MOSFET? What exactly is that? I knew the term from the audio industry but I figured I'd copy and paste the information verbatim for the purposes of explanation. From wikipedia:
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The metal–oxide–semiconductor field-effect transistor (MOSFET, MOS-FET, or MOS FET) is a transistor used for amplifying or switching electronic signals. The basic principle of this kind of transistor was first patented by Julius Edgar Lilienfeld in 1925.
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Fine, that's what it is. What does it do? Again from wiki:
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In MOSFETs, a voltage on the oxide-insulated gate electrode can induce a conducting channel between the two other contacts called source and drain.
How does this affect a regulator rectifier? Well, the vast majority of Regulator/Rectifiers use a 'shunt' type regulator. What this does is shunt (source) voltage directly to (drain) ground when voltage exceeds the rating they were set for. This makes them hot as they dissipate the heat generated by constant shunting to ground.
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In actual operation, they shunt until there is no more voltage and then resume operation. This can be a bad thing because when the regulator is shunted, the battery is not getting charged. If you add more drain, the regulator will actually shunt less and run cooler. Either way, the battery, which has to be maintained at a specific level of charge for normal operation, is not getting the amount of charge it needs. Factor in malfunctions which occur relatively frequently in any kind of mechanical switch and the benefit of using a MOSFET type switch becomes more clear.
The MOSFET switch shunts also, but less frequently and only until voltage returns to an acceptable level, not to complete dissipation. The result is, it runs cooler, and it is much more effective as a regulator, delivering continuous voltage to the battery, regardless of engine speed. With a standard shunt type regulator, the charge rate at the battery actually goes down with an increase in engine speed. It's more effective at idle rather than full throttle.
I did some online research and found that all available MOSFET type R/Rs are made by a single company in Japan. Shindengen is the name of it. Suzuki uses a MOSFET type too, but the manufacturer of theirs isn't on the RR itself. That makes identification nearly impossible.
Honda, Kawasaki and Yamaha all use Shindengen RRs in varying part or model numbers. These seem to range from an FH0001 to an FH0018A. The FH0001 can be found on R1s prior to 2006. It's huge though. The CBR/RR models use an FH0014A and the ZX6R an FH0016A. The most common ones used in the conversion are from either the R1 or the ZX10, that an FH0012A and an FH0010A respectively. There are others out there, including an FH0008A that I've seen available on Ebay. Any of these would be worth the $50-$70 asking price to do the conversion.
There is some conjecture on the web about the output amperage of these RRs. Some claim that the FH0012AA is 50A but some of the others to be at 35A. I read somewhere that Shindengen states they are 40 to 50A in all cases. Whether this is the case or not, I don't have any of these units in my hand with a test lead and my digital Voltmeter to test that claim. There are kits available now on Ebay also that include the RR and all the associated wiring, terminals and fitting to make the conversion work. Roadstercycle is the name of the site. Also, it was suggested that some sort of volt meter be added to the bike to monitor voltage being sent to the battery.
Further there is a company called Eastern Beaver that sells connector fittings and terminals. Some are packaged into kits also for just this job. Current models from the big 4 all have this type RR installed going back to 2006. Some going back to 2003 or 2004 depending on the model and manufacturer. I don't know about any of the Euro 4 doing the same. (BMW, Ducati, Aprilia and Triumph) Nothing I found during my research of this topic indicated that was the case. In fact, several forum articles I found indicated that this mod was being done on Triumphs, Aprilias and Ducatis. I don't know about BMW. I didn't see anything to indicate that.
The Stator (alternator in car lingo) creates an AC current by passing magnets over coils of wires while the engine is turning. The VR (Voltage Regulator) Regulates the voltage and to some degree the amperage created by the stator. It does this in order to not cook the battery. The faster the motor spins the more voltage it creates. Batteries shoul not be charged much higher than 14v. The stator without a regulator could run away to voltages of 24v+. Voltages higher than 14.5v will burn out a battery quickly. The shunt regulator basically shorts out all voltage over the limit of 14.5v which in some cases is shorting a lot of voltage and amperage to ground which creates a lot of heat. The Mosfets basically do the same thing but with more finess than brute force. They turn on and off several thousand times a second to keep the voltage steady. The Mosfets do not need as much power to operate and such can operate at lower rpms.
After your next ride, feel how hot your vr is. They get very warm if not hot. They are engineered just good enough for the heat they have to endure. The better way there is no significant heat therefore less stress and less possibility for failure. Its taking something that may very well break and replacing it with something that probably won't ever break. Less heat equals less stress in electronics.