Had a little fun shooting sparks and triggering solenoids via directly fed +48 VDC.
Turns out the sparks were caused by too little resistance in the coils and the large voltage difference when off/on. That's ok for the flippers where sparking is actually considered normal operation due to the way they work, but for the bumpers etc I need to either:
A) Lower the voltage over the coils
B) Increase the resistance over the coils
(A foot note: Low resistance = High power coils, so it's not all bad!)
The sparking in this case means lower lifetime per coil, more heat etc. For a normal "hold" coil, the resistance (Ohm) should be around 150-200. Mine was 4 Ohm, same as the flipper coils. A direct short circuit is anything below 1.8 Ohm, so it's walking a fine line there...
It will be easier to test this properly when it's all connected in a controlled environment.