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[on:]

I hope this is a basic question (I am at a basic level) and many thanks for trying to help me.

The Motor Shield R3 documentation states: Max current 2A per channel or 4A max (with external power supply)

and the stepper I have is 2.5A per phase 4.5V

Is the "external power supply" simply the external supply to the Arduino UNO board? Or is this the bit where it talks of cutting the pins  etc?

For the sake of completeness the motor is an 8 wire hybrid that I hope to drive as a bipolar (serial or parralel) which becomes a 4 four wire motor. I will try using the stepper motor code from the Arduino Library.

[Reply #1 on:]

I agree the statement you quoted is a bit ambiguous, but elsewhere it states this:

The shield can supply 2 amperes per channel, for a total of 4 amperes maximum.

The 4 Amps maximum corresponds to two channels each supplying 2 Amps. To support these maximum values, the motor shield must be given an external power supply (not one via the Arduino).

The stepper motor you describe takes more current than the shield can support.

[Reply #2 on:]

Peter, thanks.

I was coming to that rather unfortunate conclusion. Unfortunate as I am committed to using this motor.

I guess I need to try and find a way of using the outputs from the motor shield to trigger a larger supply. There must be some way of doing that - solenoids would be too slow.

[Reply #3 on:]

I think you need to look for an H-bridge motor driver with a suitable voltage and current rating. It doesn't necessarily need to be an Arduino shield.

[Reply #4 on:]

Peter,
Thanks.

I must learn more; trying to understand the specs is a challenge. I think I have found one at £62.