GT,
You were given misleading information. The only time the solar panels can shut down the alt is when you are at a VERY HIGH state of charge and the solar panels EXCEEDS the acceptance of your battery bank for a given voltage set point..
Currently your solar array is about 1.7% of the banks capacity so it should take them a loooong time to bring the bank to 14.6V.. Add more current to the mix and the battery voltage will come up faster.
Voltage regulators simply limit voltage, there's no magic. Controllers and wind gens do the same thing. This is all they do and they do it by pulsing the current on/off. If the voltage starts to overshoot you can see the current drop all together. On the other hand if the bank has not yet reached "absorption" then the controller, alt and wind are pumping out what ever they can or the bank will accept because the voltage "limit" has not yet been met..
With a 900Ah bank you'd need to be well into the upper 90% SOC range before the solar controller could keep the bank voltage that high. It is a current/charge capacity ratio as to when you hit absorption voltage. And this is with no loads on. Add loads to the system and you have less available current to the bank to maintain an absorption voltage. The higher the bank voltage the more current required to get it there quickly and then hold it there.
At any point below the panels exceeding the banks acceptance for a certain voltage limit the alt and reg & wind will all supply current.
As an example I have a 100Ah battery on my bench right now. It has been on float for a couple of weeks it is as full as it will ever get.
At 13.2V it accepts/needs 0.07A to maintain 13.2V
At 14.6V it accepts/needs 0.8A to maintain 14.6V
As a ball park estimate if we were to multiply that X 9 for your 900Ah bank we'd have a "full" acceptance rate of about 7.2A just to maintain 14.6V.. This should be close to what your bank may require to maintain 14.6V when 100% full. Every bank will be slightly different depending upon state of health etc.. This is an acceptance of .8% on a 900Ah bank when full.
If you take 2%, the number often bantered around that is as "full as it gets" on a cruising boat you are at roughly 18A at 14.6V... So even at 98% SOC and 14.6V your banks acceptance likely exceeds what your current panels can pump out. Hence I'd be surprised to see your bank even hit 14.6V until upwards of 95+% SOC charging with only solar.
In bulk, which is your devices pumping out constant current because you've not yet hit the "limiting voltage", your bank will accept about 225A of charge current. At 225A of charge current your banks would come up to 14.6V at about 70% -80% SOC give or take. However when you have less current available the banks will not hit absorption voltage until a higher state of charge. When you hit "absorption voltage" depends upon the current you have available and the voltage set point/acceptance..
Contrary to popular misconceptions batteries do not just jump to 14.6V when you apply current to them especially if they are below 70%-80% SOC. If they do they are sulfated. If applying low current eg: 1.7% of capacity, it will take a LOOOOOONG time to get to 14.6V..
In bulk mode, usually between 50% and 85% SOC, all of your devices will supply current because you don't have the capacity or SOC to even get to absorption voltage until you hit a higher state of charge and the acceptance and available current merge to hit voltage. Once you hit absorption voltage the controller or regulator with the highest set point wins and the others will shut off the field current or disconnect from the array until the voltage falls again.
However if the controller with the highest set point can't maintain that voltage, because it has low current ability, the voltage will fall and the alternator will kick back on and bring the voltage back up to its limit. When you get to a voltage where the solar panel can maintain the bank at 14.6V you really don't need the alt....
The easy tweak is to simply program your solar controller 0.1V lower than the alt reg if you want the alt doing the finish charging when the motor is running..
