paso alternator is it single or twin phase ?
Any one know ? as I need a new regulator.

Depends, some are single some are two phase, ST2 after the first 2 years went to 3 phase which is a big deal to convert to. Does not make a difference as to which regulator you need, only the way it gets wired up is different
The very best regulator is a Mosfett hanging in a good airstream

All Paso and Sports are single phase alternators. Two wires. Each phase 180 from the next
There is no such a thing as two phase.
Later model Ducatis are 3 phase, with 3 wires. Each phase 120 from the others.

And yes, you can use a 3 phase R/R on a single phase system, just use 2 of the leads. As long as the R/R is rated for enough wattage.
But you can not put a single phase R/R on a 3 phase alternator. You will only get 1/3 of the power out.

Cheers, Phil

I stand corrected. There is such a thing as 2 phase power.
It takes 4 leads and has two single phase circuits that are 90 degrees out.
But not likely on a motorcycle.
http://en.wikipedia.org/wiki/2_phase_power

Hi guys, A little confuseing for a non electrical person,
But I got there in the end,
I had a spare boyer reg/rec fitted it it seems to work fine.
Thanks.

The red wire is a common centre tap point to both the yellow wires. Check this diagram for the Electrex RR51 regulator which connects the 2 windings in parallel.

thats interesting, on the electrex diagram both windings connect to the same terminal on the regulator and common to the other, on the original wiring diagram it shows 3 separate connections...I think the factor that determines how many pulses you get (1 or 2 per rev) is how the stator has been wired up...ie two windings in series going the same way or the second winding reversed...I still remember the right hand grip rule from trade school

I am not sure about the '3 wire' connections from Electrex. The standard Energis reg/rec has two yellow (phase power) and one Red that is for voltage comparitor (warning light circuit). Simply joining the red to a yellow and the yellows together is not to be done! Even if they are right to say the phases are the same (0v diff) it does no harm to treat it as a 2 phase alternator, wire it up as they have and it could make flames. Besides, how are we to measure the alternator output with a static engine?

The reasons for the centre tapped alternator winding has to do with the way the Ducati Elettrotecnica rectifier/regulator works. It uses a 2 diode circuit (actually SCRs I believe) instead of a bridge rectifier.
So it is wired like this;


More conventionally a bridge rectifier is used like this;


For clarity only the rectifier part of the circuit is shown.

its all about the heat in the stator and the regulator