Wiring thermo upto auto off function of headlights?
on my VS berlina i can set a timer for the headlights to switch off after a certin time. but i want to be able to hook some electronics to thisz "function" such as thermo to keep temps down and some other items. where can i hook into the "OFF" wire? i already have a switch for the thermo to switch it on and off. but still want it to run for 30 sec or so on a 40 degree day.? i live in a shit of a place for dry crappy dusty heat. car temp gets up there on these days.
Banned
you can buy timers from jay car
but even tho my car has the auto off light feature? i wanna tap into the timer of it so tospeak
captain halfajob
whats it gonna achieve for that extra 30 seconds? cool the radiator? little bit pointless. why not just hook up a turbo timer, at least itll keep the fluid moving.
Without checking with a wiring diagram I think that the headlight relay is switched to earth (when "on") via the BCM. It might be used to earth another relay in parallel if you locate the terminal at the BCM.
Alternatively, place another relay in the circuit in place of the (BCM switched) headlight relay and use that relay to switch both the fan relay and headlight relay.
Easier may be to use an "RC timer", assembled on prototype board, to switch the fan relay = search but these might give you an idea:
http://archilochus.netfirms.com/images/q_timer.jpg
1 transistor timer.
I find it easiest to:
draw the circuit diagram schematic
lay out the components at 200% scale on 5mm grid paper (prototype board has ~2.5mm hole spacing) and sketch in the wire links
assemble the components through the board then bend the excess wire over to make the links before soldering.
Once you know it works - you might have to play with resistor and capacitor values to get the time delay you want; twist and tape before final soldering, you can epoxy it into a potting box. eg.
Jaycar Electronics - Search results
You don't have to use a full size automotive relay as it will only have to switch the current for the fan relay.
actully upto 3 minuites.Originally Posted by ari666
turbo timer no good. sends the alarm stupid.
wizfiz
having ya fans on when ya turn ya car off wont do a thing to the cooling system if ts really that hot open the bonent
captain halfajob
ok, sorry... "whats it going to do for up to 3 minutes? cool the radiator" just seems like a great way to drain your battery.
Unless you have an electric water pump which also continues to operate after the engine stops, there is no advantage to running the fan(s) after switch off.
Have a little mechanical sympathy; if you've been driving it hard and/or its a very hot day, let it idle for a bit and cool down before switching it off.
i do have an electric water pump....
VT- will switch the cooling fan on via the BCM with the engine off if coolant temp is over 117C so maybe there is some benefit to switching the fan even without coolant flow. Maybe it reduces heat soak from the exhaust?
If you want to go the RC timer route, I dug back through my notes from when I did one:
BD-681 NPN transistor
IN4004 diode
10k Ohm 1/4W resistor
SPDT 12V PCB mount relay
veroboard
6 pin PCB mount 2.5mm spacing header plug
6 pin PCB mount 2.5mm spacing header socket
Potting box
16V electrolytic capacitor: 220 uF => ~7 second delay, 1000 uF => ~12 second delay, ??? uF 30 second delay
That should total a bit less than $15.
(I have the A/C switch wired through a switch on the brake pedal so it only turns the A/C on under brakes - fuel saving. The timer circuit is to stop the A/C switching rapidly on/off after a brief brake application. I have a bypass switch for highway driving where the brakes aren't used much.)
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