remote activated sprinkler valve

[dongfang]

Hi Jimmy,

I know the capacitor is not the traditional solution. I once talked with some real experts in the field, and they recommended the capacitor over the reverse diode.

The capacitor slows down the relay insignificantly at power up.
What the people told me was that the diode, especially if it is an unsuitable type, sometimes takes longer time to get in a forward-conductive state than the relay coil takes to generate a dangerously high voltage.

The capacitor opposed any voltage change by conducting a current proportional to the speed of change of voltage, and effectively eliminates the back EMF spike.

Anyway use a diode if preferred. Seems to work OK in almost all cases. Just remember that a fast, small current diode is better than a slow power diode.

Regards
Soren