Stepper motor voltage?

Discussion in 'General Electronics Chat' started by tracecom, Jan 25, 2011.

  1. tracecom

    Thread Starter AAC Fanatic!

    Apr 16, 2010
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    I posted this question on the PICAXE forum, but the traffic here is heavier, so I'll ask here as well.

    I am beginning to learn about stepper motors. I pulled a unipolar 5 wire motor from an old TEAC 5 1/4" disc drive and, using a 9v battery, have determined which wires are connected to which coils. However, I don't really know whether the motor is supposed to run on 5 volts, 12 volts, or something else. It's a TEAC part number 14769070-30 and is also labeled Shinano Kenshi Co. Ltd, and made in China (of course.) Does anyone know its operating voltage or anything else about it?

    Thanks.
     
    Last edited: Jan 25, 2011
  2. SgtWookie

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    Do you still have the circuit board that drove the stepper motor? It holds the key to that mystery.

    Disk drives get both 5v and 12v supplied to them.
     
  3. tracecom

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    Yes, I have the board. It has a standard 4 pin disk drive power connector on the edge. So, 5v or 12v?

    Thanks.
     
    Last edited: Jan 26, 2011
  4. SgtWookie

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    Why don't you look around on the board and find out where the motor plugged in. The controller IC will be nearby. Then you can look up the specifications for the IC, and check where the board traces run to see what it's being supplied with.
     
  5. tracecom

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    The controller is a BA13002F surface mount, but the solder mask is so thick, it's impossible to follow the traces. Googling around, it seems that most are of the opinion that the steppers on 5 1/4 inch drives were 12v, but I don't know that definitively. Guess I'll try that and if it burns up the motor, it won't be a great loss.

    Thanks.
     
    Last edited: Jan 26, 2011
  6. shortbus

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    Steppers are very tolerant of over voltage. Not so tolerant of over current. Commercial stepper drives use around 40V to run 5V stepper motors. Even ink jet printers use around 30V on there motors.
     
  7. SgtWookie

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    The BA13002F has a maximum rating of 350mA, so the manufacturer was probably operating them at maybe 2/3 of that (or less) for reliability.

    Use a multimeter/DMM to measure the resistance of the windings.
    Then, calculate voltage = 0.2A * resistance.

    You could use an ULN2003 or ULN2803 (7- or 8-channel Darlington IC) to sink current from the four ends of the windings. The Darlington pairs will drop about 1v from collector to emitter. These ICs will simplify your driver build requirements, and are inexpensive. Alternatively, you could use some logic-level power MOSFETs, like IRLD024's; they are logic level N-ch power MOSFETs come in a 4-pin DIP package so they're handy for breadboarding and are rated for up to 60v, 2.5A.
     
  8. tracecom

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    @ Shortbus
    Thanks for your input.

    @SgtWookie
    Each winding measures about 72 Ω which, according to your suggestion, figures to 14.4 v. If the intended voltage was 12 v, that puts the current at 167 ma. Seems reasonable. At 5 v, it would be only 69 ma. I think the answer is 12 v.

    Just finished assembling a project board with a PICAXE 18-X driving a ULN2803A. The μc is responding. Now, I have to come up with some software to drive the stepper. For development, I am going to use a 9 v battery to power the motor, and if all goes well, replace the battery with a 12 v power supply.

    I have determined which leads on the stepper must be switched on in the correct order to move the rotor, but I don't know which is winding 1a, 1b, 2a, 2b. I am not sure whether I will need that info or not.

    Thanks for your help.
     
  9. SgtWookie

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    Don't worry about 1a,1b etc - that's for bipolar steppers. You have a unipolar stepper.

    You can just label them 1, 2, 3, 4 - whichever way stepped the motor clockwise - and label the common as +12v.

    You're going to wear out that 9v battery in a real big hurry. If you have a spare Molex connector on a tower case computer, the yellow is +12v, the red is +5v, and the two center black connectors are ground. Just be careful to not short it out, because you'll crash your computer - boink! :eek:

    Using 1A fast-blow fuses for the +5v and +12v would prevent such an accident. You can get a "Y" adapter very cheaply at any computer supply place; don't chop up your computers' harness. Don't connect/disconnect when the computer's on. Use a good-sized filter cap on the +12v line; 1,000uF should do it.
     
  10. tracecom

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    It works. I can make it turn both directions and vary the speed. The laminations on the motor get very warm to the touch when the motor runs continuously, but since it was originally used to position the heads on a disk drive, it's not intended for continuous use.

    I can concentrate on the programming now. :)

    Thanks.

    Oh, and I'm using a 12 v wall wart to power the motor. The regulation isn't much, which may be adding to the heat issue.
     
  11. SgtWookie

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    You could always use a power resistor in series with the common supply.

    The motor was originally fastened to the frame of the drive, which gave it a means to dissipate heat. If you don't provide for heat sinking and keep the motor powered, you'll probably burn it up pretty quickly.

    You'll need to dissipate about 2 Watts of power. If you don't have the motor mounted on something that will serve as a heat sink, you should use a resistor in series with the common supply. Radio Shack carries 100 Ohm 10W power resistors in 2-packs for a couple of bucks.
     
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