Hasn't gone so well today
First I removed the alternator to check which internal link was the self exciting system. I easily found the three small diodes that connect to the field input and also to the brushes through what must be the regulator???
Anyway, the wiring is shown as standard in the first picture below. The diode pack contains the 3 main rectifier diodes that handle the main current. The three field diodes shown connect to the field power bus bar, as does the field wire at the field power terminal post. This is the wire I tried to interrupt in the last 'experiment' but found it doesn't do much as once excited the alternator stays self exciting.
So, to prevent the alternator self exciting I needed to control the output of the field diodes and their power supply to the brush pack through the yellow wire.
I unsoldered connection X from the field connection post to the field power bus bar and connected the yellow wire to the field connection post. This is shown in the second 'modified' picture.
I then connected a new wire (green) to the bus car at X and ran it out of the alternator to the voltage/duty cycle dependant relays so it would only feed voltage to the field post when the control system required the alternator to be energised.
So far so good?? Well, in theory, yes.
In practice, no.
The engine ran and the alternator didn't energise until the voltage dropped below the threshold 12.4v. The alternator then energised and pumped the voltage up to a level way above the hysteresis value, switching the voltage switch off again.... and so it started cycling!! A quick turn of the hysteresis potentiometer soon had that sorted, and the engine ran with a falling voltage.
A number of times I set the low 'on' threshold and watched it switch on and then off, but for some reason in between controlled activations it would suddenly ramp the voltage up to around 16.5 volts!! My guess is that the voltage regulator wasn't working but somehow it was getting an excitation voltage
Anyhow, I tried to set a low voltage 'on' point that would correlate to 50% charge in the battery, but the draw on the battery must have been too great and the voltage collapsed too quickly to sub 10v. The switching circuit then stopped working, and there was no way of getting charge into the battery!! The engine kept running though, and the injector duty cycle meter actually showed 17% when I revved it a little (it hasn't ever showed higher than 8% even at WOT)
Maybe it needs a lower supply voltage?? LOL
I gave up and put it back to standard.
More testing to be done on a rig I think, the vehicle testing isn't too clever
I need an alternator with an easily accessible regulator and field diodes so I can ensure that the regulator is working when I need it