Re: New to forum/CB650 and my first question!

Posted by sgtslag on Oct 06, 2011; 10:28pm
URL: http://vintage-and-classic-hondas.81.s1.nabble.com/New-to-forum-CB650-and-my-first-question-tp3381249p3401311.html

The Alternator generates AC current (yellow wires), which it sends to a Rectifier, which converts (rectifies) it to DC current; the Rectifier sends the DC current to a Voltage Regulator, which controls how high the DC voltage applied to the bike, and the battery, gets -- it keeps it at less than 15 Volts (higher voltage will destroy the battery, and the electricals on the bike -- bulbs, any solid state parts in the CDI, and possibly burn up the coil wires).

The Rectifier circuit is housed in the same body as the Regulator circuit, and they share the same heatsink (usually located under the left side cover, or beneath the seat).  It is an expensive part, and it is essentially a "black box", for troubleshooting:  measure the AC Voltage at its input (yellow wires), to see that it is getting its supply of AC current from the Alternator; check its output DC Voltage (across the battery's terminals) to see if it is outputting a regulated voltage of 13-14.8 Volts DC, to the battery (voltage will vary depending upon the RPM, which governs how much AC is put out by the Alternator -- the higher the RPM's, the more AC, the more DC, up to the Regulator's maximum).

By measuring the voltage across the battery, while riding at 3,000+ RPM, you will be testing the entire charging system, from the alternator (those rings you tested the resistance on, are a part of the alternator, and are only a partial indicator of its health -- the resistance of the alternator's coils is not a foolproof test).  The voltage across the battery tells you if the charging system is working, or not.  If it is, then your battery is shot:  new or not, it has to be the culprit if there is 13-14.8 Volts DC across its terminals while riding.  This will indicate that the battery is being charged, but it is not accepting the charge because its internal parts are damaged.

There is a guy who sells his own Rectifier/Regulators for CB750's, designed to be heavier duty than OEM.  If mine goes, I will buy from him, as he over-built his units so they will probably outlast the engine...

http://www.oregonmotorcycleparts.com/Reg_rec_units.html