Uprated T120 Electrics

[Jim Griff]

Hi ,

I'm after a bit of advice with my 1970 T120. I haven't had it on the road for a few years and am slowly rebuilding it, albeit to an improved state. I've bought a low output 3 phase alternator as fitted to the later T140's and the later lucas solid state diode electronic heat sink assembly to better cope with the Boyer system, and to replace the old Zener Diode system.

My wiring harness fitted only has two conectors for the stator, so I assume now that I'll also have to re wire my bike to a more suitable loom. Which harness do I go for? When did they upgrade the T140 to this system?  

[L.A.B.]

I've bought a low output 3 phase alternator as fitted to the later T140's and the later lucas solid state diode electronic heat sink assembly to better cope with the Boyer system, and to replace the old Zener Diode system.

Hello Jim,

Can you give a bit more information about exactly what parts you have? Presumably you have the low output Lucas RM24 stator?
But what do you mean by: "later lucas solid state diode electronic heat sink assembly"?
As Triumph fitted a three-phase negative earth rectifier and negative earth single Zener when they introduced the first three-phase low output RM24 alternators, along with Lucas Rita electronic ignition.  

My wiring harness fitted only has two conectors for the stator, so I assume now that I'll also have to re wire my bike to a more suitable loom.

All you really need to do is connect the third stator output wire directly to a three-phase rectifier, or to a modern 3-phase reg/rec unit that replaces both rectifier and Zener?
However as I do not yet know what this item you have is ("later lucas solid state diode electronic heat sink assembly") then I cannot advise exactly what you need to do, so more info on that item please?

Which harness do I go for?

I don't see any need to change the harness for a simple three-phase upgrade?

When did they upgrade the T140 to this system?

For the 1979 model year production (so actually from July 1978) originally when they introduced the Lucas Rita and changed over to a Negative earth electrical system.

[Jim Griff]

Hi,

thanks for the info,  sorry for being so vague, I'm an Engineer by trade, but specialise in Aircraft mechanical stuff, so my electric knowledge is poor to say the least. I bought the upgrade stuff from a repuatble Triumph supplier up here in North Wales who specialises in belt drives. The kit comprises of a 3 phase stator (low output) a 3 phase electronic regulator to replace the zinc plate type and a 6" strip (or thereabouts) comprising of three electronic pots that I presume are diodes of some kind to replace the Zener system.

JIm

[L.A.B.]

The kit comprises of a 3 phase stator (low output) a 3 phase electronic regulator to replace the zinc plate type and a 6" strip (or thereabouts) comprising of three electronic pots that I presume are diodes of some kind to replace the Zener system.

OK Jim,

That's more helpful, but this three-phase electronic "regulator" must surely be the rectifier?
As the Zener (or Zeners) is (are) the regulator part of the system, and the "three electronic pots" you described sounds like the Lucas triple Zener pack as used with the later RM24 high output version alternators that Triumph fitted when they introduced the electric start models.
If what you have are in fact the Lucas 3DP 3-phase rectifier and XD715A triple Zener then they will only be suitable for use with a negative earth electrical system and your T120 would have had positive earth polarity originally,

So has the electrical system's polarity been changed to negative earth already, or do you intend to convert it to negative earth? As you will not be able to use those parts otherwise.

In my opinion, you would be far better off fitting a modern three-phase voltage control box, such as 'Podtronics' or 'Boyer Bransden 'Power Box' unit to replace the separate rectifier and regulator, as both the Podtronics and Boyer boxes can be wired to suit either positive or negative earth polarity systems.