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Cooling Fan Timer Circuit Answered

I'm tying to setup a 12 volt 2.5 amp injector cooling fan in a car and I want the fan to turn on for X minutes right after the ignition key is OFF. I was looking at this programmable relay - https://www.amazon.com/Miniature-cycling-Cycling-Industrial-control/dp/B015Z2EQCU/ref=pd_lutyp_simh_1_3?_encoding=UTF8&pd_rd_i=B015Z2EQCU&pd_rd_r=5202NNSP2PM3EE5DZVTA&pd_rd_w=SKMnb&pd_rd_wg=rJ4Td&psc=1&refRID=5202NNSP2PM3EE5DZVTA
Here is the website for that relay with instruction manual - http://www.3rdbrakeflasher.com/
I'm not sure if I need another relay and hook to 87a or if there is a better circuit I can make.

5 Replies

Downunder35m (author)2017-03-26

On a side note:
You can also get temperature controlled relays....
With that you put a sensor where the heat is and the fan keeps running until the temp is below set value.
Of course it would need to be combined with a relay that is on when the ignition is on and off once the ignition is off.
A NC contact on that relay switches the power for the temp controlled relay.
If the fan is no problem when the car is in use you can use the temp relay just as it is and connect it with a fuse directly to the battery.

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Damn it, still can't find the edit button here....
If you can add a screw fitting than a temp switch as used for your radiator fans might work too if the fitting and sensor hole is filled with high temp grease or similar.
Leaves the possible troubles with electronics out of the game but of course has no time control so you would need to find a temp switch that suits your temp needs.

Last but not least you get them as screw on types as well, mostly found in microwaves and similar stuff.
Rated for 10 amps at 240V AC, so good enough for your fan as well.
If you salvage a microwave of decent functions like grill hot air or similar than you will find several of these in different temp ranges mounted on the chassis.
On the side of them you find a stamped note with the electrical data plus the set temp for switching off!!
The will reset at about 5-10° below this set temp.
If you combine that with a relay you can switch your fan without electronics again.
They are basically temperature fuses with an auto reset.
On the relay you need a NC contact for the fan.

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pphantom (author)2017-03-26

Thank you for your suggestion. I never knew about turbo timers. While researching all the different ones and how they work I came across the Hella 996152131 adjustable delayed-OFF timer relay -


I would have needed to buy a relay as well with the turbo timer, but this looks like a perfect 1 piece solution. With the turbo 4 gaining in popularity I might need one of those too someday.

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Downunder35m (author)pphantom2017-03-26

They are stupid nonsense devices for racing street kids, not more ;)
Any normal driver simply won't race the car for a long time and then just turn the engine off.
In a lot of countries they are made illegal now anyway as they interfere with theft protection and emission laws.
But as a simple timer solution you can't beat their price.

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Downunder35m (author)2017-03-25

If in doubt check turbo timers.
Same thing in green, they keep the engine running to make sure your race home won't kill the turbo from overheating if you turn the engine off too soon.
Some are dirt cheap and not really more than a simple timer "relay" o bridge the ignition.
If you want to keep a relay alive for long that is soldered onto such a device than simply add a normal 12V relay at the output.
So instead of switching the load directly you only switch another relay on and if that fails you replace it in minutes without soldering.

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