This is the first time I post on the forum, but i have been reading you a lot in the last few years, and found you incredibly interesting and useful for my projects.
I am now asking advice about if and how a certain project I have in mind can be realized.
I have an alternator and two battery banks (both 12V, but different capacities). At the moment there is an electronic device between the alternator and the batteries that split the charge between the two banks.
There exists a problem with this set up: it doesn't take into account that the alternator cannot run at maximum power for more than some minute. Even if it is rated 120A, an output of 50/60A already causes overheating and belt slipping. This happens when big loads are sucking energy from the big battery bank, causing the voltage to drop and the alternator to push more current there.
Solar panel have been added to the system, but their charge regulator cut them off at a lower voltage than the alternator regulator does, so this way only the alternator charges while the solar panels are disconnected.
So what I would like to do is:
continuously charging the small bank (that is the engine battery), by connecting it directly to the alternator output. This arrangement would be like the circuit on a car, and it would be suit the start battery fine;
connecting the big bank in parallel with the start battery, electronically controlling how much current passes to it.
This way, monitoring the current at the alternator output, I can reduce the flow of current between the two battery banks and keep the charging current below 30A. If there is load bigger then 30A on that bank, then the voltage will drop and the solar panels will kick in, supplying the rest.
My idea was to control some MOSFETs (P-channel) by PWM them from Arduino, allowing wider or stricter pulses of current to pass from one bank to the other, so keeping the average voltage at the alternator output at a level that makes the alternator internal voltage regulator supply a maximum of 30A.
I think PWM was the system used until a few years ago in solar panel charge regulators, before the coming of the MPPT technology. So I imagine that the pulses shouldn't cause any damage to electronic devices connected to the charging battery, since this system has worked for decades...
But I am not sure about how fast the alternator voltage regulator is at sensing the voltage at the output and consequently setting the outgoing current. If it is slow enough, I imagine that everything should be fine, since the MOSFETs keep the average voltage at the alternator output high enough to avoid a charge of more than 30A. But if the alternator voltage regulator senses the pulses and starts doing the same with the charging current, I am not sure if that could be a problem.
I even thought of gradually "closing" the MOSFETs, and use them as variable resistors, with a DAC and an op amplifier, but I have never heard of anything similar, so I am not sure if it can be done. The MOSFET curves are a bit steep at the beginning, so it might be difficult to use them this way.
Does any of you have any idea about it? Is there a way to gradually reducing the current flowing from one battery to the other? Thank everybody.