charging circuit

hi guys, i'm new. just finished a resto on 1973 850 roadster, except i have a problem that seems to have stumped the best in australia. charge rate is 17 volts and cooked the new battery after run-in of 950 miles. so far, tried 3 new zener diodes, triple checked all earths, proxy'd wiring loom, etc. run out of ideas, begging for help. Neil Siddall, Email; jansidptyltd@bigpond.com.au (please info my Norton mechanic - Charlie Osterfield Email; costerfield@bendigos.net
any advice welcomed, thanks, neil

You are on the right track as the purpose of the zener is to turn excess current into heat and prevent overcharging the battery. Were the zener diodes your replaced failed or did you not try to test them?

The zener should be wired in parallel with the battery and needs to be mounted to a good heat sink. It is a good idea to apply heat sink compound to the base of the diode so it makes good contact. If the zener cannot dissipate the heat it will fail.

The ground strap to the Z-plate should not be fixed to the nut on the zener diode, but to one of the mounting bolts.

If you are seeing 17 volts the diode is not bleeding off the excess current.

Also make sure the rectifier is not bad. Remove it from the bike and get a good look to make sure the little wires that connect each plate are intact. I had that issue with mine. From the top it all looked good until I removed it and found one of the plate wires severed.

you "could" solve these problems by installing a boyer power box that gets rid of the rectifier and zenor diode, it is all in one!

Or a Podtronics or a Tympanium.

Or a Sparx...

thanks guys, i'll try your ideas and advise, neil