Solar Charge Controller Types, Functionality and Applications
A solar charge controller is fundamentally a voltage or current controller to charge the battery and keep electric cells from overcharging. It directs the voltage and current hailing from the solar panels setting off to the electric cell. Generally, 12V boards/panels put out in the ballpark of 16 to 20V, so if there is no regulation the electric cells will damage from overcharging. Generally, electric storage devices require around 14 to 14.5V to get completely charged. The solar charge controllers are available in all features, costs, and sizes. The range of charge controllers is from 4.5A and up to 60 to 80A.
Types of Solar Charger Controller:
- Simple 1 or 2 stage controls
- PWM (pulse width modulated)
- Maximum power point tracking (MPPT)
Simple 1 or 2 Controls: It has shunt transistors to control the voltage in one or two steps. This controller basically just shorts the solar panel when a certain voltage is arrived at. Their main genuine fuel for keeping such a notorious reputation is their unwavering quality – they have so not many segments, there is very little to break.
PWM (Pulse Width Modulated): This is the traditional type charge controller, for instance, anthrax, Blue Sky, and so on. These are essentially the industry standard now.
Maximum power point tracking (MPPT): The MPPT solar charge controller is the sparkling star of today’s solar systems. These controllers truly identify the best working voltage and amperage of the solar panel exhibit and match that with the electric cell bank. The outcome is extra 10-30% more power out of your sun oriented cluster versus a PWM controller. It is usually worth the speculation for any solar electric systems over 200 watts.
Features of Solar Charge Controller:
- Protects the battery (12V) from overcharging
- Reduces system maintenance and increases battery lifetime
- Auto charged indication
- Reliability is high
- 10amp to 40amp of charging current
- Monitors the reverse current flow
The function of the Solar Charge Controller:
The most essential charge controller basically controls the device voltage and opens the circuit, halting the charging, when the battery voltage ascents to a certain level. charge controllers utilized a mechanical relay to open or shut the circuit, halting or beginning power heading off to the electric storage devices.
Generally, solar power systems utilize 12V of batteries. Solar panels can convey much more voltage than is obliged to charge the battery. The charge voltage could be kept at the best level while the time needed to completely charge the electric storage devices is lessened. This permits the solar systems to work optimally constantly. By running higher voltage in the wires from the solar panels to the charge controller, power dissipation in the wires is diminished fundamentally.
The solar charge controllers can also control the reverse power flow. The charge controllers can distinguish when no power is originating from the solar panels and open the circuit separating the solar panels from the battery devices and halting the reverse current flow.
Applications:
In recent days, the process of generating electricity from sunlight is having more popularity than other alternative sources and the photovoltaic panels are absolutely pollution free and they don’t require high maintenance. The following are some examples of where solar energy is utilizing.
- Street lights use photovoltaic cells to convert sunlight into DC electric charge. This system uses a solar charge controller to store DC in the batteries and uses it in many areas.
- Home systems use a PV module for house-hold applications.
- A hybrid solar system uses for multiple energy sources for providing full-time backup supply to other sources.
Example of Solar Charge Controller:
From the below example, in this, a solar panel is used to charge a battery. A set of operational amplifiers are used to monitor panel voltage and load current continuously. If the battery is fully charged, an indication will be provided by a green LED. To indicate undercharging, overloading, and deep discharge condition a set of LEDs are used. A MOSFET is used as a power semiconductor switch by the solar charge controller to ensure the cut offload in low condition or overloading condition. The solar energy is bypassed using a transistor to a dummy load when the battery gets full charging. This will protect the battery from overcharging.
This unit performs 4 major functions:
- Charges the battery.
- It gives an indication when the battery is fully charged.
- Monitors the battery voltage and when it is minimum, cuts off the supply to the load switch to remove the load connection.
- In case of overload, the load switch is in off condition ensuring the load is cut off from the battery supply.
A solar panel is a collection of solar cells. The solar panel converts solar energy into electrical energy. The solar panel uses Ohmic material for interconnections as well as the external terminals. So the electrons created in the n-type material passes through the electrode to the wire connected to the battery. Through the battery, the electrons reach the p-type material. Here the electrons combine with the holes. When the solar panel is connected to the battery, it behaves like other battery, and both the systems are in series just like two batteries connected serially. The solar panel has totally consisted of four process steps overload, under charge, low battery, and deep discharge condition. The out from the solar panel is connected to the switch and from there the output is fed to the battery. And setting from there it goes to the load switch and finally at the output load. This system consists of 4 different parts-over voltage indication and detection, overcharge detection, overcharge indication, low battery indication, and detection. In the case of the overcharge, the power from the solar panel is bypassed through a diode to the MOSFET switch. In case of low charge, the supply to MOSFET switch is cut off to make it in off condition and thus switch off the power supply to the load.
Solar energy is the cleanest and most available renewable energy source. Modern technology can harness this energy for a variety of uses, including producing electricity, providing light and heating water for domestic, commercial or industrial applications.
Battery Charge Controller
For many people, building their own solar panel system and living off-grid is becoming a reality instead of a dream. Connecting the solar panels directly to a single battery or bank of batteries for charging may work, but is not a good idea. What’s needed is a battery charge controller to safely charge and discharge your deep cycle battery for a longer lifespan.
A standard 12 volt solar panel which can be used to recharge a battery, could actually be putting out nearly 20 volts at full sun, much more voltage than the battery needs. This difference in voltage between the required 12 volts need for the battery and actual 20 volts being generated by the solar panel translates into a greater current flow into the battery.
This results in too much unregulated solar generated current overcharging the battery which could cause the electrolyte solution within the batteries to overheat and evaporate off, resulting in a much shortened battery life and ultimately, complete battery failure.
Then the quality of the charging current will directly affect the life of any connected deep cycle battery, so it is extremely important to protect batteries of a solar charging system from being overcharged, or even undercharged, and we can do just that using a battery charge regulation device called a Battery Charge Controller.
A battery charge controller, also known as a battery voltage regulator, is an electronic device used in off-grid systems and grid-tie systems with battery backup. The charge controller regulates the constantly changing output voltage and current from a solar panel due the angle of the sun and matches it too the needs of the batteries being charged.
The charge controller does this by controlling the flow of electrical power from the charging source to the battery at a relatively constant and controlled value.
Thus maintaining the battery at its highest possible state of charge while protecting it from being overcharged by the source and from becoming over-discharged by the connected load. Since batteries like a steady charge within a relatively narrow range, the fluctuations in output voltage and current must be tightly controlled.
Solar Battery Charge Controller
Then the most important functions of battery charge controllers used in an alternative energy system are:
- Prevents Battery Over-charging: This is too limit the energy supplied to the battery by the charging device when the battery becomes fully charged.
- Prevents Battery Over-discharging: Automatically disconnect the battery from its electrical loads when the battery reaches a low state of charge.
- Provides Load Control Functions: Automatically connect and disconnect the electrical load at a specified time, for example operating a lighting load from sunset to sunrise.
Solar panels produce direct or DC current, meaning the solar electricity generated by the photovoltaic panels flows in only one direction only. So in order to charge a battery, a solar panel must be at a higher voltage than the battery being charged. In other words, the voltage of the panel must be greater than the opposing voltage of the battery under charge, in order to produce a positive current flow into the battery.
When using alternative energy sources such as solar panels, wind turbines and even hydro generators, you will get fluctuations in output power. A charge controller is normally placed between the charging device and the battery bank and monitors the incoming voltage from these charging devices regulating the amount of DC electricity flowing from the power source to the batteries, a DC motor, or a DC pump.
The charge controller turns-off the circuit current when the batteries are fully charged and their terminal voltage is above a certain value, usually about 14.2 Volts for a 12 volt battery. This protects the batteries from damage because it doesn’t allow them to become over-charged which would lower the life of expensive batteries. To ensure proper charging of the battery, the regulator maintains knowledge of the state of charge (SoC) of the battery. This state of charge is estimated based on the actual voltage of the battery.
During periods of below average insolation and/or during periods of excessive electrical load usage, the energy produced by the photovoltaic panel may not be sufficient enough to keep the battery fully recharged.
When the batteries terminal voltage starts to drop below a certain value, usually about 11.5 Volts, the controller closes the circuit to allow current from the charging device to recharge the battery bank again.
In most cases a charge controller is an essential requirement in any stand-alone PV system and should be sized according to the voltages and currents expected during normal operation. Understanding your batteries and their charging requirements is also a must for any battery based solar system.
Any battery charge controller must be compatible with both the voltage of the battery bank and the rated amperage of the charging device system. But it must also be sized to handle expected peak or surge conditions from the generating source or required by the electrical loads that may be connected to the controller.
There are some very sophisticated charge controllers available today. Advanced charge controllers use pulse-width modulation, or PWM. Pulse width modulation is a process that ensures efficient charging and long battery life. However, the more advanced and expensive controllers use maximum power point tracking, or MPPT.
Maximum power point tracking maximizes the charging amps into the battery by lowering the output voltage allowing them to easily adapt to different battery and solar panel combinations such as 24v, 36v, 48v, etc. These controllers use DC-DC converters to match the voltage and use digital circuitry to measure actual parameters many times a second to adjust the output current accordingly. Most MPPT solar panel controllers come with digital displays and built-in computer interfaces for better monitoring and control.
Choosing the Right Solar Charge Controller
We have seen that the primary function of a Battery Charge Controller is to regulate the power passing from the generating device, be it a solar panel or wind turbine to the batteries. They assist in properly maintaining the solar power system batteries by preventing them from being overcharged or undercharged, thus offering long life to batteries.
The solar current being regulated by a battery charge controller not only charges batteries but can also be passed to inverters for converting the direct DC current to alternating AC current to supply the utility grid.
For many people who want to live “off grid”, a charge controller is a valuable piece of equipment as part of a solar panel or wind turbine power system. You will find numerous charge controllers manufactures online, but choosing the right one can sometimes be quite confusing and to add to your worries they are not cheap either, so finding a good quality solar charge regulator really matters.
It’s best not to go for those low quality cheaper ones, as they may actually harm the battery life and increase your overall expense in the long run. For a little peace of mind then why not Click Here and check out some of the better battery charge controllers available from Amazon and learn more about the different types of solar charge controllers available as part of your solar power system helping you to save money and the environment.
Find Us On
- Energy Storage
- Deep Cycle Batteries
- Understanding Batteries
- Connecting Batteries Together
- The Deep Cycle Battery
On Sale Now Bestseller No. 1 Photovoltaic Design Installation For Dummies 13.77
On Sale Now Bestseller No. 3 Photovoltaics: Design and Installation Manual 29.45
On Sale Now Bestseller No. 4 Photovoltaic Systems 119.99
Please Speak up!
We hope this Battery Charge Controller tutorial was useful and informative for you. Are you ready to share your thoughtsand experience with us and many others. Your Комментарии и мнения владельцев are always welcome, just post them in the section below.
P.S. Don’t forget to like, rate, and share this Alternative Energy Tutorials post. Thank you for using our website.
Комментарии и мнения владельцев already about “ Battery Charge Controller ”
Hi. Im considering a combination of wind and solar power generation for my boat kept on mooring. I think a combination would be good as Scotland not blessed with lots of sun and my mooring is a bit sheltered with harbour wall. Can i plug output from 2amp wind turbine into a Renogy mppt regulator (20 amp), would it manage the power to my batteries in same way as with a solar panel?
MPPT controllers have been used for photovoltaic (solar) power for a long time, but can also be used for wind turbines. In real life the wind speed is not constant, but changes continuously, thus the ideal rotor RPM for maximum torque will also change. What is important to remember is that there is an optimum RPM for each wind speed, and that is where we want to run the wind turbine to achieve MPPT. However, to work properly the controller needs an MPPT power curve that is specific for the wind turbine that you want to hook up to the controller. So check the MPPT’s manual if you can connect it to a wind turbine. If not, then it is not advisable since unlike PV, a wind turbine can output much higher open circuit input voltages (Voc) when it is not loaded up or your batteries are full.
I have a 730 W, 76 V solar panels system charging 24 V battery set up using a Morning Star MPPT charge controller in an OFF GRID set up. Which is the best suited APC or LUMINOUS UPS/Inverter that is solar compatible that can be used.
Hello, I have read your site with interest. We have a large dwelling with a business operating from it. Our standing load without all onsite is around 4KW This is a combination of servers and IT equipment, freezers, fridges etc. When all onsite with heating lighting TV’s etc. this can reach 10KW our energy costs are spiralling out of control. We have a large paddock approx 50m from the nearest 240V electrical connection into the site wiring that is in a barn. We are looking at taking a step into solar. Our initial aim is to simply power the office load using purely solar Generated energy whenever it is operating and obviously use the grid for any shortfall. We know the property will consume all of the power generated. We had a couple of thoughts. 1) Simple system. Setup an array that can generate approx 3KW and connect it to a Solar inverter and simply connect that into the property wiring system as an input. Whatever it produces should be consumed first before we need to get energy from the grid. Is this assumption correct assuming we have a local load at or exceeding the solar-generated capacity? 2) As an expansion of 1) above. We would look to build a larger array and connect that to a battery bank (this looks like the black magic area) that has enough capacity to provide a stable supply to an inverter that would then be connected as before into the property wiring systems that would provide a variable load of between 4 and 10KW we have seen peaks of 12KW on our monitor that is clamped onto the incoming 100A 240V Grid connection. How would we size the array and battery system and corresponding Invertor etc. Are higher voltage panels better than lower voltage panels? Are higher string voltages better than lower voltages from a power conversion point of view. e.g. is it more efficient to convert from 48V to 240V rather than 12 or 24V to 240V If I have a string of 24V 1000Ah made up of a series connected 2 x parallel 12V strings of 5 x 12V 200Ah batteries giving me 24V 1000Ah of capacity or in theory 24KWh what size inverter would I need to provide power into the property and would my system use the power I have before going to the grid? I am sure some of these questions are a bit basic but we are very DIY-orientated people and want to build this ourselves. Any help in understanding this would be great. I am sure there is much left out of my note. Like cable sizing etc. Logically I think we know what we think is happening, but, that doesn’t make it so! Like will we consume all we have before taking anything from the grid? I apologise for any typos or grammer. Cheers Tony
There are a number of good points raised here, and we will attempt to answer them. Firstly, an inverter fed grid-connected, or grid-tied system is basically a bunch of solar panels (or turbines) connected to a single inverter (or a collection of small inverters) feeding power directly to the utility grid. Generally, PV inverters operate as current sources injecting electric current into the utility grid in-phase with the grid voltage. It is commonly assumed that ALL the power generated by the PV panels (array) is consumed at the point of generation but this is not always the case. Power consumed is both active (real) and reactive. PV panels generate active power only. If your average power consumption is, for example, 10kWh per day, and you generate 12kWh for the 4 hours of full sun that day, then some of the inverters output power maybe autoconsumed and some may flow into the utility grid. Equally 100% inverter current may flow into the grid and you may consume 100% from the grid, just slowing down your energy meter in the process. On average PV panels generate maximum power for 4 to 5 hours of full sun per day as they do not consistently generate power 24 hours per day at their nominal output wattage rating. Oversizing an inverter by having more DC input power than the inverters AC output power, may increase power output in lower light conditions, thus extending the 5 hours. As would solar tracking. Connecting a battery bank would allow for more autonomy but at a cost and an increased array size, as now the array has to charge batteries for 5 hours plus feed the grid. Then the size and type of grid-connected system would ultimately depend on how many hours of autonomy you require and how much you are willing to pay upfront. Higher string voltages are better providing everything stays within tolerance at worst case conditions. As P = VI, a higher voltage (V) means a lower current (I) for a given power (P) and therefore smaller diameter cabling so cheaper. PV panel voltage depends on the wattage (100W or 400W) of the panel. Higher PV wattages means physically bigger panels, which means more m 2 of installation area.
the article states the controller should stop charging a 12V battery at approx 14.2V, what about 6 volt batteries – same?
No of course not. A single 3-cell 6 volt rechargeable battery should have a fully charged terminal voltage of about 6.35 volts. To correctly charge a wet battery, the output voltage of the charging system needs to be slightly higher than the batteries fully charged terminal voltage, to ensure that the charging current flows in the direction from charger to battery. A constant voltage equal to between 2.35 to 2.45 volts per cell is recommended for charging storage batteries. Thus for a 12 volt, 6-cell battery this is between 14.1 and 14.7 volts, so the charge controller should stop charging the battery once this voltage level is reached, or switch to a low current float charge. For a 6 volt, 3-cell battery this voltage level is between 7.05 and 7.35 volts.
Victron MPPT Solar Charge Controller Kits
The System Core is what takes power from the roof mounted combiner box and feeds it into your battery bank. The essential components of a System Core include a wire harness, charge controller and circuit protection. Victron MPPT System Cores are ideal for lithium battery banks, offering a wide variety of add-on monitoring options and allow for series connected solar panels. Neither a cell phone signal nor an internet connection are needed for Bluetooth communication.
Ideal for lithium battery banks, offering a wide variety of add-on monitoring options, allows for series connected solar panels
This kit is built around a Victron SmartSolar MPPT 75|15 charge controller and comes with built-in bluetooth monitoring that can communicate with a Smart phone. It is also compatible with several optional add-on monitoring kits. It can regulate up to 200 watts of solar panels in optimal conditions (more in higher latitudes) and is compatible with our roof mounted combiner boxes. 8 gauge wire reduces lines losses for optimum efficiency. This system core is the preferred choice for our lithium battery systems, but it is also fully compatible with lead-acid battery banks.
This kit is built around a Victron SmartSolar MPPT 100|20 charge controller and comes with built-in bluetooth monitoring that can communicate with a Smart phone. It is also compatible with several optional add-on monitoring kits. It can regulate up to 300 watts of solar panels in optimal conditions (more in higher latitudes) and is compatible with our roof mounted combiner boxes. 8 gauge wire reduces lines losses for optimum efficiency. This system core is the preferred choice for our lithium battery systems, but it is also fully compatible with lead-acid battery banks.
This kit is built around a Victron SmartSolar MPPT 100|30 charge controller and comes with built-in bluetooth monitoring that can communicate with a Smart phone. It is also compatible with several optional add-on monitoring kits. It can regulate up to 450 watts of solar panels in optimal conditions (more in higher latitudes) and is compatible with our roof mounted combiner boxes. Thick 6 gauge wire reduces lines losses for optimum efficiency. This system core is the preferred choice for our lithium battery systems, but it is also fully compatible with lead-acid battery banks.
This kit is built around a Victron SmartSolar MPPT 100|50 charge controller and comes with built-in Bluetooth monitoring that can communicate with a Smart phone. It is also compatible with several optional add-on monitoring kits. It can regulate up to 700 watts of solar panels in optimal conditions (more in higher latitudes) and is compatible with our roof mounted combiner boxes. Thick 4 gauge wire reduces lines losses for optimum efficiency. This system core is the preferred choice for our lithium battery systems, but it is also fully compatible with lead-acid battery banks.
This kit is built around a Victron SmartSolar MPPT 150|70 charge controller and comes with built-in Bluetooth monitoring that can communicate with a smartphone. It is also compatible with several optional add-on monitoring kits. It can regulate up to 900 watts of solar panels in optimal conditions (more in higher latitudes) and is compatible with our roof mounted combiner boxes. Thick 2 gauge wire reduces line losses for optimum efficiency. This system core is the preferred choice for our lithium battery systems, but it is also fully compatible with lead-acid battery banks.
This kit is built around a Victron SmartSolar MPPT 150|85 charge controller and comes with built-in bluetooth monitoring that can communicate with a Smart phone. It is also compatible with several optional add-on monitoring kits. It can regulate up to 1250 watts of solar panels in optimal conditions (more in higher latitudes) and is compatible with our roof mounted combiner boxes. Thick 2 gauge wire reduces lines losses for optimum efficiency. This system core is the preferred choice for our lithium battery systems, but it is also fully compatible with lead-acid battery banks.
SunRunner™ Signature System Cores
Deluxe system cores with MPPT charge controllers, temperature compensation and remote meters with full programability
This kit is built around an MPPT charge controller and offers a digital display, system programming, battery monitoring, temperature compensation, disconnects and cable management hardware. It can regulate up to 340W of solar panels and is compatible with our roof mounted combiner boxes. Thick 6 gauge wire reduces lines losses for optimum efficiency.
This kit is built around an MPPT charge controller and offers a digital display, system programming, battery monitoring, temperature compensation, disconnects and cable management hardware. It can regulate up to 540W of solar panels and is compatible with our roof mounted combiner boxes. Thick 4 gauge wire reduces lines losses for optimum efficiency.
SunRunner™ Gold System Cores
Upgraded with temperature sensors to optimize battery charging, designed for multiple panel systems using combiner boxes
This kit offers a digital display, temperature compensation and cable management hardware. It can regulate up to 450 watts of solar panels and is compatible with our roof mounted combiner boxes. Thicker 8 gauge wire and a Maxi Fuse minimize voltage drop for optimum performance.
This kit is built around an MPPT charge controller and offers a digital display, temperature compensation and cable management hardware. It can regulate up to 400W of solar panels and is compatible with our roof mounted combiner boxes. Thicker 8 gauge wire and a Maxi Fuse minimize voltage drop for optimum performance.
SunRunner™ Essential System Cores
Low price, PWM Charge Controllers with wire harnesses designed to connect directly to solar panels with MC4 leads
This kit has a digital display and can regulate up to 165 watts of solar panels whose output cables terminate in MC4 connectors. Use MC4 T-Branch connectors or AMS Essential Add-On MC4 Wire Harness when adding more than one panel to this system.
This simple arrangement allows you to use 32 or 36 cell Solar Panels whose output cables terminate in MC4 connectors. The controller can regulate up to 315 watts of Solar Panels. Use MC4 T-Branch connectors or AMS Essential Add-On MC4 Wire Harness when adding more than one panel to this system.
The name of each Charge Controller Kit consists of a number representing the maximum current rating, PWM or MPPT referencing the type of charge controller used, and a forward slash followed by a number representing the wire gauge. Therefore, a SunRunner 30PWM/10 system uses a 30 amp PWM charge controller with a system wiring harness that uses 10 gauge cable between the roof combiner box and the controller and also between the controller and the batteries. Likewise, a SunRunner 40MPPT/4 would be based on a 40 amp MPPT controller that uses 4 gauge cable for increased efficiency and lower voltage drop at higher currents.
Our SunRunner System designs are the result of over 30 years of hands-on experience gained from selling, installing and living with these systems. We are constantly improving our designs and component offerings based on customer feedback and personal experience. If we can’t find products to meet our needs, we task ourselves to build (or have built) a product to our specifications. Because of that, our systems are unique in the field. We have thousands of satisfied customers who are living, loving and playing in their RVs which are powered by AM Solar SunRunner Systems.
Feel free to call or email our Tech Support at 541.726.1091 if you need help selecting the SunRunner System that best matches your needs.
Solar Charge Controller: The Definitive Guide
A solar charge controller, or solar charge regulator, is an important instrument in almost all solar power systems that use batteries as a chemical energy storage solution. It is used in stand-alone or hybrid solar power systems but not used in straight grid-tied systems, which don’t have rechargeable batteries.
Stand-alone solar power system
Its two basic functions are very simple:
Overcharging can result in battery overheating, or, in an extreme possibility, a fire. Overcharged deep-cycle flooded batteries could also emit gas of hydrogen, which is explosive. What’s more, overcharging will quickly ruin the battery, thus shortening its lifespan dramatically.
Solar charge controllers can preclude the flow of reverse current from batteries to solar panels at night when the voltage of solar panels is lower than that of batteries.
Furthermore, solar charge controllers have other optional features, such as battery temperature sensor compensation, Low-voltage disconnect (LVD), Load control (dusk to dawn), Displays, remote monitoring and diversion load control.
Let’s dive into the article to check these functions features one by one.
Chapter 2: Charging a battery: Multi-stage charging
But before we dive directly into Chapter 3: Functions and features of a solar charge controller, we’d better take a look at necessary information about charging a battery.
If you are already quite familiar with this piece of information, you could jump to chapter 3 from here.
2.1 Brief interpretation
Imagine pouring water into a cup – at the beginning, you will pour at a faster rate; when the cup is close to full, water flow slows down so that the water will not overflow from the cup. On the contrary, if you keep pouring water at a faster rate, it’s hard for you to stop the flow in time at the end, and water will overflow from that cup.
The same theory applies to charging a battery:
- When the battery is low, the charge controller delivers lots of energy for a quick charge
- When the battery is close to full, it slows the charger by regulating its voltage and current.
- When the battery is full, it sends only a trickle of power to keep a full charge.
This is the so-called multi-stage charging.
2.2 Example: 3-4 Stages
In order to make sure you can easily understand the following content, which refers to an example of multi-stage charging (3-4 Stages), let’s firstly explain the jargon “set points.”
the solar charge controller is set to change its charging rate at specific voltages, which are called the set points.
Set points are usually temperature compensated, and we will discuss this topic after the example of multi-stage charging.
Now, let’s go through the example in detail
The following is an example from MorningStar, which has 4 stages of charging.
Source: MorningStar, 4 stages of charging
2.2.1 Stage 1: Bulk Charge
At this stage, the battery bank is low, and its voltage is lower than the absorption voltage set-point. So, the solar charge controller will send as much available solar energy as possible to the battery bank for recharging.
2.2.2 Stage 2: Absorption Charge
When its voltage reaches the absorption voltage set-point, the output voltage of the solar charge controller will keep a relatively constant value. Steady voltage input prevents a battery bank from over-heating and excessive gassing. Commonly, the battery bank could be fully charged at this stage.
2.2.3 Stage 3: Float charge
As we know, the battery bank is fully charged at the absorption stage, and a fully charged battery cannot convert solar energy into chemical energy anymore. Further power from the charge controller will only be turned into heating and gassing, as it is overcharging.
The float stage is designed to prevent the battery bank from long-term overcharging. At this stage, the charge controller will reduce the charging voltage and deliver a very small amount of power, like trickles, so as to maintain the battery bank and preclude further heating and gassing
2.2.4 Stage 4: Equalization charge
The equalize charge uses a higher voltage than that of absorption charging, so as to level all the cells in a battery bank. As we know, batteries in series or/and parallels constitute a battery bank. If some cells in the battery bank are not fully recharged, this stage will make them all fully recharged and complete all the battery chemical reactions.
Since it follows stage 3 (when the battery bank is fully recharged), when we raise the voltage and send more power to the batteries, the electrolytes will look like they are boiling. In actuality, it is not hot; it is hydrogen generated from the electrolytes, producing a lot of bubbles. These bubbles stir the electrolytes.
Stirring the electrolytes regularly in this way is essential to a flooded battery bank.
We can consider it a periodic overcharge, but it is beneficial (sometimes essential) to certain batteries, such as flooded batteries and not sealed batteries, like AGM and Gel.
Commonly you could find in battery specifications how long the equalization charge should last, and then set the parameter in the charge controller accordingly.
2.3 Why flooded battery banks need equalization
to preclude the sulfation of a lead-acid battery.
The chemical reaction of discharging
The chemical reactions of battery discharging generate soft lead sulfate crystals, which usually are attached to the surface of the plates. If the battery keeps working in this kind of condition, as time passes by, the soft sulfate crystals will multiply and become even harder and harder, making them pretty difficult to convert back to soft ones, or even further activate materials that were a part of the electrolyte.
The sulfation of lead-acid batteries is the scourge of a battery failure. This issue is common in long-term, undercharged battery banks.
If charged completely, the soft sulfate crystals can be converted back to active materials, but a solar battery is seldom fully recharged, especially in a not well-designed solar PV system, where either the solar panel is too small or the battery bank is oversized.
Sulfation of lead-acid battery
Only a periodic overcharge at high voltage can solve this problem; namely, equalization charging, which works at high voltage, generates bubbles and stirs the electrolyte. That’s why stage 4 is essential to a flooded battery bank. In many off-grid solar systems, we usually use a generator charger to equalize the flooded solar battery periodically, according to the battery specification.
2.4 Control set points vs. temperature
Since absorption set-point (stage 2), float set-point (stage 3) and equalization set-point (stage 4) all can be compensated for temperature if there is a temperature sensor, we would like to spare some words for this little topic.
In some advanced charge controllers, multi-stage charging set-points fluctuate with the battery’s temperature. This is called a “temperature compensation” feature.
The controller has a temperature sensor, and when the battery temperature is low, the set point will be raised, and vice versa – it will adjust accordingly once the temperature gets higher.
Some controllers have built-in temperature sensors, so they must be installed in proximity to the battery to detect the temperature. Others may have a temperature probe that should be attached to the battery directly; a cable will connect it to the controller to report battery temperature.
If your batteries are applied to a situation where temperature fluctuation is larger than 15 degrees Celsius every day, adopting a controller with temperature compensation is preferable.
2.5 Control set points vs. battery type
When we come to battery type, another article about solar batteries is recommended.
Most solar power systems adopt a deep-cycle, lead-acid battery, of which there are 2 types: flooded type and sealed type. A lead-acid flooded battery is not only economical, but also prevalent in the market.
Various solar battery types
Battery types also affect the design of set-points for solar charge controllers; modern controllers have the feature to allow you to select the battery types before connecting to a solar power system.
2.6 Determining the ideal set points
Finally, we come to the theory about determining the ideal set points. Frankly speaking, it is more about equilibrium between quick charging and maintenance trickle charging. The user of a solar power system should take various factors into consideration, such as ambient temperature, solar intensity, battery type and even home appliance loads.
It is necessary to only cope with the top 1 or 2 factors; that is enough in most cases.
Chapter 3: What is the function of solar charge controller?
3.1 Preventing overcharge
When a battery is completely charged, it cannot store more solar energy as chemical energy. But if power is continuously applied to the fully charged battery at a high rate, the power will be turned into heat and gassing, which would present as a flooded battery with a lot of bubbles from the electrolytes. That is the hydrogen gas, which is generated from a chemical reaction. These gases are dangerous since they are explosive. Overcharging also accelerates battery aging. And then we need a solar charge controller.
Damaged battery due to overcharge
The main function of the solar charge controller is to regulate the voltage and current that is generated by solar panels going to the batteries to prevent batteries from overcharging and guarantee the batteries a safe working condition and a longer lifespan.
1. Current regulator
A current regulator acts like a switch. It simply switches the circuit on or off to control the energy flow to the battery bank, just like stage 1 bulk charging. They are usually called shunt controllers, which are no longer used due to their obsolete technology.
Pulse width modulation (PWM)
Shunt controllers shut down the current completely, while the PWM controller reduces the current gradually. PWM is more similar with stage 3 float charging.
We will have an in-depth discussion about PWM and MPPT when we start the topic: PWM VS MPPT which one is better.
Voltage regulator
Voltage regulation is common. The solar charge controller regulates the charging in response to the battery voltage. It is quite simple. When the voltage of a battery reaches a certain value, the controller protects the battery from overcharging by reducing the power. When the voltage of a battery drops because of a large sum of power consumption, the controller will allow bulk charging again.
3.2 Blocking reverse current
The second main function is to prevent reverse current flow.
At night, or whenever there is no sunlight, the solar panel does not have power to convert into electricity, and, in a solar power system, the voltage of the battery bank will be higher than the voltage of the solar panel, since we all know electricity flows from high voltage to low voltage. So, without a charge controller, the electricity will flow from the battery bank to the solar panel, which is a waste of power, as the solar power system takes efforts to collect energy during the day but wasting a little of them at night. Although the loss is only a little in proportion to the total energy collected, it is not hard to solve.
Blocking Reverse Current at night
A solar charge controller can deal with this problem.
Most controllers allow the flow to go only from solar panel into a battery bank by designing into the circuit a semiconductor, which only passes currents in one direction.
Some controllers have a mechanical switch, which is also called a relay. When the relay clicks on and off, you will hear a clatter sound. When the voltage of the solar panels is lower than that of the battery bank, it detects and then switches off the circuit, disconnecting the solar panels from the battery bank.
3.3 Load control
Some solar charge controllers are designed with load control, allowing you to connect a DC load, such as an LED lamp (a concrete example is on our website all-in-one solar LED street lights), direct to the solar charge controller, and the load control will turn the lamp on and off according to its pre-settings (the voltage of battery, photocell sensor, or a timer).
Solar charge controller in solar street lights
For example, there commonly are timers in LED solar street lights, and the load control will read the time from the timer and then execute the command: turn the LED on at 7:00 pm at dusk and turn it off at 6:00 am the next morning. Or the load control will read information from the photocell sensor and then control the LED on and off according to the brightness of the ambient environment.
3.4 Low voltage disconnect (LVD)
Imagine that you are boiling water in a pot and you forget to turn off the fire until the boiling water is totally evaporated; no longer any water in the dry pot and the pot overheats. The pot is destroyed permanently. In the same way, discharging a solar battery completely will result in permanent damage to a battery.
Deep cycle batteries are widely used in solar power systems. The Depth of Discharge (DOD) could be as large as 80%; however, they are susceptible to permanent damage if discharged up to 90% or, even worse, 100%.
If you wait to switch off the DC load from your batteries until you find your lights dimming, the battery damage could have already happened. Both battery capacity and life expectancy will be decreased every time when over-discharge happens. If the battery were set to work in this kind of over-discharge state for a period of time, it would be ruined quickly.
The only practical solution to protect batteries from over-discharge is to switch loads (such as appliances, LED lights and so on) off and on, provided that the voltage has recovered from bulk charging.
Typically, if a 12V battery drops to 10.9 volts, the battery would be on the verge of over-discharging. In the same way, 21.9 volts for a 24V battery.
If your home solar system has some DC loads, the LVD feature is necessary. Some LVDs are integrated into charge controllers while others aren’t.
3.5 Overload protection
When the input current flow is much higher than what the circuit can safely deal with, your system overloads. This can lead your system to overheat or even cause a fire. Overload can be caused by different reasons, such as a wrong wiring design (short circuit), or a problematic appliance (a stuck fan). Commonly, a push-button reset is designed for the overload protection circuit.
However, there is a built-in overload protection in each solar charge controller; large solar power systems usually require double safety protection: fuses or circuit breakers. If the wire carrying capacity is smaller than the overload limit of the controller, then setting up a fuse or breaker in your circuit is a must.
3.6 Displays
The displays of solar charge controllers vary from LED indicators to LCD screen displays, with information of voltage and current. Displays to solar power systems are what console dashboards are to cars. They provide you with detailed data so that you can monitor the state of your battery bank: how much energy you are using or generating.
Solar charge controller with LED indicators
If your system already has a self-contained monitor, then the display feature would not be important. Even the cheapest monitor would include basic meters, just as controllers have.
Solar charge controller with LCD Screen