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Motor Voltage question
« on: November 29, 2011, 05:33:32 PM »
I am trying to fine-tune the Bridgeport mill I recently bought.  Lots of pictures here: https://picasaweb.google.com/113966569709555812037/BridgeportPart1 and https://picasaweb.google.com/113966569709555812037/BridgeportPart2

These are the motors, and the info I was able to find on them:

Sigma pacific scientific
Bipolar stepper motor 4 wire NEMA 34
Model number 21-3437d200-B038
phase resistance 0.5 ohms
phase inductance ~680 mh

And then this:

Break down of model number
21 is the motor series
34 is the frame size NEMA 34
37 stands for 2 stack
d200 is the number of steps per revolution
B is a four wire motor
038 is the phase resistance

Modern model number is H32NRHA-LNN-NS-00

Phase current 5 Amps
Phase resistance 0.38 ohm
Phase inductance 0.38 mh I did fry my multimeter after all damn it
Holding torque 460 oz-in

Info from searching the part number and finding this thread: http://www.cnczone.com/forums/diy-cnc_router_table_machines/105716-need_help_identifying_large_bipolar.html

So, I have been learning Cambam, and have even cut some parts successfully but in my quest to know more I measured the power supply voltage and found it was only 20 Volts (Nameplate on it says 24v as seen in one of the pictures).  The controllers are homemade I think...I feel that I can stall the motors quite easily.  I have read numerous thread talking about 24, 36 and even higher voltages?


1) What voltage would be best?
2) Any other recommendation based on the pictures?

Thanks, Kenny
Re: Motor Voltage question
« Reply #1 on: November 29, 2011, 06:32:08 PM »
Stepper voltage should be 32 times the square root of the motor inductance (in mH), or as close as our motor drivers allow.  For most steppers, that will be in the 50-75V range.  At 20V, you'll get terrible high-speed performance (i.e. - you won't get high speed at all).  I think 460 oz-in motors will also prove rather small for a BP, unless you have belt reducers on them (which will further cripple your top speed).  I would think you'd want motors with at least 2X that torque.  On my BP clone, I'm running 850 oz-in peak/140 oz-in continuous servos with 2.5:1 belt reducers, and it screams (it will do 400 IPM rapids, and has enough thrust to snap a 1/2" endmill without losing position.

Ray L.
Ray L.