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Sizing A Three Phase Bridge Rectifier and Mosfet Question

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wreckedafier

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I have a motorcycle that burns through standard diode based bridge rectifiers.I have checked and rechecked the stator.Everything is in spec.I have even removed it and visually inspected it.It's good.

The stator output maxes out at 89vac on each phase at 5000 rpm.The voltage varies from low 40's vac at 1200 rpm and occasionally I measured 92vac at 5000 rpm.How many watts(or amps) should I expect from this stator?I want to size a continuous duty rectifier to the system requirements.

I would really like an efficient mosfet based rectifier, but I don't get how they work.I've read for three days on mosfets and rectifiers.Is there a diagram for dummies somewhere?I just can see paying $120+ for a mosfet based rectifier.


BTW,I searched this site and I have not found my anwsers.
 
A typical bike alternator has to put out maybe 20A ( about 250W) ballpark. depends on the bike. But that's on the DC side. The AC side will have a lot higher current. If it is a basic single phase (two AC wire) alternator output, the AC current is about DOUBLE the DC current quoted. If it's a three phase (three AC wire) type, the AC current is maybe 25% more than DC current.

I would recommend a 400VAC rated bridge, 50A would be good for single phase, 40A for a three-phase.
 
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I would really like an efficient mosfet based rectifier, but I don't get how they work.I've read for three days on mosfets and rectifiers.Is there a diagram for dummies somewhere?I just can see paying $120+ for a mosfet based rectifier.


BTW,I searched this site and I have not found my anwsers.
About 99.99% of motorcycles use a shunt regulator, where SCR(s) are used to shunt "excess" alternator output to ground to constantly regulate the system voltage. A bike uses a permanent magnet spinning in a coil so there is no way to "vary" output current with a small current bias. The alternator basically just cranks out current and whatever isn't needed by the bike gets shunted to ground through the SCR.
 
I have four of the same motorcycles.They all need new rectifiers.Can I use a SQL40A rectifier and a heat sink to make my own set up?Will the output voltage fall in the 13.9 to 14.9 volts that my motorcycle requires?If I need a regulator,which one?
 
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