VFD Questions

J

J. Hoover

Joined
Jul 2, 2006
Messages
1,782
I'm in the process of building a new grinder and need some info on VFD controlled motors.

1. Is a 2hp 3 phase motor with VFD control enough motor?

2. Do I need a variable torque VFD controller or a Constant torque?

3. What are the advantages or disadvantages of going this route over DC motor? Obviously the price is less, so I figure there must be catch. Thanks
 
I bought the vfd/2hp/3ph setup from Rob Frink, and it is plenty of power. I am not sure, but I think it is constant torque, at least the VFD enables the motor to maintain full torque at any speed. I just called Rob and let him suggest what would be best, he is the expert!!
 
yrs. ago in my past life a motor shop set up a VFD for my square wheel and they did a 1 hp DC wound motor . They told me that the DC had a more constant torque . That is all I know on the subject .
 
It seems, (from wading through my e-machines book), that field-wound DC motors still excel in motor control applications. VFDs have replaced them in most applications, but DC motors still have a much larger speed-range available. The torque curves also seem to be more controllable. For a grinder, a VFD would be more than sufficient; unless you like to run at near stall speeds.

I'm not sure what they mean by constant torque. Torque curves for all motors are anything but constant. Perhaps it means that the system follows a single torque/speed curve.

Phillip
 
Joseph

The constant torque type is all you need for something like a grinder. The variable torque VFD's have extra software features that are meant for applications that use a sophisticated control scheme, usually on something like a large conveyor system where multiple motors and VFD's are coordinated. You are likely to have to pay more $ for a VFD with variable torque capabilities.

A three-phase AC motor will inherently be able to provide full rated torque from zero to 100% of rated speed (rpm). Other types of motors will have some reduction of torque capacity when below 100% rated speed. Three-phase AC motors do not have brushed that wear out unlike DC motors.

Phil
 
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