12 volt time lag switch

CAPTAIN FANTASTIC

CAPTAIN FANTASTIC

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I am looking for a 12 volt switch (car type) that when you press, makes a circuit ie power comes on, and it goes off on its own, say after 5 minutes or so; similar to the operation of a car rear heater/demister window switch; any suggestions please?
 
CAPTAIN FANTASTIC said:
I am looking for a 12 volt switch (car type) that when you press, makes a circuit ie power comes on, and it goes off on its own, say after 5 minutes or so; similar to the operation of a car rear heater/demister window switch; any suggestions please?
Click to expand...

How about a car rear screen heater control relay and switch.
 
I used a couple of the Maplin timers for the pump on our Lavac toilet to give a long and short flush. They are adjustable over quite a wide range of times and I had to alter some components to reduce the time as the adjustment was too coarse otherwise. One thing to note is that the relay is permanently energised except when the timer is on its active cycle. The current uses is low but could cause a problem if left on for long periods when the boat is unused.

The Maplin code the the one I used is VF06G. When I searched their site for timer kits it only showed VT27E which is unsuitable as it provides a continuous cycle of on and off.
 
I've been asked a couple of times for my circuit, here it is:

Heads-Timer2_zps2f7fca10.png~original


All the components came from CPC, the relay is this one: http://cpc.farnell.com/imo-precisio...ature-power-spco-12vdc/dp/SW02553?Ntt=SW02553

Note that some relays don't work with a 75k resistor, and the circuit would be more stable if this was lowered slightly, say 68k. Doing this will drop the 60 second delay by 10%, to increase it, increase the capacitor size, or add more in parallel. S1 is the original switch (photo amended)
 
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I've updated the diagram.

Shown are the original two terminals on your existing switch, they briefly connect the 12V rail to the junction of the C and the R. If I were selling this design, I'd put a 4R7 resistor in series with the switch to limit the surge, but I've never had a problem.
 
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nigelmercier said:
I've updated the diagram.

Shown are the original two terminals on your existing switch, they briefly connect the 12V rail to the junction of the C and the R. If I were selling this design, I'd put a 4R7 resistor in series with the switch to limit the surge, but I've never had a problem.
Click to expand...

Ah, right, that makes much more sense. You're to be congratulated on maintaining the fine Practical Boat Owner tradition of publishing incorrect circuit diagrams! ;)
 
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