Help converting an RV house battery to lithium

[Hwy89]

It is time to replace the lead in my RV. I am heading out in a few weeks to spend the winter dry camping in the Sonoran Desert. I am currently in negotiations with a seller to get another Tesla module so I will have 444 18650 cells to play with. I plan on taking 2 of my 180 watt solar panels which put out 27 volts open circuit with their Mpp at around 17 volts.
I am interested in hearing from anyone who is using a lithium battery in their RV and finding out the specifics of their system. What configuration did they use to assemble the battery, ( 3s or 4 S) and what solar charge controller did they use? If they set it up for 4s (16.8 v full charge) were the RV components able to handle it and survive or was a buck converter needed to drop the voltage to ~13v.
I have, so far, disassembled 3 Tesla modules and put together a few bike batteries but this will be my first go at trying to emulate an old fashioned 12 v deep cycle battery so suggestions are welcome.

[amberwolf]

I don't have direct RV experience, but I use a 4s NMC lighting pack on my bike and trike, and have tested it out on a number of "12v" automotive items. Simple things like lighting (LED or not) work fine, and most of the electronic stuff works on it too, including a very old (1980s) car stereo, and some of the lighter-socket USB power adapters and other such devices (like an FM-radio-output "ipod" adapter). A "mini fridge" that just uses a Peltier and fan works ok, but runs very hot at the output heatsink (without making the inside any colder), despite the computer-case fan used on the heatsink running much faster at the higher voltage.

But some things either just shutdown to autoprotect, or blew up. One blown up bit is an older inverter to get 115VAC; I think it was Kensington, can't remember for sure. Blew up a few lighter-USB adapters. Another inverter autoprotects and won't even turn on, but still works when put on a pack discharged down to 15v or less.


Similarly, a number of non-simple electronics stop working on a 3s pack well before the pack is at LVC. (like the peltier-fridge and the inverter).


I don't know about other RV-specific systems, but I'd expect some to work fine and others to have issues of varying degrees.

[Alan B]

3S Lithium Cobalt voltage is too low and 4S is too high for standard 12V loads.

There are two basic directions to go for an RV system.

One is 4S LiFePO4 and doing a 12V system with a max voltage of about 14.6 which is acceptable for 12V loads. 4S LiFePO4 is well matched to 12V. Various 4S RV LiFePO4 batteries have built in BMS systems, so these are the easiest but are expensive. See Battle Born, Bioenno Power and others.

The other is a 24V system and a 24:12V down converter. 24V systems have a wider range of voltage compliance and can be adjusted for voltages in the 7S range. Two or more panels in series can be used for charging.

With a 24V (or 36V or 48V) system the 12V loads see a nice regulated voltage, and very few items see the full voltage, basically the charge controller and the 12V output converter, and if you have one a 120VAC (or 240VAC) inverter. Inverters are more efficient at 24V or higher.

[Hwy89]

Thanks Alan B, I hadn’t thought of the 24 volt system. I have several 7s packs already built that I use in series for my 14s bike.
I could make several spare bike packs and swap them in and out of house battery as needed. So I would need to find a 24/12 volt converter beefy enough to handle the load of the RV. Any suggestions on that?

[dustNbone]

24VDC is most commonly found in large commercial vehicles and boats, so those are probably good places to start looking. Figuring out your maximum likely load (on the 12V side) will allow you to choose one appropriate size and spend as little as necessary.

My RV (26', no slideouts) has a 55A converter that easily handles everything 12V running except the leveling jacks, those need help from a battery.

[Alan B]

Generally the 12V load current of the RV is not high, the exception can be high current motors like the landing gear on a fiver. Most loads are low current, and the high current jacks could be wired to operate from the vehicle 12V battery and separated from the RV house battery. RV/Solar places like Arizona Wind and Sun carry 24 to 12 volt converters, as an example. They have various sizes depending on the current required. 30 amps is generally adequate, the higher currents are for charging the 12V battery that is not needed here. But it needs to be sized for your rig.

[kcuf]

12v house system may also crank genset if equipped

could be tied to chassis cranking batteries like any power gear stuff, jacks, slides, etc

contemplating 48v tesla modules here

[Alan B]

If the 12V system has high peak demand, a small LilFePO4 battery could be floated across the 12V output converter for handling these peaks. But the bulk of the energy storage would be at 24/36/48 volts.

[Hwy89]

The RV is a 25’ Jayco bumper pull trailer. The only high amp loads would be the tounge jack and the slide motor. I will measure the amp draw on those before purchasing the DC/DC converter.
I have been researching a solar charge controller that can be set up to output 29.4 volts to match the 7 s pack configuration but poorly written and incomplete product descriptions make that a frustrating chore. Any suggestions on a charge controller?

[unklegrumpknee]

Thanks for the info. I am also wanting to upgrade my Pv system in a little camp. This is good info.

[unklegrumpknee]

Has anyone considered using 3s lithium with a large diode and charged separately. Connected to a lead acid battery?
Under a large load the lithium could support the sla reducing the Peukert effect?

[Voltron]

Be thinking fire safety... If the pack is big enough to run for a good long while, it might be too big to drag away from the RV in a worst case scenario.

[Hwy89]

This is an old thread that I should have kept up with and didn’t.
The solution that I chose and that has worked quite well for the last year is as follows.
A 260 watt solar panel feeds a 48p 6s battery bank of 18650 cells through a Victron smart solar charge controller.
The controller is adjusted to charge the pack to only 24 volts which is a very stable 4 volts per cell.
I have a 2000 W 24 volt inverter connected directly to the 24 volt bank along with a 30 amp 24 to 12.6 volt dc/dc converter. The converter feeds my two 12v lead acid house batteries.
This system handles all of my power needs with the exception of air conditioning.

[SlowCo]

Came across this really interesting video and thought about this thread:

[youtube]kYx097cVR48[/youtube]

[homegrowndiesel@gmail.com]

I know I am late to the party, Hope your vacation went well. I have been using lead acid in 3 bus conversions, and my latest van conversion. My latest electric bikes are using lithium batteries. Been watching Elon's choices, Seems we will having alot of choices coming up. Jury is still out. The last link is the old standard. The size, weight, and most important for this cost benefit analysts is the recharge cycles.

https://www.youtube.com/watch?v=p_s53GGUElQ

https://www.alibaba.com/product-detail/ ... 5a88SGLtX9

https://haomibattery.en.alibaba.com/pro ... 1e81FiUl9Y

https://www.alibaba.com/product-detail/ ... 4e01zoixG0

https://www.18650batterystore.com/colle ... amsung-40t

https://www.onlinebatterysale.com/produ ... e-flooded/

[ZeroEm]

Jury is still out

Lead is dead!

[wineboyrider]

Just got my hands on a nice RV casita camper trailer. I plan on keeping the crappy lead acid battery installed. But, I have plans to take my ebike batteries and army of 40v greenworks batteries with me to power small ac appliances I purchased a cheap $40 greenworks inverter with 300w ac power and usb ports. But, I also will buy a 36/48v 30 amp golf cart step down inverter to keep my 12v stuff running. Need to add a few solar panels down the road. But I don't want to modify anything in the camper as it's pretty nicely setup.

[ZeroEm]

I should not speak so fast on LSA. They are cheap enough and have there place at a home. Traveling would move to a lighter battery that you can use more of the charge and not be limited to 25% or 50% with the good deep cycle batteries.

Going to start a battery bank for some home power. Had let my supply of step down and buck converts run out. Have been buying replacements. Have one now to run my 12v lights on my bike's 72v battery. Bought another solar charger as my last one had quit.

Having things run on 12v or 24v DC is the best option. Would like to get away from inverters. AC is great for transporting power across distances but wasteful used in appliances.

by wineboyrider » Oct 28 2021 9:48am

Just got my hands on a nice RV casita camper trailer. I plan on keeping the crappy lead acid battery installed. But, I have plans to take my ebike batteries and army of 40v greenworks batteries with me to power small ac appliances I purchased a cheap $40 greenworks inverter with 300w ac power and usb ports. But, I also will buy a 36/48v 30 amp golf cart step down inverter to keep my 12v stuff running. Need to add a few solar panels down the road. But I don't want to modify anything in the camper as it's pretty nicely setup.

[wineboyrider]

Agreed that's why I plan to use a step down golf cart converter and use mostly 12v appliances. I already have some cool greenworks connectors that snap right in like the real deal. Need to find a 12v tv first. After that it's a small gas generator for the ac.

[ZeroEm]

Replied and started a new thread, join in.