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Three phase Regulator Rectifier on a single phase alternator?

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Hi Everyone,

Well after hours of searching the internet and reading all sorts of documents I decided that asking people who really understand electronics would be the best solution. Hopefully someone here can advise me on this situation.......

I have a Ducati which has a single phase alternator (it's a '97 model 748). The stock reg/recs frequently cook and die. There are several postings "out there" that suggest replacing the original (Triumph, Aprillia, Honda etc.) single phase SCR unit with the, no doubt better (in terms of heat factor) Shindengen FH012AA 3 phase Mosfet unit.

Disregarding the other wires for the moment, simply put, the two wires from the single phase alt are connected to two of the three pins on the reg/rec, and the other pin is disregarded.

The FH012aa is rated 40 to 50 amps, whereas the standard single phase reg/rec on my bike is around 30amps. I've seen where people have installed these regs on different makes of bikes and m/m tests show good, indeed improved output readings however since this adaptation seems quite new, there's not yet any feedback on this mod over longer periods. (that I could find)

I'm not very familiar with all the full wave, phase whatevers so my question is.... is there any risk in this practise?

I wonder whether connecting in this mannor means you're only using one phase and therefore the stated rating doesn't really apply as a consequence of not utilising it as a three phase device.

On a different note I'm also glad I found this forum, no doubt it will be a great help when I get around to fixing my amp.

Any help on this question would be really appreciated.

Thanks in advance.

Jo
 
In order to take advantage of full-wave rectification, you must have access to two wires (i.e. the coil cannot be internally grounded). Is yours that way?

I posted a complete design of a shunt regulator for a motorcycle alternator using a power FET on this web site. Find it in my posts...
 
Hi MikeMl,

I thought I posted a reply a few minutes ago but I must have done something wrong as it's not here. Anyhow, not absolutely sure if coil is internally grounded or not. Haynes manual says you can check continuity on both primary and secondary windings. Wiring dia illustrates the coil/s and plugs together. Plugs obviously directly earth but I'm not sure how to interpret the coil part as the illustration kind of incorporates the coil and plug together.

Does this help at all? Appreciate your advice. I'm not very electronics savvy so be gentle ...
 
I meant the stator coil which is part of the alternator; not the ignition coil.
 
I did think it strange asking about the "coil", of course didn't jerry at the time you meant stator coil. Of course!! Well in my defense it was about 3:30am or something.

No, I don't believe the stator is internally grounded. There are two wires comming from the stator to RR. Neither should read continuity with earth.

My concern is really whether running one of these 3 phase mosfet type of reg/recs from a single phase (2 wire) alternator could potentially do damage to any of the system's components?.

Also do you still get the same benefits from the reg in terms of the 40 - 50amps despite the fact you're only connecting two stator wires and not three as they are designed for?.
 
A single phase rectifier usually has 4 diodes, with only two conducting at any one time. A three phase rectifier has 6 diodes, with only two conducting at any one time.

Using a three phase rectifier on single phase means that the diodes take current half the time rather than one third of the time, so you should derate a bit. (That's a bit of a simplification, but it'll do for now). Using a 30 amp alternator on a three phase rectifier rated at 40 - 50 amps should be fine.
 
A single phase rectifier usually has 4 diodes, with only two conducting at any one time. A three phase rectifier has 6 diodes, with only two conducting at any one time.

Using a three phase rectifier on single phase means that the diodes take current half the time rather than one third of the time, so you should derate a bit. (That's a bit of a simplification, but it'll do for now). Using a 30 amp alternator on a three phase rectifier rated at 40 - 50 amps should be fine.

The concern is Regulator not Rectifier. His bike has a single phase alternator not a three phase alternator and the questions focus around using a three phase regulator on the single phase alternator.

Ron
 
Driver I see you took a look at the Shindengen site so Thanks for looking into it. I know that electronics are very specialised and it's best to get advice on these matters from people who have a good grounding in the fundamentals rather than presume it'll be fine.

I feel reassured it should be safe now so Thankyou all for your guidance.

All the best with your endeavours.
 
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