I have a milling machine that originally came with a 3 phase 415V motor in Dahlander configuration (2 speeds - 1400 and 2800rpm).
The fact that it is wound for 2 speeds, means it can only run at 415V. If I want to use a VFD at 240V mains, only solution is a rewinding the motor for 240V.
The original specs are as follows:
Speed 1 - 1400rpm, 0.6kw, 1.8A
Speed 2 - 2800rpm, 0.9kw, 2.3A
The goal is to replicate the original design, with the use of a VFD and a rewinding. So here are my options:
Option 1:
Rewind at 240V, 2800rpm. Judging by the original specs, say I get about 0.9Kw at 50Hz and 0.45kw at 25Hz. Even if I use torque boost on the VFD, the lower speed is still about 20% under spec. - probably worse if I consider that the new winding is 2 pole (less torque vs 4 pole to begin with).
Option 2:
Rewind at 120V, 1400rpm. Here I'm getting confused with the numbers (maybe somebody can help?), but in principle I will get standard operation at 50Hz and double speed, double torque, double amps at 100Hz. That is overdriving the original spec by a factor of 2. Some of this overdriving can be offset by uprating the winding wire to take more amps but obviously I am limited by slot space so it's hard to put a percentage on it.
I don't consider a VFD with a step up transformer, they are much more expensive and rewinding costs me nothing.
So I'm looking for the most elegant and efficient solution. If you were faced with this dilemma, what route would you go for? I'm particularly interested in option 2 so would be nice to hear from people with hands on experience on it. The electric vehicle folks are doing this on a routine basis to their motors.