Topic: What's the deal with the 750K alternator.

[rhinoracer]

All the threads I read say it starts charging at 3k rpm.

Why can't it charge at lower revs? Why does the rotor have to be that heavy?

[bryanj]

Its heavy to give flywheel effect and it needs the metal to mass to alter the field.

It dont charge till 3,000 cos thats the way it was designed, your car alternator is doing 3,000 at idle speed due to pulley ratio

Honda thought that all motocylists were nuts and would be riding as fast as possible

[eldar]

Well we do dont we?

[Jerry Rxman Griffin aka MuthaF'er]

There are cut down rotors out there from such guys as Yoshimura, etc. Obviously lighter weight but I can't attest to how it interacts with the rest of our stock charging system. ie what voltage it puts out or whether or not it accepts the starter clutch. I'd love to hear from some of the guys about this if they have had any experience using one. Is it SCondon that was planning on using one??

[Jonesy]

Mark (HondaMan) played with lightened alternators. I think they do drop off in charging capacity, as he commented about how it barely put out enough juice to keep the battery alive until the end of the race.

[dusterdude]

because its a bassacwards design,it should have been a permanent magnet alternator and its not.

[Hondell]

While a permanent magnet device may charge at low RPM, it's output is proportional to the speed it spins. Set it to produce 14.5 volts at 500 RPM and at 8000 rpm It may produce 200 volts. Very difficult to regulate easily like an exited alternator.

[eldar]

That maybe but you still use a voltage regulator so it is a null issue. Had a vr go out on an alt and the faster I drove, the brighter the lights and faster the tape deck would go and everything. Blew out a lot of headlights which I conveniently got replaced all the time by target for free!

[dusterdude]

While a permanent magnet device may charge at low RPM, it's output is proportional to the speed it spins. Set it to produce 14.5 volts at 500 RPM and at 8000 rpm It may produce 200 volts. Very difficult to regulate easily like an exited alternator.

my harleys have never had a regulator issue.

[eldar]

I suppose the whole idea is to help maximize engine power in some way. Sure would be simpler with a permanent mag alt though.

[Hondell]

Your Harley probably had a generator. A high current regulator that works at those voltage extremes is hard to manufacture. That is why field type regulators are used.

[Ricky_Racer]

I've seen European endurance racers with a shortened left side cover, presumably for a very lightened flywheel, with an external pulley-equipped alternator mounted behind the carbs and driven by a v-belt from the flywheel.  Has anyone tried this approach?  Might be kind of a trick solution...  RR

[Pinhead]

Get rid of the POS contact breaker point regulator and install an electronic regulator and the alternator will charge a lot sooner in the RPM range. Check my sig.

[Bodi]

The induced field design gives up a bit of efficiency but is mechanically simpler than rotating coil designs plus there are no brushes to wear out.
The permanent magnet system is common now, magnet metalurgy is much better and the regulator technology has advanced a lot. Regulator technology back then had only a crowbar system for permanent magnet alternators, dumping excess output into a resistor to make heat. The GL1200 is well known for problems with it's PM/crowbar alternator. The problem for a sport bike is that the alternator makes maximum power all the time, and that robs horsepower that should go to the wheel.
New technology uses a switching regulator that doesn't waste power. But we're talking about 30 year old machines here, right?