I have reconsidered the capacitor vs. battery solution. I don't want a capacitor exploding inside my control box. I do have a few SLA batteries laying around I can use...20ah capacity. I would rather use a 12v trickle charger to maintain the battery and keep this part of the project separate from other power needs (stepper motor and Arduino). Terry, I don't have an Oscope, but will take your advice and use a suitable diode across the solenoid terminals. As for switching...do you prefer the FET board over using a SSR good for 40 or 60 amps? As you mentioned, pulling 40 amps in 50ms isn't going to happen.
Thanks,
Cris