Hurst motor similar to ones in moonlite heating up with Nano+L293Dm

[Alistair samson]

hi,
I have a Moonlite focuser and based on excellent documentation here, I built two Nano+L293dmini controllers to drive the Hurst stepper used in the moonlites.
they use the LSG35012F76P geared stepper which works well with this controller.

I bought the LSG35012E98P geared stepper which has identical motor specs but a higher gear reduction gearbox as i wanted finer control, but this one heats up quite significantly.

Specs are here http://www.hurst-motors.com/lsg35geared.html but in summary

LSG35012F76P - used in moonlite focusers
reduction - 1:75
Nom Voltage - 12V
Winding Resistance - 65ohm
input power - 4.5W
Rated ind - 27 mH
steps per rev - 3600

LSG35012E98P - one I'm testing
reduction - 1:300
Nom Voltage - 12V
Winding Resistance - 65ohm
input power - 4.5W
Rated ind - 27 mH
steps per rev - 14400

As you can see, electrical characteristics are identical. i've checked my wiring, motor moves as normal. just gets pretty hot.
When I connect it to the original moonlite stepper, it doesn't get hot. just warm.
any ideas?

Thanks
Alistair

[brownrb]

Try turning CoilPower OFF