What Solar Charge Controller Do I Need for Lithium Batteries?

Solar charge controllers are an essential part of any off-the-grid system. For large solar panels they increase the efficiency of the electrical system by transferring the energy from the solar panel to the battery more effectively. For small solar powered systems (<50 watts) they are not necessarily needed. We’re here to help you understand when you need a solar charge controller and what size and type is needed for your system. As your read you will learn the basics of what a solar charge controller is, when you need one, how to select the best solar battery charger for your system, and the reasons why you may want to include one in your system.

What is a solar charge controller?

A solar charge controller takes the energy from your solar panels and transforms it into the optimal voltage to charge your batteries. By doing so it increases the efficiency of your solar panels. Think of the efficiency gains in terms of voltage. A lithium battery likes to be charged at 14.4 Volts. A solar panel may have an output of 18 volts. The solar charge controller takes the 18 Volts and converts it to 14.4 Volts, providing the optimal charge for lithium batteries. This means less energy is lost in the transfer from solar panel to battery. They are also commonly called solar battery chargers, or charge controllers.

What does a solar charge controller do?

A solar charge controller is a battery charger that is designed to charge a battery using solar energy. It sits between your solar panels and your battery in an off-grid electrical system. A solar charge controller takes the energy from your solar panels and turns it into the voltage needed to charge your batteries. Solar charge controllers increase the efficiency of your solar panels and your batteries, allowing you to use and store more of the electricity that your solar panels have generated.

When do I need a charge controller?

  • A small solar panel can charge a battery directly with no controller. For panels that are 50 watts or less we always recommend going directly to the battery.
  • If your solar panel is 100 watts or larger you want a controller for increased efficiency, especially in permanent systems where the panel and battery are installed for a long time.
  • For systems with 200 watts of solar or more a solar charge controllers is a must. 100% of electricians working on off-grid boats and adventure vans install solar charge controllers as part of the electrical system.

What size solar charge controller do I need?

To determine how large of a solar charge controller you need find the max amps spec of your solar panels. You need a controller that is rated to a higher amperage than the solar panel. For example, if you have a 300 watt solar panel with a max amp output of 15 amps you need a controller with a 15 amp input. The most common size controllers are 15A, 30 Amps, 50A, and 100A. Here’s a few of the most common solar panel sizes for boats and RVs and the size of solar charge controller needed.

Shop Dakota Lithium Off-Grid Power Systems

Off-Grid Electrical System Examples

This 12V 100Ah off grid power system bundle is a great example of the amount of panels, batteries, and associated components needed for a small camper, trailer, adventure van, or overland truck build.

dakota lithium vanlife rv trailer truck 12v 100ah off grid solar power system

The Dashboard in the middle is the solar charge controller and battery monitor. It is wired to the solar panel and the battery, telling you how much energy is being generated by the panel and how much energy is inside the battery. The red inverter then plugs into the battery allowing you to run household appliances from the battery like a coffee maker, tv, fridge, etc.

Should I use one charge controller or two?

Having one or two controllers does not changes the efficiency of your system. Just make sure the total Amp rating of your controller is less than the total amps generated by your panels. For solar panels generating <15 Amps you only need one. For systems generating more than 15 Amps there may be a strategic value to using multiple controllers. The reason is redundancy. If one fails you still have 50% of the system running.

Do my solar panels or batteries need a special charger?

Here’s a simple guide to matching what batteries, panels, and controller your need to make an efficient off grid system.

  1. Your solar panels need a controller that matches the voltage of your panels. A 12V panel needs a 12V controller. A 48V panel needs a 48V controller (these are less common).
  2. Lithium batteries need a lithium compatible controller. For example, a 12V lithium battery requires a 12V controller that is lithium compatible.
  3. The controller needs to have a max amps rating that is equal to or greater than the max amp output of the panels. 300 watts of solar panels generated a peak of 15 amps need a 15 amp solar charge controller.

Can I use my solar charge controller as a battery monitor?

Yes! Controllers are a type of battery charger. As a result they read the live voltage of the battery constantly. This means some controllers are effective battery monitors. For example, the Dakota Lithium Dashboard (15A) Solar Integration Kit provides real time monitoring of your battery, with data displayed on the DL Dashboard app (apple & android). This means you can see how much electricity your solar panels have generated and how much energy is inside your battery.

How can I tell is my controller is lithium battery compatible?

The optimal charging voltage for Lithium batteries is 14.4 Volts. Read the specifications in the user manual or online. A lithium battery compatible charger will have an output voltage of 14.2 to 14.4 volts. Some chargers have multiple settings, an AGM or lead acid setting, which is a lower voltage, and a higher voltage lithium setting. Select the lithium setting if you are charging a lithium battery. A lead acid charger will not fully charge a lithium battery, or may not charge it at all depending on the model. The Dakota Lithium Dashboard is a lithium compatible controller that also includes a wiring kit and a battery monitor.

Shop Dakota Lithium Off-Grid Power Systems

Be The First to Know

Get access to exclusive deals, hear about new products before anyone else, and enjoy tips, tricks, and DIY hacks from our community of experts.