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The world is searching for sources of renewable energy—and solar energy is a big favorite. It reduces pollution, doesn't have the fossil fuel emissions that contribute to global warming, and lowers fossil fuel prices. If you want to reduce your electricity bill, or if you’re using a recreational vehicle and you need a source of energy, you might want to run off solar power. Photovoltaic (PV) cells convert solar energy into electricity—and this electricity is stored in batteries. There are solar charging battery systems. But once the batteries are fully charged, they can be damaged if they continue to charge. Also, if there is an intensely bright sun, the batteries might not be able to handle the incoming voltage. Charge controllers, also known as solar regulators, are designed to protect the batteries to prevent overcharging. A controller will regulate the current going to the batteries, according to how much they have charged up. Once a battery is fully charged, they prevent the battery from becoming damaged as a result of being charged any more. But there are a couple of varieties of charge controllers. There are two main types of charge controllers: pulse width modulated controllers, and maximum power point tracker controllers. Each one has a different emphasis: The MPPT controller converts the voltage from the solar panels, to achieve the optimal voltage and power transfer for the batteries. The PWM controller is geared more to protect the life of the batteries, and to make sure that the charge stored in them doesn't leak out so fast.
To help you make the right choice, we have put together this buying guide including everything you need to know about charge controllers to make a good investment. It'll help you:
Choose the right type of charge controller,
See useful tips about that type of charge controller,
Read reviews of different brands of charge controllers, and what customers are saying,
Select the right brand of charge controller, and
Compare prices and find the best deals.
Charge controllers are voltage and current regulators that are designed to keep batteries from overcharging. Typical solar panels will produce between 16-20 Volts, which could damage batteries that need only 14 volts to charge up.
The first charge controllers would allow charging up a battery until a certain voltage was reached. Then it would turn off. When the battery's voltage would drop below a certain level, it would turn back on and start charging up again.
But then it was realized that the batteries last longer if there are three stages:
1) Bulk: The batteries charge up gradually to the bulk level voltage of 14.4-14.6 Volts, while the batteries are drawing maximum current.
2) Absorption: The batteries' voltage is maintained at 14.4-14.6 Volts for a specified time, and the current decreases, while the batteries charge up to the full state of charge (SOC).
3) Float: When the batteries are fully charged, at the end of the specified absorption time, the voltage is lowered to a “float” level (13.4-13.7 Volts), and the batteries draw a minimum of current, to kept it at that “float” level, until the beginning of the next cycle.
There are two types of charge controllers:
PWM—Pulse Width Modulated Controller: These use high-frequency electrical pulses to charge up batteries, and change the current by changing the length of the pulses. They work like a rapid "on-off" switch. They send a series of short charging pulses to the battery and then receive feedback from the battery to see how fast to send pulses, and how wide the pulses of charge should be. When the battery is fully charged and has no load (i.e., there is nothing that drains the charge from the battery), the PWM will only tick every few seconds, sending short pulses. If the battery is totally discharged, the pulses will be long, or the controller will be on constantly to recharge the battery. In between every two pulses, the controller checks the charge on the battery and adjusts accordingly as to how much charge to send. The deficiency of PWM is that it will cause noise interference in radios and TVs, by creating sharp pulses. These are used for 12 V batteries that give 30 Amperes of current, but you can find models suitable for up to 60 Amperes of current. A streamlined version is the Morningstar SunGuard SG-4 Charge Controller. It is a single-module, PWM controller, which has two connections to the solar panels, and two connections to the solar batteries. The controller monitors the battery charging and makes sure that the charge on the batteries doesn’t leak out at night, or when there is very little sunlight.
MPPT -Maximum Power Point Tracker—This involves a computer-driven circuit that scans the battery voltage and the photovoltaic array voltages at regular intervals. This allows calculating the match between the photovoltaic voltage and the battery voltage. This ensures that the power from the batteries is a maximum. (The electronics definition of power is Power = Volts x Current.) Since this controller is more complex, the MPPT controller is also more expensive. It is also suited for greater currents than the PWM controller—up to 80 Amperes. The SolarEpic 4215BN MPPT 40-Amp Solar Charge Controller is an example of a maximum power point tracker controller, which has the benefits of protecting against over-charging and over-current, as well as temperature extremes. The Tracer MPPT Tracer 3215RN Solar Charge Controller is designed to monitor the changes in the voltage of the solar panels during the different times of day and different temperatures.
Based on all the consumers' reviews we've scanned, these are the top things they mentioned about their new stuff:
Protection features: Make sure that the charge controller provides protection vs. overcharging, overload, short circuits, power surges, and undercharging: There also is “load control mode”, or “low voltage disconnect”, where the controller disconnects the appliances from the system when the battery voltage gets too low. Otherwise, that can also damage the batteries.
Warnings: There are some rules of caution with charge controllers:
Use identical PV modules for one MPPT controller. If you mix the types of PV modules or use different modules from different manufacturers, or use modules that take different voltages and different power ratings, this could lead to the MPPT not working properly, and the module could get damaged.
Maximum Open Circuit Voltage: “Open circuit voltage” is the voltage of the battery when there are no devices attached to it. If you exceed this voltage, the controller can be permanently damaged. PV modules produce higher voltages in cold weather—so three 45 V modules in series add up to 135 V. If the MPPT's maximum open circuit voltage is 150 V, it will be safe in the summer, but may get damaged in the winter if it is cold and sunny.
Don't exceed maximum voltage: Trying to install the PV system with a voltage of more than 48V can lead to dangerous shocks and a fire hazard. It's best to have a professional install the solar panel system in such cases.
The controller you buy will be determined by the battery bank voltage and the maximum current produced by the solar panels:
Check battery bank voltage: This will usually be 12 V, 24 V, or 48 V.
Calculate the maximum current that the controller will need to handle.
Which type of controller to choose: To decide between PWM or MPPT controllers, consider this:
PWM controllers are recommended for small systems, where the solar cell temperatures remain between 45°-75° Celsius.
MPPT controllers are recommended when the array of solar panels provides much more voltage than the batteries that store the charge. It is also the better choice when the system will be submitted to extreme temperatures (lower than 45°, or above 75° Celsius).
MPPT controllers have fewer power losses. MPPT charge controller reduces the voltage from the solar panels (say 20, or 24 V) to the 14 volts that the solar batteries need. But an MPPT will also increase the current. A PWM controller will also drop the voltage to the right level, but it will not modify the current. This means that you will lose about half of the power from the solar panels when using a PWM controller. So an MPPT controller means more power savings.
Types of batteries: Charge controllers can be specialized for regulating several types of rechargeable batteries: Lead Acid, Lithium Ion, and Flow batteries. (For example, the SolarEpic 4215BN MPPT 40-Amp Solar Charge Controller has 4 charging options for the different types of lead-acid batteries: sealed, gel, flooded, and user-defined.) Here is some information about the various types:
Lead-acid--This is the most common battery for recreational vehicles or marine applications. They will involve lead plates that store charge, with a sulphuric acid electrolyte between the plates. There are various types of lead-acid batteries:
Absorbed Glass Matte (= AGM batteries): These use fiberglass separators between the lead plate and wrappers to hold the sulphuric acid electrolyte in place. This has the advantage that the acid in the battery will not spill out, even if the battery is tilted. This type of battery is also impact-resistant and has low internal resistance. That allows for higher output voltage, lower charging time, and generates less heat.
Flooded ("wet cell") batteries: This is the familiar car battery. These also use lead plates with a sulphuric acid electrolyte and plate separators, but here the cells of the battery are not sealed, and the gasses produced do not recombine into the electrolyte when recharging. You have to supply the battery with water periodically to replenish lost electrolytes. (This is different from AGM batteries, where any gasses released by the battery are reconstituted back into the electrolyte.) Besides the maintenance, they also have a higher internal resistance than AGM batteries.
Sealed lead-acid batteries: These are filled with fluid like the flooded batteries, but not user-serviceable (there is no way for the user to add water to the cells). This is suitable for small systems, such as a 20 Watt or 50 Watt panel, but are more expensive.
Deep cycle batteries: These are meant to last a long time, and can be drained to more than 50% of their charge. These are suitable for large systems, but they must be filled with fluid from time to time.
GEL cell batteries: These use silica to turn sulphuric acid into a gel, which serves as the electrolyte. This also prevents spilling of the electrolyte. But if a gel battery is exposed to high current, it can cause corrosion of the plates. Therefore they can't be used for fast charging or discharging, although they are slightly more durable than the "flooded" type of battery.
Lithium Ion: These are more expensive, but they deliver more charging cycles than lead acid batteries.
Flow Batteries--These work on two chemical components dissolved in liquids, which undergo ion exchange through a membrane. These don't degrade over time--but they will require more equipment than the lead acid or Li-ion varieties.
Indicators: Some controllers have LED indicators that tell you the controller's status, the battery current, and the voltage. Some also have a temperature sensor to monitor the battery temperature, to prevent overheating. Some also keep logs of the data. The SolarEpic 4215BN MPPT 40 Amp Solar Charge Controller comes with PC monitoring software, and you can monitor changes using the SolarEpic MT50 remote control meter.
Other types of protections: There are other risks for which a charge controller provides protection. For example, the Windy Nation P30L PWM Solar Panel Regulator Charge Controller has an LCD display that shows the current, battery voltage, battery temperature, Photovoltaic cell/solar output current, load current, low voltage disconnect setting, low voltage reconnect setting, over-voltage disconnect setting, timer control settings, and more.
Connections: The actual wiring for most controllers is self-explanatory. For example, the Windy Nation P30L PWM Solar Panel Regulator Charge Controller has a + and - for connecting the battery, a + and - for connecting the solar panels, and a + and - for connecting the load (the device that you wish to operate using the batteries).
Dual battery controllers: Some controllers are able to control two sets of batteries. The MorningStar SunSaver Duo SSD-25RM has DIP switches that you can modify, in order to select which set of solar batteries you want to charge at a particular time, and which gets more power.
Maximize use of your solar panels: An MPPT charge controller can help you get maximum power from your solar panels. For example, the Renogy 20 Ampere MPPT Solar Charge Controller matches the changing voltages while charging solar batteries, changing the voltage according to the time of day and temperature. This method can result in a 30% more efficient transfer of power. That utilization means that you can reduce the number of solar panels by 30%, and still get the same desired amount of power. But even PWM controllers offer savings: The MorningStar TS-60 Tristar-60 Amp Charge Controller can be installed in parallel with other TS-60 controllers, so as to provide for as much as 300 Amperes of power.
More than just protecting the solar batteries: Some charge controllers do more than just protect the batteries from getting damaged. The MorningStar TS-60 Tristar-60 Amp Charge Controller is a three-function solar battery charger. It has three modes, and provides 1) solar battery charging, 2) supplying power to a load and load control, and 3) diversion regulation, utilizing excess power from the solar panels in the form of heat and the like.
Renogy—(also known as RNG Group) is a renewable energy company that makes solar energy products. They make solar panels for homes, businesses, and recreational vehicles. They are based in Ontario, California.
Tracer-- is a brand of Epsolar Technology Company, Ltd. They were established in March 2007, and are located in Beijing, China. They make solar charge controllers, off-grid inverters, LED drivers and power units.
Morning Star—was started in 1993 and are based in Newtown, Pennsylvania and Jessup, Maryland. They are makers of solar controllers and inverters.
Outback Power— was founded in Arlington, Washington in 2001. They specialize in electronics for renewable energy, backup power, and marine and mobile applications. They have designed a wide selection of products: grid inverters, grid-tie inverters with battery backup, MPPT charge controllers, and communications network products. They make equipment that can survive in harsh conditions.