Honda CRF Stator Question

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Old 03-09-15, 08:40 AM
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Honda CRF Stator Question

The headlight on my '07 CRF250X is powered directly from the alternator and I'm trying to determine if it uses all eight stator poles. I measured the AC signal yesterday using an o-scope in order to determine the engine RPM and according to my calculation, it uses all eight. The waveform I obtained from my measurement was 111 Hz, which, if my math is correct, results in an RPM of 1,665. I arrived at this number by taking the raw signal (111 Hz), dividing by four (eight poles divided by two because each pole equals half an AC cycle), then multiplying by 60 to get rotations per minute. Does this sound correct? BTW, the manufacturer spec. for the RPM is 1,700 +/- 100, so 1,665 is a valid number and the engine idles well at this number (I adjusted by ear first without knowing what the actual RPM was, then measured with the o-scope). If I use the equation for RPM of an AC generator (N = 120f/P), I also get the same number of 1,665 RPM. N = RPM, f = frequency of stator current, P = number of poles. This reinforces my assumption that all eight poles are used. My best guess is that both the headlight/regulator-rectifier coil and the ICM coil are wound around all eight poles, only with the headlight/R-R coil having less windings in order to drop the voltage to around 14V-15V for the headlight and battery charging circuit. The ignition coil winding would have as many windings as possible to maximize the voltage to the ICM. Sounds feasible to me.

This is the wiring diagram provided in the service manual. The "Ignition Pulse Generator" is the CKP sensor, which tells the ICM when to fire, the coil shown on the left of the "Alternator" feeds the headlight and the rectifier/regulator, and the coil shown on the right feeds the ignition control module (ICM).

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Last edited by mossman; 03-09-15 at 11:06 AM.
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Old 03-10-15, 02:02 PM
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From what I've been told, the ignition uses three poles, the headlight uses three poles, and the charging circuit (rectifier/regulator) uses two. Eight poles and eight magnets will create contiguous sinusoidal waveforms regardless of the number of poles. I'm pretty confident my RPM calculation is correct, but I am going to confirm this number by measuring the output of the CKP sensor so there is no math involved.
 
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