Stepper Motor only rotates at 10rpm

Hi, I’m looking for some help. I’m hooking up a Stepping Motor to an H-Bridge driver circuit, controlled by my Arduino. The Motor and Driver are shown below.
http://www.ebay.com.au/itm/190882395297

http://www.ebay.com.au/itm/271274970944

I’m running the H-Bridge from a 12v PSU – a wall-wart of about 2A.

I’m using the Stepper library.

The problem is I can only get it to rotate up to a speed of 10RPM – after that it becomes erratic.

Anybody got some ideas? I want to get 60-200 rpm.

That stepper motor is 0.6A 3 ohm, it won’t work with a 12V H-bridge, its a low impedance bipolar motor.

A4988 or similar chopper driver is needed.

Thanks Mark for your reply.

If I understand steppers - and I don't - then I should be driving at around 5v. Assuming my Ohms law is working.

If I dropped the voltage would I expect the speed to pick up? I assume I'm swamping the motor at 12v so it's performance is messed up.

If not, I should replace the motor or the driver. What would you recommend? I'm looking to turn a shaft on a home movie projector, so it's not a big load.

The voltage rating of a stepper motor is nearly useless. What you care about are the amperage and inductance of the motor.

If you want the motor to turn more quickly then you need to be able to energize the coils more quickly. All motor coils act like inductors; it takes time to get them flowing with full current and a slow driver like the L298N doesn’t help.

The A4988 or DRV8825-based drivers are faster at switching, and because they are chopper drivers (they can be set to limit current – don’t need to worry about Ohm’s law to handle that) you can use greater than a 12V supply (up to 40V typical) to get the current flowing through the coils more quickly. Where current is relative to torque in a stepper motor that means that you’ll be able to step the motors at a higher speed and still keep good current flowing while you’re doing it.

So the recommendation would be to replace the driver and try to find a higher voltage power supply for driving the motor.

ianbren:
Thanks Mark for your reply.

If I understand steppers - and I don't - then I should be driving at around 5v. Assuming my Ohms law is working.

0.6 x 3 = 1.8V. That's ludicrously low, these motors are simply not designed for H-bridge
control at all, they are for chopper drive.

Low resistance windings (0.2 to 5 ohms or so) means bipolar chopper-drive motor,
High resistance windings (10+ ohms) can be driven from an H-bridge reasonably, or if
5/6/8 wire can be driven as unipolar from ULN2803 or similar.

Thanks for the correction - I was rushing to get ready for NYE in Sydney. Must have left my brain behind!

@Chagrin - thanks for the explanation. I'll try replacing one and then the other.