Charging a 24 v using two 12 v alternator

My port main has a 32 and 24v alternators. Lots of room in front of the ole TIs.
Other idea is change out one of the 12s to a 24v alternator.

Balmar used to sell dual out-put alternators, I wonder if dual voltage rigs are still available.
https://balmar.net/contact/
Example; https://www.easternsurplus.net/PartDetails/3323/HM-248-Dual-Voltage-200-AMP-Rebuilt-Alternator-HMMWV

There is just to many isolation concerns that come to my mind in your drawing.

Tap on Tony and his forum for better Cummins ideas.
https://www.sbmar.com/community/
https://www.sbmar.com/contact-us/

Oh, long (LONG) ago I managed an ole 12Vdc Roamer.
12V Delco alternator with a box on the back. This aftermarket box tapped onto some post inside and made a few amps at 24v for the starting batteries. Rest of the boat was 12V.
I can not remember the box's vendor name.

If you want to charge a 24v bank from a 12v bank why not just get one of these?

https://www.sterling-power-usa.com/SterlingPower12volt-to-24volt-70ampbatterytobatterycharger.aspx

I have the same but opposite direction - engine alternators and starting battery bank is 24v and my house bank is 12v. I have two of these but in 24v to 12v as emergency back up in case my gen quits and I need to charge house batteries from engine alternators.

That is 70Amps (12Vdc) in,, Maybe 35Amps (24Vdc) out.

Pending the size of the 24Vdc battery bank, house load of 20-30 (more?) Amp draw could be expected.
70Amps @ 12v could be taxing on a single alternator.
Combining both 12v systems with an ACR may help share the loads on the alternators.

We use a 32 to 12Vdcv charger converter (Newmar) to keep my 12v banks up while operating without a gen-set running (SOP). Here voltage converted down, amps go way up.


Actually, I would shop around and re-consider converting the engines to 24v.
I recall it is just the 24v alternators, nice lil Cummins 24 to 12v converter & additional local wire harness next to the engine. All on that engine stays 12Vdc.

I wouldn't recommend this. The issues are due to simultaneous serial and parallel connections in this system. Each starting battery being connected (presumably) to a 12v alternator further complicates things and may result in serious damage to the equipment.

There are many DC-DC converters and chargers available from different manufacturers, e.g. as @DOCKMASTER linked above, to supply the house bank with 24v from either charging source.

If your running , then drop the anchor and light up the gen-set, This sounds good.
In a couple of hours, this charger/converter will bring down your starting battery(s).
Remember, twice the voltage out, twice the current required in. Watts must equal watts on both ends (plus charger/converter consumption).
That 5 amp potable water pump will draw 10+ amps from your starting battery.

Also the sump pump, blowers, head(s), fridge at 24v will require twice the amps also from the starting battery.
And your using a starting battery to run the house.

I know it's the weekend, have you looked at a second or dual voltage alternator on one of the engines yet.

Look forward to your final design and how it works.

For the last 2 years I have been adding a little at a time for a battery management manual on our 32v boat.
32, 24 and 12 Vdc systems on a common negative buss, 3 x 2 bank battery switches, 1 x 1 bank battery switch, 1 ACR, 5 battery banks, 24Vdc inverter/charger, 2 x 32 v alternators, single 24v alternator, 32 to 12v charger/converter, 32v battery parallel solenoid, inverter auto gen-set start and each of the 2 gen-sets have 12 v alternators each.
25 pages with pictures so far and I have not covered all of the back-up switching available.
All of this stuff is automatic when all is working correctly,, but what if ??

I still manage a 75 Hatt with 24Vdc mains and house, 48V thruster, two 12v gen-sets and the owner wants to go to a 48v monster inverter/charger system.
I found some 48V alternators that I have to hang under the front of his 12V71TAs (no place else). Rite where his power assist steering pumps used to be.
I'm 10 pages into this with just sketches and edited prints.
Back up designs are in my mind but not created or drawn out yet.
All of this stuff will be automatic when all is working correctly,, but what if ??

I bring this up to make one last thought, Keep It Simple S*, no matter what you do.

You may not be available if something needs to be adjusted to make something work.
AND, as much as I try to help and type stuff up in manuals, in a rush, nobody is going to open a manual to see how anyway..
As my slower brain cells are over come, I hope I remember there is a manual to help.

Yep, KISS is preferred ..

What a waist of efficiency.

Have you tapped on Tony yet?

The first time you flush your 24V head, that 12to24 converter will be overwhelmed.

As you commented, replacing one of your 12V alternators with a 24v unit or as I tried to point out, a dual voltage alternator.
OR, go ahead and push for that 24V inverter/charger with two 24V banks.

Hindsight sux, but I have to rub it in brother. Should have ordered the Cummins in 24V.
Still any cheap way to upgrade the engines and remove all issues.
K I S S comes back to mind.

I'm one to talk about simple (post #10), But I will be changing out my 32V for 24V starters next fall.

Victron makes good stuff. I recently installed a 50 amp 12v-12v charger in my motorhome. It allows me to charge my Li house batteries from the engine alternator. It works great! Sterling makes some good units too. I have the reverse in my boat where I have sterling 24v - 12v charger as back up to charge my 12v house bank from my 24v starting bank if I lose gen or battery charger.