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power supply for a 1.8v, 4.5 amp stepper motor — Parallax Forums

power supply for a 1.8v, 4.5 amp stepper motor

markallenmarkallen Posts: 10
edited 2006-05-25 16:56 in Robotics
Hello,

I have a surplus stepper motor I'd like to put to work, which is rated at 1.8v at 4.5amp. Can anyone advise me on how to power this motor? I'm more used to things that draw a couple amps at 24 volts. Is there a reason why the voltage is so low and current so high?

best,

Mark

Comments

  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2006-05-25 00:49
    Mark,

    ·· Are you sure it's 1.8V?· Do you have a datasheet for it?

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    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2006-05-25 07:55
    I have seen these mentioned before.
    Apparently they are old Apple II printer motors.

    The first thing to realize is that by using a transistor to control them, you have another 0.6 to 0.7 voltage drop.
    If that is the same for FETs, it would be much easier to drive them from the newer high Amperage FETs that can directly connect to a BasicStamp.· Use a 10amp rated FET for each coil to run cool.

    So, first determing your 'true voltage need' as 1.8volt or 2.6volts. Then it is a matter of inserting a current limiting resistor between the actual supply voltage and the transistor or FET that you are using.

    Last year, someone tried using these with an UNL2803 and promptly smoked the IC. He switched over to FETs and they ran fine.

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    "When all think alike, no one is thinking very much.' - Walter Lippmann (1889-1974)

    ······································································ Warm regards,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2006-05-25 16:38
    Kramer,

    ·· I asked because I had someone mention a Stepper before with these specs, but after a long search we found out the 1.8 was the degrees per step, leading to 200 steps per revolution.· The voltage ended up being from 9 to 24V.· Anyway a datasheet would be easy enough to decipher this information from since I could see where the other guy got lost on the label.

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    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2006-05-25 16:56
    My apologies, it seems the Apple II motors might be more in the 3 volt range.
    Your intuition for other people's confusion is a bit sharper than mine.
    I presumed that a data sheet might not be available and that he was reading the lable.
    I am also wrong about the current limiting resistor. You only need to provide one on the common wire, not 4.

    Incidentally, I just got through with resolving another stepper motor problem [noparse][[/noparse]my own] where the data sheet was just plain wrong.
    In that case the sequence of wires to the coils were missed documented.

    In Mark's case, reading the resistance on the coils would tell a great deal and verify his data.

    In my own case, I learned a way to sort out the phases.
    If your 5 wire Uni-polar stepper motor won't work, but you are sure the programming is correct; try the following:

    First ,exclude the common wire.

    Of the four remaining,·switch two of the end wires with each other and try it again. If it works, just stop.
    And then, if that first switch did not work, now switch the two middle wires and try it. This time it should absolutely work.

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    "When all think alike, no one is thinking very much.' - Walter Lippmann (1889-1974)

    ······································································ Warm regards,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan

    Post Edited (Kramer) : 5/25/2006 5:21:44 PM GMT
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