What Size Solar Charge Controller Do I Need – Online Calculator

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Sizing solar charge controller is important to avoid solar power system and appliance damages. This is my guide on how to size a solar charge controller and online charge controller calculator.

Read my guide on Best Solar Charge Controller Here.

Disclaimer: Actual results may differ from the estimation.

MPPT charge controller is a prominent choice for the solar power system as it limits the current and voltage input to the batteries. They have compact circuitry capable of limiting high current values according to its size standard output. That protects the solar power system but at the same time reduces the efficiency when your MPPT controller is not of the required size.

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If your know the maximum output voltage of your solar pv module and your panels are connected in series to each other, known as solar array, then simply multiply the output voltage of your solar array and get a charger that accepts voltage a bit higher than that.

For example, you have 4 panels of 200-watt. Each panel has an open circuit output voltage of 20v then. 20 × 4 = 80v. Then get a solar controller that has input accepting voltage higher than 80, let say 100v.

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The ampere rating remains the same for a single solar panel until you connect them in parallel to each other as solar array. To maintain power, solar panels are connected in series and parallel to achieve maximum power rating.

If the maximum power rating has a current of 50 amperes, then better is to get MPPT solar controller that accepts an ampere rating higher than that, otherwise, it will lower your solar power system efficiency.

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The simplest method is to know the peak output power in watts of your solar module and the storage battery voltage. Let say if you have a power output of the solar system in watts is 500 and storage battery voltage of 12v, then 500 / 12 = 41.66 ampere.

So, you can get an MPPT solar controller with a 40A rating as it is capable of regulating higher currents. The MPPT charge controller is a prominent choice for the solar power system as it limits the current and voltage input to the batteries.

They have compact circuitry capable of limiting high current values according to its size standard output. That protects the solar power system but at the same time reduces the efficiency when your MPPT solar charge controller is not of the required size.

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PWM solar charge controller is preferred where reducing the initial installation cost is the primary task. PWM solar charge controllers are usually used in a small solar power system where the battery charges full and drains out daily. Their circuitry is tasked to reduce the power flow continuously as the battery charges more. That is why they have already low efficiency even when put with correct power ratings in order with the solar power system and battery.

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The primary issue with PWM solar charge controllers is, they cannot limit the incoming current from the solar power system. If your solar power system at peak value is rated at 30 amperes, then use the PWM solar charge controller above 30 amperes. Otherwise, it will get damaged.

Usually, a factor of 1.25 is used. Like, if your solar power system is rated at 30 amperes, then 30*1.25 = 37.5A means buying a PWM charger of at least 37.5A rating, 40A would be ideal and available in the market.

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Batteries are mostly rated at 12v or 24v, and sometimes the 48v batteries are used too. Remember that voltage while sizing your PWM solar charge controller is the one that has a supply voltage according to battery demand.

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Your solar panels will add their voltages when connected in series, solar array. If you have four 100-watt solar panels connected in series and each has a voltage of 22.5. Then 22.5 * 4= 90v. Get a PWM charge controller that can at least accept 100v as input. Choose a bit higher to protect against any possible surge.

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The simplest method is to know the peak output power of the solar power system and the battery voltage. Let say if the power output of a solar system is 500w and the battery of 12v, then 500 / 12 = 41.66A. So, you must buy a PWM solar charger of 45A rating or 50A as if your ampere rating is low, then it will damage.

For a 1000 watt solar power system, a charge controller installation might cost you $530 on average. As installation process of only a solar charge controller is not much time consuming, and I assume that’s a 1 hour job. That can vary in different locations.

The installation cost of a solar charge controller depends upon the size of your solar system. The larger the solar power system, the more it will cost you. Installation of solar charge controller can be broken down into:

  • Charge controller price
  • Electrical balance of system
  • Structural balance
  • Labor cost
Service/EquipmentCost
Charge Controller$0.20 to $0.50 per watt
Structural Balance$0.03 per watt
Electrical BOS$0.05 per watt
Labor$29.35 per hour average

Since there is no moving part in the solar charge controller and the whole function is based on electronic circuits, not much maintenance is required.

It means you don’t have to check the filters, cooling methods, or anything like that. Just occasionally when you see that it is covered in a bit of dust. Take a dry fabric and clean it, and after that, make sure that you have not loosened the wires or connections as the loose wire can lower power transfer efficiency and overheat the solar charge controller.

Just keep it clean with a dry and strong fabric when it needs it.

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In a Nutshell

Solar charge controller size depends on the panel output and battery volt. When you know how many watts your solar panel produce and the volt of your solar batteries, it’s easy to calculate the charge controller size using the online calculator.

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