We have a lot of posts about solar battery systems and how to maintain them. But, we haven’t talked a lot about solar maintenance for systems that aren’t attended year round. Solar maintenance for systems that aren’t regularly used is somewhat different. Since power isn’t used on a regular basis, your charge controller settings need to be adjusted.
Charge Controller Stages
First, let’s talk about how charge controllers work. The more you understand about your solar system, the better your system will perform. Your charge controller goes through 4 stages of charging.
Bulk
The bulk stage brings the battery from its current state of charge to about 80%. Since it’s a higher constant current charge, the battery voltage will continue to rise throughout the stage. These settings are set within the controller, so there isn’t much to modify here.
Absorption
These settings are modifiable and therefore, you need to monitor them. This stage brings your solar bank from 80% to 100% charged. Both the voltage and time are modifiable. This stage supplies constant voltage and declining current. In this setting, you have the most control over fully charging your battery bank. After the system goes into float, check the state of charge of the solar bank. We suggest using a hydrometer for this test. It is accurate and easy to use. If your solar bank is fully charged, 1.265 or higher, your absorption settings are correct. If not fully charged, you either need to increase the voltage or the time in absorption. Sometimes, you have to increase both settings. With less sun in the winter, you have less time to reach a full charge. Monitoring for a full charge is also important during these events:
- Setting up a new system
- Replacing batteries in an existing system
- Change in seasons – see Blog post Solar Battery Charge Controller Adjustments
Float
Ideally, your solar bank will go into float once your batteries are fully charged. This stage is designed to keep your solar bank at a full charge until your next use of the batteries – when the sun goes down.
Equalization
This stage is a “controlled overcharge” of your solar bank. Equalization helps prevent sulfation and acid stratification. For more information on this stage, see Blog post Equalization Techniques for Solar Battery.
Suggested Settings for Proper Solar Maintenance
| Voltage Setting | Volts/Cell (VPC) | 12 Volts | 24 Volts | 48 Volts |
| Daily Charge (Absorption) | 2.42 | 14.5 | 29.0 | 58.1 |
| Equalize | 2.58 | 15.5 | 31.0 | 61.9 |
| Float | 2.25 | 13.5 | 27.0 | 54.0 |
The above suggested settings assume 2 things:
- A Depth of Discharge (DoD) of no more than 50%
- The total input amperage is at least 10 amps per 100 Ah of battery bank, or 10%
The suggested timer setting for the absorption phase is 2 hours per parallel string. We suggest no more than 2 parallel strings per inverter.
Solar Maintenance as Usage Changes
Now that we know some basics, we can get to the main reason for this post. Systems that are used everyday, with normal loads, will require absorption settings to achieve that last 20% of charge. For unattended systems, like weekend cabins or vacation homes, you probably won’t draw a lot of power when you aren’t there. You won’t need to keep your absorption charge at two hours per string.
With little current leaving your solar bank, the bulk stage might be enough to bring your solar bank to 100% If this is the case, you should set your absorption charge to the proper voltage and set the time to 5 minutes. This will keep your solar bank from overcharging. Depending on what draws on your system when unattended (furnace, water heater, etc…), you might need to adjust these settings. When you return, make sure you check to see if the bank is at a full charge. If not, you must adjust your settings again.
The earlier you correct, the better. Solar maintenance can be frustrating. The more you know, the longer it will last. Take the time to make your investment pay off. As always, American Battery Corporation is here to answer your questions and concerns. Give us a call or stop by – we love to solve problems. Remember, “We Sell Batteries – Knowledge and Service Are Fee”.