Have you ever stared at your solar charge controller, wondering if you should connect your devices to that mysterious “load” terminal? You’re not alone. We get asked this question a lot! In this article, we’ll demystify load terminals and help you decide whether you should be using it or not.

What is a Load Output Terminal?

A load output terminal is a connection point on your charge controller designed to power devices directly from your charge controller itself. Often marked with a light bulb icon, it might seem like the perfect place to connect all your lights and gadgets. But is it really? Let’s dive deeper.

How does the load terminal work on a solar charge controller?

A common misunderstanding is that load terminals draw their power directly from the solar panels. This isn’t the case. Or rather, this isn’t the case in smaller 12v/24v systems. In smaller systems, the load terminal taps into the power stored in your battery. The power flow works like this:

Solar panels → Battery → Load Terminal → Connected Devices

There are systems that prioritise solar first but you’ll find these on larger systems such as those you find for homes where most systems are sold without batteries. With no way to store the energy, the solar is either used directly by the appliances in the house or diverted to the grid (and they’re not technically charge controllers, rather they are grid-tied inverters).

Why Use the Battery as an Intermediary?

Imagine a cloud passing over just as you’re about to watch England score the winning goal in Euro 2024! Drawing power from the battery ensures uninterrupted viewing, regardless of momentary changes in solar input.

So you are probably thinking: Why not always use the load terminal instead of connecting directly to the battery. There’s a reason why we don’t recommend doing that:

Current Capacity: The Catch

Here’s the catch – unlike direct battery connections, load terminals have a limited current carrying capacity.

For example, the load terminal on the Voltanic 15 amp MPPT has a maximum output current of 10 amps. When you are only connecting one or two devices, this isn’t really a problem as most 12V devices output a small number of amps.

Current Draw of Common 12V Devices:

LED lights: 1-2 amps
12V fridges: ~4 amps
Water pumps: 4-8 amps

However, if you start connecting lots of smaller devices to the load or want to use higher-powered devices (such as a 12V Kettle), then you’ll likely be exceeding the current capacity of the load terminal.

Side-Note: Do not buy a 12V Kettle. They take 20-25 minutes to boil a cuppa. Not ok when your craving that morning coffee.

The solution is to connect them to the only thing that can handle larger currents: your leisure battery. These can handle far greater currents. To give you an example, the Voltanic 120Ah Lithium Battery has a maximum current carrying capacity of 150 amps.

This begs the question:

Why the heck would I want to use the Load Terminal?

Well there are a few scenarios where using the load terminal might be beneficial:

Simplified Wiring in Small Systems: In smaller solar setups, the load terminal provides a convenient connection point. This can be useful if you are using the system for one device only (such as shed lighting).
Easy Energy Monitoring: Most charge controllers have a screen that provides data on energy consumption for each terminal including the load terminal. If you’re keen on tracking how much power a specific device uses, then this feature can also be useful.
For Scheduled Load Control: Some advanced controllers (like Voltanic’s MPPT range) offer scheduling feautres. This is useful for automatically powering on devices at specific times (e.g., turning on lights at dusk).

Do You Need to Use the Load Terminal?

In short: No. While you can, it’s not necessary. In fact, we recommend that all 12V/24V DC devices be connected directly to the battery for the following reasons:

Avoiding Overload: You’ll be able to safely connect multiple devices & higher-drawing devices to the battery without worrying about exceeding the load terminal’s capacity.
Neater Wiring: Most people will be using multiple 12v devices therefore connecting directly to the battery will provide for neater wiring especially if you opt to use a busbar.

If you do decide to use the Load Terminal, make sure you:

Check the device’s amp draw (usually listed in the specifications)
Ensure it’s less than your controller’s load terminal capacity
Consider peak loads – some devices may draw more when starting up

FAQ

Q: Can I charge my starter battery or car battery from the load terminal?

Absolutely not. Starter batteries draw high currents from the starter motor when you turn on the ignition and that current will most certainly exceed the load terminal’s output current capacity.To charge your starter battery, use a dual battery charge controller or a DC-DC charger.

Q: Can I connect my inverter to the load terminal?

Never connect your inverter to the load terminal of your charge controller. Inverters draw much more current than the load terminal can handle. For example, the 12v Voltanic 1200W Pure Sine Wave Inverter draws over 80 amps at full load, far exceeding the capacity of most load terminals (which are often limited to 10-15 amps).

Q: Can I connect a second leisure battery to the load terminal?

While it’s technically possible to connect a second leisure battery to the load terminal of a solar charge controller, it’s generally not recommended. The main reason is the issue of charge profile mismatch.

The load terminal follows the charge profile of the main battery connected to the controller’s battery terminals. This means the second battery won’t receive an optimal charging cycle tailored to its specific needs or chemistry. As a result, you could face scenarios of overcharging or undercharging the second battery.

This mismatch can be particularly problematic with lithium batteries, which require precise charging profiles. Unless you’re constantly monitoring both batteries, this setup could potentially lead to battery damage or even safety issues.

In essence, while connecting a second battery to the load terminal might seem like a simple solution, it often creates more problems than it solves. For optimal performance and safety, it’s better to explore alternative methods for charging multiple batteries in your solar system such as by using a dual battery charge controller or a DC-DC charge controller.

Q: Should I connect my lights to the load output?

While you can, we wouldn’t recommend it. Connecting directly to the battery is often a cleaner more flexible option especially when connecting via a busbar. More importantly, you save yourself the risk of frying the controller’s.

Q: Where does the load output terminal port get its power from?

In smaller setups the load terminal draws its power from the battery. In larger systems such as those you’ll find powering homes, charge controllers with load terminals are typically not used. Power flows directly from the panels to a “grid-tied inverter” and then either to the household loads/appliances or the grid. There is no “load output terminal” in the traditional sense.

Conclusion

While the load terminal can be useful in specific scenarios, it’s not an essential feature for most 12 volt solar setups. In many cases, connecting your devices directly to the battery – especially when using a busbar – offers a cleaner, more flexible solution and avoids any chance of you blowing the in-built fuse of your controller (providing it even has one and isn’t one of those cheap blue chinese models you’ll find on ebay!).

If you’re unsure if you need any more help or have any questions, do please send us a message. We’d be happy to help!