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Zener Diode/Podtronics

Home Forums TR3OC Members Forum Zener Diode/Podtronics

This topic contains 9 replies, has 6 voices, and was last updated by  Peter Gill 1 month, 2 weeks ago.

  • Author
  • #8975

    Gareth Holder

    Hi All,

    Took the T150V out for it’s first real shakedown ride. Purring along at 80, all of a sudden I was dead in the water. Fuses blown. Replacing a fuse with the ignition off just blew the fuse again, which pointed to an earth fault, Back in the garage, I traced it to the zener diode. It was brand new, but would blow the fuses as soon as I attached the leads to it. It seems to have full continuity so is just earthing out to the frame. I’m pretty sure it shouldn’t do this, but I could do with a pointer or two. I can’t test it on the bike because it just blows the fuses as soon as I try to connect it.

    I’ve also been reading about Podtronics products that replace the zener diode and rectifier in a single black box unit. Has anyone here run those with a Boyer ignition ? Or does anyone know of another similar product. I’d like to replace the old charging system with something a little more reliable.


  • #8977

    richard beard

    I think we all have to realize that the Zener diodes and slice type rectifiers we use on our triples are probably the originals and therefore probably 45-50 years old.

    So no bad reflection on them really if they give out now.

    What do you replace it with?

    A Podtronics is a good solution and as you say replaces both the Zener diode and the rectifier.

    The charging system is independent of the ignition system.

    The Podtronics can be used with Boyer, Pazon, Trispark, Lucas Rita or points ignition systems.

    I have fitted Podtronics units to a dozen or so triples and twins and found them to be extremely reliable.

    You just have to match the spec of the Podtronics unit to the output of your alternator (single phase/three phase, output wattage etc).


  • #8980

    Angus McLeod

    You can use a 3 phase regulator/rectifier with a single phase alternator, just use any two of the three wires that go to the alternator.

    I use Nippondenso things you can pick up at autojumbles for 2 or 3 pounds. You are taking a chance that they work but all the ones I’ve bought have.

  • #9011

    nigel wheatley

    its worth checking that the zener is earthed on its mount to the bottom yoke. I had something similar happen (lots of blown fuses), the zener checked out fine but we discovered on removal that (after 40 undisturbed years bolted to the bottom yoke) the earthing connection surface was corroded – after a clean up it worked fine again. But as others say I did replace the zener in any case with the  more modern combined regulator/rectifier from Paul Goff’s website (you don’t need the expense of the Podtronics unless you want to run without a battery)


  • #9021
    David Patterson
    David Patterson

    Actually you can test the zener on the bike. As mentioned, first ensure a solid ground connection. Now connect a test light in series between the negative lead and the big terminal on the diode. If the light comes on the zener is bad.

    I guess I’m blessed. In twenty years with my ’74 Trident I never replaced one. I replaced a LOT of rectifiers though. My current ’72 has the stock charging system. It ran rough on a ride the other day, fried another rectifier. I have some good spares, replaced it today and cleaned up the common to the zener, works fine now.

    My other two Brit bikes use modern rect/regs. The BSA has a 3-phase system using a box from some model of Yamaha which uses a permanent magnet alternator. My T120 has the stock alternator using a 3-phase Podtronics unit with only two yellow wires connected. They also work fine.

  • #9026

    Gareth Holder

    I took the Zener off and checked it for continuity. It was just earthing directly to the frame. It was actually a brand new Zener Diode, and I’d just rebuilt the entire front end and rewired the bike with a fresh Lucas harness. Like you say though, the plate rectifier was original, so it very well may have been a failure of that that fried the diode, rather then the diode just failing. However, I’ve replaced them both with a new Lucas unit that does the job of both. I haven’t fully road tested it yet, but on the stand at 4500 revs, I’m getting about 22 volts at the battery and the unit heat sink warms up nicely, so we’ll see where this goes. As this point, all the wiring and associated components are brand new.

  • #9027
    David Patterson
    David Patterson

    22 volts!?!

    Are you sure that the unit you bought includes a regulator?

    The supplied DC should never exceed 15V. All of mine go to 14.5V and stop.

    Is this with the stock alternator?

  • #9043

    nigel wheatley

    22 volts will quickly fuck up the battery and probably other parts too

    Back to my original thoughts about earthing – if the zener is new than it is either faulty (and this is not unknown) or something else is wrong> if you have been on a rebuild, have you powder coated the bottom yoke by any chance? If so then the zener won’t be able to earth properly.

  • #9048

    Peter Gill

    Recent information from Tri Spark (check their Australian website directly) suggest the older Podtronics regulator/rectifier can cause interference with their ignition. They recommend the newer Podtronics unit (with combined capacitor) or an additional capacitor to fit in addition.


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