What Is The Difference Between MPPT and PWM Charge Controller?

Difference between MPPT and PWM solar charge controller featured image

Most people know that more than a solar panel is needed to use solar power effectively. By far the biggest use of solar is to charge deep-cycle batteries used for energy storage.

Battery voltage changes, depending on its state of discharge, and the charging current varies according to the difference between the terminal voltage and the charging voltage. As Voc (Open circuit voltage) for a 100 watt panel is 21 volts, then this adjustment can be considerable

A PWM charge controller adjusts the solar panel voltage down to the right level in order to charge a battery and wastes any power lost due to the adjustment. A MPPT charge controller adjusts the voltage but maintains the solar panel voltage at the Maximum Power Point. The difference in voltage is converted into current and not wasted, which is why MPPT is more efficient than PWM.

What is the difference between PWM and MPPT charge controllers?
Differences between PWM and MPPT solar charge controllers

In the last video we talked about two of the four major components of a solar power system that included the solar panels, which collect the solar energy and convert that energy into electricity, that sends it down to the battery bank, which is the second thing we talked about.

The batteries store that energy but today we’re going to be talking about the component that goes in between the solar array and the battery bank, and that is the solar charge controller. The charge controller is what is responsible for regulating the electricity that comes from the solar panels to the battery bank.

I’m going to talk about two different types of charge controllers you can buy – the PWM charge controller, as well as the MPPT charge controller. I’m also going to talk about the advantages and disadvantages to each of these style of charge controllers and then I’m also going to give you a good idea of how to calculate what size charge controller you need for your system.

How does a PWM controller work?

PWM or pulse width modulated charge controllers are the more basic of the two charge controllers. What they do is match the solar array voltage to the voltage required to charge the batteries depending on what state of charge it’s at.

What it does is, it turns on and off, that’s why it’s called pulse width modulated. It turns on, pulsates on and when it’s on it’s sending energy to the batteries, and when it’s off it’s monitoring the capacity of the batteries to make sure that it’s properly charging the batteries throughout the full state of charge.

What does an MPPT charge controller do?

MPPT or maximum power point tracking charge controllers are the more advanced and feature-rich of the two charge controllers.

Now keep in mind both of these charge controllers are going to prevent overcharging of your battery bank as well as unnecessary discharge of the battery banks, so that energy can flow really only in one direction.

With the MPPT charge controller the added functionality comes with the ability to electronically track and deliver the most optimal amount of energy from the solar array to the battery bank.

Just like the PWM charge controller, the MPPT charge controller can monitor the capacity of the batteries and then match the necessary voltage needed from the solar array to charge those batteries depending on what the state of charge is.

On top of that, why it’s more optimal, is the fact that it can account for differences in voltages coming from the solar array and then manipulate the amount of amps or current that’s sent to the batteries. As the batteries are charging they’re actually getting charged more during the same amount of time as with a PWM charge controller.

I could go into a whole video on the differences between these two and kind of how that works, and give you mathematical calculations and all this stuff. If you want to see that video, hit me up in the comments below. I may do one of those later on but this is a fundamentals video.

Now you kind of understand the differences between the PWM and the MPPT charge controller. With that being said I’m gonna go ahead and jump into the advantages and the disadvantages and for this section I’m gonna have three different categories.

The efficiency of each charge controller, the functionality of each charge controller and then as always, the price.

Which is more efficient, MPPT or PWM solar charge controllers?

When it comes to efficiency, the PWM controller, as you may have guessed is less efficient than the MPPT charge controller. This has to do with the fact that it doesn’t have the electronic tracking capabilities and the ability to optimize the amount of energy going to the batteries.

What this offers to the MPPT charge controller is the ability to increase the efficiency by anywhere from 10 to about 40 percent, depending on external variables such as temperature, charging capacity of the battery and many variables on top of that.

When it comes to functionality MPPT charge controllers win out yet again. They’re able to accommodate for differences in voltages between the solar array and the battery banks.

If you have a 24 volt solar array charging a 12 volt battery bank, you need to have an MPPT charge controller. If you have a 12 volt array and a 12 volt battery bank you can get away with having a PWM charge controller.

Another added functionality benefit to MPPT charge controllers is the ability to detect and modify the charge going to the batteries when there is a DC load or an appliance attached directly to the battery.

If you have some sort of appliance or anything that’s attached to the positive and negative side of the battery and it’s being powered directly from that battery, the charge controller can monitor that and then compensate for the amount of charge needed to charge both battery bank as well as power that DC appliance.

Are MPPT controllers worth it?

The last category I’m going to talk about is the pricing differences between these two charge controllers. The MPPT charge controller can be nearly double the cost, if not more than two times the cost of PWM charge controllers.

This has to do a lot with the fact that there’s added functionality and efficiency benefits, but it also has to do with the fact that there’s a higher manufacturing cost when it comes to MPPT charge controllers.

Now when it comes to the initial cost it may look like PWM charge controllers are the advantage but you have to consider the fact that they are less efficient.

If you’re trying to gain the maximum amount of power from a small system, if you’re limited on space or anything like that, you definitely need to go with an MPPT charge controller.

How to size a solar charge controller

Also, if there’s any voltage differences from your solar array to your battery bank you need the MPPT charge controller to increase the efficiency.

Often times, the differences in price between these two charge controllers can be made up in having to buy less of the other components, meaning less solar panels and less batteries, to account for the differences in efficiencies between these two charge controllers.

Now that I’ve got the advantages and disadvantages out of the way, I’m gonna go ahead and show you guys how to get a good idea of what size charge controller you need for your system. When it comes to sizing for a charge controller it’s a lot easier than you might think.

What you need to do is take the total wattage of your solar array, which in our circumstance is 600 watts, and then you’re going to divide that by the voltage of your system.

We have ours wired in 12 volt configuration, so what we do is, we take 600 watts and you divide that by 12 volts. That’s gonna give you a 50 amp recommendation on the size of the charge controller.

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