Why bother? Even a very large pump uses only a few watts during normal operation. The manufactor specs are just startup. On the rare occasions I turn off the comp, I leave it going. I'd be afraid the ...

Have you ever needed to power a 12-volt relay in a circuit but only had 6 or 9 volts available? This simple circuit will solve that problem. It allows 12-volt relays to be operated from 6 or 9 volts, ...