# Thread: StepperCalc unipolar resistor calculator

1. ## StepperCalc unipolar resistor calculator

For anyone interested, I have writen a program to help you select current limiting resistors for your unipolar steppermotors.

I know it can be calculated easily with ohm's law but this is easier and great for newbies.

It also calculates powersupply minimum current rating based on the motor current and the number of motors used.

The best way to use it is to enter your motor and powersupply data, then hit calculate. Since resistors don't come in values to 2 decimal places, you can then select "I want to calculate motor current" and enter the closest available resistor size to calculate actual motor current based on the resistor you choose.

You can select transistor or FET outputs on your controller, and whether you want 2 resistors per motor or one with the center taps tied together.

Let me know if you download it, and how you like it.

Here is the screen shot.

Eric

2. I cannot download the file. Can anyone send this file to me at nusar@juno.com ?

Steve

3. Here it comes!

4. Works for me...try right click and choose "Save File As"

Eric

5. Hi,

Can somebody help me and put the calculator here for downloading? I need to calculate the limiting resistors and it seems that the web domain/page was sold and the file disappeared. Thank you.

6. Hi Zoltan,

Try the link below. It seems to be a different program to the one balsaman wrote.

Jason

7. Hi,

Thank you very much.

8. Sorry to drag up this old post, but I'm new and want to do the right thing without burning my electronics up. I have 3 Astrosyn, 23LM-C708-P1, unipolar, eight wire stepper motors. I'm using the FET-3 board and purchased it with the 24V, 3A power supply and 3 Step-Syn, 103-771-18, unipolar, 5 wire, stepper motors. The Astrosyn motors are rated at 3.6V/phase and 2.4A/phase. The Step-Syn motors are rated at 24V and 0.18A. Using StepperCalc, If I put 24V as my power supply voltage, 2.4 as the Motor Current (Amps) and 3.6 as the Motor Voltage (Volts); I get 8.50 ohms as the resistor value, 48.96 watts as the minimum resistor wattage and 14.40 amps as the power supply minimum current rating. Now that I've gotten that out of the way I can finally ask some questions:
1. What are the specs on an actual resistor that will meet my needs?
2. Where can I buy them?
3. Since I have to bring all my center taps together to use the eight wire like a five wire stepper, can I use just one resistor? (I did the Stepper Calc formula using one resistor)
4. Can I keep the two coils seperated and have two center taps and wire it like a six wire stepper?
5. Is there any advantage to doing that?
6. Where can I get a 24 Volt, 14.40 Amp power supply? (It would be nice if it had a 5V, 1.5A tap to power my controller board.)
7. Since the FET-3 board can take 35V continuous and 50V start up, do you think it would hurt it to run at 36V.
8. How much difference in torque will I get if I go to 36V? (Don't need an exact number, just need to know if it's worth the risk)
9. How crappy would these motors run at 3.6V so I wouldn't need resistors at all?

Thanks for any light anyone can shed on my questions. I can't wait to get this thing running! Great site and I will be donating as soon as my router is cutting. (just in case I have to spend my last \$60 on Ebay to finish it)

Randall

3) see 4
4) this is the way they should be wired. You'll need 2 resistors per motor.
6) Ebay - http://cgi.ebay.com/ws/eBayISAPI.dll...Name=WDVW&rd=1
7) It might be OK, but will probably run hotter. You'll need even bigger resistors, though, right?
8) low speed torque will remain the same. useable high speed rpm will increase, proportional to voltage. 50% more voltage should get you about %50 more speed.
9) They turn, but probably not much more.

10. Thanks for the quick answers Ger. Do you know how much that power supply is worth? Any chance you know the answer to number 5? I realize I will have to get bigger resistors if I increase Voltage.
Thanks again,
Randall

11. Originally Posted by Xterrian
Any chance you know the answer to number 5?
I don't think that #3 is the correct way to wire it, which makes #5 irrelevant, imo. I could be wrong, though, but everything I've read says an 8 wire motor is wired like a 6 wire for unipolar drives.

12. I'll probably try it both ways. If I do the 6 wire method I can use smaller resistors and get them from stepperworld, so that's a plus. I just want to be sure I won't burn anything up. Any idea what those power supplies cost new?

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