Solar Charge Controllers: What They Are, Why You Need One and What They Cost
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- What Is a Solar Charge Controller?
- Types of Solar Charge Controllers
- Factors to Consider
- Installation Maintenance
- The Bottom Line
A solar charge controller regulates voltage and current when you use photovoltaic panels to charge a battery. Without this device, your batteries would be damaged by overcharge.
Charge controllers are only required in off-grid solar systems. They are not necessary in grid-tied systems, since the inverter sends excess energy to the grid automatically. While the price of a solar charge controller can range from about 20 to 500, it’s important to keep in mind that an off-grid system has a higher cost overall than one tied to the grid. The best solar companies will advise you on whether you need one and will ensure everything is set up correctly.
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What Is a Solar Charge Controller?
A charge controller can be described as a Smart battery charger, and this device is very important when charging a battery with solar panels. Their voltage and current output varies depending on sunlight, and batteries need a stable and controlled input.
The main function of solar charge controllers is regulating battery charge, but they can also provide electrical protection by:
- Switching off the battery when it reaches an excessively low voltage
- Preventing reverse current from the battery to the solar panels when they are not generating power
- Lowering the charge voltage when the battery temperature rises
When Do I Need a Solar Charge Controller?
Solar charge controllers are only necessary in off-grid systems. Most home solar systems are connected to the grid, and no charge controller is needed in this case.
- If your solar panel system does not include batteries, there is no charging process to control in the first place.
- If you use a solar battery system, the inverter acts as a charge controller. Once the battery is fully charged, excess energy is simply sent to the grid.
The configuration of a solar power system with a battery bank changes depending on the type of inverter. You can use a hybrid inverter, which connects to solar panels and batteries simultaneously, or you can have a separate solar inverter and battery inverter. In both cases, the inverter has a built-in charge controller function, and you don’t need a separate device.
Types of Solar Charge Controllers
Solar charge controllers can be classified into two main types: pulse-width modulation (PWM) controllers and maximum power point tracking (MPPT) controllers.
Pulse-Width Modulation (PWM)
PWM solar charge controllers are simpler and more affordable, but also less efficient. PWM controllers reduce their current output gradually as the battery charges. Once the battery reaches 100% charge, the controller can keep it full by providing small amounts of power without overcharging.
PWM charge controllers are designed to be used with solar panels that match the battery voltage. For example, if you want to charge a 12V battery, you also need photovoltaic modules with a rated output of 12 volts.
According to EnergySage, you can expect to pay between 15 and 125 for a PWM solar charge controller, where the price depends on the rated wattage and amperage. PWM controllers have a typical efficiency of less than 80%.
- affordable than MPPT charge controllers
- Smaller and easier to carry around
- Suitable for DIY solar energy systems
- You cannot charge batteries with higher-voltage solar panels
- Less efficient than MPPT charge controllers
- Less efficient in cold weather
Maximum Power Point Tracking (MPPT)
MPPT solar charge controllers are also known as Smart DC-to-DC converters, and they are more advanced than PWM controllers. An MPPT charge controller can match a battery system with solar panels of higher voltage.
- An MPPT charge controller keeps your solar panels at the ideal voltage and current for maximum power output.
- At the same time, the controller keeps a suitable charging voltage for the battery system.
According to EnergySage, you can expect to pay between 28 and 324 for an MPPT solar charge controller. The best MPPT controllers can reach an efficiency of over 95%.
As a quick example, assume a small solar array is operating at 36 volts and 10 amps, providing 360 watts of power. Using a PWM charge controller, you cannot use this power output to charge a 12V battery. However, an MPPT charge controller can lower the voltage to 12V while increasing the current to 40 amps, which makes charging possible.
You can charge batteries with solar panels of higher voltage
Up to 20% more efficient than PWM charge controllers
– Can handle higher wattages efficiently
– MPPT technology is more expensive
– Installation is more complex
– Less efficient in systems smaller than 170W
Factors To Consider When Choosing a Solar Charge Controller
Before purchasing a charge controller, you should check its technical specifications carefully. If there is a mismatch between your charge controller and your solar panels and batteries, your system will not work, and you may even damage components.
Your charge controller should be compatible with the output voltage supplied by the solar panels and the input voltage required by the battery. These voltages are equal when you use a PWM controller, but the solar panel voltage can be higher when you use an MPPT controller.
Maximum Current Rating
Like in any electrical system, you also need current compatibility between components. Your charge controller should not exceed the rated input current of your battery, and it should be able to handle the highest possible current from the solar array. For example, if your battery system has a maximum current of 30 amps, you should not use a 40-amp charge controller.
Diversion Load Control
The charge controllers used for renewable energy systems such as solar panels and wind turbines are often equipped with a diversion load, which is used to dump excess energy once the battery is fully charged.
Display and Monitoring Capabilities
Many charge controllers include an LCD display where you can check operating parameters or a Bluetooth module that allows monitoring via smartphone. Ideally, you should look for a charge controller capable of displaying its operating conditions.
High temperature can greatly reduce the service life of your battery, but the best charge controllers have a temperature compensation feature. They monitor the battery with a temperature sensor, and they reduce the charging voltage as necessary to prevent overheating.
The efficiency of your charge controller is an important metric, since it determines the amount of solar energy that gets converted into battery charge. MPPT charge controllers can achieve a charging efficiency of over 95%, but they are more expensive. PWM charge controllers are generally less than 80% efficient, but they are also more affordable.
Solar charge controllers are not very expensive on their own. Even a high-quality MPPT controller may only cost a few hundred dollars, making it one of the cheapest components of an off-grid solar system. However, the total cost of an off-grid system is typically much higher than one that’s connected to the grid, potentially by tens of thousands of dollars.
Installation and Maintenance of Solar Charge Controllers
The difficulty of installing a charge controller can vary depending on the specific product you purchase and the size of your system. Some charge controllers have a simple plug-and-play design, which means you only need to connect solar panels and batteries of matching voltage and current ratings.
However, if you need a large off-grid solar system for a home, a professional solar installation is strongly recommended. The power and current ratings involved are higher, and DIY projects can be dangerous.
Since charge controllers have no moving parts, their maintenance needs are very simple. However, you should check the wiring regularly, since loose connections create electrical resistance and heating. Having a charge controller with an LCD display is also helpful for maintenance purposes, since the screen will notify you of any issues that need attention.
Solar Charge Controller Providers
There are many charge controller providers in the market, and reading product reviews is strongly recommended before making your purchase. Victron Energy and Renogy are widely regarded as two of the best brands:
Victron SmartSolar Series = 12/24/36/48V, 10–100 Amp MPPT controllers
Renogy Rover Series = 12/24/36/48V, 20–100 Amp MPPT controllers
The Bottom Line
Solar charge controllers are necessary to charge batteries safely in off-grid solar systems. They can be used with both lead-acid and lithium batteries, but you must ensure that their voltage and current ratings match.
- PWM charge controllers are more affordable, but less efficient, and they are only suitable for lower wattage systems.
- MPPT charge controllers are more efficient and suitable for higher wattages, but they also have a higher price.
If you plan to install solar panels in a home that will remain connected to the grid, there is no need for a charge controller. A hybrid inverter or a battery inverter can control the charging process by itself, and excess electricity is simply sent to the grid.
Keep in mind that off-grid home solar systems are more expensive than grid-tied systems. The typical cost of a home solar system is 15,000 to 20,000, and it can drop below 10,000 after incentives like the federal tax credit. However, an off-grid solar system can exceed 50,000 since it needs large batteries and additional control systems.
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.
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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.
Choosing the Right Solar Charge Controller/Regulator
A solar charge controller (frequently called a regulator) is similar to a regular battery charger, i.e. it regulates the current flowing from the solar panel into the battery bank to avoid overcharging the batteries. (If you don’t need to understand the why’s, scroll to the end for a simple flow chart). As with a regular quality battery charger, various battery types are accommodated, the absorption voltage, float voltage can be selectable, and sometimes the time periods and/or the tail current are also selectable. They are especially suited for lithium-iron-phosphate batteries as once fully charged the controller then stays at the set float or holding voltage of around 13.6V (3.4V per cell) for the remainder of the day.
The most common charge profile is the same basic sequence used on a quality mains charger, i.e. bulk mode absorption mode float mode. Entry into bulk charge mode occurs at:
- sunrise in the morning
- if the battery voltage drops below a defined voltage for more than a set time period, e.g. 5 seconds (re-entry)
This re-entry into bulk mode works well with lead-acid batteries as the voltage drop and droop is worse than it is for lithium-based batteries which maintain a higher more stable voltage throughout the majority of the discharge cycle.
Lithium batteries (LiFePO4) do not benefit from re-entry into a bulk mode during the day as the internal impedance of the lithium batteries increases at high (and low) states of charge as indicated by the orange vertical lines in the chart below and it is only necessary to occasionally balance the cells which can only be done around the absorption voltage. A related reason is to avoid the Rapid and large variation in voltage that will occur in these regions as large loads are switched on and off.
Lithium batteries do not have a defined “float voltage”, and therefore the “float voltage” of the controller should be set to be at or just below the “charge knee voltage” (as indicated in the chart below) of the LiFePO4 charge profile, i.e. 3.4V per cell or 13.6V for a 12V battery. The controller should hold this voltage for the remainder of the day after bulk charging the battery.
The Difference Between PWM and MPPT Solar Charge Controllers
The crux of the difference is:
- With a PWM controller, the current is drawn out of the panel at just above the battery voltage, whereas
- With an MPPT solar charge controller the current is drawn out of the panel at the panel “maximum power voltage” (think of an MPPT controller as being a “Smart DC-DC converter”)
You often see slogans such as “you will get 20% or more energy harvesting from an MPPT controller”. This extra actually varies significantly and the following is a comparison assuming the panel is in full sun and the controller is in bulk charge mode. Ignoring voltage drops and using a simple panel and simple math as an example:
Battery voltage = 13V (battery voltage can vary between say 10.8V fully discharged and 14.4V during absorption charge mode). At 13V the panel amps will be slightly higher than the maximum power amps, say 5.2A
With a PWM controller, the power drawn from the panel is 5.2A 13V = 67.6 watts. This amount of power will be drawn regardless of the temperature of the panel, provided that the panel voltage remains above the battery voltage.
With an MPPT controller the power from the panel is 5.0A 18V = 90 watts, i.e. 25% higher. However this is overly optimistic as the voltage drops as temperature increases; so assuming the panel temperature rises to say 30°C above the standard test conditions (STC) temperature of 25°C and the voltage drops by 4% for every 10°C, i.e. total of 12% then the power drawn by the MPPT will be 5A 15.84V = 79.2W i.e. 17.2% more power than the PWM controller.
In summary, there is an increase in energy harvesting with the MPPT controllers, but the percentage increase in harvesting varies significantly over the course of a day.
A PWM (pulse width modulation) controller can be thought of as an (electronic) switch between the solar panels and the battery:
- The switch is ON when the charger mode is in bulk charge mode
- The switch is “flicked” ON and OFF as needed (pulse width modulated) to hold the battery voltage at the absorption voltage
- The switch is OFF at the end of absorption while the battery voltage drops to the float voltage
- The switch is once again “flicked” ON and OFF as needed (pulse width modulated) to hold the battery voltage at the float voltage
Note that when the switch is OFF the panel voltage will be at the open-circuit voltage (Voc) and when the switch is ON the panel voltage will be at the battery voltage voltage drops between the panel and the controller.
The best panel match for a PWM controller:
The best panel match for a PWM controller is a panel with a voltage that is just sufficiently above that required for charging the battery and taking temperature into account, typically, a panel with a Vmp (maximum power voltage) of around 18V to charge a 12V battery. These are frequently referred to as a 12V panel even though they have a Vmp of around 18V.
The MPPT controller could be considered to be a “Smart DC-DC converter”, i.e. it drops the panel voltage (hence “house panels” could be used) down to the voltage required to charge the battery. The current is increased in the same ratio as the voltage is dropped (ignoring heating losses in the electronics), just like a conventional step-down DC-DC converter.
The “Smart” element in the DC-DC converter is the monitoring of the maximum power point of the panel which will vary during the day with the sun strength and angle, panel temperature, shading, and panel(s) health. The “smarts” then adjust the input voltage of the DC-DC converter – in “engineering speak” it provides a matched load to the panel.
The best panel match for an MPPT controller:
- The panel open circuit voltage (Voc) must be under the permitted voltage.
- The VOC must be above the “start voltage” for the controller to “kick in”
- The maximum panel short circuit current (Isc) must be within the range specified
- The maximum array wattage. some controllers allow this to be “over-sized”, e.g the Redarc Manager 30 is permitted to have up to 520W attached
Choosing the Right Solar Controller/Regulator
The PWM is a Good Low-Cost Option:
f or solar panels with a maximum power voltage (Vmp) of up to 18V for charging a 12V battery (36V for 24V battery, etc).
When the solar array voltage is substantially higher than the battery voltage e.g. using house panels, for charging 12V batteries
An MPPT controller will yield higher returns compared with a PWM controller as the panel voltage increases. I.e. a 160W panel using 36 conventional monocrystalline cells with a maximum power amp of 8.4A will provide around 8.6A at 12V; while the 180W panel having 4 more cells will provide the same amperage but 4 additional cells increases the panel voltage by 2V. A PWM controller will not harvest any additional energy, but an MPPT controller will harvest an additional 11.1% (4 / 36) from the 180W panel.
For the same principle, all panels using SunPower cells with more than 32 cells require an MPPT charge controller otherwise a PWM controller will harvest the same energy from 36, 40, 44 cell panels as it does from a 32 cell panel.
Solar Charge Controller Features and Options
Boost MPPT Controllers
“Boost” MPPT charge controllers allow batteries to be charged that has a higher voltage than the panel.
Combined MPPT and DC-DC Chargers
The MPPT function is a natural adjunct to the DC-DC charger function and there are several quality brands that provide this with more under development. A single unit can be used by itself, as it automatically switches between alternator charging and solar charging. For larger systems, our favoured arrangement is to use a separate MPPT controller for the fixed roof-mounted panels and use the combined MPPT/DC-DC with portable panels. In this case, an Anderson connector is placed on the exterior of an RV which is then wired to the solar input of the MPPT/DC-DC unit.
Note that the battery capacity must be sufficient so that the combined charging current from simultaneous charging from the alternator and the roof solar panels does not exceed the manufacturer’s recommended maximum charging current.
Cheap controllers may be marked as an MPPT but testing has shown that some are in fact PWM controllers. Cheap controllers may not have the over-voltage battery protection which could result in the battery being overcharged with potential damage to the battery; caution is recommended. Normally, due to the increased circuitry, MPPT solar charge controllers will be physically larger than PWM solar charge controllers.
Multiple Solar Chargers
Properly wired, it is possible to add multiple solar chargers (any combination of type and rating) to charge a battery. Proper wiring means that each solar charger is wired separately and directly to the battery terminals. This ideal case means that each controller will “see” the battery voltage and is unaffected by the current flow coming from other charge controllers. This situation is no different from charging a battery from the grid/generator at the same time as charging from solar. With modern controllers, the current will not flow backwards from the battery to the controller (excepting a very small quiescent current).
Increase Solar Charging With An MPPT Charge Controller
MPPT stands for Maximum Power Point Tracking, a technique to regulate the charge of your battery bank. The function of an MPPT charge controller is analogous to the transmission in a car. When the transmission is in the wrong gear, the wheels do not receive maximum power. That’s because the engine is running either slower or faster than its ideal speed range. The purpose of the transmission is to couple the engine to the wheels, in a way that lets the engine run in a favorable speed range in spite of varying acceleration and terrain.
Let’s compare a PV module to a car engine. Its voltage is analogous to engine speed. Its ideal voltage is that at which it can put out maximum power. This is called its maximum power point. (It’s also called peak power voltage, abbreviated Vpp). Vpp varies with sunlight intensity and with solar cell temperature. The voltage of the battery is analogous to the speed of the car’s wheels. It varies with battery state of charge, and with the loads on the system (any appliances and lights that may be on). For a 12V system, it varies from about 11 to 14.5V.
In order to charge a battery (increase its voltage), the PV module must apply a voltage that is higher than that of the battery. If the PV module’s Vpp is just slightly below the battery voltage, then the current drops nearly to zero (like an engine turning slower than the wheels). So, to play it safe, typical PV modules are made with a Vpp of around 17V when measured at a cell temperature of 25°C. They do that because it will drop to around 15V on a very hot day. However, on a very cold day, it can rise to 18V!
What happens when the Vpp is much higher than the voltage of the battery? The module voltage is dragged down to a lower-than-ideal voltage. Traditional charge controllers transfer the PV current directly to the battery, giving you NO benefit from this added potential.
Now, let’s make one more analogy. The car’s transmission varies the ratio between speed and torque. At low gear, the speed of the wheels is reduced and the torque is increased, right? Likewise, the MPPT varies the ratio between the voltage and current delivered to the battery, in order to deliver maximum power. If there is excess voltage available from the PV, then it converts that to additional current to the battery. Furthermore, it is like an automatic transmission. As the Vpp of the PV array varies with temperature and other conditions, it “tracks” this variance and adjusts the ratio accordingly. Thus it is called a Maximum Power Point Tracker.
What are the advantages of MPPT?
That depends on your array, your climate, and your seasonal load pattern. It gives you an effective current boost only when the Vpp is more than about 1V higher than the battery voltage. In hot weather, this may not be the case unless the batteries are low in charge. In cold weather however, the Vpp can rise to 18V. If your energy use is greatest in the winter (typical in most homes) and you have cold winter weather, then you can gain a substantial boost in energy when you need it the most!
Example: MPPT On a Cold Winter Day
If the outside temperature is 20°F (-7°C) and the wind is blowing a bit, the PV cell temperature rises to only around 32°F (0°C). The Vpp = 18V. Batteries are a bit low, and loads are on, so the battery voltage = 12.0.
The ratio of Vpp to battery voltage is 18:12 = 1.5:1.
Under these conditions, a theoretically perfect MPPT (with no voltage drop in the array circuit) would deliver a 50% increase in charge current. In reality, there are losses in the conversion just as there is friction in a car’s transmission. Reports from the field indicate that increases of 20 to 30% are typically observed.
What is PWM Charge Controller?
The energy from the sun is turned into power using solar panels. An important yet unnoticed component is responsible for keeping a balanced voltage between the solar panels and batteries. It is PWM charge controller that optimizes energy transfer and safeguards the batteries. So, let us today find out more about what is PWM charge controller, and discover its true potential.
What is PWM Charge Controller?
A PWM (Pulse Width Modulation) controller is a digital link between the solar panels and the batteries. The solar charge controller (also known as the regulator) functions similarly to a regular battery charger in that it manages the current flowing from the solar panel to the battery bank to prevent overcharging. It can accommodate several types of batteries, much like a regular battery charger.
The absorption voltage can control the float voltage as well as the time and tail current. They are most suited for lithium-iron-phosphate batteries because, after fully charged, the controller remains at the fixed float or maintains a voltage of around 13.6V (3.4V per cell) for the rest of the day.
The most common charging profile is the same straightforward sequence seen on a good mains adapter: Bulk mode – Absorption mode – Float mode.
If the battery voltage drops below the specified voltage for a longer period of time, such as 5 seconds (re-entry), this re-entry into bulk mode works better for lead-acid batteries because the voltage drop and drop are greater than for lithium-based batteries, which retain a higher, more stable voltage for the remainder of the discharge period.
In PWM solar charge controller:
While the charger mode is in bulk charging mode, the switch is turned On.
The switch is turned On and Off as needed (pulse width modulated) to maintain the absorption’s battery voltage.
When the battery voltage drops to the float voltage at the conclusion of absorption, it turns Off.
To keep the battery at the float voltage, the switch is turned On and Off as needed (pulse width modulated).
When the switch is turned Off, the panel voltage is at the open-circuit value (Voc). When the button is pressed, the voltage is equal to the battery voltage plus the voltage difference between the board and the controller. After this, let’s learn the PWM charge controller working principle.
What is PWM Charge Controller Working Principle?
Your solar panel system and home battery must have matching voltages when using a PWM controller. The basic PWM charge controller working principle is that it efficiently prevents overcharging and makes full use of solar energy to charge the battery, a pulse width modulation (PWM) charge controller has been developed in recent years.
PWM charge controller to pulse mode switch PV module input, when the battery tends to be full, the frequency of the pulse or duty cycle changes, so that the on time is shortened, and the charging current gradually goes to zero.
As the battery voltage reaches its lowest point, the charging current will gradually increase again. This charging technique can extend the total cycle life of the battery in the photovoltaic system by producing a more complete state of charge. The charging state is protected by pulse width modulation, which can extend the total cycle life of the battery in a solar system. Now, let’s explore the advantages of PWM charge controller and disadvantages of PWM charge controller.
PWM solar charge controllers are the most common form of charge controller seen in solar shops. They are less expensive and simpler than MPPT controllers. PWM controllers reduce the amount of power going into your battery gradually as it nears capacity.
What are Advantages and Disadvantages of PWM Charge Controller?
The advantages of PWM charge controller and disadvantages of PWM charge controller are as follows:
- At demodulation, a signal may be easily separated, and noise can also be easily separated.
- High capacity for power handling.
- Can use extremely high frequency.
- Noise interference is reduced because there is less heat generated while operating.
- When used to convert the voltage or to power a light bulb, it consumes very little energy. All three types of systems have moderate inefficiency.
- Unlike pulse position modulation, no synchronization between the transmitter and receiver is necessary.
- The system necessitates the use of a semiconductor device with short turn-on and turn-off timings. So, the cost to get one is rather expensive.
- The circuit is complex.
- Interference with radiofrequency signals.
- Communication requires a huge bandwidth.
- Due to the high PWM frequency, there is a large switching loss.
- The transmitter’s instantaneous power varies.
What are PWM Solar Charge Controller Settings?
A solar charge controller can manage a wide range of battery voltages, from 12 volts to 72 volts. But the most expensive ones can manage up to 72 volts, which is required if you intend to store your energy for an extended period of time. While solar panels can be connected in parallel to give maximum output voltage, a simple charge controller may only accept 12 or 24 volts as input voltage.
To use a solar charge controller, the voltage and current settings must be specified. You can accomplish this by altering the charge controller’s voltage setting. The voltage setting controls how quickly your solar cells recharge. These parameters can be changed using Computer software or on your charging controller. To get the most out of your solar energy system, it is advised that you follow the manufacturer’s guidelines. Otherwise, your system will fail to reach its full potential.
- Correctly connect the solar charge controller to the battery bank and panels.
- If power is detected, the controller screen will illuminate.
- Hold down the Menu button for a few seconds to access the settings menu.
- The charge current will be displayed (PV to Battery).
- Long press the Menu Button to access the Batter Type Selection menu.
- The controller will automatically detect the battery voltage.
- According to the battery user manual, set the float charge voltage, absorption charge voltage, low voltage cut-off value, and low voltage recovery value.
- Set the discharge value for the DC load (if present), and the charge controller will begin the installation process.
Is PWM a Good Charge Controller?
After learning about PWM solar charge controller settings, let’s check if PWM is a good charge controller or not. Charge controllers are necessary for the vast majority of solar buyers. Rooftop or ground-mount solar installations with a battery backup are virtually always linked to the electric grid, and if your battery is fully charged, your excess solar energy will be rerouted there automatically.
If you want to establish a small off-grid solar energy system with battery backup, you should consider getting a charge controller to ensure that your battery is properly charged. A PWM charge controller should suffice for relatively small batteries paired with low-output solar panels. An MPPT charge controller may be appropriate for more complex DIY solar projects with higher output panels.
Pulse Width Modulation is widely employed in off-grid solar solutions for homes and businesses. PWM necessitates matching the voltage of the panel array to the voltage of the battery bank. Otherwise, the charging power would be lost. And the greater the mismatch, the greater the power loss. As a result, PWM is less expensive but has less flexibility and efficiency.
Olivia is committed to green energy and works to help ensure our planet’s long-term habitability. She takes part in environmental conservation by recycling and avoiding single-use plastic.