Frequency Counter

Actually, using a tap into one of the ac phases on the generator output sounds like an intriquing idea. I believe my frequency meter can do DC square waves as well as AC sine waves, but I will try the tapped generator line as it may work without any extra parts.

Post edited by: dnpurdy, at: 2007/07/12 16:12

A frequency counter can work fine on AC or pulsed DC (which is what the ignition creates). The counter just filters out the DC component. Once the DC is filtered, all that's left is AC.

The alternator does not put out sinewaves unless it is disconnected from reg/rect. While connected, it basically looks like square waves, but should still work fine.

The only problem is, if some phases start to shunt, the freq. counter may not acknowledge those pulses. It should work at idle with the lights on, since there probably won't be any shunting, but to work at higher RPMs you'll have to disconnect the alternator from the reg/rec and run the bike off the battery or an external power supply (or charger).

If the alternator will be connected to the reg/rec while testing, I would use one yellow wire and ground as the test connections. It should be a nice square wave, like Fig. 5 on this link:
www.geocities.com/loudgpz/GPZAltntrWaves...rnatorWaveforms.html

Post edited by: loudhvx, at: 2007/07/13 08:29

So I tapped the sense wire against one of the yellow stator output wires last night. At idle it was showing 117 hz @ ~ 1050 rpm. Any guess as to why?

Curiously, this is almost exactly 6 times the value I'd expect, but I can't think of any reason why it would register 6 for each crank rotation.

Post edited by: dnpurdy, at: 2007/07/13 17:32

Your stator has 6 pole pieces for each phase. The rotor has six magnets. For one rotation, each phase has 6 positive pulses ( and 6 negative, but the negative half of each pulse is near ground potential). So it looks like 6 square pulses per revolution. It should have been around 105 hertz, though, at 1050 RPM.