How to reduce current

Question

I need help reducing current in my motor driver. The chip is the L293D motor driver with output max 600mA. My stepper motors draw maximum 350mA per phase and operate at 12V, so I am concerned about overcurrent. Is this ok to do, or do I need to add resistors? I looked at some other questions similar in askings, but not the answer I was looking for. The power supply is switching between 8 AA batteries and a wall wart that supplies 5A @ 12V. I am concerned because I wonder if I would need to limit the current at all, and if needed, what do I do. I am also thinking about if I use the batteries, since they are rated in Amp-Hours, the circuit could draw only the needed current. I don't know. Please Help!

Answer 1

If the stepper motor only draws 350mA max, it will only ever consume that much (and probably only at high loads). The driver is capable of supplying 600mA, but that doesn't mean it's going to insist the motor uses it all! There should be no overcurrent problems from the motor's perspective, and I would expect the driver IC to have in-built protection to prevent more than 600mA being drawn if the motor were to take leave of its senses and go crazy.

Any rudimentary current-limiting may just add unnecessary drain on the batteries, or have a detrimental effect on the circuit in general. The whole point of a motor controller is to eliminate these sorts of headaches

Answer 2

Assuming your stepper motor windings are rated for 12V continuous you should not have a problem (though it may run quite warm).

If your windings were rated for (say) 6V, you would get a potential performance boost by running the from a 12V drive with a series resistor. The maximum ramp rate would be improved, at the expense of throwing away a lot of power in the series resistors. Since you have a 12V motor and a 12V supply, you can't do that, in fact the best you'll be able to do is probably a bit less than 10V at 350mA, since the driver eats a volt and change at either rail (and turns it to heat).