What Size MPPT Controller Do I Need?

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If you have a solar power system, you know that choosing the right components is essential to maximizing its efficiency and longevity.

One of the most important components of a solar power system is the Maximum Power Point Tracking (MPPT) controller. The MPPT controller is responsible for optimizing the power output of the solar panels and charging the battery bank efficiently.

Choosing the right size charge controller is crucial for the overall efficiency of your system.

In this article, we will discuss the factors to consider when choosing the size of an MPPT charge controller and how to calculate the appropriate size for your system.

If you want an MPPT charge controller that has all these features, check out my article about the best MPPT charge controllers.

Calculating the Size of MPPT Controller

Charging current

  • Determine the total amount of power of your solar panels. This is the power rating that is indicated on the back of the solar panel.
  • Divide the amount of power by your battery voltage

500W solar / 12V battery = 41.6A charging current -> 40A charge controller

500W solar / 24V battery = 20.8A charging current -> 20A MPPT charge controller

500W solar / 48V battery = 10.4A charging current -> 10A MPPT charge controller

We can see that a higher voltage battery will be better because the current reduces. An MPPT with a lower current is cheaper.

  • If you have a 100Ah battery and the charging current is 20A, then you need 5 hours to charge the battery.

100Ah / 20A charging current = 5 hours

  • Keep in mind the recommended charge rate of a battery. For a lead-acid this will be 0.2x the rated capacity. For lithium this will be 0.5x the rated capacity

Max charging current lead acid: 100Ah * 0.2C = 20A

Max charging current of lithium: 100Ah * 0.5C = 50A

Placing more batteries in parallel will increase the charging current.

Maximum input voltage

The maximum input voltage also plays a role in selecting an MPPT charge controller.

Most charge controllers limit their input voltage to 100VDC.

If your solar panel has the following specification:

specification from the back of a solar panel

You need to use Voc as your voltage and multiply it by the amount of panels in series and then multiply by a safety factor or 1.25.

This is an example:

21.0V * 3 panels in series * 1.25 = 78.25V -> 100VDC input charge controller

Now if we calculate it with 5 panels in series:

21.0V * 5 panels in series * 1.25 = 131V -> over 100VDC input

We now have two options:

  • Get a charge controller with a higher input voltage
  • Split the solar panels into 2 panels in series and 3 panels in series and get a second charge controller.

Conclusion

Determining the size of your charge controller is easy. We need to calculate these two values:

  • Max charging current in respect with the battery C-rate
  • The maximum input voltage of the charge controller
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FAQ

What size charge controller for 1000w solar panel

  • 1000W/12V= 83A -> 100A charge controller
  • 1000W/24V = 42A -> 50A charge controller
  • 1000W/48V = 21A -> 30A charge controller
  • Keep in mind the maximum input voltage of the charge controller

What size charge controller for 800w solar panel

  • 800W/12V= 67A -> 80A charge controller
  • 800W/24V = 34A -> 40A charge controller
  • 800W/48V = 17A -> 20A charge controller
  • Keep in mind the maximum input voltage of the charge controller

What size charge controller for 600w solar panel

  • 600W/12V= 50A -> 50A charge controller
  • 600W/24V = 25A -> 30A charge controller
  • 600W/48V = 13A -> 20A charge controller
  • Keep in mind the maximum input voltage of the charge controller

What size charge controller for 400w solar panel

  • 400W/12V= 33A -> 40A charge controller
  • 400W/24V = 16A -> 20A charge controller
  • 400W/48V = 8A -> 10A charge controller
  • Keep in mind the maximum input voltage of the charge controller

What size charge controller for 300w solar panel

  • 300W/12V= 25A -> 30A charge controller
  • 300W/24V = 13A -> 15A charge controller
  • 300W/48V = 7A -> 10A charge controller
  • Keep in mind the maximum input voltage of the charge controller

What size charge controller for 100w solar panel

  • 100W/12V= 8.3A -> 10A charge controller
  • 100W/24V = 4.2A -> 10A charge controller
  • 100W/48V = 2.1A -> 10A charge controller
  • Keep in mind the maximum input voltage of the charge controller
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