relay that when power is applied stays on till power cut

[wjw]

hi All,

I'm after a relay that if I apply power to it momentarily will stay on, until the main power drops. I know they exist but can't think of the name and the guys at Jaycar and RS didnt get what I meant.

Anyone know?

Cheers,

Bill

[chevrolux]

When you say you want the relay to stay on until the main power drops.. do you mean drop below a certain point? or drop out completely? What is the relay going to run?
My first thought is put a little bistable circuit on the input to the relay but that will only hold the relay on for a fixed amount of time each time.

[00falcon]

Couldn't you use the 'Normally closed' output of the relay as opposed to the 'normally open' circuit.

That way when you switch it off, it will actively break the normally closed circuit, but a power failure will not effect it...

But unsure if that's right...

[churchill]

A latching relay might be what you're after.

[Rotazuk]

Just get a normal relay . Take a power feed from the main contacts output and feed it back to the coil power input .
with power on the main contacts in , the relay will not be closed . When power is put on the coil closing the main relay , power is taken from the main relay and feeds the coil , thus holding it on . When power is cut to the main relay , it is also cut to the coil and thus delatches . When power is restored to the main contact in the relay will still be open until power is fed to the coil again .
Hope that makes sence and is what you want to do , maybe tell us what you want to do and they can answer a bit better .

[Pedro]

Just get a normal relay . Take a power feed from the main contacts output and feed it back to the coil power input .
with power on the main contacts in , the relay will not be closed . When power is put on the coil closing the main relay , power is taken from the main relay and feeds the coil , thus holding it on . When power is cut to the main relay , it is also cut to the coil and thus delatches . When power is restored to the main contact in the relay will still ve open until power is fedd to the coil again .
Hope that makes sence and is what you want to do , maybe tell us what you want to do and they can answer a bit better .

will need to put a diode in the "signal" wire to prevent the power being back fed up the signal wire, may not be a issue .

pedro

[sibainmud]

A latching relay might be what you're after.

That's what they are called. last one I got from Simpson Electrical Wholesalers. Blood expensive thou, when you have to get a base as well
One of those will suit your purpose.

Cheers,

[wjw]

A latching relay might be what you're after.

That's what they are called. last one I got from Simpson Electrical Wholesalers. Blood expensive thou, when you have to get a base as well
One of those will suit your purpose.

Cheers,

Thats the one... thanks

[GTS]

run a wire from the out put on the relay to the switch post on the relay then once the relay is open it stays open till power is cut to it

[wjw]

Found what I needed when looked for latching relays:

[pjb]

Found what I needed when looked for latching relays:

Capture.PNG

This is good when you want to isolate your input pulse from the output.
But if your input pulse is from the same 12V system (either + or -), then you only need one (regular) relay.