Help Request: Simple Stepper Hardware with EMC's HAL

[adamziegler]

Hello all,

I have some 8 wire 5.4V 1.5A 0.9 deg/step stepper motors. I think they are in the realm of 100-120 oz/in. For the time, I plan to go unipolar with the steppers. This is the stepper : http://www.cnczone.com/forums/showth...t=vexta+8+wire

I have successfully configured EMC's HAL to act as a half stepping 4 phase pulse generator. Pins 1-4 on my parallel port single through an optocoupler. The optocoupler output triggers a combination of 4 transistors... (1 transistor for each phase.)

My power source comes from an old computer. It is a ~150W switching power supply.

My electronics background is "ok" but I have been out of it for a number of years, and have been re-climbing the learning curve.

I need some help picking out an adequate transistor. I think I am looking for a mosfet NPN that can handle at least 1.5A. I managed to parallel a couple (per phase) 800mA NPN's I had laying around for a test... stepper moves fine, but when I stop the stepper the transistors get very hot. (They were only rated at 1.8W a piece) These were not meant to be permanent... just a test.

I have also noticed that I can run my steppers faster at greater 5.4V... is this a bad idea? Do I need to add something else to the circuit to protect the stepper?

Should the power source be modified in any way? Any other suggestions or words of caution? Any other information I can supply?

Thank you in advanced for your help.

[adamziegler]

ps... this is the stepper I have:
http://www.cnczone.com/forums/showth...t=vexta+8+wire