Motor rewind

[brewdexta]

Right, I understand it better now, given power = torque x rpm divided by a constant that depending on what units your working in, if the motor has constant power between two speeds then the torque must decrease as the speed increases. So if you have an application classed as a constant power then if your using a VFD, choosing a motor that has a flat power curve around the normal speed of the machine is a good idea.

So the Tom Senior usually has a 1450rpm motor, so if I reuse the motor pulley etc. getting the 6 pole motor where the power is flat between 940 and 1880 rpm seems to make sense. Less chance of stalling the motor and less chance of cooling issues at lower motor fan speeds. Still plenty of power down at 470rpm and full power all the way up to 1880rpm so less belt changing.

I've always bought motors with the same speed at 50hz as the machine was designed for, this seems to suggest that if your buying a VFD then depending on the use then this is not necessarily the best idea. At least that is my take on it

 

[daleyd]

Yeah I think that’s about right, obviously you have to take into account the reduced torque as you go above base speed (50hz) where the motor frequency increases but voltage can’t (the “constant horsepower” region). I’d think either a 6 or standard 4 pole would be suitable for what your doing, you could probably do some tweaking on the drive settings to give you the response you want.

 

[Matrixx]

Poles on motors are related to the running speed 2 pole are fast speed ie 3600rpm, 4 pole 1800 rpm, 6 pole 1200rpm torque is the relationship between rated speed and running speed (slip) on an induction motor. A synchronous motor is different.