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stepper motor wiring — Parallax Forums

stepper motor wiring

bobroanbobroan Posts: 37
edited 2005-06-29 16:00 in BASIC Stamp
An acquaintance of mine took a look at my stepper motor wiring and insisted that I should be connecting the leads via diodes to the common and even showed me a diagram at a university electronics lab page that has that happen.

I tried disputing him, but am wondering if I might as well add those diodes?· Would they do any good?· Should I connect them betwen the leads and the 12 v common?

thanks

bob

Comments

  • dandreaedandreae Posts: 1,375
    edited 2005-06-24 14:24
    If you are connecting the stepper motor to the BASIC Stamp you will need to protect the I/O pins using diodes.· We do have a ULN2803 line driver chip for $1.50 that would great for this project.· There is a PDF file that has·information on how to connect·the ULN2803 to the BASIC Stamp·available on the link below:
    · http://www.parallax.com/detail.asp?product_id=500-00005

    Dave

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    Dave Andreae

    Tech Support
    dandreae@parallax.com
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    Post Edited (Dave Andreae (Parallax)) : 6/24/2005 2:28:02 PM GMT
  • bobroanbobroan Posts: 37
    edited 2005-06-25 05:36
    Dave,

    Sorry, I forgot to mention that I am using the ULN 2803 already.· I want to know how to add diodes to that circuit.



    bob
  • Bruce BatesBruce Bates Posts: 3,045
    edited 2005-06-25 07:42
    Bob -

    If you're already using the ULN200x to drive the stepper motor, you will note on the data sheet that there are integral supression diodes built into the chip. No need to add additional diodes.

    Regards,

    Bruce Bates
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2005-06-25 21:29
    ·· As a side-note, for those diodes to be connected, the V+ pin must be connected to the positive supply rail for the device.· Otherwise the diodes effectively won't be connected.

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    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
  • ChipCircuitChipCircuit Posts: 23
    edited 2005-06-27 04:50
    IF you get into large steppers, and larger machines, the energy in the machine can spin the stepper, in essence making it a generator. that power would then be fed back to the chips.

    There are schematics that use diodes on each line to the power supply so that any back EMF (ElectroMotive Force) is not routed to the drive chip.

    http://www.allegromicro.com/demo/a3977sed/schematic.pdf

    look at the far right, center of the schematic. the output lines are to a Bi-polar (4 wire) motor.

    But, that driver chip, the Allegro A3977 is rated for 35 volts and 2.5 amps. probably quite a bit more than you are using.

    If you read the thead of NewZed about torque, the Gecko driver is rated for 80 volts and 7 amps, but the chips on the board are rated for 100 volts and 10 amps. the de-rating eleminates the problems associated with back EMF.

    Dave

    Dave
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2005-06-29 16:00
    Dave's reply is right on.

    Some stepper motors have the diodes already inside their housing.· If you buy or are consider buying an undocumented stepper, you should Google to find out what is inside it.

    This grows more common with the larger more powerful steppers.

    Otherwise, you may be assuming that everything is simply a few standard configuratons.

    Fortunately, once you see how the diodes are configured, they are working for you and not against you.· You don't have to by-pass or modify them.· You just need to understand how to properly use them.

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