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1974 850 Commando alternator wiring

Submitted by gary_standley on Tue, 03/02/2015
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Commando

I have just in the process of fitting a new wiringloom to a bike I purchasedlast year. Unfortunately I didn't take enough notice how the bike was wired before I removed the old loom and have nowdiscovered the bike has a 3 phase alternator & Lucas 3DS5 rectifier fitted. Can anyone adviseme how to connect the alternator to the rectifier etc. The alternator has 3 wires White/Green, Green/Black & Green/Yellow also 2 Zeners mounted on the right side rear foot rest plate.I assume the 3 wires from the alternator go to the 3 small connectors on therectifier and the Zeners are connected to thelarge connector on the rectifier (two wires). Therewas an additional wire connected to the large spadeon the recifier (Brown/Blue I think) but don't know where this was connected to. Any advice please would be very much appreciated.

KR Gary

Submitted by john_holmes on Tue, 03/02/2015

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You can fit any of the 3 alternator wires to the 3 individual AC terminals on the rectifier as all it does is rectify the AC to DC, its only on the 2 phase with 3 wires that you have to follow the original wiring. On the modern 3 phase recitiers with wires coming out of them the 3 phases are all yellow. The Blue/Brown ends up at the battery.

Submitted by gary_standley on Tue, 03/02/2015

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Previously john_holmes wrote:

You can fit any of the 3 alternator wires to the 3 individual AC terminals on the rectifier as all it does is rectify the AC to DC, its only on the 2 phase with 3 wires that you have to follow the original wiring. On the modern 3 phase recitiers with wires coming out of them the 3 phases are all yellow. The Blue/Brown ends up at the battery.

John

Further thought, you say a 2 phase alternator could have 3 wires. I have assumed that because my alternatorhas 3 wires and the rectifier is a 3DS5 which I understand is3 phaseand the head light is a H4 Halogen that it must be a 3 phase alternator. Could I be wrong and it's actually a 2 phase alternator with 3 wires connected to a 3 phase rectifier? Is it possible to do this? I gues the only way to be sure is remove the primary and stator and count the segments which I think should be 9 if it is 3 phase alternator.

Submitted by gary_standley on Tue, 03/02/2015

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Thank you Tony. I did read this thread previously but wasn't 100% sure I fully understood the set up. It now makes more sense reading it through again and OK with the wiring for the alternator/rectifier& zener's. What I am not sure about is that the new loom has 3 wires running to the connection point for the alternator. Two of the wires go to the rectifier which is fine but the 3rd goes to the warning light assimulator.Looking at the wiring diagram in the Norton workshop manual there is a Green/Yellow wire runs from the rectifier to the assimulator. If I have got this right then the 3rd wire in the new loom needs connecting to a double connection with the Green/Yellow from the alternator. Or have I got it wrong?

Thanks Gary

ps Spooky the other Gary had the same problem.

Submitted by john_holmes on Tue, 03/02/2015

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The single phase alternator has 6 coils so when you take ithe stator off you will see 6 steel cores on the ID, a 3 phase has 9 coils and 9 steel cores on the ID. You can use a 3 phase rectifier as a single phase rectifier by just connecting to 2 terminals, this gives you a spare set of diodes if one set go bad.

Submitted by gary_standley on Tue, 03/02/2015

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Just removed the primary cover and can confirm it is a Lucas 3 phase alternator. Should be OK now with the wiring. Thanks for everyones advice.

Gary

 


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