Warco WM16 Mill - Conversion to AC motor with VFD

[m_c]

Jonathan, more poles = slower ;)

2pole @ 50Hz theoretically gives 3000RPM, while 4pole gives 1500rpm.

[Jonathan]

Jonathan, more poles = slower ;)

I know. I've corrected the post and highlighted that in bold. I'd have hoped it would have been obvious from the 4 other correct statements in my post giving the synchronous speed for 4 and 2 pole motors.

2pole @ 50Hz theoretically gives 3000RPM, while 4pole gives 1500rpm.

Only if your theory is no good. Those speeds are the synchronous speeds and if the rotor was spinning at that speed, there would be no current induced upon it and therefore zero torque. For that reason the theory shows the rotor speed will always be below those values, by an amount known as the slip, else the machine is not acting as a motor.

[John S]

Normal stated speeds are 1425 for 4 pole and 2850 for 2 pole

[m_c]

wobblyjelly

[birchy]

OK, here's my dilemma: absolute maximum distance from motor shaft centre to Z dovetail is 90mm. It looks a bit touch and go whether or not a 90 frame motor will fit. According to THIS thread, which is an almost identical machine, they used a 1.1kW 2-pole motor with an 80 frame size and report that it only *just* fits. As said by Jonathan earlier in this thread, a 4-pole motor will give better torque but will have to be run up to 100hz to get the desired speed of around 2800RPM. But I can't find a 1.1kW 4-pole motor with a frame size less than 90...

So, assuming I use an 80 frame size, would I be better off using a 2-pole 1.1kW OR downsizing to a 0.75kW 4-pole? Or can anyone provide a link to a 1.1kW 4-pole in an 80 frame size?

[John S]

Just spoke to my motor supplier.
You can get 4 pole in 80 frame at 1.1Kw, if you move to 2 Pole you can go up to 1.5kw
They don't have them but about 3 days lead time.

You need to talk to Martin at M&R Controls 01773 875795

[birchy]

Thank you John. The 2 pole 1.5kW might be a nice solution as it means 2800RPM without running the motor at twice its rated frequency.

As a man with experience of these machines, what would you normally choose?

[Mark P]

Hi there birchy, I am planing to do the same thing to my WM16 (fed up with changing brushes) but am thinking about keeping the 2 speed gearbox but replacing them with steel gears to give me a degree of backgear. The primary drive will be by toothed belt I think. Have you come across ant major problems with your conversion?

Regards Mark P.