Hey guys. Basically what I want to achieve is have a +12v output for around 5 or 6 secs when a +12v is applied to the circuit.

I have fished around on the12volt.com and found this:

The capacitor allows the coil of the relay to be energized until the capacitor stores a charge, thus de-energizing the coil. The resistor bleeds off the charge of the capacitor when positive voltage is removed from the other side of the coil. You can increase the output time by simply changing the value of the capacitor. This one will give you about a 1/2 second output.

My question is what value resistor would give me around 5 or 6 secs? Would it need to go up or down in value to achieve a longer output time?

Thanks

The resistor needs to be of higher value,so that it takes longer to drain the voltage down on the capacitor. I would estimate the value to be 12 times higher i.e. 120 K (120,000 ohms). In most experimental electronics ,you have to put a resistor in and see what results you get. I would try a 250 K (250,000 ohms) variable resistor (potentiometer,or volume control in laymans terms),altering its value to suit,and then replacing its value with a fixed resistor. You could also increase the size of the capacitor ( or put two in parallel),which would also increase the time.

I dont know how accurate the time needs to be, but if this is for the car ,the supply voltage will be anything from 11.5 volts (car engine off) to 17 volts (car being driven in daytime) .This will alter the expected times by a few seconds (less time at 11.5 volts)( more time at 17.5 volts).

Hope this helps , and doesn't put you off!!

Edited 8 May, 200917 yr by AndyPandy

That's brilliant thanks.

Will grab a variable one and just use that. Never thought of that.

It is for the car and will be used just when the engine is running.

It is to lower to mirrors down when I put it in reverse btw.

Phil

It is to lower to mirrors down when I put it in reverse btw.

You having two of these then? One to go down and one to come back up?

You having two of these then? One to go down and one to come back up?

Yup. Thats the plan. Should be easy enough to do now I know how.

I will then also have a third relay that will supply the power to each of them when the car is either in reverse or not.

Phil