At 05:44 PM 4/14/2006 -0400, Christopher Zach wrote:
Ferguson Apiaries wrote:> Dose any one know if the 36v could be run on 48v without harm to the motors?The 36 volt mower motors? Probably not. They are PM type motors, and since the field strength would not change they would be running in a permanent "field weakened" condition. Probably overspeed and burn out.
Um, applying a higher voltage to a PM motor doesn't weaken the field. The motor speed will be approximately proportional to the applied voltage. No overspeed. As you said the field strength does not change (IE it's not weakened)
Now, if the current gets high enough the field developed in the rotor can demagnetize the magnets in the motor which would give you a permanent field weakening and subsequent loss of torque.
Unless the motors are close to the edge I doubt increasing them to 48 V will give enough current to demagnetize them but the extra 30% tip speed might be dangerous. Also the extra load from the higher speed may cause the motors to warm up more quickly.
As for the shunt motors? They might. EV people run series and shunt motors at 2x nameplate ratings all the time without much trouble, but in that case the field and the armatures both go up in voltage together. Might need some more cooling, and this might be a problem since the drive motors are sealed.
I'de be a little worried about the field in a shunt wound motor. You are going to get a lot more heating there (close to double).
Robert" 'Freedom' has no meaning of itself. There are always restrictions, be they legal, genetic, or physical. If you don't believe me, try to chew a radio signal. " -- Kelvin Throop, III
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