Hammerfall
If you are restricted to 120V, you will be restricted to motors of about 1hp, maximum. If you connect a bigger motor than that, you will draw more than 15A and trip your circuit breaker. Most AC drives are designed to work with an input voltage of at least 220V. There are very few that will work from 120V since most industrial applications require more power than a 120V connection can provide. A different division of my current employer, Toshiba, does make some that will work from 120V but they are not the most cost effective units on the market. Please note that when running a drive on 120V, one may have to use a drive with a higher rating, say a 2hp, 220V drive on a 1hp, 220V motor. The reason is that the capacitor bank in a 1hp, 220V rated drive may not be big enough to support operation at 120V and the voltage ripple on the internal DC bus gets too big causing the control ciruit to freak out. This may raise your cost somehwat. Please also note that you will be using a 220V, 3-phase motor. The 120V input drives have an input voltage doubling circuit built into them.
Tracey is correct. A propperly designed AC drive will cause the motor to produce almost 100% full rated torque from near zero speed all the way up to 100% rated speed. An AC drive may be used to drive the motor at somewhat over 100% rated speed, although this depends on what your motor will withstand. There is usually some way to control the ramp up speed of motor as well at the maximum motor current. This will reduce the starting surge of the motor significantly from 6 to 8 times the running current to something more reasonable like 2 to 3 times. This will reduce the dimming of the lights when you turn your grinder on.
Tracey
Have you checked the wiring to your pot and the pot itself? Is your drive new or used? Some manufacturers have virtually no protection for the auxilary inputs like this and they can be damaged easily by wrong connections, being shorted or static electricity.
Hope this helps.
Phil
