I have a solar water heater which uses a 12v march 809br dc brush motor powered by a pv panel. My problem is that sometimes even with full sun the motor won't start pumping. If I tap the pump housing with a hammer it will start and continue running until a cloud goes buy sometimes it will restart on its own sometimes not. I am guessing that it is a friction problem with the impeller. Is there something Capacitor? simple circuit that I can add to give the motor a boost?