Thanks for the link, will start reading.
So that also means I better start replacing some other 100 nF film caps... used those as I didn't have the ceramics yet.
Grumpy_Mike:
You are doing two things:-
You are lowering the source impedance of the voltage input to the regulator. The motors will have the effect of raising this source impedance.
You are trying to remove very short spikes of under and over voltage caused by the motor. Because they are short then they are a very high frequency.
That's the why. I mean, I wonder what exactly those pumps do to the power supply, but I'm afraid that will have to wait until I can get my hands on a scope.
Same accounts for the brushed motors of my peristaltic pumps, so far no issues there but I am getting worried. They should spark and spike. Would it be a good idea to solder a ceramic cap across their connections? Or 10 cm away on the perfboard - basically in parallel to the flyback diode?