Early Triumph Alternators

This is a diagram lifted from the Triumph 650 manual. It shows a 3-wire alternator, with output wires being the main two, G/W and G/B, always connected,

and the third wire, G/W, connecting an internally paralleled set of coils, A and B, during periods of high demand, when they're connected by switching. Note that the actual connections to the lights or ignition circuit are not shown, just the shorting or wiring into parallel with the main pair, C, depending on demand of the lights. This appears to have been a primitive voltage control trick.

When the ignition is on, and the headlight is off, A and B are shorted in parallel, which must increase the field magnetism for coilset C, but which at any rate would serve to reduce the total output of the alternator to the rectifier.

When ignition and headlights are on, it will be seen that all 3 pairs of alternator windings are connected in parallel, making for maximum alternator output into the system - into which the output is passed by means of the G/B and G/W wires through the rectifier.

What this tells us is that the 3 pairs of coils may be connected in parallel, and the output passed to the AC terminals of the rectifier, provided voltage regulation is incorporated on the rectifier output. The problem will be to figure out which two of your alternator output wires wires want to be connected together, using the third single wire as the other side of the output. This would be, in this diagram, using the G/W wire as one output, and the G/Y and G/B connected together as the second output.

It seems to me that, if the wrong two wires are connected and used as an output, no voltage at all will be developed, or a very slight one. If the two proper ones, corresponding to the bottom ones in this diagram, are connected and used as an output, thus paralleling all three sets of coils A, B, and C, the best output voltage (and current potential) will be developed.

So, the procedure looks simple enough to me. Start up bike, with a voltmeter handy. Take it to ~1500 rpm, and connect voltmeter, on AC, to the pair of wires which will indicate best voltage. Then, with engine still running, try connecting the third wire to each of the two now connected to the voltmeter one at a time. The combination which gives the best voltage is the correct one. Make a note of the output voltage at 1500 and temporarily raise the rpm even more to see what sort of max voltage you can have at reasonable (~2500) rpm.

Now, connect the twin pair permanently by soldering to one of your AC output wires to the rectifier. Connect the other wire, the single one, to the other side, and you're all ready to work on voltage regulation.

What was the best open voltage you got from the alternator during the a above testing? If it was in the neighborhood of 18-20V, you can have a 12V system. If only in the 8-10 range, you'll have to settle for 6V.] In either event, using a Zener diode of the correct voltage will regulate your output - connect it in parallel with the battery, and be sure to heatsink it properly, and, if using a Lucas Zener, (I know of no other Zener set to regulate 6 or 12 Charging voltage) be sure to remember that you'll have a positive ground system, meaning the Zener case is +, and the "hot" terminal negative. You can use a capacitor as described elsewhere in this series of articles, either in conjunction with or as a substitute for a battery.