Thursday, April 30, 2020

Fixes and Fails - LiFePO4 Lithium Battery upgrade - Part 1

As I previously mentioned the Lead Acid Golf Cart batteries that came with our RV, had trouble maintaining the minimum 50% charge when the furnace was running.  The furnace is Propane, but the fan pulls over 11 amps.  After watching prices for Battleborn LiFePO4 (Lithium Iron Phosphate) batteries, I finally found a good deal on Cyber-Monday (they were offering blemished batteries for $750, which is about 25% off!)  They still come with the 10 year warranty, so, I ordered 4 of them...

I had originally wanted six of the 100 Amp-Hour batteries, but after working for months on different ways I could mount them on their side or upside down or whatever,  I just couldn't find a good arrangement and truth be told, I didn't have the money. 

After researching Lithium vs Lead Acid, I had determined that since the Lithium batteries could last 20 years and Lead Acid rarely last more than 5, the cost of the Lithium over time is actually less and there is no regular checking and filling of the batteries, which is quite a hassle.  Combine that with the fact that Lithium batteries of the same size have more than twice the usable capacity and weigh considerably less.

So replacing the 4 lead acid golf cart batteries with Battleborn batteries with the same GC2 form factor was what we planned.  Turns out the Battleborn batteries were a little bigger, so the existing  hold-down bracket would not work.

Existing 6 volt Golf Cart batteries
New Battleborn 100 Ah GC2 batteries
Battleborn State of Charge
Unlike Lead Acid batteries, there is not a good translation between Lithium Battery Voltage and State of Charge (SOC), which means the only way to really gauge how much you have remaining is with a Battery Monitoring System.

As you can see from the table to the right, one volt could mean a 1% difference in the state of charge, but .1 volts could mean a 20% difference. Also, those voltages assume the battery is not under load and in our RV, they are always under load or being charged. The Battleborn batteries have a build-in BMS, but that is designed to protect them from things such as over-charge, low voltage, low temperature and a host of other parameters that could turn your investment into some really expensive bricks.  After a lot of research, I selected the Victron BMV-712 battery monitoring system.  It monitors the power going into or out of the batteries and calculates your SOC based on the total battery capacity you provide. Plus, it uses the same Bluetooth app for setup and monitoring as the Victron Solar Charge controller we installed earlier.

Our Thor Palazzo 33.2 comes with a Battery Isolation Manager (BIM) that will allow both the Chassis Batteries (the two Lead Acid AGM batteries that are used to start the engine) and House Batteries to both charge from the engine Alternator, Magnum Inverter/Charger, or the Solar.  Basically the alternator is connected to the Chassis Batteries and the rest are connected to the House Batteries and the BIM connects them together when it detects that there is charging voltage on one and the other needs charging or when you press and hold a switch on the dash (used when the Chassis Batteries are dead).  Since the Battleborn batteries have different voltages than the original batteries, the BIM will not work correctly and since the alternator doesn't have great voltage control it may not be best for the new batteries. The folks at Battleborn obviously recognized this as they sell a Li-BIM, which appears to be identical to the original and is even made by the same company, but is programmed to operate at different voltages and for specific intervals.
Original Battery Isolation Manager
Finally, the Firefly control does not have a setting for Lithium batteries, but the Magnum inverter will support them, so I decided I needed to get the Magnum RC-50 remote, which would allow me to configure all settings on the inverter and monitor it.  I found a document on Battleborn's site with specific instructions for programming the Magnum inverter.

So, my shopping list is:

Straps to hold the batteries in place
Victron BMV-712 battery monitor
Some 4-0 welding cable for connecting batteries
Ends for the cable along with some shrink wrap
A Li-BIM - Battery Isolation Manager from Battleborn
Magnum RC-50 inverter remote

The battery bay was designed for Flooded lead acid batteries, which can produce explosive gas when charging, so they provided ventilation holes in the top and bottom.  Lithium batteries do not produce gas and neither do the AGM batteries used for the engine, so I decided to block those vents which would hopefully prevent water from getting in when driving in the rain.  I had noticed water in there several times and there was rust starting to form on the bottom.

I had a piece of Plexiglas leftover from making a barrier to keep Krikkit from falling down the stairs, so I decided to just glue that over the holes in the bottom.

In Part 2, I discuss the installation and the issues we encountered.

1 comment:

  1. No, problem. It was over my head until I started researching.