Is my inverter compatible for new LiFePO4 batteries?

[merryfish]

Hi all,

I bought an off-grid house with a system already installed. I’m new to this and keen on learning more about my system so I can maintain it over time. I have outlined the setup below. My current batteries are dead/not holding a charge (Crown CR-235 deep cycle flooded). I want to purchase some LiFePO4 batteries (either Battle Born, Li Time or Renogy).

Before I purchase any of these batteries, I am unsure if my current system/setup is compatible with LiFePO4 batteries? I tried pulling up the operator manuals, etc. and it didn’t specify so wanted to check in here.

Current batteries: 8x Crown CR-235
Magnasine MS2024 inverter
Magnum energy MC-ARC50 Remote Control
TriStar Solar Charge Controller TS-M-2

Will this inverter, remote control, controller setup work with LiFePO4 batteries? Attaching a couple pictures of my setup if helpful too. Thanks!

 

[Horsefly]

24V 8S LiFePO4 batteries will work with that inverter, just in terms of the input voltage range. The TriStar TS-M-2 is a battery meter, not a solar charge controller. Do you have another device in the system that might be the SCC, or did you get the model number wrong?

Edit: I guess the TS-M-2 is called a "meter" but is used to control a solar charge controller, so it must be connected to an SCC.

 

[merryfish]

Thanks for your reply! I have a Magnum energy ME-ARC50 Remote Control (updated serial # vs. my original posting). It's in the top right in the picture, although hard to see. Is this an SCC that you were referencing?

Do I need to change any charging settings (or other settings) in my SCC switching from older batteries to LiFePO4

 

[Horsefly]

The short answer is yes, you will need a different charge setting for your SCC and your inverter/charger (if it is connected to a generator or grid). The charge profile for LiFePO4 is different.

First thing: You are probably looking at 12V drop-in replacements for your existing lead-acid batteries. If you want to stay with a 24V system, you would be much better off buying 24V LiFePO4 batteries, as they will be designed to maintain the cell balance across all the cells. If you us separate 12V batteries in series, you will probably end up with imbalance between the batteries. I don't mean this as a hard rule, so if you really want to get some of the 12V batteries you can probably make it work.

For charging, you would want to set your bulk / absorption voltage to between 27.6V and 28V. I use 28V for my 24V LiFePO4 system, but many folks prefer the "softer touch" 27.6V (3.45V per cell) instead of 28V (3.5V per cell). You should probably set the float voltage to something close to 26.8V (3.35V per cell).

You want the charger to drop out of absorption and into float soon enough to keep the batteries happy. There are two ways to do this:

(1) If you charge controller has a "tail current" setting, you should take the total Ah capacity of your cells and multiply it by 0.05, and set that as the tail current. So if you have a 200Ah battery, 200 x .05 = 10A, so you would set the tail current to 10A. When the current going into the battery goes down to 10A, the charger would drop out of absorption and into float.

(2) If you don't have a tail current setting, set your max absorption time to something like 30 minutes. The time recommended by folks here on the board can vary by quite a bit, so there may be some strongly worded rebuts to this recommendation. I think it doesn't matter that much, but shouldn't be much longer than 30 min.

Your inverter probably has a LVCO (Low Voltage Cut Off) setting, where the inverter will turn off because the battery is too low. For LiFePO4, a reasonable LVCO is 3.1V per cell, or 24.8V for your 24V system.