Zener Diode location
- Thread starter Wolfman
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Zener diodes dissappait heat thus need a large lump to dissapait the heat. I assume someone looked at the two ******* great vastly over engineered rediculously heavy footrest support plates and thought 'Ah now there is a real heat sink!. Now whether they also thought to run an earth wire from the heat sink back to the main earth point on the frames......it would NOT suprise me if they relied upon the plate making contact with the frame to do this but I could well be wrong. Paint does not make a good electrical connector as many a car and motor cycle owner has learnt over the years as bulbs give out little light etc. Copper wire is a good electrical conductor....
Have you never heard of those U.S.A. made Tympanium regulators? (Look them up on the web). Small lumps that take the place of the rectifier/s and zener/s. They were / are available positive or negative earth along with single or three phase. I and friends fitted them a great many years and they have to date, as far as I am aware, worked perfectly. Mind you in those days when we first fitted them the Pound against the Dollar was vastly different ..........
Have you never heard of those U.S.A. made Tympanium regulators? (Look them up on the web). Small lumps that take the place of the rectifier/s and zener/s. They were / are available positive or negative earth along with single or three phase. I and friends fitted them a great many years and they have to date, as far as I am aware, worked perfectly. Mind you in those days when we first fitted them the Pound against the Dollar was vastly different ..........
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J. M. Leadbeater said:
Those "ridiculously heavy support plates" weigh about 24 ounces each! :roll:
J. M. Leadbeater said:
You would be wrong.
All standard Commando harnesses have a positive return (red) wire for the Zener (Mk3s have two Zeners so have two returns).
The return wiring going to the battery positive terminal regardless of any other earth/return connections on the frame (the exception being the Mk3 where the final return to battery positive should only be through the heavy gauge positive starter cable).
maylar
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The right side footrest attaches to the Z plate with 2 studs (front 2) and one through bolt (rear hole). The red ground wires for the zener attach to that bolt on the back side, secured with a nut and washer. Those red wires go back to the battery and I think to the engine ground at the head steady.
The factory even saw fit to machine a flat spot on the Z plate for the zener, to insure it had the best possible heat transfer rather than rely on the casting to be flat. Aluminum is a great heat sink.
The factory even saw fit to machine a flat spot on the Z plate for the zener, to insure it had the best possible heat transfer rather than rely on the casting to be flat. Aluminum is a great heat sink.
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Wolfman said:
A few companies make boxes that do that and they are inexpensive, about $60 or so and also is a way to convert to negative ground if desired (they can be wired either way)....am still running the stock items on my Commando too as they work fine.
FWIW can remember reading somewhere that the Mk3 dual zener diodes need to be replaced as a matched set...makes sense, if the diode breakdown curves were much different one would be doing all the work dissipating excess power and probably would not live long.
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bluto said:
Not the 850 Mk3 charging system, as the diodes are on the AC side, they don't need to be a matched pair.
If two Zeners were to be connected to the DC side of the rectifier they would have to be a matched pair, however, this system wasn't used on Commandos but was a feature of the Lucas 3-phase RM 24 'Powerbase' conversion kits.
http://atlanticgreen.com/images/lucasrm24.jpg
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I like the Zener as well. Mine quit after 40 or so years and I put a new one on there. They are not cheap though. The one from Canada was $40 or so. You can get them much cheaper in the correct voltage range but have to add the 1/4 inch or so stud to mount them per original. If you run the stock set up, be aware that if the Zener fails in the closed position, shunt to ground mode, you will immediately blow your trusty fuse. All forward motion will cease at this point. I am talking now about a 71 Commando with one fuse. It behooves you to understand how to hot wire the ignition system so you can avoid the tow truck ride home. I have a spare spade terminal tipped wire permanently hooked to the negative battery post. In the event of a dead short or zener failure, I merely pull the white wire from the ignition switch and plug it into the negative battery wire to power the ignition system. Problem solved, ride home on battery power only. Been there done that. Never been stranded and nothing fallen off in many years of Norton riding.
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steelcap said:
Although there is a battery positive wire included in the Mk3 harness and one is also shown on the wiring diagram, if there is a working starter motor then it is not a good idea to also have a light gauge positive return wire connected to the battery as under certain conditions (a loose or corroded heavy gauge positive cable terminal) the 100+ Amp starter motor current will attempt to return to the battery through the harness return wiring (and the fuse won't blow because it's on the negative side of the battery) which can result in a burnt-out harness or even cause the bike to catch fire!
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