Solar Charge Controller Load Output Terminals: Why You Shouldn’t Ignore Them and How to Use Them Safely

You’re probably familiar with the Solar PV, battery positive and negative terminals, and less so the load output terminals after all, not all charge controllers have them and even then the use of the word “load” may not be clear to some people.

And so, this begs the question, what are the load output terminals, what are they for and how can you use them safely?

Read on to learn how to use them safely and what you can do in case your charge controller does not have them.

What are the Load Output Terminals for

These are terminals usually between the Solar PV and battery terminals labeled “load +” and “load -” on a solar charge controller.

Not all charge controllers have them. But for those charge controllers that do, you can wire appliances such as:

  • a LED light bulb, street light
  • a relay, or any other DC appliance directly to the solar load output terminals provided you do not exceed their current handling limits.

Using the load output terminals is optional

It is not a must to connect an appliance to the solar charge controller load terminals.

The controller will work fine even when no appliance is wired to them!

Should You Connect an Inverter?

Do not connect an inverter to the load output terminals. The inverter should be wired to the battery terminals instead.

The current draw by the inverter (especially the surge) can exceed the load current handling limit and damage the charge controller!

Instead:

1. The current draw of the connected appliance should be within the limits of the charge controller terminals.

Make sure that the current (amps) that is connected to the charge controller load output terminals does not exceed what the charge controller can handle or else you may damage the controller or its load output terminal circuit.

So, as a must check the maximum current the solar load output terminals can handle.

The current limit can vary from one charge controller to another.

You can find this in the solar charge controller owner manual technical specifications.

If it is 5 amps, for example, the current draw by the connected appliance must not exceed 5 amps otherwise you risk damaging the charge controller!

Note: The load output terminals for your charge controller may be protected by a fuse that blows in case of an overload and can be replaced to get the charge controller working again!

2. Do not reverse the polarity of the connected appliance

The load output terminals usually have a positive and negative side. For some appliances such as an incandescent DC lamp, it does not matter which light terminal is connected to the positive and which one is connected to the negative.

But for a LED light or even a relay, inspect their terminals and confirm that the positive side of the device or appliance is connected to the positive terminal and the negative side to the negative terminal of the charge controller.

How to Use the Load Output Terminals

Here’s how you may use the load output terminals.

1. Automatically Switch On and Appliance at Dusk and Off at Dawn

You can use the load output terminals to control and automatically switch on/off a security light or any other appliance whose on/off operation should be synchronized with dusk or dawn.

The light can be switched on when the solar panels no longer detect any sunlight and switched off in the morning when the sun comes up (light is detected by the solar panels in the morning)

2. Convenient On/OFF Switch For an Appliance

You can also switch an appliance on or off from the charge controller instead of walking to the on/off switch that may be installed several feet away closer to the appliance.

In effect, the load output terminal on/off switch works as a remote switch!

3. Switching on Solar Charge Controller Load Output (Selected Controllers ONLY)

A frequently asked question regarding charge controllers is how to switch them on.

After all, wiring an appliance even when you follow <the guidelines> does not mean that it will work when the wiring is connected.

To get the appliance working, check whether there is an on/off switch for the terminals.

You may have to manually toggle the switch to on. How you do this can vary from one controller to another so consult the owner manual.

The output may also only be switched on automatically when the sun goes down and off when the solar panels detect sunlight.

Note: Some controllers have the option to set delay intervals

When to use the solar charge controller load output terminals

  • Do you have an appliance, perhaps a street or security light you’d like to switch on at dusk and off at dawn? You can use the solar charge controller to achieve this for you by wiring the appliance to the load output terminals.
  • Switch ON/OFF the appliance conveniently from the solar charge controller.
  • (Selected controllers only) the charge controller can be used for over-discharge protection of the battery and automatically disconnect the appliance when the low voltage disconnect of the battery is attained.

Not All Charge Controllers Have Load Output Terminals

Solar charge controllers that handle higher currents usually more than 20-30 amps are likely to to have load output terminals.

The loads/ appliances in this case should be connected to the battery directly or to the inverter in the case of AC appliances.

The downside to this approach

There’s a risk that the batteries may be deeply discharged (shortening their lifespan) because you’re relying on the much lower inverter low voltage cut-off which may be as low as 11.5V!

To guard against this, provide enough battery capacity for your appliances. Err on the side of more battery capacity.

You may be interested in the solar off-grid sizing calculator.

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What to Do When the Solar Load Output Terminals Don’t Work

If there’s no voltage reading (with a DC voltmeter) or there’s a very low voltage across the load output terminals, check the following:

Check that the wires are firmly connected to the load output terminals. Inspect the wire connections visually.

You may have to gently tug at each wire to confirm that it is firmly connected.

It is possible for only the insulation to make the connection or the wire strand to break or get disconnected from one or both terminals.

Check that the load output terminals are switched on. You may have to do this manually or wait for the inbuilt timer to switch.

Lastly, if the wire connections are firm and the load output terminals are switched on yet there is no output voltage, it is possible that the internal circuit supplying the terminals has failed.

Contact the charge controller supplier for support or replace the charge controller.

Can You Overload a Solar Charge Controller?

Yes, the load output terminals can only handle currents up to a certain limit. Consult the charge controller user manual for what this limit is for your controller.

Do not exceed this limit or else you’ll damage the charge controller from overloading.

Final Word

Not only do charge controllers have load output limits but even when they do, it is not a requirement that you can use them.

Do not connect appliances with a current draw that exceeds the load output limits of the charge controller to avoid damage.

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