Stepper motor ?

Bladerunner

Hi All
I am usinf a 12 V stepper info:
Insulation resistance: 1000 MOhm @ 500VDC
Dielectric strength: 500V 50Hz/minute
Ambient temperature: -10°C to +55°C
Step angle: 1.8°
Number of phases: 4
Drive System: Unipolar
Phase resistance: 30 Ohms
Current 400mA
Phase inductance: 23mH
Detent torque: 220 g-cm

With a BS2 and a ULN2803 and the stepper is very hot what could be wrong?
It runs and I have a heat sink on it...

Thanks

Jon Williams

Every stepper motor I've ever worked with gets hot; I think it's a function of the amount of current flowing through the coils.

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Jon Williams
Applications Engineer, Parallax

Bladerunner

Thanks,
I can touch it, and maybe cook an egg on it but it has been running for over 2 hours... must be OK

kelvin james

The coils on a stepper are always powered on through the common power lead to provide maximum holding torque, and this causes the motor to become a little on the warm side. I have a stepper controller ( little stepu ), that has a function to only power up the coils when it is about to move, and powers down again when the position has been reached, thus keeping the motor from getting hot.
But, of course this is only useful if the holding torque is not actually required, you would just be relying on the detent torque to hold the position. I'm not sure how this is done, but it is probably a simple circuit to switch off and on the power to the motor as needed with a serial command from the stamp. Maybe someone else here could give some advice for a circuit to do this.

kelvin