barnaclebill - Any recommendations for a way to...

Any recommendations for a way to determine when a small outboard is running? 8HP/6kW, no access to any spinning parts (except the prop). I was thinking maybe an IMU to detect vibration. Pull start, so no electrical/alternator, but maybe I could insert a voltage sensor between the magneto and the spark plug.
5 Replies
Teppo Kurki
Teppo Kurki8mo ago
vibration sensors are readily available
Roger
Roger8mo ago
A wire wrapped around the spark plug lead will generate a ac voltage when it’s running. Run that through a suitable circuit and you have an rpm counter.
barnaclebill
barnaclebillOP8mo ago
Interesting. I suppose the current would vary with the number of wraps? (And the voltage in the wire, which presumably is pretty high).
Roger
Roger8mo ago
You would have to experiment with it to see what you get. The current should be fairly low, and the number of wraps will affect the voltage. Spark plugs normally operate at several thousand volts, but with very little current. You would basically be creating an induction coil around the plug lead. Another, ready made option is to use an induction clamp from an automotive multi meter.
Unknown User
Unknown User7mo ago
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