Solar Charge Controllers Battery Charging
Hey, do you know what solar charge controllers are? They’re devices that regulate the voltage and current coming from your solar panels to your batteries. They prevent overcharging, over-discharging, and reverse current flow. They’re pretty important if you want to keep your solar system running smoothly and efficiently. There are different types of solar charge controllers, such as PWM (pulse width modulation) and MPPT (maximum power point tracking). PWM controllers are cheaper and simpler, but they waste some of the solar power by reducing the voltage. MPPT controllers are more expensive and complex, but they can adjust the voltage and current to match the optimal power point of the solar panel. So, depending on your budget and needs, you might want to choose one or the other. Or maybe you want to have both, just in case. You never know when you might need some extra juice from the sun, right?
Charge Controllers
Midnite Classic 150
Midnite Classic 200
Midnite Classis 250
Midnite Hawkes Bay
Why a charge controller?
Proper Battery Charging prevent excessive overcharge of the batteries within a battery based power system. Unlike other types of generators, solar panels can be short circuited or open circuited without causing damage to them. Controllers contain a relay that opens the charging circuit, terminating the charge at a pre-set high voltage and, once a pre-set low voltage is reached, closes the circuit, allowing charging to continue. Manage your battery life, Get the amp needed using mppt
Charge controllers are the gizmo that goes between the solar array and the batteries and are sized to the systems they protect by the short circuit array current and watts matched to the battery voltage. Most common are 12, 24 and 48 volts. Because of cold temperatures and the “edge of Cloud effect”, sporadically increased current levels are not uncommon. For these and other reasons, the size of a controller’s amperage should be increased by a minimum of twenty five percent of the peak solar array current rounded up. You can also use the manufactures string calculator to correctly size the right charge controller for your battery based system for your zip code.
What Size do I Need?
Take the number of panels x watts to get the total watts of the solar array. You then divide it by the voltage of your battery bank to get amps, add 25% to allow for cold temperatures and as always, round up. Example: 2. 140 watt solar panels in series = 280 watts / 12 VDC battery bank 25% = 29.18 amps. You would choose a 30 amp, 12 VDC charger in this example. Another example would be 4. 250 watt solar panels = 1,000 watts / 24V battery bank = 41.7 amps 25% = 52.09 rounded up = 60 amp controller. Note; Solar charge controllers are rated and sized by the solar panel array current and system voltage. These examples are simple calculations for small systems. If you have a larger system with muliple strings you are considering, you should look at our Off-Grid Living page for some preconfigured systems that include the right sized charge controller or consult the charge controllers manufactures string calculator.
MidNite Solar
Midnite Solar is an American manufacture that produces a wide range of alternative energy products primarily used in off-grid battery applications. MidNite’s Classic series of Maximum Power Point Tracking (MPPT) charge controllers are the most powerful, full featured controllers on the market as well as being the only ETL listed controllers designed to work with Solar, Wind, and Micro Hydro Electric systems.
The typical solar string for battery based systems is three common 60 cell solar panels in series. Throughout North America, 3 in series is a safe string for MPPT most controllers. The higher voltage Midnite Classic controllers may accept strings of 4 or even 5, depending on the solar panels and the local climate.
On a cold clear morning if your solar panel or string of panels Voc exceeds the controller’s limit, the charge controller will protect itself by refusing to turn on. If you grossly exceed the Voc for example by wiring a large string of panels in series or miss-match your single panel to the controller for instance, you’ll get smoke. Smoke coming our of your charge controller is a bad thing.
Most MPPT charge controllers work with higher array voltages, which can greatly reduce the required wire size between the array and the charge controller. While more expensive than PWM controllers, MPPT charge controllers can boost system performance by up to 30% making them very cost effective.
Pulse Width Modulation (PWM) is an effective means to achieve constant voltage battery charging by switching (or pulse) the charge controller’s power devices. When in PWM regulation, the current from the solar array tapers according to the battery’s condition and recharging needs. The PWM charge controller constantly checks the state of the battery to determine how fast to send the electrical pulses, and how long the pulses will be. In a fully charged battery with no load, it may just tick every few seconds and send a short pulse to the battery. In a discharged battery, the pulses would be very long and almost continuous. The charge controller checks the state of charge on the battery between pulses and adjusts itself each time.
Maximum Power Point Tracking (MPPT). A solar panels ideal voltage is that at which it can put out maximum power. Maximum power point, also called peak power voltage abbreviated Vpp is the maximum energy produced. Maximum power point tracking (MPPT) is a electronic design that charge controller manufactures use to get the maximum possible power from a solar panel. The cells that make up a solar panel have a complex relationship between solar irradiation, temperature and resistance that produces a non-linear output efficiency known as the I-V curve. It is the purpose of the MPPT controller to sample the output of the cells and apply the proper load to obtain maximum power for any given environmental conditions. Essentially, this defines the current that the inverter should draw from the solar panel in order to get the maximum possible power, as power equals voltage times current. MPPT controllers are more effective that PWM controllers and save considerable money on larger systems since they provide 16% to 30% more power to the battery.
Charge Controllers, Off-Grid, Deep Cycle Battery Chargers.
Charge controllers are solid-state electronic devices used in nearly every solar and wind energy system that uses batteries. A charge controller is often times used in off-grid solar systems with 12 volt to 48 volt battery banks to keep the voltage to the batteries within acceptable limits. A charge controller automatically tapers, stops, or diverts electrical power when systems batteries become fully charged. Charge controller capacities range from 4 to 80 A and multiple charge controllers can be used in parallel for larger solar battery systems. Some charge controllers offer additional features, like charge status display, data logging, automatic battery equalization charging and generator starting.
The simplest charge controllers cut the power when the battery reaches a set voltage, and turn it on when a low voltage set point is reached. Pulse width modulated (PWM) charge controllers turn on and off very rapidly, maintaining the batteries at full charge with whatever power is available. Maximum power point tracking (MPPT) charge controllers optimize the voltage of the PV array to maximize total power output then convert that to the correct voltage to charge the battery. This process significantly increases the power from a solar array, particularly in low temperatures when battery voltage is significantly below the PV array voltage. Most MPPT charge controllers work with higher array voltages, enabling the use of larger solar modules, which can be more economical on a cost per watt basis. A higher voltage solar array also minimizes the required AWG wire size between the solar panels and the charge controller. While more expensive than PWM controllers The Charge controllers Blue Pacific Solar sells employ the latest in power electronics to regulate the battery charge by controlling the charging voltage and current from a solar panel array. Charge controllers regulate the charge of the battery, but also prevent the battery from being over discharged which can damage the battery bank.
Charge controllers have multiple stages of control it uses to regulate different voltage and current levels. The voltage and current of a battery varies over the different stages of battery charge. Though the amount can vary, the bulk charge usually is approximately 80%, the absorption charge is 10% with the float charge representing the balance of the battery charging process. The bulk charging stage of the charge controllers process is the first stage to used to bring the battery depth of discharge (DOD) back to 100%. The bulk charge stage happens first in in the morning after the batteries DOD has drained down since sunset the previous day. The bulk charging stage pushes as many amps into the battery bank as possible from the solar panels and gets the voltage up in the process. The effect of a charge controller is not unlike trying to fill a glass of water from a faucet. You first turn the faucet on full while the glass if filling, then slowly taper off the pressure until the glass is full. When the battery bank reaches a predetermined level known as the bulk voltage set-point, the charge is then substantially slowed. Because the bulk voltage set point is determined by the type of battery you are using, many charge controllers have to be pre-set to the type of battery which will dictate the rate of charge.
The second state of charge a charge controller employs is the absorption stage. After a battery system has been brought up to the bulk voltage set point, the charge controller slows down the charge rate because the battery bank cannot accept the same Rapid charging pace without overheating and damaging the battery bank. At the absorption stage a battery bank is only about 80% full. The absorption charge is the function level in the process that tops off the battery bank. During the absorption stage, the charge controller holds the battery volts constant and reduces the amount of current sent into the battery. When the absorption stage is complete, the battery bank is fully charges.
The final step a charge controller performs is the float charge. Typically a charge controller enters into a float charge state when the other charge levels of the battery bank has been achieved. When the number of peak sun hours is limited, a solar charge controller may not be able to get the battery bank back to the float stage before the next cycle begins.
MorningStar, Outback and Xantrex are adding new and updated charge controllers technology everyday. Various new charge controller models are released every year making what seems like a dilemma at first, but is actually a better solution. There is in fact a right charge controller for every off-grid solar application. Blue Pacific Solars’ consultants can help you sort through the different challenges of matching the right charge controllers to your battery bank.
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January 7, 2022 Jason Svarc
Best mid-range MPPT solar charge controllers up to 40A
In this article, we review six of the most popular, mid-level MPPT solar charge controllers commonly used for small scale solar power systems up to 2kW. These are more affordable, lower voltage (100-150V) units, which are generally designed for 12V or 24V battery systems, although several can be used on 48V batteries. A number of these charge controllers also feature inbuilt load control terminals for basic DC lighting and other loads.
In this review, we don’t list simple PWM controllers used for DC lighting and basic systems since there are many sites already covering these entry-level PWM controllers. For high-performance MPPT solar charge controllers with higher input voltages up to 300V and current ratings from 60A to 100A, see our high-power MPPT solar charge controllers review.
What is a solar charge controller?
A solar charge controller, also known as a solar regulator, is a battery charge regulator connected between the solar array and battery. Its job is to regulate the solar output to ensure the battery is charged correctly and not overcharged. DC coupled solar charge controllers been around for decades and are used in most small scale off-grid solar power systems.
Top 6 Solar Charge Controllers
Mid-level solar controllers up to 40A
Smaller capacity MPPT solar charge controllers with a current rating from 20A to 40A are used for many different applications including off-grid cabins and homes, RV’s, boats, caravans, telecommunications and remote site backup. These mid-range MPPT solar charge controllers are available from many different manufacturers, but this review will FOCUS on the most popular and best quality charge controllers from the most reputable manufacturers which have been on the market for several years.
| 1 | Victron SmartSolar MPPT | 35 A | 150V | 12V 24V 36V 48V | 350 to 480 | |
| 2 | EPever TRIRON Series | 40 A | 150V | 12V 24V | 150 to 250 | |
| 3 | Morningstar ProStar MPPT | 40 A | 120V | 12V 24V | 460 to 540 | |
| 4 | EPever XTRA Series | 40 A | 150V | 12V 24V 36V 48V | 130 to 190 | |
| 5 | Renogy Rover | 40 A | 100V | 12V 24V | 150 to 190 | |
| 6 | EPever BN Series | 40 A | 150V | 12V 24V | 170 to 250 |
Comparison Criteria
In this review, we rank the various charge controllers according to a number of important criteria including build quality, MPPT tracking speed, battery voltage range, operating temperature range (heat dissipation), monitoring, real-world performance and price. In our reviews, we generally rank performance and quality over affordability, so in this case, we rate the unit price lower than other criteria. This may come across as bias towards the more expensive models, but based on real-world results, testing and performance monitoring, the higher-end controllers have proven to out-perform the cheaper models.
Read more about selecting and correct sizing a solar charge controller in the MPPT solar charge controllers explained article.
Victron SmartSolar
Victron Energy is considered a world leader in power electronics and specialise in manufacturing equipment required for off-grid and stand-alone power systems including, inverters, batteries, chargers, monitors and of course, solar charge controllers. Based in the Netherlands, Victron manufacture many products in India and have become well known for producing quality, reliable off-grid battery inverter/chargers and a wide range of quality MPPT solar charge controllers.
Victron offer a huge range of solar charge controllers, from small 10A PWM models, to high-performance 100A MPPT varieties with high voltage inputs up to 250V. The MPPT 150V models appear very simple in design, and may not have a display or load control terminals like many others, however, where Victron out performs the competition is in MPPT tracking performance, communications and monitoring.
Victron have by far the most advanced system monitoring with inbuilt Bluetooth connection offering easy programming and configuration, plus remote firmware updates which add extra features and options. The display-less design may not please all users, but the fast, accurate MPPT tracking, high build quality, and V.E. Smart networking options are stand-out features.
Smartsolar MPPT 150V 35A
- Fast MPP Tracking
- 150V max Voc
- 12V, 24V or 48V batteries
- Compatible with LiFePO4 Lithium batteries
- Very advanced monitoring app
- Wide operating temperature up to 60°C
- Inbuilt temp sensor
- Optional wireless battery sensor
- Easy remote firmware updates
- 5 Year warranty
See the detailed Victron Energy Review
EPever TRIRON Series
EPever was founded in 2007 and has grown rapidly to become one of the largest Chinese manufacturers of cost-effective power products including a wide range of MPPT solar charge controllers. The Triron series is the next evolution to the well-known Tracer series of MPPT’s.
The TRIRON series from EPever is a much more advanced and user-friendly version of the original AN series of charge controllers. The TRIRON controllers have a unique swappable display module as well as a swappable interface module with an RS485 communication option that can be used for a number of different applications. Note, maximum PV voltage is either 100V or 150V depending on the model. The 5 button display module is very easy to use and provide all the important information you need about the PV, battery and load. Wireless access is available via the eBox-BLE Bluetooth adapter or the Wi-Fi adapter is available for remote monitoring.
TRIRON Series MPPT 150V 40A
- Fast MPP Tracking
- 150V max Voltage Voc (TRIRON 3215N 4215N)
- Easy to use with a large clear display
- Compatible with Lead-acid and Lithium batteries
- 40A Load control
- Swappable display and interface modules
- RS485 Interface for communications and remote control
- USB Port and relay control options
- Optional Temp sensor
Morningstar Prostar MPPT
Morningstar are a well-established company based in the US with 25 years of experience in engineering and manufacturing high-performance solar charge controllers. Morningstar is widely recognized as developing some of the best quality products on the market with high levels of protection against extreme environments, lightning surges and high operating temperatures.
The Prostar range of MPPT charge controllers are available in 25A and 40A versions with a 120V input voltage limit. The extremely fast MPP tracking can perform a full voltage sweep in less than 1 second using the Trakstar technology. The device features good size terminals protected under a front cover, including load control output terminals rated up to 30A, plus a clear backlit LCD display and can easily programmed using the 4 large buttons. However, the very high price tag means the Prostar MPPT series is out of reach for many users.
Prostar MPPT 120V 40A
- Very fast MPP Tracking
- 120V max Voc
- Compatible with LiFePO4 Lithium batteries
- Wide operating temp up to 60°C
- 30A Load control
- High surge protection
- Optional Battery sensor
- 5 Year warranty
EPever XTRA Series
EPever, also known as EPsolar, was founded in 2007 in Beijing, China and has grown rapidly to become one of the largest manufacturers of cost-effective solar power products including a wide range of MPPT charge controllers. The XTRA series of MPPT’s released in early 2018, have only recently become more popular due to the low cost, easy setup, and lithium battery compatibility.
The XTRA series is available in 10 different options with 3 display types, current ratings from 10 to 40A, battery voltages from 12V to 48V, and input voltage limit up to 150V. In comparison to the older AN series which had a 100V input limit, the XTRA series features lithium battery compatibility and a higher input 150V voltage (Voc) on the 30 and 40A models, plus a modern look and concealed screw terminals. Note, the two-button version with LCD is basically the older AN series controller in a modern package.
XTRA Series MPPT 40A
- Good MPP Tracking
- Three display options with a clear simple LCD
- Compatible with most Lithium LiFePO4 batteries
- 40A Load control
- Optional MT50 display
- Optional Temp sensor
- Optional Wi-Fi and Bluetooth module
- Low cost
5. Renogy Rover
Renogy, founded in the US in 2014, recently became a very popular choice for solar enthusiasts across the world due to the low-cost, easy setup and good MPPT tracking. Renogy manufacture a wide range of affordable inverters, DC converters and solar charge controllers in China.
The Rover series from Renogy is a feature packed MPPT controller with a clear inbuilt display, plus a low-cost (optional) Bluetooth adapter which provides a great, easy to use interface with many configuration options. Load control terminals are built-in, although the output is limited to 20A. The overall build quality is quite good, however there are some area’s which could be improved, most notably the cable terminals which are far too small for a 40A controller.
Rover MPPT 100V 40A
- Good MPP Tracking
- Clear Simple display
- Compatible with Lithium (12.8V LiFePO4)
- 20A Load control
- Advanced Bluetooth app and user settings
- Temp sensor included
- Low cost
6. Outback BN series by EPever
The Outback Power Flexmax40 is made by EPever and is commonly known as the Tracer BN series which is a well known affordable MPPT controller.
EPever one of the leading manufacturers of cost-effective power products including a wide range of solar charge controllers. The well-known Tracer and TRIRON series of MPPT’s are a very popular choice for solar enthusiasts across the world due to the easy setup, good MPPT tracking, and low cost.
The first generation AN series is the best-known MPPT in the range, being a low-cost 100V unit with an inbuilt display. However, the BN series is the more expensive higher-performance version with many extra features including a 150V input voltage limit, heavy-duty robust design, large heatsink, and huge input terminals which can accept a cable size up to 50mm2 (1 AWG).
The obvious feature lacking from the BN series is the display. However, monitoring and configuration is available via the additional remote MT50 display which features a good clear LCD screen showing all the basic information required. Wireless access is also available via the eBox-BLE Bluetooth adapter.
Tracer BN Series MPPT 150V 40A
- Very large screw terminals
- Large heatsink and wide operating temperature range
- 12V, 24V batteries
- 150V max Voc
- Wide MPP voltage range
- 20A Load control
- Remote MT50 display with settings and load control
- Optional Temp sensor
How Does a Solar Charge Controller Work?
Solar charge controllers are an essential element to any solar electric panel system. At a most basic level, charge controllers prevent batteries from being overcharged and prevent the batteries from discharging through the solar panel array at night.
Note: While the principles are largely the same regardless of the power source (solar panels, wind, hydro, fuel, generator, etc.), we’ll be speaking here in terms of solar electric systems and will be using the terms “charge controller” and “solar charge controller” interchangeably. Similarly, our term “battery” represents either a single battery or bank of batteries.
What Is a Solar Charge Controller?
An essential part of nearly all battery-based renewable energy systems, charge controllers serve as a current and/or voltage regulator to protect batteries from overcharging. Their purpose is to keep your deep cycle batteries properly fed and safe for the long term.
Solar charge controllers are a necessity for the safe and efficient charging of solar batteries. Think of the charge controller as a strict regulator between your solar panels and solar battery. Without a charge controller, solar panels can continue to deliver power to a battery past the point of a full charge, resulting in damage to the battery and a potentially dangerous situation.
Here’s why a charge controller is so critical: most 12-volt solar panels output anywhere from 16 to 20 volts, so it’s very easy for the batteries to overcharge without any regulation. Most 12-volt solar batteries require 14-14.5 volts to reach a full charge, so you can see how quickly an overcharging issue could occur.
How Does a Solar Charge Controller Work?
While you don’t necessarily need to understand the technical intricacies of a charge controller, being familiar with the basics is helpful – whether you’re doing a DIY solar installation or turning the job over to the professionals.
The basic functions of a controller are quite simple. Charge controllers block reverse current and prevent battery overcharge. Some controllers also prevent battery over-discharge, protect from electrical overload, and/or display battery status and the flow of power. We’ll examine each function individually below.
Modern solar charge controllers work by detecting and monitoring the battery’s voltage level and closely regulating the flow of current from the panels to the battery. Battery charging is best done in three stages: maximizing the current to charge the battery up to approximately 80% as quickly as possible (the “bulk charging” stage), then reducing the current as the battery approaches a full charge (the “absorb” stage), and finally maintaining a “float” or “trickle” charge to keep the battery topped off and ready for use. For more information about three-stage charging for solar batteries, check out the first video in our How to Charge a Deep Cycle Battery Properly video series.
Types of Solar Charge Controllers
When you begin searching for solar charge controllers for sale online, you’ll quickly realize that there are many different options. You can find a broad range of brands, sizes, price points, and features to choose from, which gives you the benefit of having great options – but it can also be overwhelming.
Generally, the three primary charge controller types are 1- or 2-stage solar charge controllers, 3-stage and/or PWM solar charge controllers, and maximum power point tracking (MPPT). You’ll also find charge controllers for electric vehicles and golf carts. The most commonly used charge controllers range from 4 to 60 amps of charging current, but there are newer MPPT controllers that can achieve upwards of 80 amps.
Simple 1- or 2-Stage Controllers
These charge controllers use shunt transistors or relays to control voltage in either one or two steps (hence the names 1-stage or 2-stage controller). These are the oldest types and are extremely basic – and sometimes inefficient – in their components. However, their reliability and affordability do still attract some people.
3-Stage and/or PWM Controllers
Manufactured by well-known brands such as Xantrex, Morningstar, Steca, and Blue Sky, PWM charge controllers are inexpensive and reliable. Their drawback is that they should only be used when the nominal voltage of the solar panels matches the battery voltage – and even then, they have inefficiencies in larger systems.
Maximum Power Point Tracking (MPPT) Controllers
MPPT charge controllers are the highest-quality, most advanced option available, but they come with the high to match. Produced by brands like Victron Energy, OutBack Power, MidNite Solar, and others, MPPT controllers provide an impressive 94-98% efficiency level, delivering about 10-30% more power to the solar battery than other types. Unless your solar system is small (cabin-sized or smaller) and its battery voltage is no more than 24V, an MPPT controller is usually worth the extra initial investment. With larger, more advanced systems and 48V battery banks becoming much more common over the years, MPPT charge controllers are the new standard.
Why Having a Solar Charge Controller Is Important
Blocking Reverse Current
Solar panels work by pumping current through your battery in one direction. At night, the panels may pass a bit of current in the reverse direction, causing a slight discharge from the battery. The potential loss is minor, but it is easy to prevent. Some types of wind and hydro generators also draw reverse current when they stop (most do not except under fault conditions).
In most controllers, charge current passes through a semiconductor (a transistor) which acts like a valve to control the current. It is called a “semiconductor” because it passes current only in one direction. It prevents reverse current without any extra effort or cost.
In some older controllers, an electromagnetic coil opens and closes a mechanical switch (called a relay – you can hear it click on and off.) The relay switches off at night, to block reverse current. These controllers are sometimes referred to as call shunt controllers.
If you are using a solar panel array only to trickle-charge a battery (a very small array relative to the size of the battery), then you may not need a charge controller. This is a rare application. An example is a tiny maintenance module that prevents battery discharge in a parked vehicle but will not support significant loads. You can install a simple diode in that case, to block reverse current. A diode used for this purpose is called a “blocking diode.”
Preventing Overcharge
When a battery reaches full charge, it can no longer store incoming energy. If energy continues to be applied at the full rate, the battery voltage gets too high. Water separates into hydrogen and oxygen and bubbles out rapidly. (It looks like it’s boiling so we sometimes call it that, although it’s not actually hot.) There is excessive loss of water, and a chance that the gasses can ignite and cause a small explosion. The battery will also degrade rapidly and may possibly overheat. Excessive voltage can also stress your loads (lights, appliances, etc.) or cause your inverter to shut off.
Preventing overcharge is simply a matter of reducing the flow of energy to the battery when the battery reaches a specific voltage. When the voltage drops due to lower sun intensity or an increase in electrical usage, the controller again allows the maximum possible charge. This is called “voltage regulating.”
It is the most essential function of all charge controllers. The controller “looks at” the voltage, and regulates the battery charging in response. Some controllers regulate the flow of energy to the battery by switching the current fully on or fully off. This is called “on/off control.” Others reduce the current gradually. This is called “pulse width modulation” (PWM). Both methods work well when set properly for your type of battery.
PWM solar charge controllers hold the voltage more constant. If a PWM controller has two-stage regulation, it will first hold the voltage to a safe maximum for the battery to reach full charge. Then, it will drop the voltage lower, to sustain a “finish” or “trickle” charge. Two-stage regulating is important for a system that may experience many days or weeks of excess energy (or little use of energy). It maintains a full charge but minimizes water loss and stress.
The voltages at which the controller changes the charge rate are called set points. When determining the ideal set points, there is some compromise between charging quickly before the sun goes down, and mildly overcharging the battery.
The determination of set points depends on the anticipated patterns of usage, the type of battery, and to some extent, the experience and philosophy of the system designer or operator. Some controllers have adjustable set points, while others do not.
Understanding Control Set Points vs. Temperature
The ideal voltage set points for charge control vary with a battery’s temperature. Some controllers have a feature called “temperature compensation.” When the controller senses a low battery temperature, it will raise the set points. Otherwise when the battery is cold, it will reduce the charge too soon. If your batteries are exposed to temperature swings greater than about 30° F (17° C), compensation is essential.
Some controllers have a temperature sensor built in. Such a controller must be mounted in a place where the temperature is close to that of the batteries. Better controllers have a remote temperature probe, on a small cable. The probe should be attached directly to a battery in order to report its temperature to the controller.
An alternative to automatic temperature compensation is to manually adjust the set points (if possible) according to the seasons. It may be sufficient to do this only twice a year, in spring and fall.
Control Set Points vs. Battery Type
The ideal set points for charge controlling depend on the design of the battery. Up until the mid-2010s, the vast majority of renewable energy systems used deep-cycle lead-acid batteries of either the flooded type or the sealed type. Flooded batteries are filled with liquid. These are the standard, economical deep cycle batteries.
Sealed batteries use saturated pads between the plates. They are also called “valve-regulated” or “absorbed glass mat,” or simply “maintenance-free.” They need to be regulated to a slightly lower voltage than flooded batteries or they will dry out and be ruined. Some controllers have a means to select the type of battery. Never use a controller that is not intended for your type of battery.
Typical set points for 12V lead-acid batteries at 77° F (25° C)
(These are typical, presented here only for example.)
High limit (flooded battery): 14.4V High limit (sealed battery): 14.0V Resume full charge: 13.0V
Low voltage disconnect: 10.8V Reconnect: 12.5V
Temperature compensation for 12V battery:
-.03V per ° C deviation from standard 25° C
What is Low Voltage Disconnect (LVD)?
Lead acid deep-cycle batteries used in renewable energy systems are designed to be discharged only by about 50-80%. If they are discharged 100%, they are immediately damaged. Imagine a pot of water boiling on your kitchen stove. The moment it runs dry, the pot overheats. If you wait until the steaming stops, it is already too late!
Similarly, if you wait until your lights look dim, some battery damage will have already occurred. Every time this happens, both the capacity and the life of the battery will be reduced by a small amount. If the battery sits in this over-discharged state for days or weeks at a time, it can be ruined quickly.
The only way to prevent over-discharge when all else fails, is to disconnect loads (appliances, lights, etc.), and then to reconnect them only when the voltage has recovered due to some substantial charging. When over-discharge is approaching, a 12V battery drops below 11 volts (a 24V battery drops below 22 volts).
A low voltage disconnect circuit will disconnect loads at that set point. It will reconnect the loads only when the battery voltage has substantially recovered due to the accumulation of some charge. A typical LVD reset point is 13 volts (26 volts on a 24V system).
All modern inverters have LVD built in, even cheap.sized ones. The inverter will turn off to protect itself and your loads as well as your battery. Normally, an inverter is connected directly to the batteries, not through the charge controller, because its current draw can be very high, and because it does not require external LVD.
If you have any DC loads, you should have an LVD. Some charge controllers have one built in. You can also obtain a separate LVD device. Some LVD systems have a “mercy switch” to let you draw a minimal amount of energy, at least long enough to find the candles and matches! DC refrigerators have LVD built in.
If you purchase a charge controller with built-in LVD, make sure that it has enough capacity to handle your DC loads. For example, let’s say you need a charge controller to handle less than 10 amps of charge current, but you have a DC water pressurizing pump that draws 20 amps (for short periods) plus a 6 amp DC lighting load. A charge controller with a 30 amp LVD would be appropriate. Don’t buy a 10 amp charge controller that has only a 10 or 15 amp load capacity!
Have Peace of Mind with Overload Protection
A circuit is overloaded when the current flowing in it is higher than it can safely handle. This can cause overheating and can even be a fire hazard. Overload can be caused by a fault (short circuit) in the wiring, or by a faulty appliance (like a frozen water pump). Some charge controllers have overload protection built in, usually with a push-button reset.
Built-in overload protection can be useful, but most systems require additional protection in the form of fuses or circuit breakers. If you have a circuit with a wire size for which the safe carrying capacity (ampacity) is less than the overload limit of the controller, then you must protect that circuit with a fuse or breaker of a suitably lower amp rating. In any case, follow the manufacturer’s requirements and the National Electrical Code for any external fuse or circuit breaker requirements.
Why Displays and Metering are Important
Charge controllers include a variety of possible displays, ranging from a single red light to digital displays of voltage and current. These indicators are important and useful. Imagine driving across the country with no instrument panel in your car! A display system can indicate the flow of power into and out of the system, the approximate state of charge of your battery, and when various limits are reached.
If you want complete and accurate monitoring however, spend about 200 for a separate digital device that includes an amp-hour meter. It acts like an electronic accountant to keep track of the energy available in your battery. If you have a separate system monitor, then it is not important to have digital displays in the charge controller itself. Even the cheapest system should include a voltmeter as a bare minimum indicator of system function and status.
Have it All with a Power Panel
If you are installing a system to power a modern home, then you will need safety shutoffs and interconnections to handle high current. The electrical hardware can be bulky, expensive and laborious to install. To make things economical and compact, obtain a ready-built power panel. It can include a charge controller with LVD, the inverter and digital monitoring as options. This makes it easy for an electrician to tie in the major system components, and to meet the safety requirements of the National Electrical Code or your local authorities.
Charge Controllers for Wind and Hydro
A charge controller for a wind-electric or hydro-electric charging system must protect batteries from overcharge, just like a PV controller. However, a load must be kept on the generator at all times to prevent overspeed of the turbine. Instead of disconnecting the generator from the battery (like most PV controllers) it diverts excess energy to a special load that absorbs most of the power from the generator. That load is usually a heating element, which “burns off” excess energy as heat. If you can put the heat to good use, fine!
Is a Solar Charge Controller Always Required?
In most battery-based renewable energy systems, yes. However, a charge controller may not be necessary if you are using a small maintenance/trickle charge panel (such as panels rated 1-5 Watts). It is widely accepted that charge controllers aren’t a required component if your panel puts out no more than 2 Watts for each 50Ah (amp-hours).
Is My Solar Charge Controller Working?
How do you know if a controller is malfunctioning? Watch your voltmeter as the batteries reach full charge. Is the voltage reaching (but not exceeding) the appropriate set points for your type of battery? Use your ears and eyes-are the batteries bubbling severely? Is there a lot of moisture accumulation on the battery tops? These are signs of possible overcharge. Are you getting the capacity that you expect from your battery bank? If not, there may be a problem with your controller, and it may be damaging your batteries.
Conclusion
A good charge controller is not expensive in relation to the total cost of a power system. Nor is it very mysterious. The control of battery charging is so important that most manufacturers of high quality batteries (with warranties of five years or longer) specify the requirements for voltage regulation, low voltage disconnect and temperature compensation. When these limits are not respected, it is common for batteries to fail after less than one quarter of their normal life expectancy, regardless of their quality or their cost.
Shop the Best Solar Charge Controllers at the Lowest Prices
Your unique needs, budget, and setup can help you determine the best charge controller options for your system – and whatever you choose, you can count on finding it at the best price from altE.
Our selection of solar charge controllers features all the top-rated models from leading brands, saving you the hassle and time of having to check multiple stores to narrow down your options. And with altE, you can be confident that you’re getting the best possible price without sacrificing product authenticity or quality.
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.