PWM vs MPPT Solar Charge Controller: Which One To Choose?

by Lindsey Carter

Do you have a solar system that uses a battery for storage? Chances are that you want to be able to extend the life of the battery while making sure everything is safe.

If that is so, a solar charge controller is one piece of equipment you shouldn't overlook. It prevents the premature damage of batteries so that you can enjoy flawless power while avoiding unnecessary replacement expenses.

When shopping for a suitable solar charge controller, you might end up feeling overwhelmed by a large number of options on the market. I am here to help you out.

At the basic level, there are two major categories - PWM and MPPT controllers.

Maybe you've heard about these, but you don't have time to deal with all the technical stuff being thrown around.

Don't worry, I will break down the two types for you in a language everyone can understand.

By the time you're finished reading (in just a few minutes), you should understand clearly the PWM vs MPPT controllers.

Let's take a closer look.

PWM vs MPPT Solar Charge Controller: Which One To Choose?
PWM vs MPPT Solar Charge Controller: Which One To Choose?

What Is A Solar Charger Controller?

What Is A Solar Charger Controller
What Is A Solar Charger Controller

Also called a solar charge regulator, this is a little device that regulates the power flowing from the panels to the batteries.

You see, each battery has a rating for the maximum voltage capacity. Without a charge regulator, the battery can get overcharged, resulting in its damage.

The main objective with a solar charge controller is to ensure the batteries are fully and optimally charged while preventing overcharging.

That way, the device helps prevent battery damage. It preserves the life of the battery for as long as possible while preventing explosions.

Before we talk about the difference between the MPPT and PWM solar charge controllers, let's quickly see what each of these entails.

PWM Solar Charge Controllers

PWM Solar Charge Controllers
PWM Solar Charge Controllers

PWM is an initial, standing for "power width modulation".

In the older days, solar charge regulators simply monitored the voltage of the battery and would stop the current when the voltage rose above a certain level.

With the advent of the PWM controllers, it was possible to lower the current flow slowly as the voltage approaches a certain level. That reduces the stress on the battery while ensuring it is fully charged. And that's just what the PWM controllers do.

When the battery gets fully charged, these controllers take the charge rate into a "trickle" state, where only a very little amount of current flows into the battery. That way, the battery stays topped off.

PWM controllers are more appropriate for small solar panels serving a specific purpose at home, such as powering the lights, as opposed to large systems that power the entire home.

Why ?

First, because these controllers are not designed to deal with very high voltages, which the large panels can emit.

And secondly, because with these controllers, the battery and the solar panel should have the same voltage levels. And that's the order of things with the small panels. Larger panels don't always have the same voltage with the battery they're attached to.

MPPT Solar Charge Controllers

Mppt Solar Charge Controllers
Mppt Solar Charge Controllers

MPPT is also initial, standing for "maximum power point tracking".

Like the PWM controllers, these keep the voltage of the battery in check, reducing the power flow rate as the battery nears the full capacity.

But contrary to the PWM models, these are able to work with panel and battery voltages that don't match.

MPPT regulators are also versatile, capable of adjusting the flow rate up or down depending on the needs of the battery. They can make an adjustment that brings in the maximum possible power from the panels.

Also, these regulators can change excess voltage into amperage. That means the MPPT controllers are more efficient than the PWM controllers.

Note: however, that this benefit makes them costlier than the PWM controllers.

MPPT vs PWM Controllers: Key Differences

In this section, we're going to look at various areas where MPPT and PWM regulators are different and help you choose.

Voltage tolerance and power loss

One of the major areas where these two controllers are different is in the voltage tolerance.

Realize that most solar panel batteries have a voltage of 12V, like most car batteries.

If you're using a PWM controller, the voltage from the solar panels has to be a little higher than that, at around 18 volts for the power to flow efficiently to the battery.

That's because there's low voltage in the wires, which can cause energy loss.

Unfortunately, PWM controllers are not designed to handle high voltages, so there's often lots of energy loss.

MPPT controllers, on the other hand, can tolerate higher voltages. As there's high voltage in the wires, there's lower energy loss.

If you're using a solar panel that puts off VOC voltages over 35v to charge 12v batteries, you want to get an MPPT unit rather than a PWM controller.

Charging efficiency

As mentioned earlier, a majority of solar panels are connected to a 12V battery for energy storage. But solar panels can deliver higher voltages than that.

MPPT controllers usually convert the excess volts into amps. That way they keep the charge voltage at an optimum. This also reduces the time needed to charge a battery to full capacity.

PWM controllers are not able to do the conversion of amps into volts. That means the charge rate is not as efficient.

The pros and cons of PWM and MPPT controllers

Now, let's look at the benefits and drawbacks associated with each type to better understand what you're getting.

PWM Controllers - Pros:

  • Very durable - they use passive heat sinks to cool and avoid damage
  • Relatively inexpensive - typically costing less than 350 USD
  • Available in a wide range of sizes for varying applications
  • Relatively smaller in physical size

PWM Controllers - Cons:

  • The voltage of the solar panel must be similar to that of the battery for it to work
  • Only for a power of 60 amps and below
  • Cannot be used with high-voltage solar panels
  • Many models are not UL listed for safety
  • They allow a limited room for system upgrades

MPPT Solar Controllers - Pros:

  • Great potential for growth through upgrades
  • Able to work with high-voltage solar systems
  • Can increase the charging efficiency by up to 30 percent
  • Can work with high-amp systems, even up to 80 amps
  • Able to change extra volts into amps for better charging efficiency

MPPT Solar Controllers - Cons:

  • Physically larger on average than PWM controllers
  • Relatively costlier - even twice the cost of PWM units
  • Can be hard to install without a reliable user guide

Final Word for Solar Charge Controller Buyers

A solar charge controller is a very important device for several reasons. It regulates the flow of power from your solar panels and ensures that the battery doesn't get overcharged.

That way, it prevents the battery from getting damaged and saves you from incurring unnecessary expenses. No more getting lost in the technical lingo.

It is my hope that this guide has cleared the confusion and helped you understand what PWM and MPPT units are, as well as the difference between them.

About Lindsey Carter

Lindsey and Mike C. grew up in the same neighborhood. They also went to the same Cholla Middle School together. The two famillies from time to time got together for BBQ parties...

Lindsey's family relocated to California after middle school. They occasiotnally emailed each other to update what's going on in their lives.

She received Software Engineering degree from U.C. San Francisco. While looking for work, she was guided by Mike for an engineering position at the company Mike is working for. Upon passing the job interview, Lindsey was so happy as now she could finally be back to where she'd like to grow old with.

Lindset occasionally guest posted for Mike, adding other flavors to the site while helping diverse his over-passion for baseball.

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