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Delay on relay

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Leuven:
Hi, can anyone take a few moments to scribble down a schematic for a 12V delayed-on relay?

From the moment it's triggered with a 12V source, the relay must still stay open for 1-10 sec (pot adjustable) and only close after the set time. If trigger voltage last lesser than the set time, cycle resets.

It's for some car audio components which turn on at different times and I want to get the amp to turn on after everything else.

Many thanks!

Jimmy:
Try asking mr google


R1   1   1 Meg Pot   
R2   1   10 K 1/4 Watt Resistor   
C1   1   10uf 25V Electrolytic Capacitor   
C2   1   0.01uf Ceramic Disc Capacitor   
D1,D2   2   1N914 Diodes   
U1   1   555 Timer IC   
RELAY   1   9V Relay   
S1   1   1A 120V SPST Switch   
MISC   1   Board, Wire, Socket For U1

R1 adjusts the on time.

You can use a different capacitor for C1 to change the maximum on time.

S1 is used to activate the timing cycle. S1 can be replaced by a NPN transistor so that the circuit may be triggered by a computer, other circuit, etc

Leuven:
Thanks Jimmy, can you confirm this is a delayed-on circuit and NOT a timed-on (meaning it stays on for a set time)?

sacherjj:
I believe that is a timed on.  Shorting trigger to ground will activate output.  Discharge C1 until below the threshold and turns off the output.

The Industrial Term you are looking for is Delay-on-Make. 

Here is a circuit that will turn on the relay after a certain delay of holding the button down.  It is discharging the cap through the 1M resistor, and turns on the output when it reaches the trigger threshold (I think that is 2/3 Vcc if I'm remembering correctly.)  Look at the LM555 Data sheet.

The problem with something for this in your solution is when the switch is released, the cap will charge through the diode and 10K, turning off the relay pretty quickly.  You would need to either use a latching relay or modify the trigger portion to stay on.   But it sounded like you are using voltage to drive this anyway, so if you trigger with a MOSFET instead of the switch, with a signal that stays on, I think you will be good.

Note: This doesn't "reset" the delay until a little bit of time.  It is kind of accumulating on time for the button press.  I think this will still work in your situation.

Jimmy:
Sorry Leuven after reading your post again it seams I gave you the wrong circuit

try

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