Re: I need a relay with about 10 seconds of delay

["Bernard Littau" <bernardl@acumenassociates.com>]

>I'm installing a low oil pressure warning system in my boat.
>I always drive my 1989 Audi 100 to my boat.
>I'm hooking a buzzer and light to an oil pressure light.
>This means the alarm is going to go off as soon as I key the ignition.
>That's going to be annoying.  I'd like to put a relay in the circuit
>that will cause it to delay closing until the switch is opened by oil
>pressure.

You could achieve the desired result with another relay.  It would need to
be DPDT.

I assume you have hooked the light so it turns on when the oil pressure is
low.  Hook the light to the buzzer through the new relay such that the
buzzer will only get power if the oil pressure is OK. (I know this might not
make sense...)

If you turn on the ignition now, this light will come on, but the buzzer
will not.  Good so far.

Now hook the other pole of the new relay to provide power to the relay if
the relay has power. (And you thought I wasn't making sense before...) This
creates a latch relay.  The relay will stay powered, and the circuit to the
buzzer will be complete regardless of the state of the oil pressure.

When you remove power to the whole system, it resets back to no buzzer,
until you get oil pressure once again.


The key is to make the relay latch itself in the on position once it gets a
signal to go on.

I think this is better than a delay circuit if the motor is hard to start.
The downside is no buzzer if the engine never gets up to pressure -- like if
you forget to add oil.

Let me know if you wish a better explanation or a diagram.

Best,

Bernard Littau
Woodinville, WA
'88 5kcstq