Rectifier

The original 6 volt system controlled the charge by having just one set of alternator coils to charge the battery and switched in more coils when needed to power the headlight. Most times, when a bike was uprated to 12v a zenner was fitted mostly to protect the battery from overcharging although this is a very crude way of doing so.

Typical wiring position for the time was to takea wire from the switch side (SW orWHITE wire) of the coil to the zenner. Fit the zenner on a good heat sink in a free flowing air position. This kept the zenner out of the circuit when the engine was not running. If you have a mag ignition you could simply connect the zenner to the live side of the battery.

Zenners control the rising voltage by dumping current to ground which is wasteful, a better way is to fit an electronic voltage control unit, which I would imaginecame supplied with wiring information and instructions.

For a buying tip, There are good quality 12 v controllers available from India which are fitted as standard to the Royal Enfield bikes. See Ebay ads.

Les

Thanks very much for the feedback as regards the crankshaft pillion puller.

If you still have the same original wiring system, then perhaps you can get a way with just the zenner diode and it is cheaper. It will require less wiring changes. It seems that only two of the six coils are used for yourbasic battery charging so the surplus current you need to sink (lose) does not amount to much, unlike some sytems that use the full alternator outputall the time.

Les

There appears to be a number of anomalies here. If you have a '12V' alternator then it would most likely have only two wires (connected to the bridge rectifier)then you would probably NOT have the original 6V control of the alternator output by switching the alternator. So yes you would need some sort of regulation. The Zener diode is not that wasteful, perhaps 10watts or so ie 1/7 of a horsepower!! Now is this really worth worrying about?? The modern regulator/rectifiers maybe will save you a 'couple watts' but they do tend to hold the battery voltage a bit low at times. Regulator/rects are more fussy on decent(or not!!) wiring. While Zeners can be very variable, ie a low voltage one is worse than a reg/rect while a high voltage one would keep the battery better topped up.

There is no reason to switch the Zener out of circuit, in fact the reverse would be better. Another NO NO is to use a straight Zener with a magneto. The lack of coil ignition load will push the Zener beyond its limits if you use it with the full output of a decent RM21 ie 12V alternator. A lot of the time people run old bikes with old alternators with low outputs and get away with it, but it is not recommended).

I sell a good regulator/rectifier for 12V and 6V sourced from China and tested by me, but do not abandon the Zener with out real reason.

AL Osborn A O Services.