One for the electrical gurus........auto switch off

[thailoz]

I have an Idea but not sure how to go about it

I want to have some of my switches auto reset when ign is off.. for example :-

Fuel pump circuit

What I would like is when the ign is on I could push a momentary on button which will then switch power to my fuel pump also lighting an ind lamp telling me I have power.
Then when switch the ign off the switch resets ,so that every time you get in the car you have to push the button to start the car (sort of security device if you like).

So can any one shed any light on how to do this please.

Laurence

[davedew]

I would have thought if you used a latching relay that was fed from an ignition switched feed would do this.

Turn ignition on to provide power. Momentary push switch to earth relay and activate.
Turn ignition off, relay looses power and resets.

[thailoz]

Maybe ive answered my own question

would this work I dont have any relays at the moment to test it




any comments or additions greatly appreciated

[SeriesLandy]

You could do this with a 4 or 5 pin relay.
I'm assuming that you want to be able to switch the fuel pump off (hidden switch for security?)
If you were going to use the 5 pin, what is the purpose of the link between pin 86 and 87? All that does when the relay is active is feed the power back to pin 30.

[Stot]

The link from 87-86 would provide live to the coil only after the momentary switch had been pressed once and while the ignition is still switched on. Turn off ignition and you need to press the switch again to power the fuel pump.

It would work however you have fuel Pump - on your diagram and that system would provide fuel pump +

Cheers
Stot

[SeriesLandy]

Now stot has explained it, yes it would work. I didn't realise that that was a momentary switch.

[Stot]

Depending on the reasoning behind a fuel pump relay here is a diagram showing the way I ran the fuel pump on my old carbed crossflow car.



Turning on the ignition would energize the coil meaning that to get power to the fuel pump you had to be cranking the engine. Once the engine starts the oil pressure has built and the coil de-energises supplying power to the fuel pump from IGN live. If the engine stalls or you lose oil pressure for some reason the coil energizes and the fuel pump will stop again until you crank it again.

Cheers
Stot

[flyerncle]

Many years ago we used to service a fleet of vehicles that was imobilised until you touched a screw or other point that was connected to the imobiliser and the ignition barrel metal,brilliant idea if you did not know it was there,unknown as to who made it.

[thailoz]

thanks for the replies. I am after putting a hidden switch for the fuel pump.Would I need a second relay for the pump using the relay in the diagram as a trigger?