LiFePO4 Battery
Xiaoxing BMS App
I watched some YouTube videos on constructing your own lithium iron phosphate (LiFePO4 or LFP) batteries and it seemed straight forward and well within my comfort zone. So when I found that they could be ordered from the manufacturer in China for 1/2 the MSRP in the US I decided to go for it.
I order a set of four 200Ah Liitokala battery cells on AliExpress. They were $312 and lead time was 60 days. My credit card fraud alert immediately tripped when I made the purchase, I guess because "China", but I crossed my fingers.
Eventually the batteries arrived. They were all close to zero state of charge (SOC) but they seemed in good shape. That was a relief since I'd been reading horror stories online about degraded, bloated cells ever since I placed my order.
Checking out the battery voltage in the shipping container
There are a lot of really good YouTube videos on building DIY batteries. The ones by Will Prouse are my favorites.
There is some debate about the best approach to "balance" the cells and your intended use seems to matter. For my purposes the first step is to "top balance" the cells. That is bring them all to the same full state of charge. You do this by connecting them in parallel and then charging them to 100% SOC. Since my batteries were near zero SOC this took a long time - almost a week with my little DC 10A constant voltage/amperage power supply. You just set it to the max cell voltage (3.65V) and wait till the amps drops close to zero.
Cells connected in parallel at the start of top balance process
There are other ways to charge the cells to near full SOC faster, but this is simplest and I had the time.
After verifying the cells were closely top balanced you can assemble the cells in series. This creates a single "12V' (actually 14.4V) battery.
Verifying cell voltages after top balancing
There are a lot of ways to mechanically connect and physically house the battery cells to create the final product. They sell battery housings for just this purpose, but they are pricy. I chose to use an inexpensive group 24 battery box that would typically be used to hold a trolling battery in a small boat.
I mechanically connected the battery cells using double stick VHB tape between them and "Kapton" tape around the outside.
The LFP battery cells require a battery management system (BMS) to keep them balanced and also protect them during use. There are a lot of BMS systems available, but for an RV that will have solar power to keep the batteries charged it's important to have a low temp charging cutoff. LFP batteries will be ruined if you try to charge them under freezing conditions, so you need a BMS that disables charging when the cells are cold. You also need a BMS that will provide sufficient amperage from the batteries. In my case that's at least 85A (1000W inverter/12V).
I ended up choosing one of the variants of the 120A Jaibaida (aka JBD) BMS. It came with two battery temp sensors and a bluetooth module for about $100. You can get them cheaper by buying direct on AliExpress, but I went through Amazon and bought a unit from RadioBTech.
Hooking up the BMS is pretty easy. You wire a connection to each terminal in the series of cells and then the BMS connects between the main negative terminal on the battery and the negative connection to your load. May seem complicated but it's not.
Cells physically connected and BMS installed
After you wire it all up you can test it by downloading an app to you android or apple phone and connecting to the BMS via bluetooth. I found two versions of the Android BMS app available online. The first was on the Google Play store but it was very limit in ability - essentially you can only monitor the battery, you can't change any of the various BMS features and parameters to find tune things.
On the RadioBTech website I found a link to the "administrative" version of the Android app. It allows you to set many different parameters available in the BMS. For example the minimum battery charge allowed before the BMS shuts off power output (to prevent battery damage).
While checking out the battery via the app I found some issues. Eventually I isolated the problem to the leads connected to each cell. I hadn't crimped the connectors very well so the connections were flaky. That was an easy fix.
As I mentioned earlier, I put the whole thing in a NOCO group 24 battery box and installed some external connection terminals on lis of the box.
Cells and BMS installed in group 24 battery box
Final product
I'll install the battery in the Boles this weekend. I've got a battery tray and a hold-down strap to keep it firmly in place under one of the dinette benches. The exterior dimensions of the box (including the terminals) is about 13"x9"x11.5" (LWH) and it weighs about 39 lbs. Not bad when a 200Ah AGM is 20"x9.5"x9.5" and 120lbs.
UPDATE:
I installed the battery in my '48 Boles and it works great. The NOCO battery box came with a hold down strap and anchors but I decided to beef it up a bit. I used a QuickCable universal battery tray (part 302120) that fits the battery box perfectly. It was a hunt to find a suitable tray because the battery box outer dimensions are larger than the group 24 battery standard. I also used a hold down strap with 316 stainless steel anchors and buckle. There are several different ones targeted for marine use available on Amazon.
Battery installed in dinette bench
MPP Solar 1012LV-MS All-In-One
With the exception of the lighted pump switch I installed upside down, it all checked out 4.0. Even the DIY remote inverter switch I rigged up worked! I was surprised that there was so little rework.
We have power!
I was unable to check out the shore power circuitry because I bought the wrong 30A-to-15A adapter. The Furrion 30A connection I installed uses a screw-on type marine connector vs the typical one you find on RVs. So I'll just have to wait until the replacement adapter arrives.
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