Step 5: Choosing a Solar Charge Controller

There are two types of Solar Charge Controllers on the market. One is a "PWM" Charge Controller and the other is a "MPPT" Charge Controller. Both Controllers will properly charge and maintain your battery(ies). The PWM Charge Controller is the most popular controller because it is the less expensive of the two.

As we recommend throughout the solar resource, read and implement the first four sections prior to purchasing a Charge Controller:

  1. Step One: Selecting lifestyle. Just camping or Full-timing?
  2. Step Two: Reducing power consumption - LED Lighting
  3. Step Three: Choosing the right battery solution for travel trailers
  4. Step Four: Selecting Solar Panels for Scamp - Molded Fiberglass Travel Trailers

What does a Solar Charge Controller Do?

The charge controller takes the power generated by your Solar panel(s) and manages the voltage going into your battery(ies) based on the "State of Charge" (SOC) of your battery. As an example: when your battery is deeply discharged the battery can accept more electrons at a higher voltage (bulk charging) than it can when it is nearly full (absorption charging).

Why do I need a Solar Charge Controller?

A 12 Volt Solar Panel is capable of generating more than 12 volts. Without a Charge Controller the higher, unregulated voltage from your Solar Panel(s) would simply kill your battery in a very short time, it would literally boil the acid right out of the battery.

Additionally, if your Solar Charge Controller has an "Equalize" voltage capability it can increase the longevity of your battery by "conditioning" the battery on a periodic basis.

What's the difference between PWM and MPPT Controllers?

The difference is in how they operate. Your battery can only accept a certain voltage depending on its State of Charge (SOC), your Solar Panel(s) is/are capable of generating a higher voltage than your battery can accept (i.e: 18 volts for a 12 volt panel). So, let's say your battery can accept a "Bulk" charge at 14.6 volts (based on its SOC), a PWM controller is simply going to "ignore" the extra voltage from the Solar Panel (up to 18 volts) and send 14.6 volts to the battery. In the case of an MPPT controller it will use the excess voltage (3.4 volts) to increase the amperage being fed into the battery. This increased amperage means that more electrons are being forced into your battery and that your battery will be fully charged quicker.

Which Solar Charge Controller Should I Buy?

That depends on how large your Solar System is. If your Solar System is 400 watts or less and you will be charging a 12 volt battery, or a pair of 6 volt batteries configured as a 12 volt battery bank, then a PWM controller (30 Amp) will do the job for a lot less money than a MPPT controller. If you have a larger Solar system, or you want to configure your Solar panels for higher voltages (above 24v), then you will need to go with the MPPT controller.

Why Not Use a MPPT Controller?

If you have a Solar System that is larger than 400 watts, or you want to configure your Solar panels to operate at higher voltages (above 24v) then you will need to buy a MPPT controller.

Aren't MPPT Controllers Better?

While an MPPT controller might be "better" on a larger system, their advantage is much less on a smaller Solar System (less than 400 watts). Additionally, they are larger and they produce more heat than a PWM controller.

If you are considering a MPPT controller, you might consider spending your money on higher wattage Solar panels (or buying an extra panel) instead.

Buying Tips and a WARNING !!!!

When buying your controller you should look at controllers rated for 20 or 30 amps instead of the smaller 10 amp controllers. This will allow you to add another Solar panel or to deploy a portable Solar panel to catch the morning sun.

Many of the new controllers have a LCD screen on them, I would recommend them over the ones with just status lights.

BIG WARNING !!!!  There are several counterfeit MPPT controllers on the market. Many of these counterfeit MPPT controllers are simply PWM controllers with "MPPT" lettering written on them. Additionally, some of these counterfeit MPPT controllers with LCD screens actually show "PWM" on the screen when powered up. Become familiar with the appearance of both PWM and MPPT controllers, many of the counterfeit MPPT controllers look exactly like a PWM controller with "MPPT" written on the case. Also, if the price is TOO LOW, then you should be suspicious and check it out very well before you decide buy it.

Tech Tip for PWM Controllers.

Many of the PWM controllers use the positive wire as the grounding wire. This is directly opposite from how campers and vehicles are wired in the United States. All vehicles use the negative wire as the ground. This will not be a problem if you remember to completely isolate the charge controller from any metal inside your camper. Simply mounting the controller to a wooden surface (or fiberglass) will be sufficient to protect your PWM controller. Note: there are a few PWM controllers which use "Negative" grounding.

Whether your PWM controller uses positive or negative grounding you will still make all connections as positive to positive and negative to negative.


  1. PWM Controllers on Amazon
  2. MPPT Controllers on Amazon

Part 6 - Putting it all Together - Coming Soon

Contributed by SOI Lifetime Member ManWithAVan