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Power Resistors and stepper motors — Parallax Forums

Power Resistors and stepper motors

metron9metron9 Posts: 1,100
edited 2004-11-16 00:09 in General Discussion
I have a 5 volt, 1 amp 5 ohm stepper motor. After reading that stepper motors should be driven 3 to 25 times higher voltage
I would like to at least try 12 volts on the one I am using as I am using an old PC power supply and running it at 5volts now.

The numbers work out to drive this motor at 12 volts, I need a 7 ohm 25 watt resistor

I have looked at the listings on resistors and I am confused as to what kind of resistor I should use as there are quite a few different kinds.
Ceramic, thin film, and others.

I also would like to verify my thinking as to the wattage needed. If I need 25 watts and 7 ohms
could I use 2-14 ohm resistors with say 15 watts power rating that would give me a 7 ohm 30 watt resistor?

Could I even use 4 28 ohm resistors in parellel ith say 7 watts power rating

I would tend to think a variable resistor would work so I could experiment with higher voltages and keep my current at 1 amp.

Comments

  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2004-11-13 01:48
    I'm curious...Where did you read to run a Stepper Motor at 3 to 25 times higher than the rated voltage?· I'm not sure if your Stepper Motor will spin at 125V (25 times 5V), but I bet it will be a nice smoke & light show...shocked.gif

    If the Stepper Motor is rated at 5V @ 1A, then that's what it needs...If you're giving it 5 Volts and not getting what you expect, then either it's not getting the 1A of current it needs @ 5V, or it doesn't have a high enough rated torque spec for your application.

    Wow...125V...That would interesting to see...tongue.gif

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    Chris Savage

    Knight Designs
    324 West Main Street
    P.O. Box 97
    Montour Falls, NY 14865
    (607) 535-6777

    Business Page:·· http://www.knightdesigns.com
    Personal Page:··· http://www.lightlink.com/dream/chris
    Designs Page:··· http://www.lightlink.com/dream/designs
    ·
  • kelvin jameskelvin james Posts: 531
    edited 2004-11-14 04:28
    Actually, stepper motors can be " voltage overdriven" by up to ( what i have read ) 50 times the rated voltage, but only voltage, not current. It is basically used to attain a higher speed and torque for the motor. Though i have not personally done this, it is possible with what they call a "current limiting or chopper drive circuit". The electronic circuit uses resistors and a comparator for the operation. It works by driving the coils on the motor up to its maximum instantaneously, and drops to the normal voltage after it cycles. Chopper drives use a dual power supply to acheive this. Many drawbacks to this in power consumption and a lot of heat generated.Stepper motors are sometimes rated at the minimum voltage, rather than the maximum. Better and easier to move up to a bigger motor. If you want some technical and somewhat mind boggling info on steppers, go here
    http://www.cs.uiowa.edu/~jones/step/
    lots of tech info beyond me, but it is a good resource.
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2004-11-14 22:47
    Yeah, but see, someone unfamiliar with the operations of such circuits, and the theory of operation, should probably stick within the specs of the device, so as not to damage the device OR the Stamp.· This kind gets into the same area as people who overclock CPUs, and those who over-drive amps, it's one of those areas I think should be reserved for those with experience.· I would still recommend the rated voltage of the device, or a device more capable than the one being used.· My 2 cents...Please, don't ask for change!· tongue.gif

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    Chris Savage

    Knight Designs
    324 West Main Street
    P.O. Box 97
    Montour Falls, NY 14865
    (607) 535-6777

    Business Page:·· http://www.knightdesigns.com
    Personal Page:··· http://www.lightlink.com/dream/chris
    Designs Page:··· http://www.lightlink.com/dream/designs
    ·
  • kelvin jameskelvin james Posts: 531
    edited 2004-11-15 19:29
    just a quick follow-up note, yes Chris you are absolutely right about playing with voltages someone doesn't understand . It can turn out to be a rather expensive or dangerous mistake.
    Better to play safe. And i shall keep that in mind on future posts. kelvin
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2004-11-16 00:09
    What might be a better thing in the future, is not so much to NOT mention advanced thing, but rather to explain them in greater detail for a novice to be able to comprehend.· I remember posting something once that was probably too advanced for a newbie and the trouble it caused.· I myself am not going to try and cover that, but you are more than welcome if you have a fix for his dilemma, if you provide details, or references, he may be able to figure it out.

    metron9, I hope you get the information you need from someone/somewhere.· Good luck!· wink.gif

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Chris Savage

    Knight Designs
    324 West Main Street
    P.O. Box 97
    Montour Falls, NY 14865
    (607) 535-6777

    Business Page:·· http://www.knightdesigns.com
    Personal Page:··· http://www.lightlink.com/dream/chris
    Designs Page:··· http://www.lightlink.com/dream/designs
    ·
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