# PWM Charge Controller Calculator

Free PWM Solar Charge Controller Sizing Calculator

Other useful free solar power calculators:

How to use PWM Charge Controller Calculator?

(If you need to learn more about charge controllers you may check out our  Definitive guide to solar charge controllers in off-grid solar power systems)

You are provided with two charge controller calculators to solve the Forward and Reverse tasks:
• Forward task: Calculate the charge controller rating once you have got solar panels current data
• Reverse task: For the solar charge controller you have available, calculate the solar panel(s) it can support

Some prerequisites:
To use both calculators, here is what you should know:
• The rated current of the PWM solar charge controller
• Isc, in Amps – the short circuit current of your solar panel
• Imp, in Amps – the maximum power point current of your solar panel

Usually, you get solar panels with both currents (Isc and Imp) labeled on.

If you don’t know solar panel currents data about Isc and Imp, scroll down to find out a useful workaround.

For the Forward task: Just enter one of both currents (either Isc or Imp) in the corresponding field of the solar calculators and calculate the PWM charge controller rating.

Click the “Update” button below to get the calculated values.

PWM charge controller should be selected based on its rated current.

Always choose a charge controller with rated current higher than calculated.

For the Reverse task: Enter the charge controller rated current and get calculated the maximum short circuit current (Isc) and the maximum power point current (Imp) of your solar panel.

Click the “Update” button below to get the calculated values.

What does rated/de-rated solar charge controller mean?

Some solar charge controller manufacturers, like Morning Star, list their charge controller rated current de-rated in advance by a coefficient taking into account the minimum needed value of the charge controller current.

So, in such a case you have to choose ‘De-rated’ from the solar charge controller drop-down menu of the calculator to get the value of the maximum charge controller current that should be supported.

Remember: If you have several panels connected in series, thus forming a solar array, any currents of such a solar array are equal to the pertaining currents of a single panel.

If you have several panels connected in parallel, any currents of the solar array are equal to the sum of the pertaining currents of every single panel.

For example, if you have a solar array with N panels connected in parallel, the resulting currents of such solar array would be:
• Isc_solararray = N*Isc_solarpanel
• Imp_solararray = N*Imp_solarpanel

Last but not least, always check whether the solar panel or solar array voltages fall within the input voltage operating window of the PWM charge controller.

This calculator is applicable for solar module/array consisting of more than one solar panel.

In case of a single solar panel, the calculator gives slightly inflated values, which means that either charge controller for the Forward task or the solar panel for the Reverse task are slightly oversized.

Such an oversizing is good for the safety of the pertaining component, whether charge controller or solar panel.

To find the approximate value of Isc in Amps of the solar panel, just divide solar panel rated power by your system voltage.

For example, you have bought a 100W rated solar panel and you are going to use it for a solar power system of 12V nominal voltage.

Therefore, you have:
100W /12V = 8.33 Amps
Now, you should enter this value in the Imp filed of the above calculator to get the value of the PWM charge controller current.

Warning: In this case, you will get some slightly inflated results for the rating of your charge controller, since the typical solar panel voltage for 12V system voltage is about 18V.

Therefore, the solar panel current is about 100W /18V = 5.5 A.

However, if you don’t have any manufacturer data available, the best approach is to err on the side of caution.

You also may like:

The definitive guide to solar charge controllers in off-grid solar power systems

What is a charge controller

Solar Power Calculator

The following two tabs change content below. #### Lacho Pop, Master of Science in Engineering

Lacho Pop, MSE, holds a Master's Degree in Electronics and Automatics. He has more than 15 years of experience in the design and implementation of various sophisticated electronic, solar power, and telecommunication systems.  He authored and co-authored several practical solar books in the field of solar power and solar photovoltaics. All the books were well-received by the public. You can discover more about his bestselling solar books on Amazon on his profile page here: Lacho Pop, MSE Profile 