I am building a motorized barn door tracker using an Arduino UNO and a stepper motor I took from an old scanner (Mitsumi M35SP-7T). I have been unable to find the datasheet for this motor specifically, only that the motor has a 140 Ohm mark on it and that I assume it should be powered from 24V.

I was planning on running the system with the Adafruit Motor Shield which claims to power motors up to 25V, but I am having difficulty finding a power supply that can push 24V. Frankly I am also concerned that I shouldn't even be using a full 24V power source, but I'm not sure that feeling is justified.

Any recommendations on power configuration for this setup? If I should be using a 24V power source, what kind of source is recommended? This was the only datasheet I could find that came close to this stepper motor: http://vinvin.dyndns.org/projects/M35SP-7T.pdf

On a related note, on the Arduino forums, it looks like someone else was trying to use the exact same stepper motor with a 24V power source: http://arduino.cc/forum/index.php/topic,13711.0.html


UPDATE: It seems that the scanner itself ran on 12VDC 1A. Not sure how that might affect this situation. I just need to be able to run the motor with as much torque as possible.

  • \$\begingroup\$ Well... What was the power supply voltage of the donor scanner Mitsumi M35SP-7T? Did the power supply unit of the scanner survive? By any chance, did you power up the scanner and measure the voltages (before cannibalizing it for parts)? \$\endgroup\$ Commented Oct 14, 2012 at 2:01
  • \$\begingroup\$ Good question; I didn't have the power supply, but I did keep the plastic housing, which states it ran on 12V DC 1A. Interesting. \$\endgroup\$
    – Eli
    Commented Oct 14, 2012 at 2:14
  • \$\begingroup\$ And no, I didn't power it up before killing it :( \$\endgroup\$
    – Eli
    Commented Oct 14, 2012 at 2:15
  • \$\begingroup\$ Higher resistance motors typically have higher inductance as well, which sharply limits current and thus torque at higher switching (step) speeds. Even with low inductance motors, higher performance designs use a supply several to many times the winding nameplate voltage, and chopping current regulation to achieve the rated current. Even many of the small IC H-bridges can support his, up to the working voltage limit of the IC. \$\endgroup\$ Commented Mar 13, 2013 at 15:47
  • \$\begingroup\$ By 'barn door' do you mean a device after the lens on a theatrical lamp, or something you drive a tractor through? \$\endgroup\$
    – shuckc
    Commented Jun 11, 2013 at 18:11

1 Answer 1


There are 2 versions of the motor in the datasheet, which is liked in the O.P.: +6V version and +24V version. But the datasheet doesn't say what the markings on the motor are in either of the versions. However, the datasheet tells what the DC resistance of the windings should be in each version (table on p.2). 8Ω for +6V version. 50Ω for +24V version. If you measure the resistances of the windings, you'll be able to tell which version you've got. This stepper is unipolar, so it should have a common connection. Measure resistance between each winding and the common.

  • \$\begingroup\$ Does the fact that the motor has 140 Ohms printed on it mean anything? I notice that the datasheet says M35SP-7 but I have an M35SP-7T. \$\endgroup\$
    – Eli
    Commented Oct 14, 2012 at 2:54
  • \$\begingroup\$ @Eli Moving a carriage in the scanner, doesn't require a lot of torque, probably. May be, the motor wasn't used at its maximum torque in the scanner. \$\endgroup\$ Commented Oct 14, 2012 at 3:13

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