Two input power sources for buck-boost converter

Another shout for help to the experts.

What I have:
1. Two machines driven by two ICE Engines. Both have onboard alternators that is used for ignition and charging the battery as in any vehicle.
2. Engine 1 is a smaller one that has a 12V equivalent alternator #1. Output current is in the range of 8-9 amps. Generally is running all the time
3. Engine 2 is the bigger one that has a 48V equivalent alternator #2. Output current is in the range of about 10-18 amps. This one is running on-and-off
4. Both engines run at varying rpm depending on the load, hence their respective alternators also have varying outputs within their operating range

What I intend to do:
There is some power demand for other tasks on the shop floor. I intend to install an appropriate AC Inverter (approx 4kW)to cater to that demand. Only difference that I intend to use a huge bank of used LFP lithium battery packs in a 19SXP/60V configuration. These batteries are used and lower capacity, but still better able to deliver enough juice for the inverter and load.

How I intend to do what I intend to do:
1. Since both engines are running, I tap both the alternators, feed the output into a buck-boost converter.
2. Output of the buck-boost converter feeds the BMS for the Li Battery pack to charge the battery pack

My problem:
1. Engine 1 is running all the time - Li batteries can all be charging as long as Engine 1 is running, albeit at a lot lower charge rate since Alternator 1 is at 12V while the output of the buck-boost would be approx 65V. Increase in voltage, loss in current
2. Engine 2/Alternator 2 on the other hand has a higher voltage and current, but not running all the time. I'm trying to see if I can feed the output of Alternator 2 also to Buck-Boost converter so that I get lot more voltage and current to charge the Li battery pack quicker.

I read up and I understand that we can add two voltage sources in series as input to an SMPS. Of my limited understanding, a buck-boost converter is also essentially an SMPS. If that indeed is the case, would the attached configuration work? Or is there a better way of achieving what I intend to do?



Regards,
Deepak

I think there has to be a diode across + and - terminals of each alternator output before the same is fed to the buck/boost converter.

Any ideas?

The two alternators should never be hooked up in series. It would cause the weaker unit to carry 3-4 times its nominal current. It will burn up.

It may be feasible to interleave multiple boost converters, taking output from both alternators in turn. Output waveforms can overlap to charge the 60V battery bank .

Very right and fundamental @BradtheRad. Thanks for your inputs. Might be I can build a MOSFET switch to switch between two alternators. I've had my share of grief building such MOSFET switches (have a long thread on that on EDABoard). I hope this one is simpler and easier to design.

Thanks for your inputs.

Regards,
Deepak