Turn off gas engine with arduino

After searching 1000’s of engine posts on arduino.cc with no success I thought I would pose the question for the experts.

I have a Harbor Freight 301cc predator engine with a recoil pull start, that has a manual kill switch that is also connected to the oil sensor. I would like to be able to “kill” the engine with an arduino. Basically the arduino is monitoring a few sensors not related to the operation of the engine. If the arduino loses power (battery runs low, etc) I need the engine to power down as well. I am guessing a NC SSR would work? I am not sure what type of voltage comes out of the black wire from the coil or its amperage. Is it DC or AC? Can I use my multimeter to measure it without frying it? Can anyone recommend a solution?


Use a relay.

There could be 1000V on a wire from the coil but it is more likely to be 12V plus some nasty interference and spikes +/-24V.

Look up how magnetos work. Most references will be to airplane engines but it is all the same. Basically connecting that wire to ground will stop the magneto ignition.

Hi Morgan thanks for the speedy reply. Is the voltage type being grounded by the existing switch DC or AC? I see lots of different SSR for AC and DC with varying current handling capabilities. I have been shocked by the spark plug wire before and lived, so I assume its low current and high voltage, like my fence charger for our cows.

Sorry I didn't make that clear. 12V DC. Use a regular relay, not an SSR.

Morgan. I know this is a noob question, but why could you not use a SSR vs a regular relay? Is this a good choice to try? Pololu Basic SPDT Relay Carrier with 12VDC Relay (Assembled)

SSR's are usually AC only. I don't know if they have problems with inductive spikes but the voltage you get on that wire will destroy most electronics.

So use the Pololu relay.

You want the NO on the electromechanical relay, not the NC.
Keep relay 'on' and completed circuit. When power fails, you want relay to go open/break circuit. Normally open. No power, it's open.
Assumes kill switch is breaking a circuit.

INTP. The engine is running when the relay is open and the arduino has power. If there is a power failure I need the relay to close to complete grounded condition. So without power I need it closed. That would be NC relay correct?


Thanks MorganS.