2 wire regulator with 3 wire alternator?

[DaveR]

I’ve been having a few electrical & starting issues recently, finally pin- pointed as a fried regulator/ rectifier. I have sourced a mosfed type from eBay, but it’s taking a while to turn up. In the meantime I have ‘borrowed’ the one from my 900ss ‘project’ (where project means in bits in the garage & has been for 2 years).
The one off the 900 has only 2 wires, whilst the S4R has a three wire alternator. My question is will I be doing any damage running the bike using this set up, I am seeing 14.3V at the battery with the engine running
Dave

[manwithredbike]

Dave, it's been a while since i worked at alternators etc and i've never worked at ducati ones but, i think your 3 wire alternator is three phase. The 2 wire rectifier will be for a single phase one which the older ducatis were. You would get voltage ok but you wouldn't be drawing from all three coils of your stator in a balanced way which could possibly damage it under load.
Anyone, please feel free to correct me on this, i'm rusty on this stuff nowadays.

[utopia]

I'm fairly crap at electrics too but I can at least confirm that Phil is correct about the three wire alternator being the later, three phase one and the two wire system being the earlier, single phase system.
Beyond that I can't help much other than to say that if it were my bike I would wait for the correct reg/rec rather than risk using potentially mismatched components (any more than you already have done).
Both systems are somewhat prone to failure anyway so I would be very wary of taking any liberties with either.
Hopefully someone with better knowledge of electrics will chime in shortly.

[Mr Gazza]

I also have only a tenuous grip on electrical theory, but I think I would be much happier running a three phase reg/rec with a single phase alternator and not the other way round.

Those yellow wires melt when there is an increase in resistance and this often damages the rectifier. Is having the wire not connected, the ultimate resistance? The power from those alternator coils on that phase has got to go somewhere. Would it work better (or at all?) if you ran the spare wire from the alternator, to earth?

It all sounds like dodgy practice though. It would be a shame for your nice new reg/reg to arrive and then have a fried alternator and/or a fried reg/rec for the SS.

I feel your pain though. I know you want a ride on Sunday.

[slob]

If the third wire isn't connected to anything, you've turned the three phase alternator into a single phase one. With no circuit on two of the coils there's no current flowing in them and they're not making power, so no problem. The risk is whilst clearly you're getting good AC voltage that the reg/rec is turning into ~14V DC, you're probably only getting 1/3 of the wattage(amps) out of the active coil, so over an extended period your battery isn't going to receive enough charge to keep it topped up. I wouldn't head off on any long trips until you have the right reg/rec.

[jerry]

I’ve been having a few electrical & starting issues recently, finally pin- pointed as a fried regulator/ rectifier. I have sourced a mosfed type from eBay, but it’s taking a while to turn up. In the meantime I have ‘borrowed’ the one from my 900ss ‘project’ (where project means in bits in the garage & has been for 2 years).
The one off the 900 has only 2 wires, whilst the S4R has a three wire alternator. My question is will I be doing any damage running the bike using this set up, I am seeing 14.3V at the battery with the engine running
Dave

Many of the MOSFET ones on EBAY from china that are cheap are fakes and a shunt types and burn easily ,, beware genuine ones for Ducati, triumphs or yamaha R1 R6 are always about £100 shindengren is the make

[DaveR]

Thanks for the info & advice which I intend to follow, ie not use my bike until the replacement arrives. I have had a tracking link that shows that after visiting 4 US states it has finally left for the UK. Due to me by Friday🤞🏼
Jerry I had seen that, this one cost around £100, is secondhand, hope it works.
Dave

[alan s4]

Mine came from a Yamaha R1. I also relocated under the seat on the S4, I needn't have bothered as it is only slightly warm to the touch with the bike running. The old one would set your pants on fire it got so hot!

[Darren69]

Thanks for the info & advice which I intend to follow, ie not use my bike until the replacement arrives. I have had a tracking link that shows that after visiting 4 US states it has finally left for the UK. Due to me by Friday🤞🏼
Jerry I had seen that, this one cost around £100, is secondhand, hope it works.
Dave

£100 for a s/hand one? Jeez you should have said I have a spare 3 wire one which I think would be ok for £30, not tested but fairly easy to do a diode test which would prove it could be potentially ok.

I have a couple of 3 wire ones and a 2 wire one which I am keeping as a backup but I have a 3 wire spare one for what it cost me. I know it's a gamble but hey ho? :)