How to best get 12V from 24V

[Mark7]

I am going to install an inverter and lithium batteries soon and I have an dilemma I am trying to work out.

I want to use a Victron Multiplus II (split phase) inverter and I want to use the 24 volt model (I would use 48V if they made one) for the convenience of running smaller primary wire, especially when I get around to adding solar.

My dilemma... I obviously still need 12V to run all of the RV systems.

I see 2 ways to go.

• Use 2 - 12V batteries wired in series so I could use one of them for the 12V load. Perhaps not desirable because of more frequent use of 1 of the batteries?

• Use 1 24V battery and use some sort of 24V to 12V charger to keep an additional 12V battrery charged for the RV systems.

What do you folks who have dealt with this do? Planning ahead!

Edit: Maybe answered my own question... Victron ? Think that might work even without a battery? Maybe not enough for hydraulic pump?

[Daryles]

Maybe a Victron DC-DC converter.

https://www.victronenergy.com/dc-dc-...v-24v-48v-110v

You will need a 12vdc battery to run the hydraulic system. The battery provides the high current output required by the hydraulic pump.

[Mark7]

Originally Posted by Daryles

Maybe a Victron DC-DC converter.

https://www.victronenergy.com/dc-dc-...v-24v-48v-110v

You will need a 12vdc battery to run the hydraulic system. The battery provides the high current output required by the hydraulic pump.

That is kind of what I was thinking. With that charger it looks like I could get by with a garden tractor battery to absorb inrush current of a hydraulic pump and that would easily run the other 12 V loads in the camper.

Am I thinking right?

[Daryles]

IF, you boondock in the winter, your furnace will draw 14A DC from the 12v battery. A 100Ah FLA battery will last about 5 hours (asked me how I know, lol).
If you have a good 24dc battery bank feeding the 12vdc system you will be fine.

The hydraulic system can draw about 90A when running the main slides. Plan your battery output for that.

[Mark7]

Originally Posted by Daryles

IF, you boondock in the winter, your furnace will draw 14A DC from the 12v battery. A 100Ah FLA battery will last about 5 hours (asked me how I know, lol).
If you have a good 24dc battery bank feeding the 12vdc system you will be fine.

The hydraulic system can draw about 90A when running the main slides. Plan your battery output for that.

I could leave my current deep cycle flooded battery in place as long as it lasts.

Thank you for the advice.

[TomCat]

How about something like this? They can be stacked to provide for more draw if need be.

[c2itcliff]

This is what I'm doing. Leaving the 12v DC side of my panel as-is. I'm going to convert the AC side using a 48v hybrid solar inverter/charger (there are several different options). The battery charging profile for the 12v house battery, can be changed to LifePO4 via the "wizard" button or by moving a jumper on the circuit board. I selected a 12v, 300ah mini LifePO4 battery by E-Lektech that has a 250a BMS. This can handle the hydraulic pump for the slides and jacks. Next, I plan to power the AC side of my electric panel with a single 48v 200ah, 150a BMS, LifePO4 battery, connected to a 10000w off grid hybrid solar charge controller. Both battery and controller are made by POW-MR. I have an Onan 6500 generator that requires a dedicated starting battery (NOCO NLP20 LifePO4 12v, 7ah, 600a BMS). This small starting battery is charged by a dedicated charger, plugged into the refrigerators 1000w inverter drawing power from the 12v 300ah mini LifePO4 house battery by E-Lektech.

[Mark7]

Originally Posted by c2itcliff

This is what I'm doing. Leaving the 12v DC side of my panel as-is.

That is essentially what I am doing, except with 24V because Victron does not make a 48 V split phase inverter.

You sill still need to have a 12 V battery to run the house stuff, correct? Are you leaving the existing 12 V converter and battery in place and isolating it from the new inverter?

I don't want to do that. Adding a 24V to 12V converter charger and a smaller 12V battery will work just fine. Only one inverter / charger (Victron) keeping everything topped off.

[AZ Traveler]

Easiest way - use 2 12v batteries in series for your 24v battery bank. Pull 12v off one of the batteries.

[Mark7]

Originally Posted by AZ Traveler

Easiest way - use 2 12v batteries in series for your 24v battery bank. Pull 12v off one of the batteries.

I did consider that, and still may go that route. Not knowing LiFePO4 batteries I am concerned about the cell "Balancing" people talk about, especially when drawing off of 1 battery for the 12V load.

Maybe someone can enlighten me!

[Foldbak]

Originally Posted by Mark7

I did consider that, and still may go that route. Not knowing LiFePO4 batteries I am concerned about the cell "Balancing" people talk about, especially when drawing off of 1 battery for the 12V load.

Maybe someone can enlighten me!

You're right but it's not cell balancing in your case. It's battery balancing. The cells should be matched to be balanced. That's a manufacture thing. If you're pulling more load off one battery then the other then one batteries SOC will be less then the other. I don't think it's going to be much depending on the load. Might be 5% or 10%. If you manage properly it will charge and catch up.

[Mark7]

Originally Posted by Foldbak

You're right but it's not cell balancing in your case. It's battery balancing. The cells should be matched to be balanced. That's a manufacture thing. If you're pulling more load off one battery then the other then one batteries SOC will be less then the other. I don't think it's going to be much depending on the load. Might be 5% or 10%. If you manage properly it will charge and catch up.

Good to know. Maybe I could put in an A/B switch the 12V load from time to time.