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 Chris

"CFoley1064" schreef in bericht news: snipped-for-privacy@mb-m01.aol.com...

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 itself.

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.

--------- Bill Sloman, Nijmegen

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 :-) regards john

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 snipped-for-privacy@eskimo.com Washington State resident