The Best Solar Charge Controller Settings For LiFePO4 Batteries

LiFePO4 (lithium iron phospate) batteries are popular for many reasons. But basically it comes down to the fact they provide better performance compared to AGM, gel and other lead acid batteries. To get the best results, however make sure the controller settings are optimized.

Your charge controller probably has default settings, or suggestions in the instructions. You can use those or you can try the following which is optimized for most LiFePO4 batteries including the Ampere Time LiFePO4 200ah.

Best Charge Controller LiFePO4 Battery Settings

Go to the settings in your charge controller. Adjust the parameters so it looks like the following.

Charge Limit Voltage
For 12V battery, 14.2V
For 24V battery, 28.4V
Float Voltage
For 12V battery, 13.5V
For 24V battery, 27V
Low Temperature Cutoff
5 C / 41 F
Set Equalize Time To:
0 or Disabled
Set Temperature Compensation Coefficient
0

If there are other setting options, leave the default as is. The following settings are for Epever MPPT charge controllers and Battle Born Batteries. Yours might be different so refer to the solar controller set up instructions.

These are for 12V systems. Double the voltage if you are charging 24V batteries.

Boost Duration
180 minutes
Discharging Limit Voltage
10.5
Low Voltage Disconnect
11.0
Under Voltage Warning
11.5
Low Voltage Reconnect
10.0
Boost Reconnect
13.0V
Boost/Bulk Charging Voltage
14.6
Over Voltage Reconnect
14.6V

Important: LiFePO4 batteries do not require temperature compensation. Most controllers turn this off by default. But check anyway just to be sure. If it is turned on, shut if off. If you leave this on, the voltage charge is going to produce inconsistent results.

LiFePO4 Depth Discharge

The following is the depth discharge for a typical 12V battery. Double the values if your battery is 24 volts and running a 4kw solar system.

• 13.6 to 14.4V – 100%
• 13.4V – 99%
• 13.3V – 90%
• 13.2V – 70%
• 13.1V – 40%
• 13.0V – 30%
• 12.9 – 20%
• 12.8V – 17%
• 12.5V – 14%
• 12V – 9%
• 10V – 0%

Some solar charge controllers may not have options for lithium iron phospate. in that case, look for a “user” or custom configuration mode. Adjust the settings similar to the ones given here.

If you are a seasoned solar power user, you might want to tinker with the settings to get the results you want. Even at the default however, lithium batteries will outperform lead acid, AGM and gel.

Lithium batteries charge faster and have a longer depth discharge rate. For heavy duty applications it is better to invest in lithium batteries than lead acid. Of course you must have an MPPT charge controller to take full advantage of it.

Most of these batteries need at least 13.6V to charge. Anything under that and charging will take too long, if at all. Above 13.6V and the battery will get to 95%. At 14V the controller needs only a few hours to recharge the battery up to 95%.

Speed wise there is not much of a difference beyond 14.2V. So you can set absorb at 14V to 14.6V and the charge should run fine.

LiFePO4 Battery Charge Settings Explained

The following are some of the most common specifications you will find in charge controllers. Check your controller instructions for more detailed information.

Boost charge mode. The controller charges at the highest power level until the boost mode value is attained. The controller will attempt to draw max power until it reaches the target voltage. The duration can be adjusted.

Boost reconnect voltage. When the system is at float, the voltage can change due to solar output. The system goes back into boost if the voltage drops below the boost reconnect voltage value

Charge limit voltage. The controller stops charging the battery if the battery voltage is higher than the charge limit voltage.

Discharging limit voltage. Sends a warning at the given voltage set.

Equalize charge voltage. Refers to the voltage used over a specific period. This is applied after the boost
target voltage has been attained.

Equalize duration. This is the absorption phase. When the boost period is reached, voltage is now constant.

Float charge voltage. Once the boost stage is finished, the controller adjusts the power search. The panels are set to generate a constant voltage float.

Low voltage disconnect. When this voltage is reached, the battery load output is disconnected.

Low voltage reconnect. This is turned on if the load is disconnected because of low battery power.

Over voltage disconnect. The load output gets disconnected if the battery voltage goes over this value.

Over voltage reconnect. If the load is disconnected because the battery goes over voltage, the system will reconnect at the given value.

Under voltage warning. This is where warnings are set.

Under voltage warning reconnect. The warning is turned off at this value.

Boost, Bulk Charging and Other Settings

Some charge controllers use the terms boost and bulk interchangeably. Others consider them two different settings.

In some charge controllers, the bulk is the first part of the charge cycle. A controller remains in this phase until constant charge voltage is attained.

Constant charging follows and consists of boost and equalize. During the equalize cycle, the battery electrolytes are stirred and gassed. The boost cycle prevents too much gassing and overheating.

You can think of it this way. When you charge a LiFePO4 battery, the controller commences with the highest setting the solar panel can generate. The voltage will remain constant when the boost level is reached. The boost period can be any duration but usually it is two hours.

Boost duration is the same as the absorption phase, and absorption voltage is the same as boost charging voltage.

After the charge reaches the float phase, the controller will try to keep the voltage constant. The voltage will drop to boost reconnect under certain conditions. For instance, unfavorable weather might affect solar performance, or the load might be too much for the system. If it drops to boost reconnect the charging process will restart.

The equalization duration period is usually at zero for LiFePO4 batteries. The equalization voltage must be lower than boost or equal to it. in most cases it is better to have the equalization voltage lower.

Important Reminders for Charging LiFePO4 Batteries

• Avoid 100% SOC charging whenever possible.
• Avoid a 100% SOC float.
• Cycling under 10%-15% SOC is not recommended.
• The battery temperature should be kept above 0 C / 32 F when you discharge.
• Discharge and charge currents has to be below 0.5 C / 32.9 F
• The battery temperature has to be under 30 C / 86 F

Majority of charge controllers will have no problems charging a LiFePO4 battery. its voltages are similar to AGM, gel and other lead acid batteries. All high quality LiFePO4 batteries including the BTRPower 100ah also have a BMS (battery management system) that protects it from overheating and overloading. The BMS also makes sure the battery operates at the ideal temperature and the cells are properly balanced.

To recap: when aLiFePO4 battery is charged, the system tries to maintain the current. If you are using a solar array, that means the system tries to send as much current as the solar system can deliver (without overcharging the battery).

The voltage then starts to rise until the absorb phase is reached. At the absorb level the battery is around 90% filled. For the rest of the charge the battery current tapers while the voltage remains the same. The battery reaches 100% SOC (state of charge) at 10% to 5% of its ah rating.

Compared to lead acid, v batteries are simpler to charge. Just make sure the voltage is high enough and the charge will proceed. There is no equalizing or sulphating to worry about. You do no even have to charge the battery 100%.

Lastly, do not purchase a LiFePO4 battery without a BMS. This is very important as it can mean the difference between a long lasting battery and one that dies off quickly. Buying from a reputable manufacturer is always a good thing as well.

Conclusion

There are many other settings you can try with LiFePO4 batteries. You can tweak the other options but that is best left for experts. If you are a beginner, we suggest using the settings given here.