View Full Version : Help determining correct power resistor

04-16-2004, 03:34 PM
Here's the scenario:

I have build my own driver board for my cnc wood router. It is based off of the piker. The driver uses TIP120 Transistors. I am trying to use stepper motors harvested from some old HP LaserJet III's.

Here are the motor specs:

5.2 V/phase
1.4 A/phase
1.8 deg/step

I'm using a modified 12V ATX power supply to power the whole setup.

I'm trying to figure out what type of power resistor I need to keep the motors from burning up.

I also want to run two resistors per motor, 1 per coil center tap.

I have tried using balsamans stepper calc and now I want the run the numbers by you guys in order to see if I used it correctly.

According to the calculator I need the following resistor specs:
4.21 ohms minimum
8.26 watts minimum

Is this accurate?

04-16-2004, 03:38 PM
Can you guys suggest any good sources for the resistors?

Thanks in advance,


04-16-2004, 04:54 PM
That is what I got too.

I used those same motors. Great little motors. Select "I want to calculate motor current" and put some available resistor sizes in the box to see what's best after you know what is available. 4.5 or 5 ohms will be great. 4 ohms will run your motors just over the max, but on the other hand 12 volt atx supplies are rarely 12 volts. More like 11.5 volts.

www.mouser.com is one place that has power resistors