We often receive questions about wiring a solar system. For those new to solar, this might seem intimidating, but it’s actually straightforward. In this blog, I’ll guide you step-by-step through the wiring process for our dual output controller.
Let’s start with a few key terms:
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MC4 Connector: This is a waterproof connector commonly used in solar wiring. Most solar panels come with MC4 connectors pre-installed on a 3-foot solar wire pigtail from the panel's junction box. These connectors are easy to disconnect.
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Solar Controller: Essential for most solar systems (except small trickle chargers), a solar controller regulates charging to prevent overcharging, optimizes the current for charging the battery bank, and stops reverse current from flowing back to the solar panel at night. Controllers are rated by their amperage capacity. Residential and commercial controllers are often too large and not ideal for marine applications.
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Temperature Sensor: Connected to the controller, this sensor monitors the battery bank's temperature. If the batteries start to heat up due to heavy charging, the sensor signals the controller to reduce the charging current. Temperature sensors are most beneficial for larger solar arrays; smaller systems usually don’t generate enough power to cause overheating.
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Solar Wire: While various wire types can be used, solar wire is specifically designed for high conductivity and durability. It features UV-resistant insulation and is typically a single conductor with a diameter of 0.25 inches.
The wiring diagram below, from our dual output controller manual, illustrates the setup for a two-panel system with a dual output controller and two battery banks. Most solar controllers are single-output, meaning they only charge one battery bank. In these cases, the positive wire is often connected to the common terminal on a 1-2-both battery switch to select which battery bank to charge.
Let’s dive into the wiring steps.
A few things to note in the diagram:
* The two solar panels are wired in parallel using an MC4 T-branch connector, If one panel is shaded, the other panel will still provide full power to the controller.
* There is a switch in the positive wire between the solar panel and the controller. This is optional. The purpose of the switch is to turn off the panel should it interfere with the alternator output when the auxiliary engine is generator is running. It has been reported that some smart regulators are confused by the power coming from the solar panel. It sees the sum of the battery charge plus the panel output and senses the batteries are fully charged so goes into float mode prematurely. This is easily remedied by flipping the switch thus disconnecting the solar panel.
* The optional temperature sensor is shown to the left of the larger house battery bank. It is simply taped on to the top of the battery.
* If you have a battery monitor such as a Link or Xantrex 1000 or 2000, it is important to connect the negative wires from the controller to the shunt of the battery monitor. Otherwise, the monitor doesn't see the power coming in from the solar panel and will give inaccurate readings.
* There is a sequence to follow in connecting the solar system. Connect the controller to the battery banks first. Then connect the solar panel to the controller.
Additions to this article:
Choosing the Right Charge Controller: PWM vs. MPPT
When setting up your marine solar system, a crucial decision is choosing between a Pulse Width Modulation (PWM) and a Maximum Power Point Tracking (MPPT) charge controller. This choice significantly impacts your system's efficiency and overall performance.
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PWM Charge Controllers: The simpler and more affordable option, PWM controllers act like a switch, connecting and disconnecting the solar panels to regulate battery voltage. They are suitable for smaller systems where the panel voltage closely matches the battery voltage. However, they are less efficient, especially in colder climates or when the panel voltage is significantly higher than the battery voltage.
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MPPT Charge Controllers: More sophisticated and expensive, MPPT controllers use advanced technology to constantly track the maximum power point of the solar panel, adjusting the voltage and current to maximize energy harvest. They are significantly more efficient than PWM controllers, especially in varying light conditions and with higher voltage panels. This increased efficiency can result in up to 30% more power extracted from your panels, meaning faster charging and less reliance on shore power or a generator. They are preferred for larger systems and optimal performance.
Making the Right Choice:
The higher initial cost of MPPT controllers is often justified by their enhanced efficiency, especially for larger systems or those seeking maximum energy independence. Consider your budget, the size of your solar array, and your desired performance level. If you prioritize long-term efficiency and want to maximize the return on your solar investment, an MPPT controller is often the better choice. If you have a very small system and budget is a very big concern, PWM is an option.