I'd like to further add to this...You may wonder why I rated the 14.5 volt condition lower in current on the alternator :
Wonder why your CB350 with a 110 Watt alternator is losing its charge?
110 Watts at 12V = 9.2 Amps
110 Watts at 14.5 Volts = 7.6 amps
But then raised the current on the coil amp when voltage went up.
There is something many do not realize about these permanent magnet (PM) type alternators. They do NOT generate voltage at all. They generate CURRENT (AMPS). At a given RPM, the PM alternator generators a specific, fixed amount of current.
Let's figure out the capacity of the alternator from the manual.
The last of the CB350 Manuals list the loads:
For Nightime, is has 1 35W lamp, 3 3W lamps, 2 ignition coils and the battery. For this instance, let's consider the battery fully charged.
At 5000 RPM, the Alternator is rated 14.5 Volts, with 1.5 to 2.5 amps left over for charging.
Lets convert the coils to amps at 14.5 V : V=IR, so I=V/R... 14.5/5 = 2.9 Amps, there are 2 coils, so 5.8 amps for coils. The coils are only activated for about 25% of the time (when the points are closed for that coil) so the ignition requires 1.45 amps. Let's say 1.5 to keep it simple.
Lights are 35 + 9 = 44 watts. Watts = Volts *Amps so Amps = watts/volts = 44/14.5 = 3 Amps....
Finally, the book says 1.5 to2.5 available, assuming the alternator system is "optimum", lets assume 2.5 A.
So, we get 1.5 + 3 + 2.5 = 7 amps. Lets double check our work: 7 A x 14.5 V = 101 watts. The Alternator is rated 110 watts, and I bet my coils use that wee bit more. So say 2 Amps for the coils and the math checks out. That makes the system 7.5 Amps at 5000 RPM.
that's the "rating".
Let's go back to the rating at 14.5 volts, 7.5 amps. We are missing Resistance... R = V/I so 14.5/7.5 = 1.933 Ohms. The Bikes electrical system, with all the lights in parallel, the battery, and coil resistance in the alternator, total 1.933 ohms.
So back to the original idea, the Alternator produces CURRENT. the volts in the system are dependent on the resistance in the system. Add 2 more lights and the reisistance drops. Lower resistance means lower voltage. the amps may still be 7.5, but you notice the voltage is now 14.0 volts. do the math, the resistance of the system is now 1.866 Ohms. This is how the voltage regulator works. when the regulator senses the voltage above 15 volts, it starts to decrease the resistance in it's circuit to ground, lowering the overall resistance, causing the voltage to drop. the alternator is still putting out the SAME current, but now the system is lower resistance, so the voltage is too.
If you grounded the output of the stator at 5000 RPM, on this particular bike, through an ammeter, the voltage would drop to zero (shorted voltage is zero) but the current would still be 7.5 amps.
The capacity (or ampacity) of the alternator goes up as the RPM climbs. However, since the resistance stays the same until the voltag regulator kicks in, the voltage rises with the current,and then the regulator starts reducing the resistance to maintian the maximum allowed voltage in the system
this may clear up how the system works for some, confuse it for others. It is unusual to think of the system as current based, but it is. The rest of the system defines the voltage.
Remember though, there are losses. The magnets get weaker over time, the internal resistance of the alternator coils can change, other items can cause the current you want to go somewhere besides the lights, coils and battery.
This outline for a permanent magnet alternator does not apply directly to field excited alternators. While they output current alos, their output is not tied to the RPM like a PM alternator is. That's for a different post and a little more complicated.