Troubleshooting ACr on Charger Controllers

Lithium Battery Activation

Lithium batteries with a battery management system (BMS) typically have a protection feature against abuse or inoperable conditions. They will lock out and disengage the battery from the circuit and slip into a low power discharged state that gradually depletes if not charged or activated.  The Renogy charge controllers or battery chargers are equipped to activate batteries under this scenario and recharge batteries so that they can be serviceable again.

The following causes highlight the different scenarios where a battery may need to be activated as well as their respective troubleshooting procedure. It is important to verify the causes so that the correct action could be taken to clear the ACr code since some locked batteries due to user error connection have the potential to not clear ACr until the circuit is fixed.

The following fixes require a multi-meter to better understand your system and to properly troubleshoot your system. If you do not have one, it is advised to get one. In addition, Lithium activation requires the assistance of PV charging power. For activation to work, the solar panel(s) must be connected correctly and providing charge power for lithium activation to take place.

Cause 1: Break in the Circuit

  1. The controller is connected to PV and a battery set to Lithium but is not properly connected to the battery because it might be experiencing a break in the connection. The ACr code is shown because it is powered by the PV circuit and not the battery circuit during this time. ACr will remain until the connection to the battery is fixed.

Fix 1: Restore the Broken Connection

To check for a break in the connection, use a multi-meter to measure the battery voltage and get that reading. Then, measure the battery terminals on the charge controller to see if they are roughly the same. Drastic reading differences indicate a bad connection.

In addition, certain meters will have a continuity tester; refer to your meter for those instructions. Measure continuity between the controller and battery positive connections to verify no breaks in the connection. Repeat for the negative connections. The beeps indicate a connection. No beeps indicate a missing connection and could be the root cause. Once the connection break has been restored, the controller will be able to send a charge and clear the ACr code automatically.


Cause 2: 12V Lithium Incorrectly set to 24V on Controller

Renogy Lithium batteries are nominally 12V and need to be manually selected on Renogy charge controllers. The charge controller is set to Lithium and incorrectly set to 24V, resulting in the controller believing the 12V Battery Lithium battery is depleted and needs to be activated.


Fix 2: Manually set your controller to 12V Lithium

Renogy controllers require manual programming of lithium batteries, including their voltage. The controllers will usually have an option for a 12V or 24V system as well as the specified charging voltage. When first connecting your battery, change the battery type to Lithium and select 12V. Different controllers might have different instructions on selecting your 12V lithium battery, but the concept is the same. When changing from 24V to 12V, the ACr code will clear automatically upon detecting the battery and starting normal PV charging. For those batteries that are too discharged to meet the minimum voltage of the controller, then you should connect a separate 12V Battery (perhaps a vehicle battery) and change the settings from 24V to 12V. 


Cause 3: Your Demand is higher than your Lithium Battery Capacity

The controller and lithium battery are correctly set to 12V; however, the battery was not able to keep up with power demand and is now out of power resulting in disconnecting from the charge controller via BMS protection.


Fix 3: Limit Load Use or Increase PV or Batt Size

The battery has been over-discharged, whether it was intentional or accidental, and needs to recharge. Make sure to disconnect any loads from the battery and make sure the above causes are not the issue. The battery is currently locked out and upon no loads being connected, the controller will attempt to send a small charge to the battery to activate it assuming adequate PV charging. Some batteries will need to have a voltage of at least 10V to be recognized by the charge controller. The ACr will automatically clear upon the battery being activated.

Limiting your load use will be effective in not draining the battery as quickly. This may not be a favorable solution so the next best would be to increase the battery capacity as well as increasing the charging rate through your solar panels. Having a larger capacity will slower the rate of discharge and can be better sized to your application so that you have a sustainable system. Contact Renogy for sizing your specific application to ensure this does not happen.

Cause 4: Lithium Reverse Polarity w/ Solar Connected

WARNING! Prolonged reverse polarity connections with lithium batteries will likely cause permanent damage to the controller

The controller is connected to PV and a battery set to Lithium but is reversely connected to the battery terminals. The ACr code is shown because it is powered by the PV circuit and not the battery circuit during this time. ACr will remain and has will not clear for the duration of solar power since the battery circuit can not be detected.



WARNING! The controller may experience permanent damage in this scenario

Fix 4: Fix the Poles, then Observe for Change

Disconnect the solar panel first just in case. To check for reverse polarity, use a multi-meter to align the positive meter pole to the battery positive pole and the negative meter pole to the battery negative pole to get a voltage reading. Using the same convention on the charge controller battery terminals to measure the respective battery poles. If the voltage indicates a negative number, the poles are reversed. Positive indicates correct polarity.

If your poles are reversed, restore the proper battery poles to the controller and the controller may/may not turn on depending on your battery voltage. Once this has been checked with a meter as being correct, you can then connect your PV source again to restore charging and activate the battery. Long-term (after a few days) ACr code indicates internal controller damage and you may need to contact our Tech Support Team for next steps.

Renogy is the author of this solution article.

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