My Question
To add more run time to my 12 volt house system, is it feasable to use a DC to DC charger to charge the Lead Acid battery from the Lithioum battery bank?
Background (drawing attached)
On my boat I have the existing 12 volt house battery system which is a 100 Ah lead acid system with a 16 amp charger that is powered by shore power and generator. This 100 AH is only enough power to run lights and refrigeration for about 5 hours.
I have recently install a lithium bank 3x100 Ah with a Victron Multiplus to provide AC power for times when I dont want to start the generator. I also have a solar panel and solar controller that I will be adding to charge the lithium bank when at anchor.
My problem is on the 12volt house side, having no room for another lead acid battery and not wanting the change the charger which also charges two starter battery (3 bank Lead acid Charger). I need more 12 volt run time to keep the 3 refrigerators running all night long.
Not shown on the drawing, I also have smarts shunt on both the lead accid and the lithium banks, as well as, the Cerbo GX and 7" touch panel install for monitoring and control (if it matters).
Yes you could add a DC to DC charger to do what you are proposing, something like an Orion 12/12-18A isolated unit. You would need to think about how you set it up to do the charging because you would want it sending power to the house battery even when the lithiums were not charging.
I am in agreement with @CharlieJ here, can you do some work to simplify the 12V DC loads rather than creating a frankenstein system. Personally, I have always had the domestic batteries cover the 12V DC loads and the inverter from one bank.
You can leave the Orion in power supply mode and set the voltage to the sustain voltage of the lead acid. That will disable any charge logic and send what the system needs from the lithium bank. I did something similar for a while to keep the lead acid start battery topped up at the sustain voltage to stop it from cycling, and checked on the lithium while it was in storage. It would only drop 1% a day, so every month, I would just top it back up to 80%.
You can still use the voltage lockout to stop the power supply.
I purchased an Orion XS 12-12 50 A Non-Isolated. I saw that you recommended and Isolated unit, but would this non-isolated unit work?
I was also thinking I would bring the max charging setting down to something like 20 amps so it would match up more closely to the load my lights, pumps, and refrigeration put on the lead acid house battery.
Yes the non isolated unit will work, bit you will have to add a common negative cable capable of ideally 50A between the lead acid battery negative and the lithium negative. Your drawing did not show this, it showed them as separate isolated systems. The negative terminal on the Orion connects to the closest bank, it does not matter which one.
Yes, you can easily change the current limit on the Orion XS, just a little higher than required.
