AU Killswitch

[Cadge]

Hey guys,

Looking for anyone with a bit of wiring knowledge of the AU.
Im racing one in an off road series, and I need to install a kill switch that kills the engine, stops the fuel pumps and Isolates the battery all in one hit.

Any suggestions on where i might start? Isolating the Battery seems easy enough, its killing the engine thats the problem

CHeers.

[robboxr8]

i think its only a diesel that will run on with the battery disconnected i reckon just killing the battery will kill the fuel pump at the same time

the only pain is the ecu will drop out each time and will need resetting every time you use the kill switch

[T3man]

You only need the one emergency kill switch - on the battery. Hopefully you never have to use it, and the ECU reset will not be an issue.

[Windsor220]

Originally Posted by robboxr8

i think its only a diesel that will run on with the battery disconnected i reckon just killing the battery will kill the fuel pump at the same time

the only pain is the ecu will drop out each time and will need resetting every time you use the kill switch

Petrol cars can do it too. We change batteries on cars sometimes by just leaving the engine running. Saves reentering radio codes etc.

[T3man]

WOW! Where do you work? In fairness to all members on the forum you should tell us. I sincerely hope it isn't anywhere I'd ever be taking my car for service work. I wonder how many ECUs have been spiked when you've worked your magic? Had any owners come back a short time afterwards with a dead car? Oh, wait ... they couldn't ... 'cos their car was DEAD.

Believe me, if the ECU didn't die immediately it surely was fatally injured and it's use-by date brought forward lots - it's only a matter of time before you kill one dead!

[Windsor220]

Originally Posted by T3man

WOW! Where do you work? In fairness to all members on the forum you should tell us. I sincerely hope it isn't anywhere I'd ever be taking my car for service work. I wonder how many ECUs have been spiked when you've worked your magic? Had any owners come back a short time afterwards with a dead car? Oh, wait ... they couldn't ... 'cos their car was DEAD.

Believe me, if the ECU didn't die immediately it surely was fatally injured and it's use-by date brought forward lots - it's only a matter of time before you kill one dead!

I dont do it very often. This practice was actually suggested by one of the head trainers at a factory training course. Considiring he was one of the engineers of the manufacturer he didnt have a problem with it. Really when you think about it nothing would happen as the car is running off the alternator.

[T3man]

Exactly - and the output from the alternator can cause high voltage spikes of up to 400volts if it is not connected to a battery. The act of "unloading" the battery from the alternator can cause this - and then upon reconnecting it takes the alternator a split second to adjust to the load - it is the extreme voltage spike that can occur during this procedure that can and WILL lead to premature death of the ECU and other solid stae devices in the vehicle.

[lofty]

So does that mean if the battery-isolating kill switch is ever used, it could kill the ECU?

[Mr Hardware]

What we'd always do with the cabs when changing batteries we'd connect a jump pack to the cables and change the battery so it always had a live 12v feed.

[T3man]

Mr Hardware> Yes, that is the correct and safest method.

lofty> No, disconnecting the battery via a circuit (kill switch) is no different to turning off the ignition (which immediately isolates the alternator) - much different thing to disconnecting a terminal from the battery while the alternator is still operating.

[Cadge]

Sorry, i should have copied the Regs in:

7.8. At least one battery isolation switch is to be fitted. It must perform the following
duties when switched off.
a) Disconnect the battery.
b) Stop the engine and any fuel pumps that may be fitted.
7.9. The isolation switch(s) shall also include the ignition wire, so as to stop the
engine.

So if my kill switch is connected to the ignition wire and the battery it should do both right. But From what ive read, every time i turn the switch, ill have to reset the ECU, but there is also a possibility that the ECU could be fried?

[T3man]

You aren't listening.

You need just one switch which will do all the above. All you need to do is wire your ignition power supply via a (normally-open) relay so under normal "battery on" circumstances you will have ignition. If the battery is isolated via the kill switch then power to your ignition relay is cut and therefore your ignition and all accessories (like fuel pump) which operate through the ignition are also cut.

YES, you will have to reset the ECU if the emergency kill switch is activated. However that should very rarely, if ever, happen. It would only be activated (the kill switch) by a marshall if your car was disabled and caught on fire. In which case the fried ECU is very likely going to be a fried ECU anyhow. In any event, again, you haven't been listening ... turning off the ECU via a battery isolation switch is NO DIFFERENT to switching it off by the ignition switch/key.

[Cadge]

Nah, we have to show them the kill switch works before competing inevery event.

Thanks for the help champ

[T3man]

That's OK - it will work every time, and as long as it's switched on again pretty quickly after the "test" you may not even have an ECU "reset" problem. However, if you find the ECU is mucking up you might be able to wire in a capacitor to the ECU power supply line so it will have some residual voltage available to it for a long enough period to allow you to do the kill test. You really only need to keep voltage to the ECU for 10-15 secs and it won't require a very large capacitor to do the job. An auto elec should be able to help you with this if no wizard comes forth here with a solution for you.

[Cadge]

Yeah i think i could rig up the Ignition wire, now i know what im looking for, but i might just get and auto elec to do it for that reason... and piece of mind