease the rating.
And you will get a low power factor (big air gap).

 

[sonix1680]

thank you friends! : )

 

[aolalde]

In theory a 4 pole induction motor can be rewind to have 8 poles. The SC. or squirrel cage rotor will follow automatically the stator flux induction. Slip Ring Wound rotors must be rewound to match the stator poles.
The principal compromise is in the magnetic circuit. It will not work optimized handling the new 8 poles magnetic distribution. The back iron will handle very low flux densities but the teeth will be highly saturated. The winding that will produce acceptable magnetic circuit saturation will probably result in less than 1/2 of the original 4 poles output Power (HP). The power reduction will lower the motor losses but a temperature rise test must be done to ensure that the actual cooling fans ( at lower speed) provide cooling into acceptable operating temperature rise.

 

[mc5w]

According to the people at a motor rewind shop the 2 principle problems are the number of stator slots and how much the rotor can take. Rotor current is more or less dependent on the output torque which means that rewinding for a lower speed will cut the horsepower by half or more.

In your application you might need a seperately powered cooling fan.

If the machine is going to operate the motor at close to it's new rating, you would be better off getting a new motor. If getting an 8 pole motor is a problem, then a VFD and an oversize 4 pole motor is your best bet.

In 1 plant where I worked some of the thread rolling motors used 40 horsepower 10 pole motors. Instead of trying to get a replacement 10 pole motor they put in 100 or 125 horsepower 4 pole motors and used VFDs to feed them 24 Hertz power.

Mike Cole, mc5w@earthlink.net

 

[acmotorengineer]

Actually it can be quite simple to convert a 4 pole motor to 8 poles.

In some cases, All you have to do is to reconnect the groups to a consequent pole connection - all group ends are positive. This is the standard connection for one winding, two speed motors. Usually you would have to rewind to get the short winding pitch used in multispeed motors.

The motor also must be re-rated to constant torque (1/2 HP) or variable torque (1/4 HP). If you need the same HP rating (twice the torque) you're out of luck. This requires a much larger motor for most of the reasons stated.

There are a lot of other hooks, of course, which may cause problems depending on your application.