On Wed, 01 Oct 2003 00:54:28 GMT, "ATP"
wrote:

Charles A. Sherwood wrote:
A while back I bought a Rockwell 11 inch lathe with a mechancial
variable speed drive. This drive works well but seems to have a lot
of friction. The lathe came with the original 1HP 3PH motor. I
installed a 1HP VFD and I managed to make the lathe run. The VFD
could not start the lathe unless the Mechancial VS was set to less
than 1/2. I Adjust some parameters in the VFD to increased the
starting torque which pretty much solved the problem. However the
VFD indicates the motor is drawing nearly full current just turning
the spindle at max RPM. And yes the spindle bearings are fine!

The original motor starter was set up for a 2HP motor even though the
lathe only has a 1HP motor. Its very difficult to read the motor tag
inside the lathe cabinet and the front swithc say 2HP, so the
electrician probably put on a 2HP contactor with 2HP heaters.

So anyway I am considering installing a larger motor. I found some 1.5
HP 1140RPM motors fairly cheap. I think the lower RPM motor will
develop more torque and the VFD will still allow me to achieve full
spindle speed by increasing the freq to 90.

I am considering a 1.5HP to replace the exisiting 1HP motor. My logic
is that the lower speed motor will develop more starting torque and I
can still get the same spindle speed by increasing the freq on the
VFD. For example the 1140 RPM motor will develop 1HP at 900 RPM
(900/1140x1.5) where the existing motor will only develop 1/2
HP(900/1800) at the same RPM (assuming constant torque). I think a
1.5HP 1140 RPM motor will develop more low end torque that a 2HP 1740
RPM motor that I was originally considering.

what do you think?

chuck

You're aware that most VFDs when fed from single phase power must be derated
to 75%?

Pretty much true. Or even lower, depending on manufacture and age of the
unit (Ie the older ones are not as efficent as the newer bleeding edge
ones)

Gunner



"If I'm going to reach out to the the Democrats then I need a third
hand.There's no way I'm letting go of my wallet or my gun while they're
around."

"Democrat. In the dictionary it's right after demobilize and right
before demode` (out of fashion).
-Buddy Jordan 2001