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Honda CB750K5 Restoration by Royhall

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Bryanj:
The yellows have no connection to ground, its a 3 phase alternater with the 3 phases being each pair of yellow wires
A- B
B-C
A-C
 And that is the ac voltage INTO the rectifier.
If you want to check DC OUTPUT of rectifier its red(or red/white) to green BUT  not with battery disconected or the volts can go high enough to fry the diodes in rectifier

K2-K6:
That must be doing phase-to-phase then Bryan ? The peak reversal from alternating swop. Would that mean it's output would be something like 17 volts checked against earth ?

I think as Bryan has pointed out before, the assembly windings are usually very reliable, with any check to see that the resistance is correct and that the output is at parity for each of the three yellow, then the problem will ordinarily be located somewhere else.

Often the integrity of those first three inline connections going to the multi pin can be suspected, and need verification before moving down the line to see what arrives at reg/rec and if it comes out of there.

The manual doesn't suggest a check in voltage of three phase (just that resistance check) output, just an ammeter on DC line out of reg/rec.

royhall:
So if I disconnect the three yellows at the rec/reg and check the ohms are below 0.2 from that point it should check the entire circuit up to that point without having to strip the bike to get at it. If it fails that test then I will have to strip it back to find the problem, if not then I can check voltage from each yellow to earth looking for around 17 volts. Is that correct, will have a go this afternoon.

royhall:

--- Quote from: AshimotoK0 on October 02, 2023, 08:32:35 PM ---This is Honda Bulletin on 3phase alternator on SOHC Fours
https://www.dropbox.com/s/2oqrx5cvv7byqao/3-phase%20Honda%20Charging.pdf?dl=0

--- End quote ---
Thanks for that Ash. I had a read through and I think it may have helped, not sure.

Just to clarify something. The static voltage on the new AGM battery is at 13.1 volts. If this is classed as high voltage as in the document above, would that mean that the battery wont charge until the battery voltage drops as in scenario 3? That clearly shows no output to the battery. But don't forget the system I am on is a modern combined Rec/Reg so may be a different scenario.

BigAl (Alan):
The alternator wiring (3 yellow wires) are not connected to the frame/earth
To test - low voltage continuity, any combination should read 0.4 ohms (yellow to yellow x 3)
If you can carry out a high voltage test (100-250 volt) - any yellow to frame/earth it would confirm that the 3 phase windings are OK
Due to age a number of Japanese classics alternators are starting to fail... Image Kawasaki alternator windings (S1'S2s KH250's)

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