Connect with us

need help to make stepper motor controler

Discussion in 'Electronic Design' started by richard, Dec 8, 2004.

Scroll to continue with content
  1. richard

    richard Guest

    I have a stepper that i want to run a machine tool rotary
    table with.
    From memeory it's 4 phase[8 wires] and it's rated 9.6A 2.1V ?
    it's pretty big about 4" diameter and 10" long, rated at
    something like 840ozin.
    I plan on controling the controler with a laptop.

    the 2.1V rating, surely it doesn't want 2.1V?

    any schematics?

    thanks in advance
  2. CFoley1064

    CFoley1064 Guest

    Subject: need help to make stepper motor controler
    Hi, Richard. Try the Stepper Guru first, Jones on Stepping Motors:

    2.1V @ 9.6A? Yes, that's not uncommon for steppers. For something simple, I'd
    try a 5VDC supply at mongo current, along with resistance limiting. For a
    2.1V, 9.6A coil, you've got about .22 ohms. That would mean you need an 0.33
    ohm, 50 watt resistor for each coil to even it up for 5V, and a little less if
    you take into account the voltage drop across the transistors. It might be
    easier to use a power FET as the bridge switching element. It will have a
    lower voltage drop.

    Once you're there, you can control the stepper through a laptop by using the
    parallel port.

    Read Jones first. If you need help with the printer port, look at Axelson's
    Parallel Port Complete. It's available from the library, and also from
    hobbyist sources or Axelson's Lakeview Research. The website has a number of
    helpful links.

    Good luck
  3. Bill Sloman

    Bill Sloman Guest

    The Jones web-site is good. The advice to try a 5V supply with series
    resistors to limit the the coil currents to less than 9.6A is good, as far
    as it goes, but misses a piece of crucial advice.

    Stepper motor manufacturers traditionally specify their motors in terms of
    the maximum continuous current you can put through the coils (here 9.6A) and
    the ohmic voltage drop acros the coils at this current.

    In order to get the stepper motor to rotate at any sort of speed, you have
    to apply a lot more volts across the coils, mainly to counter the back-EMF
    developed as the coils rotate in the magnetic fields that make the motor
    work, but also to allow you to rapidly change the currents through the -
    necessarily inductive - coils.

    Your driver circuit has to be designed so that if the stepper motor stalls
    (eliminating the back-EMF), this high voltage won't burn out the coils - the
    dumb but reliable way of doing this is to put suitable power resistors in
    series with each of the coils. This wastes a great deal of power -
    particularly when the motor is stalled.

    A better solution is to monitor the coil currents, and provide a system for
    turning off the drive voltage to a coil if the current through that coil
    approaches the maximum permissible current - effectively making the driver a
    kind of switching regulator. This can be a potent source of electrical
    noise, so it can be a good idea to make the switching happen at a frequency
    appoaching about a MHz and to put high current filter inductors (one per
    coil) on the driver board, close to the switch, to prevent the high
    frequency currents from circulating through the motor leads and the motor

    Someone is bound to ask you why you've put a lower value filter inductor on
    the driver board in series with the (usually) much higher inductance of the
    motor coil, but you can usually respond that at frequencies approaching a
    MHz the impedance of the motor coil is dominated by the inter-winding
    capacitances and it looks like a short circuit to the high frequency
    components of the chopped drive. There is also the risk that the high
    frequency current through the coil would induce secondary current in the
    metak in the motor's flux paths, further heating the motor, but one reason
    is usually enough ...

    Hope this helps.
  4. john jardine

    john jardine Guest

    Good advice in other replies.

    The "2.1V" comes from how the manufacturers figure a rating for their
    motors. Under test, they'll inch up the voltage to the coils, until the
    motor stabilises at its maximum temperature, (say 55 degreesC above
    ambient). Whatever final voltage value is, goes on the rating plate. The
    motors are rough and ready as far as voltage/current precision is concerned.
    Just don't rum 'em too hot.

    That's a big motor. I wouldn't care to be within 100' of the cutting tool if
    its control steps were coming via windows :)
  5. Mark Zenier

    Mark Zenier Guest

    It's probably 2 phase. It's pretty commmon for (larger) stepper
    motors to bring out all the wires for the dual windings on each
    phase, so they can be run with either a unipolar or bipolar drive.
    (A five wire unipolar drive motor is just an eight wire motor with
    the right four wires connected internally).

    If you have a bipolar drive, you can connect the two windings in each
    phase in parallel or series. The problem for a parallel connection is
    the amount of current. For series connection, the inductance is
    up to four times higher than a single winding, as they're coupled
    magnetically, and this can limit the top stepping rate.

    Mark Zenier Washington State resident
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day