RV Solar Charge Controllers
RV solar systems are more than just panels on the roof. Any well designed RV solar system has a Charge Controller or Regulator as part of the system. It is the heart of the solar system. Without it, the batteries will not be properly charged and damage to the battery pack will occur. Or, at the very least, shorter battery life will result. One should NEVER EVER connect a solar panel directly to a battery pack without a controller….unless the solar panel is so small it is classified as a trickle charger.
PWM RV Charge Controllers.
These controllers are designed to charge batteries at different voltages slowing plate sulphating, and extending battery life. These controllers are easy to identify. The features describe different charging modes such as bulk charge, absorption charge, float charge, and equalize. These controllers are usually low cost, come with a host of other features, and work well for most applications. They are the most commonly found controllers on the market today and cost anywhere from $50-$400 depending on the power rating and other features.
MPPT RV Charge Controllers.
The latest Charge Controller technology to be brought to the RV industry employs MPPT or Maximum Power Point Tracking. A charge controller with MPPT (a technology borrowed from the commercial and residential solar industry) will deliver 10%-30% more energy from the solar panels to the RV batteries than one without this feature. This is not because MPPT makes the controller more efficient, instead MPPT is just smarter. Every solar panel made has a different maximum power point. A point at which current (amperage) and voltage peak. An MPPT controller is designed to sense this point and adjust itself for maximum output. This point is referred to as the ‘knee of the curve' and is shown on the IV graph found on almost every solar panel datasheet. MPPT controllers are more expensive than PWM types. A good MPPT charge controller can cost $250-$700 depending on the power rating. So, the added value of the energy produced, versus the added cost, must be considered. Depending on the size of the system, it could make as much difference as adding another panel. In some cases updating just the controller itself to MPPT is about the same cost as adding another solar panel to the system with the same benefit and cost. Something to consider for those with older controllers.
All Solar Charge Controllers have a power rating. This is usually measured in AMPS. It is the maximum amount of electrical current the controller can handle without failing. A label is found on the back of every solar panel will detail the maximum amount of amps the panel will output. This is usually expressed as ISC or short circuit current. Since most RV solar panels are wired in parallel, the amperage from every panel is added together. The total solar panel current or battery current should not exceed the maximum power rating of the charge controller. It is a good system design practice to oversize the controller by 20%. The controller will run cooler, be more reliable, and last longer. Power does come at a price. Therefore, the higher the power rating of the charge controller, the more it will cost.
Environmental concerns and placement.
Solar charge controllers are usually mounted inside the passenger compartment of the RV and recessed in a wall cavity. While this installation looks good, it can sometimes be problematic if larger than 30amp rating. Heat must be dissipated otherwise the charge controller will fail. We would never suggest locating the charge controller in the battery compartment. There are many reasons for this, the biggest of which are corrosion caused by battery off-gassing and the potential for fire should there be a spark.