# Thread: G540 running 570oz/in.. temporarily? check my math please.

1. ## G540 running 570oz/in.. temporarily? check my math please.

Hey guys,

I am in the process of CNC'ing a new mill for my shop and my budget is limited right now. i already have a G540 and 48v 12.5a power supply packaged for my cnc plasma table. i would like to try and save some money initially and use that package to run the mill as well. the plan is to upgrade in the future to larger more suitable drives for the nema23 570oz/in steppers.

So according to my math which i would love if someone can verify if i am calculating this properly,

570 oz In. Hybrid Motor
1.8° /200 Steps Per Rev.
5 Amps Current Per Phase
2.5 mH Inductance per Phase
4-wire Bi-polar, NEMA 23 Frame

sqrt of inductance * 32 = voltage requirement

1.58113883008419 * 32 = 50.5964425626941 volts

so the power supply should be good for this motor if my math is correct and i'm using the formula correctly.

but the amps per phase is 5 Amps and the G540 is limited to 3.5 Amps so if my math is correct here it would seem that i calculate as follows:

3.5/5 = .7
.7 x 570 = 399oz/in

so running the 570 stepper with the G540 would ultimately give me 399oz/in of torque which i am fine with.

Now is there anything special i need to do to connect this motor to the G540 such a installing the current set resistors and if so how do i determine what size, is there a formula somewhere for this?

Chris

2. Use a 3.5K 5% 1/4W current set resistor. The formula is in the manual.

The resistor is calculated by taking the current in amps and multiplying by 1000
You can get away without the resistors, but current standby won't work and the motors will get hotter.

3. Ger21,

Thanks alot! I read the manual but didn't catch that, i remember it saying if the motors were greater than 3.5 amps it wasn't as much an issue but wanted to verify with some experienced people such as yourself!

I appreciate the help!

Chris

4. I found on digikey some 3.6K resistor in the 1/4 watt 5%, i ordered 20 of them, they were really cheap. will the 3.6k be fine for it? or am i splitting hairs? its within 3%, i figure the tolerance was bigger then that so it should be ok, but would like a second opinion.

Thanks!

Chris