They don't seem to work well, mine certainly doesn't or didn't.
The stock alternators don't have a high output, only 14.5V*13A=188.5W at 5000rpm, but when they're in good condition they are adequate for the bike.
It doesn't look like you've ever figured out what your charging issue is. You've mentioned in a few places that it only charges above 5000rpm. It should be able to charge charge at much lower rpms.
Have you done the resistance tests for the stator windings and field coil?
Have you done the tests for the regulator in the manual?
How are you determining the rpm when it starts charging?
The field generator makes it difficult to upgrade to a more modern system.
Yamaha certainly never designed it to be upgraded. You'd have to replace the field coil with one that can generate a greater magnetic flux or replace the entire alternator with a PMA setup.
The problem with somehow increasing the magnetic flux of the field coil is that in our alternators it's not the magnetic flux of the field coil that rotates, interacting with the stator. The stationary field coil magnetizes the iron of the spinning rotor. It's the rotor's magnetic field that induces a voltage in the stator.
I suspect that our rotors are probably operating near saturation and any additional field coil flux would be wasted.
I have been upgrading all the electrical components on my bike but have been stuck on the charging system for an embarrassing amount of time. My theory is that regulating the current by modulating the field coil is the problem and by constantly powering the field coil and regulating power by changing the resistance of the stator with a modern mosfet regulator rectifier is the best solution.
It's possible that your stock regulator wasn't working properly. It should be giving the field coil constant power when the bike needs that much power.
The problem is that the My biggest fear was heat build up in the wires to the stator and field coil especially. So i ran 12 gauge wire from under the engine to where the stator and field coild wires come out. A trick i learned from hotrodding ebikes. The thicker wire acts as a heat sink allowing heat to flow from the stator and field coil preventing heat from building up and melting the insulation and causing a short.
It'll also slightly reduce the voltage drop in the wires and might squeeze a bit more efficiency out of the system.
I ran the stator wiring to a mosfet regulator rectifier and directly wired the field coil to my main circuit and grounded to the frame. It works much better than stock. I can drive around town without worrying about my battery draining. Idle doesn't drain the battery and it starts charging at three thousand rpm instead of five thousand rpm.
Cool.
What I'm curious about does the stator resistance affect the field coil current?
No. Stator resistance never changes beyond slight temperature variations. If you're thinking of increasing stator current causing an increase in field coil current by some kind of mutual induction, also no.
Voltage shouldn't hurt the field coil, to much current would hurt the field coil.
Within reason. If you somehow hotrodded the field coil to run at a voltage much higher than battery voltage, like 60-100V+, the insulation on the field coil wire would eventually degrade and short circuit.
Excessive voltage in the stator WILL burn it out. There are numerous threads on other bike forums about stators being burned up by mostfet shunt-type regulators. Some manufacturers are starting to switch to series type regulators that do not run the stators at maximum voltage.
I imagine the current the field coil draws is based on the resistance of the stator.
Again, no. The current draw of any alternator with a field coil, whether on our bikes or a diesel generator, depends on the resistance of the field coil windings themselves and the resistance inserted into the field coil circuit by an automatic regulator. Maximum field coil current is restricted by the resistance of the field coil windings.
I'm guessing the field coil draws more current the more energy the stator is producing.
It's the other way around. In any alternator, our's included, when there's a load on the alternator the stator will have a given current and voltage. To limit the output voltage to the desired value the field coil current is kept low by inserting a high resistance.
When additional loads are added the current draw on the stator goes up. When the current draw on the stator goes up the magnetic fields cause the output voltage to drop. The regulator senses that drop and reduces the field coil resistance, increasing field coil current.
As more loads are added the regulator lowers the resistance of the field coil circuit until it's down to just the resistance of the wire in the field coil windings, and that's the maximum output of the alternator.
My theory is that the field coil is drawing the same amount of current to produce the same amount of power whether your controlling the current by modulating the field coil or stator.
Now you're comparing apples to oranges.
Field coil current and stator current are two very different things.
In the stock setup field coil current is varied by the regulator to meet the demands of the bike.
In your mosfet shunt/constant field coil power is at
100% all the time and stator current is at
100% all the time. Your bike doesn't need 100% all the time so the mosfet shunt regulator shunts the excess to ground, only letting through what the bike needs.
But since the mosfet is much more efficient it might be drawing less current even though its always at full voltage.
I think you may have bypassed whatever the problem with your charging system was.
Any input or ideas for testing these theories would be appreciated.
Do a whole bunch of different tests with varying loads, at different RPMs, on both your system and a perfectly functioning stock system.
Or run it until it burns out.
