Stepper motor and L293dne getting hot

Question

I purchased some steppers motors with relatively little known about the specs. I'm hoping to drive them with a L293DNE wired up like this. I've got it working and it all seems to be going well - except the L293DNE is getting quite hot. It would burn my finger quite quickly if I left it running long.

I understand they can run quite hot, but I'd rather not have it that hot if I can reduce it. I require minimal torque for my application, so I was hoping to be able to run it off a 5v 700ma wall wart.

I'm pretty new to all this, but I thought increasing the resistance would lower the current and solve my problem, but it didn't didn't seem to help (or very possibly I did it wrong).

What should I do to reduce the heat?

Answer 1

Use L298s with heat sinks. They can handle a lot more current and are intended for use with heat sinks, unlike the DIL L293D.

Answer 2

Open loop drivers of this sort work best when the back EMF of the load does the work of limiting current; i.e. there is very little load. In the case of a stepper motor, this generally means that the motor is moving a light load quickly, with only rare 'hold' operations.

Higher loads normally require current sensing, or at least some form of current limiting. Some drivers, for example the L298, can do this by measuring the voltage across a resistor in series with the outputs.

Alternatively, if you have a good idea about what your load will look like, you can use the same L293 with a reduced duty cycle during periods of high load, just estimating how much current the motor will draw.