Connecting Two Charge Controllers To One Battery Bank | What You Need to Know
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A solar charge controller is among the most essential equipment for any off-grid solar power system. Its importance is evident in the protection it provides to the battery bank, as it regulates the energy of the solar panels that are sent to the battery bank according to the state of charge.
Each charge controller has its own specifications, the most important of which is the range of voltage and current limits that must be respected. If you have a connected solar array within this range, you will not consider using two solar charge controllers. However, if you want to add more solar panels to your system, you will need to upgrade your charge controller, or add multiple solar charge controllers.
In the subject of this post, we will learn how to safely connect two solar charging controllers to one battery bank, Is it better to connect two solar charge controllers or use one with a high current unit?
Can I Use Multiple Solar Charge Controllers?
Solar controllers regulate the charging process by regulating the current they send to the battery terminals using a voltage-based state of charge (SOC).
For example, if the battery is low, the solar charge controller will send the charging current in bulk. And when the battery is almost full, the solar controller will reduce its charging current.
Charge controllers sense the state of charge of the battery continuously, so connecting the outputs of several charge control devices directly (in parallel) to the battery will not pose any problems with each other, and they will all work at the same time because they will all sense the same state of charge of the battery.
So it is possible to connect two or more solar controllers because this type of setup does not make them compete or reduce their efficiency.
Can I Connect 2 Charge Controllers to 1 Battery Bank?
One battery can charge seamlessly with multiple charge controllers because all charge controllers connected in parallel with the battery will work synchronously. As a result, the battery will be charged with a total amount of current equal to the sum of the charging current that each individual charge controller sends to the battery.
This is exactly the same as connecting panels in parallel, where the current increases and the voltage remains constant. Refer to the article about series and parallel wiring of solar panels if you want to know more about how to wire your panels.
For example, if the charge controller A sends 3 Amps to the battery and the charge controller B sends 2 Amps, the battery will charge with a charging current of (8 + 7) = 15 Amps.
Thus, you can connect two solar charge controllers to the same battery bank, and they will work well together without having charge controllers able to communicate with each other. However, it is important to make sure that the charge controllers are compatible with the battery and with each other to avoid any problems or damage that may occur.
Here are some points to be sure of before connecting two or more charge controllers to the same battery bank:
Maximum Charge Current (C-rate)
You must know exactly how much current the charge controllers will send to your battery bank. and the recommended charging current for the type of batteries you are using.
Most lead-acid battery manufacturers recommend charging them at a C-rate of 0.20 of battery bank capacity C (Maximum charge current = 0.2xAh capacity). While lithium batteries can be charged at a C-rate of 1C (Max charge current = 1xAh capacity).
So if you have a 200Ah lead acid battery bank, the maximum charging current that the charge controllers must send to the battery bank is:
Maximum Charging Current = 200Ah x 0.20 = 50A
You have to make sure that the battery capacity is high enough to accommodate the current of two or more charge controllers. If the combined charging current is higher than the battery C-rate, you will overcharge your battery bank.
Multiple Charge Controllers with Equalization Mode
If the batteries will be equalized, such as lead-acid batteries, and you want to connect multiple charge controllers, it is important to turn off the automatic equalization on the other charge controllers so you only have one charge controller performing the equalization function if it can provide enough charging power to complete the equalization.
It is important to ensure that equalization is done at the same time for all controllers. In some cases, manual equalization is the best way to ensure that equalization starts at the same time for all charge controllers. Auto equalization may not synchronize between multiple controllers, which may continuously cause a High Voltage Disconnect (HVD) alarm for charge controllers that do not equalize at the given hour.
The Victron SmartSolar charge controller uses the built-in Bluetooth module to communicate with each other and with dedicated apps on portable gadgets you can access to adjust the equalized charge cycle settings, and also to monitor the performance and efficiency of the systems.
Here are some other considerations that must be taken into account to ensure that the battery bank is properly charged with multiple charge controllers without them having to communicate with each other:
- Each solar charge controller should have its own separate PV array sized according to the solar controller specifications. even if specifications are different from each other.
- All charge controllers must have the same settings (same charging profile: battery type, cutting voltage, etc.).
- Ensures that each controller measures the same battery bank voltage. The solar charge controllers must all be connected in parallel in order to share a single connection with the battery bank.
- If the controller supports external battery temperature sensing, each sensor must be connected to the battery to compensate for the voltage temperature. You may not need to hook up the battery temperature sensor, if the battery bank is located in a climate-controlled location.
- The wires of the charge controller must be the same length and width, if one of the charge controllers is far from the batteries, it may enter float mode earlier than other charge controllers due to the voltage drop.
The 4 Cases Where Multiple Charge Controllers Can Be Used
Here are some of the reasons/benefits of using multiple charge controllers
1. Support an expanding solar system
If you are willing to expand your solar system, you will need to add more panels, which will increase the voltage of the system. As a result, the existing charge controller will not be able to handle the expansion capacity well.
Fortunately, it is possible to connect multiple solar controllers in parallel to support large and expanding solar systems.
2. Expanding the solar system with panels of mixed specs
In many cases, when expanding your solar system, you may not find panels with similar specifications to the ones you have already acquired. So even if your charge controller has not already reached its maximum limit, you will need another charge controller to add solar panels that have different specifications than the ones you already have.
Connecting solar panels of different specs (voltage and current) either in series or in parallel, will result in some losses in the total power produced by the array.
3. East-West facing solar panels on two charge controllers
Orienting the panels east-west can be an effective solution to make the most of the available solar energy in a limited space. This is because half of the panels facing east will get the most amount of solar energy in the morning, and panels oriented to the west will get the most amount of solar energy in the afternoon and evening.
In such a setup, you will need two charge controllers to charge the same battery bank: One for the panels facing east and the other for the panels facing west. However, connecting solar panels oriented in different directions to the same charge controller is inefficient and will result in a total loss of power for the entire assembly.Check out our article to learn about east-west vs. south solar panels.
4. Shading conditions
If it is difficult to avoid shade in the place where the solar panels are installed, then distributing the solar panels to multiple controllers may be the best solution. Shading one or more panels on one string will affect the output of other strings.
Shading one panel on string one is as if another panel on string two were shaded.
Multiple Charge Controllers vs. Upgrading to a Bigger Charge Controller
If you install an off-grid solar energy system, you may later expand your system to run more loads. However, adding another charge controller is not the only option to handle the new expansion capacity, you can sell the charge controller you started with and upgrade to a bigger charge controller as well.
This gets us to our question: is it better to network multiple solar charge controllers, or is upgrading the charge controller to a bigger one the right option?
A double system of two charge controllers will have somewhat more wiring, on the other hand, with a single system composed of a large controller, the wire size used between the controller and panels will be larger.
Larger controllers can handle higher voltages, such as 140 to150 volts. As for smaller control units, they may be limited to 75 to100 volts only.
Larger charge controllers often have more features and programs.
Multiple charge controllers or one high-current unit? (Example)
Let's say you have 4 Renogy Solar Panel 200 Watt (Voc 23V) panels installed in series, a 24 volt battery system, and a 100|20A MPPT charge controller.
You have space to add 4 other panels with the same specs by upgrading to a bigger charge controller 150|40A, you will not be able to install all 8 panels in series because the voltage generated by this setup will be greater than 150 volts.
Therefore, you will need to install two arrays of panels in parallel, each array consisting of four panels, which is approximately the same setup that you would do if you chose to add another controller 100|20A.
Therefore, in this case, there is no need to upgrade to a bigger charge controller.Advantages of multiple charge controllers on a high-current unit
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- If one fails due to a bad product, bad wiring, or perhaps a problem with a particular solar panel, you always have something else to back up or rely on.
- Networking multiple controllers allows you to use solar panels of different specs.
- Wiring multiple controllers allows you to distribute solar panels in different locations and orientations.
- In some cases, multiple solar controllers can regulate the energy produced by the panels more efficiently than one large charge controller. Because the larger the solar panel array (the combination of series and parallel connections), the greater the possibility of mismatch losses in a PV system due to the effects of shading, dirt, and hot spot problems.
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Additionally, it may be cheaper to buy two 30 amp charge
controllers (that give you 200 Volts of solar panels charging
your batteries at 60 amps) instead of one 60 amp charge
controller.
Conclusion
It's okay to use two charge controllers connected to the same battery bank, as long as you use identical settings. You just have to be careful not to exceed the charging rate specification of your battery bank. In terms of single versus multiple charge controllers, single has the advantage of simplicity and centralization, while multiple is theoretically more efficient in some cases and provides some redundancy.
Mohamed Bellamine
I'm the blogger behind Goo SolarPower. As a solar engineer, and a strong supporter of renewable energy. I've always been interested in Solar devices. I loves to write articles, guides, and tutorials about solar PV technology. Through goosolarpower.com I want to help people build and understand how solar power systems work.