What Size Charge Controller Works for a 200W Solar Panel

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Solar panels are a life-changing invention, and these panels get used in a variety of ways for operating different equipment. However, harnessing solar power for your devices and equipment is not at all possible without transmitting that energy into a properly charged battery. This is when charge controllers come into the picture; these help when it comes to optimally charging your batteries.

If you have a 200W solar panel and a 12v battery, you will need a charge controller of around 20 Amps. The size requirements are different for different integrations, but there is a way to calculate it. Curious about what it is?

Let’s find out and learn some interesting things along the way as well.

What is a Charge Controller?

The controller’s primary role is to protect and automate the battery charging process.

The charge controller is a small device that runs between the solar panel and the battery. Its design prevents a reverse flow of the current and charges the battery by matching the voltages.

Controller charges the batteries at voltage higher than the battery voltage and disconnects the circuit when maximum battery charging voltage achieves (13.8 Volts in case of 12 Volt lead-acid battery).

The battery is discharged, and charge controller again starts charging when it sense specified low voltage that is suitable for chagrining again.

Charge controller adjusts the current to the battery the solar panel will be reduced according to the battery condition and charging demand. When the voltage returns to a safe level, the system will start charging again.

Solar panels are connected to the controller through positive and negative cables, and the charging function is provided only when connecting the controller to the battery.

The solar controller takes the voltage and current produced by solar panels and supplies the correct voltage and current to the batteries. Moreover, the charge controller and batteries must all share a standard voltage for proper compatibility.

Types of Controllers

Now that you know what a charge controller is, let’s get acquainted with the types of controllers.

There are two types of controllers:

  • MMPT – Maximum Power Point Tracking
  • PWM  – Pulse Width Modulation

The MPPT and PWM charge controllers regulates the voltage that solar panel transmits to the battery. However, the big difference between these controllers is that the MPPT variation constantly tracks the voltage and current of the solar energy and takes the best quality and amount of power (product of voltage and corresponding current) out of it, and the PWM simply provides a constant output (Product of voltage and current that is available at that time).. That is why the MPPT type is more efficient than the PWM type. MPPT is the most common option today, and this type can provide you with 30% additional power compared to a PWM controller.

Most MPPT controllers allow much higher voltages to be injected, which allows you to go further with fewer wires from panels to the controller.

MPPT controllers also allow panels to be connected in a series for higher voltages while maintaining lower amperage and smaller cable sizes, especially for long PV array cables.

Since MPPT charge controllers can handle input voltages from a solar array containing higher voltages than battery banks, you may also use these charge controllers with solar modules that do not match the typical system voltage. MPPT controllers draw current from the panel at the high supply voltage. They limit their power to ensure that the battery is not overloaded.

In many cases, the use of multiple MPPT controllers is ideal, although this depends on the amount of solar energy required.

The PWM solar charge controller, on the other hand, will only use the maximum current that the panel can provide, which is 10 amperes. Hence, the PWM controller is most suitable for small applications.

How to Determine the Size of the Controller Required?

Since the solar controller works in series with the solar array and batteries, it would make sense that these components also influence its size requirements.

It is indeed true: the size of the controller gets directly affected by these components. Hence, if you know the solar panel’s power along with the amount of battery voltage, you can easily calculate the ideal size for your solar panel integration.

Here is a step-by-step process for calculating the size of the charge controller for your solar power integration. Have a look:

Step 1

You must first know how many watts of power your solar panel or solar panel array has. If you have a single panel—say, 200W—the required value would be 200 watts. However, if you have a solar panel array, you will have to calculate the total wattage by multiplying the number of panels with the power of each panel.

For example, if you have three panels of 200 watts each, the required value would be 3 (panels) x 200 (watts) = 600 watts total. Let this value be denoted by a.

Step 2

Next, you need to know the battery’s voltage connected to your solar panel or solar panel integration. For example, if the battery you are using is 12 volts, the required value—say, b—would be 12v. For series connected batteries, voltages add up. Note this voltage because it is very important for charge controller voltages to be matched with battery voltage.

Step 3

Check the required current for your battery to charge and determine the maximum to ensure you’re staying in a safe range. Charging a battery with a high current may damage the battery if it’s incapable of handling the load. If it is a lead-acid battery, it can be charged with C/10 maximum. That is, the total capacity of the battery divided by 10 will give you the maximum current it can take. (For example, for a 200Ah battery, you can charge it at a maximum of 20 amps.) Note this value.

If the batteries are in parallel, currents can be added together. (E.g., two parallel batteries can be charged on a 40 amp source.)

Step 4

Note the current coming from your solar array. When multiple solar panels or arrays are joined in parallel, their current rating is added. So, look on the name plate of your solar panel and find the current rating. It should be less or equal to the battery charging rating.

Lastly, the charge controller rating will be slightly more than the battery charging current, and the input of the solar array should not exceed that rating.


So, summarizing the steps, the charge controller must have:

  • Current rating equal to charging current of battery(s)
  • Voltage output matching with voltage of battery(s)
  • Proper protection for disconnecting the circuit when batteries are fully charged
  • Start charging batteries when batteries are discharged

Frequently Asked Questions

Although solar panels have been around for quite a few years now, people still have many doubts. Likewise, there are also a lot of questions surrounding the charge controllers as well. This is why we have picked some of the most popular questions and answered them briefly for your convenience.

1.    How does a charge controller help?

If there isn’t a charge controller, the battery will overload and overcharged. Consequently, battery life gets shortened due to overload as well, resulting in premature battery failure.

However, you can solve such problems by using a charge controller. A controller allows you to maintain the highest possible battery charge level while protecting it from overloading the source and discharging the connected load.

2.    How does the charge controller work?

The charge controller provides control by activating blocking diodes or relays to prevent battery current from reversing and flowing back into the array, thereby avoiding battery discharge during hours of less sunlight or at night.

Hence, it works by making a balance. When the battery gets almost fully charged, the controller will reduce the charging current to maintain the voltage required for the battery to be fully charged and maintain its charging state.

3.    What is the main role of the charge controller, and why is it important?

The controller’s primary role is to protect and automate battery charging.

It is essential to use a charge controller as it increases the efficiency of a solar power system by up to 50%, can prevent overcharging of batteries, and extends battery life if used correctly.

4.    Why is it necessary to prevent overcharging?

The quality of charge directly affects the life of any connected battery. Hence, it is vital to protect the batteries of a solar charging system from overcharging or even undercharging and having any issues.

See Also:
Running Cold: Can a 100W Solar Panel Run a Refrigerator?
What Can A 300 Watt Solar Panel Run?
What Can I Do With A 1.5 Watt Solar Panel?
How To Charge Solar Lights For The First Time

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