The issue with a vehicle alternator is the voltage regulator.
Newer alternators don't have the voltage spike issues (pre-computer cars) had, but they are very capable of 120-200 amps, or more,
That can be a problem 'Charge Controllers'.
A vehicle alternator is designed for lead/acid batteries, which are very tolerant, metal batteries not so much, they like clean, consistent power at a slow charge rate.
Vehicles do NOT have a clean, consistent use of power,
From air conditioning clutches cycling on/off, DC motors creating line noise (cycling), ignition systems cycling, brake/turn signals cycling, it all makes erratic loads on the electrical system.
The second issue is a preset voltage in the regulator, between 13.5 & 14.5 volts.
The 'Optimum' charge voltage for the lead/acid batteries.
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SO FIRST,
You have to clean the power supply up A LOT.
I'm NOT an Electrical Engineer, so the easiest COMMON way I found was with capacitors.
(The same way alternator capacitors take the 'Ripple' out of rectified AC to DC power)
Since high powered ignition systems use capacitors to smooth out electrical system noise, and they are available, I used them.
I used diodes to isolate the the second battery type from the vehicle system.
Then it was a DC to DC power converter, a DC to DC 'Buck' converter.
I had to jack the power around a little to match the charger volt/amp requirement of the charger.
Then the battery charger with thermal sensor.
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No one wants to hear this,
But a second alternator, isolated 'Ground' (Negative) and adjustable voltage regulator is actually the 'Easy' button.
24 volt alternator on a 12 volt vehicle is not an issue with isolated 'Ground' (negative).
12 volt 'Source' will Excite a 24 volt alternator in the event residual magnetism doesn't start the charging process.
Voltage is adjustable means about 20% up or down in voltage output to match charge controller.
With an additional (1) capacitor, the line voltage is maintained, and the line noise is reduced to almost zero.
With line voltage constant, then it's off to the charge controller directly.
As long as you use a charge controller that can handle the volts/amps from the alternator you are golden.
I use a small amp Leece-Neville alternator,
Isolated negative, adjustable regulator, common and dirt cheap, all over salvage yards & rebuilt surplus sites.
I use them for welders, since the AC taps are exposed, they will even produce high frequency AC easily.
With regulator removed and direct access to rotor, it's continuous voltage controllable, an adjustable power supply, assuming constant engine speed, a simple rheostat controlling rotor power, and you can control output voltage/amperage.
A double pole, double throw switch to control rotor, you can switch back & forth between voltage regulator & manual control, with wiring harness attached, it charges batteries,
With welding leads swapped for harness, and manual control of rotor it's an adjustable welder with considerable capacity.
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Watts are Watts, what you do with them is your business...