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Old Nov 14, 2009, 06:45 PM
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Tacoma, WA
Joined Nov 2001
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How to use Brushless Sensor to measure RPM on Spark Ignition Gas motor?

Has anyone used the Brushless Motor RPM sensor to measure RPM on a Gas motor? I am looking for wiring suggestions to pick up off the Spark Plug wire like the on board tachometers that are available. If I just wind a coil of wire around the spark plug lead and hook both ends of the wire to the leads from the Brushless RPM sensor will it pick up the pulse from the spark plug wire through induction? I want to measure RPM on a Zenoaha G260 PUM motor in a boat. The boat has a cover over the engine so the optical sensor will not work as it is dark inside and I figured the spark plug fires every cycle so that would be the best way to get RPM. Has anyone done this.
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Old Nov 15, 2009, 12:58 AM
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Son, Norway
Joined Sep 2004
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Originally Posted by ebourlet View Post
The boat has a cover over the engine so the optical sensor will not work as it is dark inside and I figured the spark plug fires every cycle so that would be the best way to get RPM. Has anyone done this.
The optical sensor actually works best in the dark, as it has it's own light source (IR) and seems to be jammed in daylight. The magnetic sensor would probably also be a better choice.

Fred
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Old Nov 17, 2009, 10:22 PM
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Joined Nov 2003
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ebourlet, we have had reports that wrapping one (or both) of the brushless rpm sensor leads around the spark plug wire results in a usable reading. But, we've not tested that in house, so I have no idea how reliable this method is.

Most people do what Fred is suggesting, and use the magnetic sensor in conjunction with the magnet(s) that are most likely already mounted in your flywheel, that drive the magneto.

Regards,

Bill, for Eagle Tree
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