Is it OK to Oversize Solar Charge Controller?

In this article I will tell you if you can oversize your charge controller or not.

The function of a charge controller is to do the following:

  • Decrease the solar panel voltage to the appropriate battery charging voltage
  • MPPT charge controllers increase the current while PWM doesn’t.

It is important to note that the input voltage of a charge controller is limited.

For a PWM charge controller, this will be 50VDC.

For an MPPT this can be 100VDC+

Can you oversize MPPT and PWM charge controller?

Yes, it is possible to oversize your solar charge controller.

Oversizing your charge controller can provide some benefits, such as:

  • Allowing for future expansion of the solar system
  • Improving the efficiency of the system

When you oversize a charge controller, you are selecting a controller with a higher capacity than what is required for your current solar system. This means that the controller will have extra capacity that is not being used, which can help reduce the stress on the controller and prolong its lifespan.

Furthermore, oversizing the charge controller can also provide more headroom for the solar system on cold sunny days. It’s not unheard of to have 120% output power on a sunny winter day. That’s another reason to oversize your charge controller.

It is important to keep in mind that oversizing the charge controller will increase the cost of the system, so it is essential to weigh the potential benefits against the added expense. Additionally, it is important to ensure that the controller is compatible with the solar panels, batteries being used, and the overall electrical system.

What happens if your solar charge controller is too big?

If your solar charge controller is too big, the following things will happen:

  • The charge controller will operate at a cooler temperature which increases its lifespan.
  • There will be room for expansion later down the road.

If you want to expand your system later on but do not like to invest upfront, having multiple charge controllers is an option.

Keep in mind that you should not go over the maximum allowable input voltage of the charge controller. This is written in the manual of the charge controller.

Let’s say you have a 100W solar panel that delivers 5.2A to the charge controller.

The MPPT charge controller will take the 19V and 5.2A and convert it to 13V to charge the battery at 7.7A. Totaling 100W theoretically (without losses). We still have 12.3A left so we can add another 100W solar panel in series later.

Oversizing an MPPT charge controller

The PWM charge controller will take the 19V and 5.2A and convert it to 13V to charge the battery at 5.2A. Totaling 67W theoretically (read more about PWM efficiency here). We still have 14.8A left so we can add another 100W solar panel in parallel later.


Oversizing an PWM charge controller
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You can oversize your solar charge controller. This will even give you a few benefits, like increased lifespan and flexibility for expansion. The drawback will be that the cost will increase.

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6 thoughts on “Is it OK to Oversize Solar Charge Controller?”

  1. I’m new to solar power and will be privileged if concerns are addressed as I progress with my system, though of limited budget.


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