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Engine Shutdown

Practical Motorsport Wiring - Club Level

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I have been trying to worut a better solution for shutting down my engine by use of a TYCO high current relay. What I am concerned about is that if I isolate the battery from the alternator at the same time as killing the power to the PDM (hence Ign and Injectors) that the current dump from the alternator will have nowhere to go. What I want to achieve is ideally upon activation of either kill switch send a message to the PDM to kill power to the injectors and ignition, fuel pumps etc then wait 2 seconds for the engine to stop rotating then kill power to the TYCO relay to isolate the battery from the system. This way the current from the alternator will still dump to the battery and allow the logging to continue until 2 seconds is up. I have drawn a little diagram to try and explain this attached.

I do understand that the MSEL CANbus isolater can achieve this but this is outside of my budget...

Can anyone please offer any advice or suggest a better method of doing this please?

Many Thanks

Attached Files

If the PDM is aware of the engine speed, then it can turn off the Tyco relay when the kill switch is off and the engine is stopped. Otherwise, it just turns off fuel and ignition if the kill switch is off.

Thanks so we use the engine speed = 0 to trigger the relay. also in my diagram I have no way of actually resetting the TYCO relay after it has been activated which makes me think there must be a smarter way to do it...

I would be wary of using the PDM to control the Master Relay in this manner. Some regulations do not allow for the Master Relays to be controlled by a device that is being powered directly by the Relay and/or require that the switching circuit for the Master Relay is a totally separate circuit to the main vehicle relay.

My solution would be to have the switching circuit for the Master Relay monitored by the PDM, and when the circuit collapses to disable the Master Relay, also turn off the injectors and ignition. If you are worried about a alternator surge, you could have a short delay (around 250ms) between the circuit turning off and the injectors/coils being depowered to absorb some of the current from the alternator that would normally go to the battery.

OK thanks. That makes sense. It was getting a bit complicated which usually means to go back to basics...

Karl, what class are you planning on running in? It is nice to have an isolator of course, but for most racing in NZ you only need to meet Schedule A requirements which doesnt specifically require an isolator. They only specify a "Kill switch" that "breaks all circuits that could keep the engine running". I.e. a small toggle switch or button on the dash and outside with the correct triangle decal that switches off ignition and fuel pump is all you need.

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