Commando wiring

Sounds like someone has fitted the MK3 uprated alternator and also fitted the matched pair zeners as the output exceeds the capacity of a single Zener, so you will need to look at the MK3 wiring diagram for the charging circuit and then try to see how it compares to yours.

The Mk 3 has a single phase alternator to the best of my knowledge so two wires would be correct. (three phase would be three wires) I thought that the Mk 3 utilised the two matched zenners as a half of the wheatstone bridge (rectifier) not sure what forms the other two diodes. To be honest I would treat yourself to a modern regulator rectifier unit as sold by Paul Goff or a Boyer Power Box. Zeners and rectifiers are dark age stuff now, unless you want to keep that original look. I presume you bought the bike to ride not look at so a proper workshop manual from Andover Norton would be money well spent.

Al Oz and Goffy sell an excellent modern single phase rectifier, does away with the Zeners, it's also easy to mount being smaller than the podtronics unit. Coupled with a BSM (Battery Status Monitor) you can disconnect the warning light assimilator and have less wires, less connections, less loss and thus more confidence in what your charging circuit is doing. I have done this upgrade in the past year and wish I had done ages ago to my MK3 as it highlighted that the old wiring in the charging and control circuit was past its sell by date.

The MK3 wiring diagram is in the back of Haynes in the MK3 supplement unless you have a very old version. Whatever replaces the zeners will need to handle the max output of the MK3 alternator which probably rules out the Powerbox. If the zeners work then keep them.

Previously david_evans wrote:

The Mk 3 has a single phase alternator to the best of my knowledge so two wires would be correct. (three phase would be three wires) I thought that the Mk 3 utilised the two matched zenners as a half of the wheatstone bridge (rectifier) not sure what forms the other two diodes. To be honest I would treat yourself to a modern regulator rectifier unit as sold by Paul Goff or a Boyer Power Box. Zeners and rectifiers are dark age stuff now, unless you want to keep that original look. I presume you bought the bike to ride not look at so a proper workshop manual from Andover Norton would be money well spent.

There are a number of 'misnomers' in this thread but the most are in this post. The Zeners are NOT matched when used with the high output MK3 Commandos (and JPN) The matched Zeners were only used in parallel with the high output three phase system as sold by Mistarl engineering (several years ago). The traditional bridge rectifier is not a 'wheatstone' bridge, either. The Boyer power box will handle theoutput from the single phase RM23 (as used on MKIII Com.). Rectifiers and Zeners are no more 'dark age' devices than these 40 year old machines. There are a couple snags with Zeners-they can have high or low voltage-a high one will give you a 'well' charged battery, a low one will give the symptons of 'no charge' Zeners are becoming scarcer and expensive, and their wiring is a little more messy than a modern recg/rect. A basic single Zener system in working order has no issues, leave it alone.

One small area where the RM23 high output (MKIII Com) system using two Zeners (on the alternator side) is at a disadvantage is that this system does run at a slightly lower voltage than would be prefered (due to the natue of the Zeners being part of the bridge) in this case, especially as the MKIII needs all the battery capability you can get, it would be worth converting to a reg/rect.

By the way 3 wires does NOT mean three phase, the RM19 (6V or 12V) has three wires. 9 pole pieces means three phase. ( I even used to sell a version of the RM23 single phase high ouput alt. with three wires at one time-yes the wires were GRN/YLW-GRN/BLK-WHT/GRN. I think Lucas had the worlds supply of these wires)

Al Osborn.