CB750 vs CB900 Charging Systems

[Half-Caf]

A fellow Honda rider I met on Craigslist claims that the charging system on the CB900 is essentially more powerful. Can anyone verify this?

"The Charging system only charges at rpms over 3000 which means much of city riding you are draining your battery unless you are reving the engine to keep it charging- its called the breakeven rpms-(the CB900f according to the owners manual charges at rpms over 1700 on the 1981 so if your new charging system is along those lines you may have less problems)"

[Re-run]

Well I doubt it is much more powerful if at all. The manual usually lists the output wattage of the alternator.
I also do not think the system starts charging at 3000rpm. My 78 starts kicking out charging at 2k rpm. I doubt they would have raised it.

[mikefootusa]

I find this odd as they both use the same parts.

[rich]

I've got a 79 750K and it goes to full charge (14.7v) at 1700 RPM. From all the test procedures I've read all the DOHC 750s and 900s are the same. The 900 had an oil cooler so the rotors from those may last a little longer. The problem with the design is heat + rpm. The 900 with its oil cooler may not have seen as high an engine temp as the 750. Just a theory on why you may want to seek out one from a 900 if you're looking at used parts.

[mikefootusa]

I bought a 900C parts bike ($100) specifically for the rotor...failed two months later.  Just bought one new...$130.  Going to put it in tomorrow.