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  1. #1
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    stepper motor load resistor and figuring out phases?

    I bought a stepper motor controller a while a go, a small simple one from Herbach, and recently tried to connect it to a new motor- the chip blew up. I then looked at the info sheet and realized I should have used load resistors (the motor I had on it before worked fine without load resistors). SO I bought a new controller, and before I connect it to the motor, can anyone help confirm what size resistors I should be using? I have two options for the motor:

    1. Superior Electric slo-syn motor- 11v DC, .44 amps, 8 wire. I assume this is four coils, so using the formula I received with the controller (Rload = +V-Vcoil/ Icoil) I get (11v-2.75v/ 440) and get 18.75 ohms? is this the correct rating for the resistor? what size wattage resistor should I use?

    2 (second option)- 5vdc, 3.5w motor, 8 wire. so that would be (calculating .7 amp because of the watts) 5v-1.25v/700ma= 5.35 ohms? These readings seem very small.


    ALSO- on the Superior Electric, I have found the pairs in the eight wires, but how do you figure out the sequence of the coils- trial and error?

    Thanks for any help anyone can give. I realize by looking over all the threads that I am asking simple, newby questions, but hopefully someone out there can spare the time.

    Thanks in advance...

  2. #2
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    What is your power supply voltage??

  3. #3
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    12 volts- the board says it can handle 5- 30v.

  4. #4
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    You also need to know the rating of your controller, since that is what blew up last time.

  5. #5
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    Some info

    I Googled "slo-syn stepper 8 wire" and found http://www.bessrc.aps.anl.gov/Steppe...nnections.html. Looking at their page, they show an 8 wire slo-syn (by color code) as:

    Phase 1+: Red, Phase 1-: Blk
    Phase 2+: Red/Wht, Phase 2-:Wht
    Phase 3+: Grn, Phase 3-: Org
    Phase 4+: Grn/Wht, Phase 4-: Wht/Blk

    Google is our friend! At least if your wires are these colors.

    Your controller is rated to 30 VDC and 1.25 Amps per phase. As far I can tell from the ads on the Herbach site, this is not a chopper-type controller. Because of this, power it with a supply close to the stepper's requirements: 12 VDC.

    Using ohms law R = V/I; 12 V/0.44A = 27.3 Ohms. Nearest standard values are 24, 27, 30, and 33 ohms. Use the 27 ohm or a higher value.

    Power dissipated is I*I*R. So, assuming 27 Ohms @ 0.44 Amps, Power dissipated will be 0.44 A*0.44 A*27 Ohms, or 5.23 Watts.

    You will most likely find 5 Watt or 10 Watt resistors-use the higher rating. Running a 5 watter at 5 watts is like running your car all day long at 6000 RPM. It might be rated for 6000 RPM, but not continuously.

    So: 27 Ohm, 10 Watt resistors for a 12 Volt supply. Hmmm. Better make sure your supply is good for a couple of amps too. Again, overkill is good-don't run right up against the ragged limit.

    Have fun!

  6. #6
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    Quote Originally Posted by Evodyne
    Google is our friend!
    They sure am! I shorted their stock at $200 so the more it goes down, the more :banana: I'll be doing.

  7. #7
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    Hmmm...

    Kind of makes me wish I'd caught that train with you! A day late and a dollar short. Oh well!

  8. #8
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    Thank you peepols

    Well God Bless,

    Thank you all for your wonderful help. I had done some googling but I was just looking for the company and hoping to find specs and diagrams there, but alas, I guess the motor is old (it's a surplus buy). Again thank you all. This cnczone is great.

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