in a car, i want to supply a solenoid with a 2 position rocker switch, but i only want the soleniod to have a supply if the switch is closed after the ignition is turned on. if the switch is closed before the ignition is turned on, then i don't want the solenoid to have a supply. I'm trying to do this using relays, but haven't been successful so far. Any ideas would be much appreciated.
Have the relay coil energised off the ignition switch. Then have the rocker switch in series with a set of normally open contacts on the relay and then to your solenoid.
That way, if the ignition is off, no voltage is present at the rocker switch, so the solenoid cannot energise. When the ignition is on, the relay is energised, allowing voltage to be present at the rocker switch.
Ignition off – no power to switch
Ignition on – no power to switch if switch was in the on position (ever?)
Ignition on - power to switch if it was off when ignition was first turned on.
Ignition off – no power to switch
Ignition on – no power to switch if switch was in the on position (ever?)
Ignition on - power to switch if it was off when ignition was first turned on.
RLY 1 & 2 C - IGN
RLY 1 NO - RLY 1 coil a
RLY 2 NO - RLY 2 coil a
RLY 1 NC - RLY 2 coil a
RLY 2 NC - RLY 1 coil a
SW (1) C - IGN
SW (1) NO - RLY 1 coil a
SW (1) NC - RLY 2 coil a
SW (2) C - RLY 2 coil a
SW (2) NO - Solenoid
RLY 1 & 2 coil b - GND
*SW (2) indicates second pole of switch, IGN = Ignition V+
This will latch one relay that will disable the other relay when the ignition is switched on depending on the position of the switch. Power is taken from the relay that latches on the switches NC position to power the solenoid. To reset turn off the ignition.
If you want an electronic version of this let me know.