Alternator W terminal pics wont exceed 3200 rpm.

[BruceK]

Optically tested engine rpm to 3780 rpm. Tacho remains in perfect sync until near 3000 rpm then under reads all the way topping out at 3200 rpm.
Id think guage fault but the discrepency is mirrored in the sync guage which connects to both W tacho inputs. Can a diode in an alternator start breaking above certain rpm? I'll disconect the sync guage. Just in vase its interfering with the pulse signal.

 

[halcyon]

Optically tested engine rpm to 3780 rpm. Tacho remains in perfect sync until near 3000 rpm then under reads all the way topping out at 3200 rpm.
Id think guage fault but the discrepency is mirrored in the sync guage which connects to both W tacho inputs. Can a diode in an alternator start breaking above certain rpm? I'll disconect the sync guage. Just in vase its interfering with the pulse signal.

Passing question, what happens to the output voltage during the above test ?

Brian

 

[BruceK]

Not something I tested at guage. Voltmeter climbs to ~13 V but batt monitor shows 14.4 or above.

 

[halcyon]

Not something I tested at guage. Voltmeter climbs to ~13 V but batt monitor shows 14.4 or above.

Could be field diode failing, depending on alternator, it may regulate voltage by cutting rotor feed pulses, if the volts stopped rising at the same point you have something to look at, a main neg diode could be failing shorting field diode pulse above a certain frequency, but not likely.

Brian

 

[BruceK]

Thanks Brian.