A charge controller goes between the solar panels and the battery bank. Its main function is to prevent the solar panels from overcharging the batteries. The algorithm, or control strategy, of a charge controller determines the effectiveness of battery charging and solar panel utilization, which ultimately influences the ability of the system to meet the load demands, and give you power when you need it.
Additional features such as temperature compensation and equalization can enhance the ability of a charge controller to maintain the health, maximize capacity, and prolong the life of the batteries.
Modern charge controllers come in two basic types, PWM (Pulse Width Modulation) and MPPT (Maximum Power Point Tracking). For an automotive analogy, a PWM charge controller would be like a three-speed manual transmission, and an MPPT controller is an automatic transmission. MPPT type charge controllers automatically find the voltage at which panels produce power most efficiently.
PWM (Pulse Width Modulation)
The PWM type charge controllers are the simplest and usually the lowest priced. PWM controllers operate by regulating a pulsed, direct connection from the solar array to the battery bank. As the battery bank approaches a full charge, the length of the connection pulses decreases to gradually taper off the charging current from the solar array. On a 12V battery bank, PWM charge controllers can only be used with a solar array that has an open circuit voltage of 24.0V or less. This excludes large 60 cell or 72 cell residential panels.
In systems with multiple solar panels of different voltages (e.g. 32 cell panels mixed with 36 cell or 40 cell panels), PWM charge controllers are preferable to MPPT controllers because their operation algorithms are less finicky.
Our most popular PWM charge controllers:
Morningstar Prostar 15 & 30amp
SNS PWM 30amp
MPPT (Maximum Power Point Tracking)
The MPPT type charge controllers use a much more efficient method of feeding power from the solar array to the battery bank. Instead of a regulated direct connection, MPPT type controllers transform the optimum balance of current and voltage from the solar array into something that can safely be fed into a battery bank. This means that excess voltage from the solar array is transformed into more charging current.
For example, with a PWM charge controller you may have a solar panel operating at 18.0V and 5.0A, feeding 5.0A in to your battery bank. If your battery bank is at 13.0V you are only getting 65W (13.0V x 5.0A = 65W) from the panel. With an MPPT charge controller on that same panel you will be able to use that extra voltage (18.0V – 13.0V = 5.0V) and turn it into more current. Your charging current will be about 6.9A and you will be getting 90W from the panel.
Our most popular MPPT charge controllers include:
Victron Bluesolar 75/15
Victron Bluesolar 100/30
Victron Bluesolar 100/50
Charge Controller System Design
There are several factors that should be considered when selecting a charge controller system:
Price and Performance – The MPPT charge controllers will cost more, but they will also give you more power. Using an MPPT type controller is like having extra panels in your array. If roof space is at a premium, which it usually is with an RV, MPPT controllers will help you make the most of what you have.
Array Voltage/Battery Bank Voltage – In order to charge a battery bank, the solar array voltage has to be slightly higher than the battery bank voltage. This potential (pressure) differential causes the electrons to flow from the panels to the batteries. Without this differential, the batteries will not receive a charge. Typically a solar array operates at around 18.0V and a battery bank will range from about 11.0V to 14.6V.
Voltage Limits – PWM type charge controllers on 12V battery systems typically have an open circuit array voltage limit of 24V. Other MPPT controllers have voltage limits of up to 150V, and in some cases even higher. To avoid damaging your charge controller, make sure the Voc (Voltage open circuit) for each panel does not exceed your charge controller’s limit. The Voc is usually printed on the label on the back of the solar panel.
Current Limits - Charge controllers are rated on their output current (from the controller to the battery). As long as your panels are connected in parallel (which they should be for an RV) you can determine the maximum output current by summing the operating current, or Impp (Current maximum power point) for each panel. The Impp is usually printed on the panel label.
Multiple Charge Controllers – If your desired solar array has a charging current that exceeds the current rating of your preferred charge controller, you can use multiple charge controllers. These charge controllers would be connected in parallel to each other across the battery bank.
Charge Controller Tuning
In order to maintain battery health it is important to program your charge controller with the correct system parameters such as maximum voltage, total battery Ah capacity (if applicable), etc. All Solar N Sat installed systems are calibrated for optimum performance and efficiency based on decades of experience with a variety of battery types under real world operating conditions.
Charge Controller Accessories
To get the most out of your system it may be important to incorporate battery temperature sensors and monitors.
Battery temperature sensors (Not needed for Lithium batteries) – To maximize the potential of your lead-acid battery bank without boiling off electrolyte, you will want your charge controller to be able to compensate for the temperature of your battery bank.
Monitors – With a charge controller monitoring system you will be able to see the key system details like Charging Current, Battery Charge Level, Battery Voltage, etc. Advanced monitoring systems like the Victron BMV7++ let you set and control various parameters of your system, which will further help you to maintain healthier batteries, thereby maximizing their longevity.