Can I Use Two Solar Charge Controllers?

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A charge controller performs several important functions in a solar system, such as overload and overcharge protection. But if you have a large array, can you use more than two charge controllers in one system? And will you need two battery banks?

Two or more charge controllers can be connected to one battery bank, but the controllers must all be MPPT or PWM. Multiple controllers can be connected to one solar system, but the panels must be in separate parallel arrays and the panels in each array must be the same size.

Can I Use Two Charge Controllers in One Battery Bank?

Yes, you can use two or more controllers with a single battery bank. In fact that is how large solar arrays are usually set up to produce the best results. There are a few things that you have to remember before getting multiple controllers though.

Charge controller capacity. MPPT and PWM controllers have a limit to how many watts it can handle. The capacity depends on the watts and the voltage. The following are common charge controller sizes and their watt capacities.

  • 15A up to 300W
  • 20A up to 480W
  • 30A up to 600W
  • 60A up to 720W at 12V / 1440W at 24V / 2880W at 48V

These figures are only to give you a general idea. Newer controllers are more efficient and can handle more watts, amps and voltage than older models. Be sure to check the product manual to be certain. Depending on the design, the controller may be able to run handle more solar watts.

Each controller must have its own solar panel. The two solar panels must not be wired to each other, except only through the battery bank. Each controller will be plugged into the battery bank. Under this configuration, each charge controller will evaluate the battery voltage and determine how much current goes into their respective solar panels.

Using two controllers (or more) with one battery bank is not uncommon. In fact it is standard practice in large scale arrays due to the way MPPT controllers work.

Manufacturers – and solar power users – will also tell you not to use solar controllers to their limit. If your system is up to 480 watts already, you should get two 20A controllers. This is something you should do with solar panels, inverters, batteries and charge controllers.

Every MPPT controller functions according to the battery voltage it is connected to. Each one runs independent of the other. These controllers will also rarely synchronize because of the varying wire lengths used for each battery and controller.

The varying cable length means different voltage readings, affecting how the MPPT functions. The behavior of each controller will also vary depending on the manufacturer design.

What Battery Types Can I Use?

MPPT and PWM charge controllers work with different types of batteries like AGM, lithium, gel and others. However you should never mix two different battery types together.

If you are going to use AGM, every battery in the bank has to be AGM. If it is lithium, do not use gel, FLA or SLA. These batteries have different properties and using them together can damage the system, controller or inverter if you have hooked one up.

Lithium batteries have a superior discharge rate and a completely different chemical composition than lead acid batteries. Even lead acid batteries have different types like AGM and gel. Do not mix them together and always refer to your controller documentation for the best batteries to use.

The charge controller settings may have to be adjusted depending on what type of battery you use. Can you use different types of batteries with separate solar arrays? Yes it is possible, but it really does not make sense since they have unique properties. It is better to use the same type for your entire system.

Can I Use Multiple Charge Controllers with One Solar Panel?

If you can use multiple solar controllers on one battery bank, can you do the same with a solar panel?

You can use two charge controllers in one solar system, but each controller must have its own solar panel block or array. Theoretically you can connect two controllers in one array, but it could cause problems later on. If one controller can handle the array, do not add another.

Two or more controllers in an array can cause confusion because both will think they are the “lead one”. Both will attempt to adjust the LMP and VMP, which can result in miscalculations and the output will be less than it can be.

If the charge controller can handle the solar panel output, there is no need to add another one. But if your calculations show another is required, you should configure the solar panels into separate arrays and add a controller to each one..

What Solar Panel Sizes Can I Use?

You can use any solar panel size as long as the total output is within the controller capacity. However, the solar panels must all be the same size, otherwise the controller will defer to the smaller panel.

For example, if you connect 2 x 200W and 1 x 150W solar panels in one array, the controller will rate all the panels as 150 watts. So make certain the panels have similar watt outputs.

You can have solar arrays with different voltages however. Array 1 could have six 12V 100W solar panels and array 2 can have four 24V 100W solar panels. If you have MPPT controllers the panels can have varying voltages and the system will still produce optimum results.

Parallel or Series Connection?

In almost all cases you should use a parallel connection. There are instances where a series connection is better, but for two or more controllers, a parallel setup is the best.

To set up a parallel connection, simply connect the positive to positive terminals and the negative to negative terminals. With a series you connect the positive to the negative.

In a parallel configuration, the amps increase while the voltage remains the same. But in a series, the voltage goes up but the amps are unchanged. In our examples you want to get the maximum power so you should use a parallel configuration.

Connecting your system in a series will boost the voltage and might make it harder for the controller to function. All the connections in a multiple controller setup has to be in parallel if you want to increase the amps.

Can I Use Different Types of Charge Controllers Together?

PWM controllers are best suited for small systems, while MPPT controllers are for large solar arrays. But can you use the two together in one system?

Do not use PWM and MPPT charge controllers together in one system. These controllers have different properties and using them together can lead to a systems malfunction. At the very least you will not get the best results from your solar panel and batteries.

An MPPT controller is more efficient than a PWM, and it can handle solar panels and batteries with different voltages. With a PWM the panels and battery voltages have to match. Imagine if you have an MPPT and PWM controller in one system, and there will be conflicts on how to adjust the voltage.

What if you have two solar arrays wired together, can you use different controller types then? No, as long as the arrays are linked, it is still considered a single system. And there is a potential for conflict if you use different types of charge controllers.

So if you are going to use an MPPT, use MPPT only. These can be different sizes but as long as they are the same type your system will be fine. Of course now the question becomes, how many charge controllers should you have?

How Many Charge Controllers Do I Need?

One question you should be asking of course is, do you even need more than one charge controller? Fortunately the answer is pretty easy to figure out.

Total solar array watts / battery voltage + 25% = charge controller size

If you have a 4000 watt solar array running on 24V batteries:

4000 / 24 = 166 + 25% = 207.5

Your charge controller needs 207.5 amps or 210 amps rounded off.

210 amps x 24V = 5040 watts

A 60A charge controller can handle up to 2880 watts, so you need two 60A MPPT charge controllers to run a 4000 watt solar array.

The battery size will depend on how much power you want to store. For a 4000 watt system you probably need a minimum one 24V 200ah battery, either one 200ah or two 100ah 24V will do.

These are simple calculations, but they work with different types of solar charge controllers. Also note that MPPT charge controllers have a higher voltage capacity. Their other advantage is they can adjust the voltage output as required by the battery bank.

Conclusion

Charge controllers are crucial parts in any solar system, so knowing how they function is crucial. If you have a small system, a single controller will be enough. but if your system is several thousand watts, two or more charge controllers are in order.