Skip to content
20A 12V Lithium Battery Solar Charge Controller. 20a solar controller

20A 12V Lithium Battery Solar Charge Controller. 20a solar controller

    A 12V Lithium Battery Solar Charge Controller

    Solar charge controllers are essential for ensuring the smooth functioning of a solar panel and its battery. This model features full electronic protection and fully automatic operation with a PWM charge mode (SOC). The unit has large terminals, with considerable distance between each, as well as a digital LED display. Also features temperature compensation provided by the built-in external temperature sensor. This 20A model is suitable for charging 12V/24V DC Lithium batteries. Finally, there are two built-in USB slots, allowing you to charge a wide variety of devices.

    • Voltage: 12V/24V
    • Current: 20A
    • Two 5V USB charging ports
    • LED digital display
    • Charge protection for batteries/panels

    Customer Reviews

    Not used it yet. Dan from Los Fresnos Tx Want to make a solar bank for charging my lithium bats. The product is very nice and petite. Fast delivery. Surely I’ll get it going this weekend. Thanks I’ll be dropping by for projects.

    lithium, battery, solar, charge

    44.99 12V 10W Waterproof Solar Panel

    Welcome to, your one-stop shop for all your scientific and STEM needs! Our extensive selection of science supplies has been carefully curated by real scientists and educators, ensuring that you’ll find only the best and most educational products on our site. Whether you’re a teacher looking for classroom supplies, a student gearing up for a science fair, or a science enthusiast looking for the perfect gift, we’ve got you covered. From chemistry glassware and lab equipment to robots and science kits, we have everything you need to explore the exciting world of science. Browse our store today and discover the wonder of science!


    Founded, owned operated by a physicist. 21 years in business. 100% satisfaction guarantee. 90-days easy returns. Most orders are shipped the same workday! FREE shipping w/99 (contiguous USA). FREE gift w/49. Shipping to over 100 countries worldwide.


    We accept all major credit cards and PayPal via encrypted secure server.

    A Charge Controllers

    It’s important to add a charge controller to any solar system with an energy storage. By using it, you prolong the lifetime of your battery and increase the overall safety of your system. The size of the regulator depends on your array. For small solar systems we’re glad to offer 20A solar charge controllers.

    What is a 20A Charge Controller?

    A solar regulator performs a number of functions that keep your battery and entire solar system safe:

    • A controller lowers the voltage of the solar array so it doesn’t hurt the battery.
    • It keeps your energy storage from overcharging and deep discharge.
    • It blocks reverse currents which may flow from batteries back to panels at night. Reverse currents potentially can start a fire on your roof.
    • Displays the battery’s load and its state.

    How to choose the right 20A controller?

    A 20A solar regulator is a good addition to small installations. It can be a good pick for an RV or a boat solar system. To size it right, you have to calculate the voltage and current in your system. Keep in mind that these values depend on the type of connection that you choose. When you connect panels in series, add together the voltages of all panels in the string. The current in this connection stays equal across panels. It is the opposite with a parallel type of connection: currents of all panels combine, but the voltage stays low. By combining two types of connection, you can adjust the amps and volts in the system to your needs.

    A controller has a maximum amperage and voltage, both numbers you can find in specifications for a model. In cold weather panels tend to reach their peak production levels. This is why it makes sense to pick a controller with a size 25% bigger than the amperage that the system produces. For example, if your system gives out 12A of current, the size of your controller must be 12A 1.25 = 15A and a regulator solar 20A is an excellent choice here.

    Average Price of 20A Charge Controllers

    The price of a regulator depends primarily on its price and type. PWM controllers are cheaper: they range from approximately 50 and 150. They tend to live longer than MPPT controllers, because they are less complex. Their lifespan is somewhere between 10 to 20 years. However, they lose a fair amount of power: their efficiency is around 75-80%. Plus they aren’t suitable for every installation. Check the current for 20A charge controllers in our store.

    MPPT-controllers often give you more control over the system and let you customize the charging process. They cost anywhere between 100 and 1000. They are usually 20-25% more efficient than PWM-regulators even in systems where both types can be used. Their lifespan is somewhere between 10-15 years and overall efficiency goes up to 90-95%.

    Panels and batteries suitable for 20A Charge Controllers

    20A regulators are good in small installations and usually only work with 12V panels. It’s important to know that PWM controllers lose too much energy when voltages of panels and batteries don’t match. The losses with a PWM regulator are minimized in a system with:

    • 30-cells panels and 12 V batteries
    • 60-cells panels and 24 V batteries
    • 120-cells panels and 48 V batteries

    Free and usefull digest on solar energy. No spam

    Best Cheap PWM Solar Charge Controllers

    Just so you know, this page contains affiliate links. If you make a purchase after clicking on one, at no extra cost to you I may earn a small commission.

    Top Pick

    The Wanderer 30A is easy to use, versatile, and dependable. It’s great for solar power systems of 400 watts or less, making is the best PWM controller for most people.

    • Handles up to 400 watts
    • Compatible with flooded, sealed, gel, and lithium batteries
    • Optional remote monitoring with Renogy app

    Budget Pick

    The Wanderer 10A is a good choice for smaller 12 or 24 volt systems. The features and build quality you get for the price make it the best cheap PWM charge controller.

    • LCD display
    • Compatible with 12 and 24 volt flooded, sealed, gel, and lithium batteries
    • Optional remote monitoring with Renogy app
    • Current rating of 10 amps limits its use to lower-wattage systems
    • No temperature sensor port

    Honorable Mention

    The SunSaver comes with the best out-of-the-box battery protections. It’s pricier, but it may pay for itself by increasing the lifespan of your batteries.

    • Excellent build quality
    • Maximizes battery life with good voltage accuracy and a built-in temperature sensor

    I spent weeks testing 5 of the best PWM solar charge controllers available. After wiring them to custom-built solar power systems, assessing their user-friendliness, and researching their safety features and battery compatibility, I think the Renogy Wanderer 30A is the best PWM charge controller for most people.

    The Wanderer 30A is designed for 12 volt batteries and can handle up to 400 watts of solar. That’s a good amount of power for most small-scale solar projects, such as those used in small vehicles and buildings. With that much solar you can power lights and some small devices and appliances — like phones, laptops, and maybe even a small 12 volt fridge.

    The best PWM charge controller

    The Wanderer 30A is my favorite PWM controller because of its blend of build quality, ease of use, and value. It’s ideal for 12 volt batteries and can handle up to 400 watts of solar.

    Nominal battery voltage: 12V Charge current rating: 30A
    Battery compatibility: Sealed, gel, flooded, lithium Operating temperature range: -20°F to 113°F (-35°C to 45°C)
    Max. PV open circuit voltage (Voc) 25V LCD display: No
    Temperature sensor: Yes (requires additional purchase) Bluetooth monitoring: Yes (requires additional purchase)

    The Wanderer 30A is easy to use and has plenty of built-in safety features, such as overcharging protection, to protect your system and maximize your battery’s lifespan.

    It also has a place to add a battery temperature sensor for improved temperature compensation. Many PWM charge controllers don’t have a temperature sensor port, and it’s important if your batteries experience wide temperature swings.

    The LED indicators are easy to understand and useful for monitoring your system at a glance. They’re all you need for set-it-and-forget-it systems. But if you want to see exact specs like charging current and battery voltage, you can purchase the Renogy BT-1 Bluetooth Module to monitor your system from your phone.

    All Renogy PWM charge controllers I tested, including the Wanderer 30A, are compatible with sealed, gel, flooded, and lithium batteries. That’s another great thing about this controller — most other PWMs work with only lead acid batteries.

    The Wanderer 30A is also one of the cheaper 30-amp PWM charge controllers available. Overall, it’s a great value.

    The best cheap PWM charge controller

    The Wanderer 10A is an excellent budget option for smaller solar systems. It’s compatible with 12 and 24 volt batteries and has an LCD display for easy monitoring.

    Nominal battery voltage: 12/24V Charge current rating: 10A
    Battery compatibility: Sealed, gel, flooded, lithium Operating temperature range: -31°F to 113°F (-25°C to 45°C)
    Max. PV open circuit voltage (Voc) 50V LCD display: Yes
    Temperature sensor: No Bluetooth monitoring: Yes (requires additional purchase)

    The Wanderer 10A is a great cheap charge controller for lower-wattage 12 or 24 volt systems. For 12 volt systems, it can handle up to 130 watts of solar. For 24 volt systems, Renogy recommends a maximum of 260 watts.

    That’s enough power to run some lights and charge your phone and laptop. For instance, I paired this controller with a 20 watt solar panel to solar power some LED lights in my dad’s shed. It was the perfect size for the project.

    You could also use it to solar charge 12 and 24 volt batteries. It’ll treat your batteries better than most other cheap charge controllers, which tend to be low-quality.

    There are a couple other features worth mentioning: Its LCD display makes it easy to see if everything is working properly. You can also use its 2 USB ports for charging phones and other USB devices.

    In the sea of cheaply made charge controllers, the Wanderer 10A stands out as a top option.

    A PWM charge controller that’s built to last

    The SunSaver line has excellent build quality and is backed by a 5-year warranty. It has some of the best out-of-the-box battery protections to help maximize your battery’s lifespan. It’s expensive, though, and limited to sealed or flooded lead acid batteries.

    Nominal battery voltage: 12-24V (depending on model) Charge current rating: 6-20A (depending on model)
    Battery compatibility: Sealed, flooded Operating temperature range: -40°F to 140°F (-40°C to 60°C)
    Max. PV open circuit voltage (Voc) 30-60V (depending on model) LCD display: No
    Temperature sensor: Yes (built-in) Bluetooth monitoring: No

    The Morningstar SunSaver is the buy-it-for-life option. It’s expensive, but it’s built to last and comes with a 5-year warranty.

    Cheaper controllers cut costs by using plastic cases and screws that are all too easy to strip. The SunSaver, on the other hand, sports marine-grade terminals and an anodized aluminum case. It feels like you could drop it off a building with little consequence.

    It has a built-in temperature sensor and, according to Morningstar, good voltage accuracy. There are also models available with low voltage disconnect (LVD). This means it has some of the best out-of-the-box battery protections.

    It’s pricey, and only works with sealed or flooded lead acid batteries. If it’s right for your system, though, this controller may pay for itself by maximizing your battery’s lifespan.

    Best PWM Solar Charge Controllers

    • Top Pick:Renogy Wanderer 30A
    • Budget Pick:Renogy Wanderer 10A
    • Honorable Mention:Morningstar SunSaver
    • Renogy Adventurer 30A
    • Allpowers 20A Solar Charge Controller

    Top Pick: Renogy Wanderer 30A

    Nominal battery voltage: 12V Charge current rating: 30A
    Battery compatibility: Sealed, gel, flooded, lithium Operating temperature range: -20°F to 113°F (-35°C to 45°C)
    Max. PV open circuit voltage (Voc) 25V LCD display: No
    Temperature sensor: Yes (requires additional purchase) Bluetooth monitoring: Yes (requires additional purchase)

    PWM charge controllers, with their low cost and limited current ratings, are best suited for small-scale solar projects of roughly 400 watts or less. For these sorts of applications, the Wanderer 30A is likely all you need.

    It has a current rating of — you guessed it — 30 amps, which works out to around 400 watts of solar. That’s enough to power quite a bit, like lights, phones, laptops, and maybe even a small appliance.

    It’s simple to mount and set up. Just connect the battery then the solar panel to their respective terminals. LED indicators let you know if everything is working properly. The manual has step-by-step setup instructions and a legend detailing what the various indicator lights mean.

    For set-it-and-forget-it solar systems, I think the LEDs are all you need. For closer monitoring, you can buy the Renogy BT-1 Bluetooth Module to monitor your system from your phone. It’s convenient but by no means necessary.

    Selecting your battery type is as simple as pressing the buttons a few times. You can choose between 4 types: sealed, flooded, gel, and lithium. Most other PWM controllers only work with lead acid batteries.

    The Wanderer 30A is a good choice if your battery will experience wide temperature ranges — such as in a building or vehicle without air conditioning. Temperature affects a battery’s ideal voltage and charging current set points. But many budget PWM controllers don’t compensate for temperature. So on hot and cold days, they can overcharge or overdischarge your battery and shorten its lifespan.

    However, with the Wanderer 30A, you can get the compatible battery temperature sensor. It gives a more accurate battery temperature reading, allowing the charge controller to provide better temperature compensation. It can help your battery last longer, saving you money in the long run.

    I’d still consider using the Wanderer 30A with 100 watts of solar or less. It gives you the ability to add more solar panels if you want to expand your system later on. You could start with LED lights and add a Wi-Fi router later, for instance. PWMs with lower current ratings are more limited.

    It’s sized well for 12 volt solar systems of 400 watts or less. It’s easy to set up and a good value for the price. For most people, I think the Renogy Wanderer 30A is the best PWM solar charge controller for the job.

    Full review: Renogy Wanderer

    Budget Pick: Renogy Wanderer 10A

    Nominal battery voltage: 12/24V Charge current rating: 10A
    Battery compatibility: Sealed, gel, flooded, lithium Operating temperature range: -31°F to 113°F (-25°C to 45°C)
    Max. PV open circuit voltage (Voc) 50V LCD display: Yes
    Temperature sensor: No Bluetooth monitoring: Yes (requires additional purchase)

    The 10-amp model in the Wanderer lineup is my pick for low-wattage solar systems. It has a current rating of 10 amps and is compatible with 12 and 24 volt batteries. It can handle about 130 watts of solar in 12 volt systems and 260 watts in 24 volt systems.

    That’s enough energy for powering lights and charging small devices and batteries. For example, here’s a solar lighting system I built with mine:

    It has an LCD display that tells you charging current, PV voltage, battery voltage, and other useful system specs. Like it’s big sibling, it’s compatible with the Renogy BT-1 Bluetooth Module for remote monitoring.

    Cheap solar controllers can treat your battery poorly, so I checked the Wanderer 10A’s battery voltage reading against a multimeter. Turns out it’s pretty accurate.

    Many budget controllers are usually off in their battery voltage readings by a tenth of a decimal place or so, which — depending on the direction of the error — can lead to slight chronic overcharging or overdischarging and reduce your battery’s lifespan.

    The Wanderer 10A doesn’t have a temperature sensor port, so it can’t provide accurate temperature compensation. Because of this, I recommend using it with batteries that are placed indoors where they won’t get too hot or too cold. Or, at the very least, use it with a cheap battery whose lifespan you aren’t trying to maximize.

    I’d caution against buying the Wanderer 10A if you plan to add more solar panels later on. Its current rating is limiting, so you might have to replace it with another charge controller when you do.

    There are cheaper charge controllers with higher current ratings, but be warned — they’ve been known to make wrong or misleading claims. The quality of the Wanderer 10A is a step above those.

    That’s not to say it — or any cheap PWM — is perfect. I’ve had issues with mine. Like I said, I used it to solar power some lights for my dad’s shed. Well, he accidentally left the lights on too long and drained the battery. The Wanderer 10A was unable to recharge the battery with such a low voltage, and reported a constant “PV over-voltage” error. Replacing the battery didn’t fix the problem, so I eventually had to replace the controller itself.

    Cheap PWMs are cheap for a reason. They work but lack some of the protections of more expensive PWM and MPPT controllers. They leave less room for user error. If you decide to get one, take care when designing and building your solar setup.

    Honorable Mention: Morningstar SunSaver

    Nominal battery voltage: 12-24V (depending on model) Charge current rating: 6-20A (depending on model)
    Battery compatibility: Sealed, flooded Operating temperature range: -40°F to 140°F (-40°C to 60°C)
    Max. PV open circuit voltage (Voc) 30-60V (depending on model) LCD display: No
    Temperature sensor: Yes (built-in) Bluetooth monitoring: No

    The SunSaver is built to last. It has an aluminum anodized enclosure and marine-grade terminals. It can work in incredibly hot and cold temperatures.

    It feels like a brick. Compared to the plastic cases of the other controllers I tested, the SunSaver seems indestructible. It’s even backed by a 5-year warranty.

    It has a built-in temperature sensor and, according to MorningStar, a voltage accuracy of /- 25mV. Models with low voltage disconnect are also available.

    These features give it some of the best out-of-the-box battery protections among PWM controllers. It may pay for itself by extending your battery’s lifespan.

    It’s compatible with sealed or flooded lead acid batteries, and is available in 12 or 24 volt models. Current ratings range from 6 to 20 amps.

    It’s pricey and has limited battery compatibility. (If you’re using lithium batteries, you’ll have to look elsewhere.) But for systems using lead acid batteries, the SunSaver is worth a look. Morningstar is known for making charge controllers that last.

    Renogy Adventurer 30A

    Nominal battery voltage: 12/24V Charge current rating: 30A
    Battery compatibility: Sealed, gel, flooded, lithium Operating temperature range: -13°F to 131°F (-25°C to 55°C)
    Max. PV open circuit voltage (Voc) 50V LCD display: Yes
    Temperature sensor: Yes (requires additional purchase) Bluetooth monitoring: Yes (requires additional purchase)

    The Adventurer 30A combines the best of both Wanderer models in one.

    Start with the 30 amp current rating and temperature sensor port of the Wanderer 30A. Combine that with the LCD display and 12/24V compatibility of the Wanderer 10A. Make sure it’s still Bluetooth compatible. Add a battery voltage sensor port. And don’t forget the Adventurer’s own party trick — flush mounting.

    This combination of features means the Adventurer 30A is great for 12 volt systems of up to 400 watts and 24 volt systems of up to 800 watts. That’s almost a 1kW system — we’re starting to talk serious power. That’s enough power for some small vehicles and off-grid buildings.

    Flush mounting means the Adventurer is well-suited for vans, campers, RVs, and anywhere else you want an aesthetically cleaner flush mount.

    But if you don’t, it can also be surface mounted to the wall like any other charge controller. It comes with an included surface mount attachment that lets you decide.

    Then there’s the battery voltage sensor (BVS) port. Adding a BVS helps the controller maximize battery life when your charge controller and battery are far apart. On longer wire runs, there can be a voltage discrepancy between the battery and controller terminals.

    The downside is the Adventurer 30A is one of the pricier PWM models out there. The Wanderer 30A performs similarly and costs less. For most 12 volt systems, I’d go with the Wanderer 30A.

    But if you want its blend of features — or a flush mounted controller — the Adventurer 30A is a good option.

    Allpowers 20A Solar Charge Controller

    Nominal battery voltage: 12/24V Charge current rating: 20A
    Battery compatibility: Sealed, gel, flooded Operating temperature range: -31°F to 140°F (-35°C to 60°C)
    Max. PV open circuit voltage (Voc) 50V LCD display: Yes
    Temperature sensor: No Bluetooth monitoring: No

    Nearly all the cheap charge controllers on Amazon look identical to this one: a small blue and black box, similar graphics, similar labels. The misspelled “build-in timer.”

    It’s not a coincidence. You’ve just stumbled upon the most popular design for cheap charge controllers.

    And when I say cheap, I mean it. A quick search on Aliexpress for “solar charge controller” turns up one of these blue-and-black models for just 2 USD. Two dollars!

    As you’d expect, the Allpowers 20A charge controller was the cheapest model I tested. It works fine, but — as you’d also expect — the quality is lacking.

    I nearly stripped the screws when applying a normal amount of torque. The controller got warm to the touch with only 3-4 amps of current running through it. No other controller heated up as much as this one.

    The model I bought has a claimed current rating of 20 amps. I’d be nervous to give it 10.

    It does have an LCD display, though it doesn’t show charging current (I only knew because I’d installed an inline watt meter). This is a nitpick, but the screen is also quite fuzzy. You might think my photos of it are out of FOCUS. That’s just what the screen looked like.

    I checked the battery voltage accuracy against a multimeter, and it was off by about a tenth of a volt. That’s not great, but for the price it’s acceptable.

    The user manual mine came with says the battery charging voltage has an error margin of ± 0.15 volts. That’s not great. Voltage discrepancies can cause the charge controller to chronically overcharge or overdischarge your battery, shortening its lifespan.

    If you want a budget PWM, I’d recommend spending a few bucks more for the Renogy Wanderer 10A if you can afford it.

    But there is a use case for these budget models. I’d reserve them for very low-wattage solar projects with cheap lead acid batteries. They should work fine if that’s what you’re using them for. Just understand that they can have little margin for user error. You’ll have to design and build your system well, otherwise they may not last long.

    How to Choose the Best PWM Solar Charge Controller for Your System

    Nominal Battery Voltage

    Your charge controller’s nominal battery voltage should match the nominal voltage of your battery bank.

    If you’re using a 12 volt battery, you need a solar charge controller compatible with 12 volt batteries. Got a 24 volt battery? Use a charge controller compatible with 24 volt batteries.

    Some PWM charge controllers are compatible with 12 and 24 volt battery voltages, making them more versatile.

    Charge Current Rating

    Choose a charge controller with a current rating that is greater than the expected max charge current from controller to battery. You can damage a charge controller if you exceed this number. You’ll also want to make sure this number is below the battery’s maximum recommended charge current.

    You charge controller’s charge current rating (in amps) is usually included in the product name. For example, the Renogy Wanderer 30A can charge a battery at up to 30 amps, and the Wanderer 10A can do up to 10 amps.

    If you don’t see the current rating in the product name, at the very least it should be listed on the product page and in the instruction manual.

    Once you know how much current (amperage) your charge controller can output, you need to use a solar panel, or build a solar array, that stays below this limit.

    You find out how much current your panel can produce by looking at the specifications label. The label will list a short circuit current (Isc) in amps. Make sure the controller’s current rating is greater than the panel’s short circuit current. Add a small buffer to be safe.

    If you have solar panels connected in parallel, add together all panel’s short circuit currents to get your array’s short circuit current. Add a small buffer, then use this number for your comparison.

    Maximum PV Input Power: Some brands, such as Renogy, also list a maximum PV input in watts for their charge controllers. This is simply another way of helping you to stay below the controller’s current rating.

    Battery Compatibility

    Pick a charge controller that is compatible with your type of battery. All PWM models I tested are compatible with sealed and flooded lead acid batteries. Some models are also compatible with gel batteries.

    The most versatile PWMs are also compatible with lithium batteries.

    Operating Temperature Range

    Choose a charge controller with an operating temperature range suited to the location you plan to put it. Some PWMs have narrow operating temperature ranges that could exclude them from being used in buildings or vehicles without air conditioning.

    Example: Let’s say you live in Florida and want to solar power your workshop. Your workshop doesn’t have AC, so on hot summer days it can get up to 110°F (43°C) inside.

    The maximum operating temperature for the Renogy Wanderer 10A and 30A models is 113°F (45°C). The temperature inside your shed will get close to this limit, so you may want to choose a charge controller with a higher maximum temperature.

    Note: Batteries have their own temperature ranges. Consider these as well when designing your system.

    Maximum PV Open Circuit Voltage (Voc)

    The maximum open circuit voltage (Voc) of your solar panel(s) shouldn’t exceed the maximum PV voltage of your charge controller.

    Use our solar panel maximum voltage calculator to calculate your maximum open circuit voltage. Then, make sure you pick a charge controller whose max PV voltage is greater than this number.

    25-30V: Models in this range can handle one 12V solar panel wired in series and are designed for use with 12V batteries. To add panels, you’ll need to wire them in parallel.

    50-60V: Models in this range can handle one to two 12V solar panels wired in series and are usually designed for use with 12V and 24V batteries.

    60V: It’s rare to see PWMs with a PV voltage limit greater than 60V. Models in this range are usually designed to handle 3 or more 12V solar panels wired in series.

    Maximum Wire Gauge

    Many charge controllers list the maximum wire size compatible with their terminals. The max wire gauge often allows much more current than the controller’s current rating. This means you can over-gauge your wires for added safety if you want.

    Some charge controller reviews pay close attention to the wire terminals as a proxy for quality. I generally found this to be true in my testing.

    Additional Features

    LCD displays: LCD screens make it easy to see important specs at a glance, such as charging current or PV voltage. The alternative is LED indicators that flash at different speeds and glow in different colors to convey system status.

    Temperature compensation: As batteries get hot or cold, the charging current and voltage set points should be adjusted. Not doing so risks damaging the batteries. This feature, called temperature compensation, is important for batteries that experience wide temperature swings, such as those placed outside or in buildings or vehicles without air conditioning.

    There are two ways that charge controllers provide temperature compensation:

    Built-in temperature sensors are convenient, but can only monitor the ambient temperature near the charge controller. If your battery is far away or has heated up from working, its temperature could be quite different.

    Temperature probes can be taped directly to the battery for a more accurate battery temperature reading.

    Some cheap PWM charge controllers claim to have temperature compensation. However, unless they have a built-in temperature sensor or a port for attaching a temperature probe, they have no actual way of measuring temperature. They usually just assume a set temperature of 25°C (77°F), regardless of how hot or cold the battery gets.

    Remote Bluetooth monitoring: Bluetooth monitoring lets you monitor and control your system from an app on your phone.

    Bluetooth monitoring is common on more expensive MPPT charge controllers, but rare on cheaper PWM models. In fact, none of the 5 PWM models I tested have it built-in.

    All the Renogy PWM charge controllers I tested come with an RS232 port. It’s used to connect the Renogy BT-1 Bluetooth Module. You can then sync the BT-1 to your phone via the Renogy DC Home app.

    These sorts of apps let you monitor your system in real time. You can also adjust system parameters, such as which type of battery you’re using.

    PWM vs. MPPT Charge Controllers

    PWM charge controllers are cheaper, but less efficient at converting incoming solar energy to the right current and voltage parameters to safely charge the battery. The rule-of-thumb efficiency for PWM charge controllers is around 75%.

    PWM models are often used for small-scale solar power systems where efficiency isn’t a top priority.

    For instance, I recently installed solar power lights in my dad’s shed. He didn’t need to use them that often, meaning charge controller efficiency wasn’t an important consideration. Accordingly, I chose a PWM controller for the project.

    MPPT charge controllers are much more efficient, around 95% or so. However, they are much more expensive.

    lithium, battery, solar, charge

    MPPT controllers are best for solar systems where efficiency is important. They also have higher current and PV voltage ratings, making them better suited for larger systems of around 400-1000 watts.

    An example where an MPPT could be ideal is on a van with limited roof space. Because of the limited space, you want to maximize the amount of solar energy you can pull from your panels. You decide to go with an MPPT for its conversion efficiency.


    Reviews and information on the best Solar panels, inverters and batteries from SMA, Fronius, SunPower, SolaX, Q Cells, Trina, Jinko, Selectronic, Tesla Powerwall, ABB. Plus hybrid inverters, battery sizing, Lithium-ion and lead-acid batteries, off-grid and on-grid power systems.

    What is a solar charge controller?

    A solar charge controller, also known as a solar regulator, is basically a solar battery charger connected between the solar panels and battery. Its job is to regulate the battery charging process and ensure the battery is charged correctly, or more importantly, not over-charged. DC-coupled solar charge controllers have been around for decades and are used in almost all small-scale off-grid solar power systems.

    Modern solar charge controllers have advanced features to ensure the battery system is charged precisely and efficiently, plus features like DC load output used for lighting. Generally, most smaller 12V-24V charge controllers up to 30A have DC load terminals and are used for caravans, RVs and small buildings. On the other hand, most larger, more advanced 60A MPPT solar charge controllers do not have load output terminals and are specifically designed for large off-grid power systems with solar arrays and powerful off-grid inverter-chargers.

    Solar charge controllers are rated according to the maximum input voltage (V) and maximum charge current (A). As explained in more detail below, these two ratings determine how many solar panels can be connected to the charge controller. Solar panels are generally connected together in series, known as a string of panels. The more panels connected in series, the higher the string voltage.

    • Current Amp (A) rating = Maximum charging current.
    • Voltage (V) rating = Maximum voltage (Voc) of the solar panel or string of panels.

    MPPT Vs PWM solar charge controllers

    There are two main types of solar charge controllers, PWM and MPPT, with the latter being the primary FOCUS of this article due to the increased charging efficiency, improved performance and other advantages explained below.

    PWM solar charge controllers

    Simple PWM, or ‘pulse width modulation’ solar charge controllers, have a direct connection from the solar array to the battery and use a basic ‘Rapid switch’ to modulate or control the battery charging. The switch (transistor) opens until the battery reaches the absorption charge voltage. Then the switch starts to open and close rapidly (hundreds of times per second) to modulate the current and maintain a constant battery voltage. This works ok, but the problem is the solar panel voltage is pulled down to match the battery voltage. This, in turn, pulls the panel voltage away from its optimum operating voltage (Vmp) and reduces the panel power output and operating efficiency.

    PWM solar charge controllers are a great low-cost option for small 12V systems when one or two solar panels are used, such as simple applications like solar lighting, camping and basic things like USB/phone chargers. However, if more than one panel is needed, they will need to be connected in parallel, not in series (unless the panels are very low voltage and the battery is a higher voltage).

    MPPT solar charge controllers

    MPPT stands for Maximum Power Point Tracker; these are far more advanced than PWM charge controllers and enable the solar panel to operate at its maximum power point, or more precisely, the optimum voltage and current for maximum power output. Using this clever technology, MPPT solar charge controllers can be up to 30% more efficient, depending on the battery and operating voltage (Vmp) of the solar panel. The reasons for the increased efficiency and how to correctly size an MPPT charge controller are explained in detail below.

    As a general guide, MPPT charge controllers should be used on all higher power systems using two or more solar panels in series, or whenever the panel operating voltage (Vmp) is 8V or higher than the battery voltage. see full explanation below.

    What is an MPPT or maximum power point tracker?

    A maximum power point tracker, or MPPT, is basically an efficient DC-to-DC converter used to maximise the power output of a solar system. The first MPPT was invented by a small Australian company called AERL way back in 1985, and this technology is now used in virtually all grid-connect solar inverters and all MPPT solar charge controllers.

    The functioning principle of an MPPT solar charge controller is relatively simple. due to the varying amount of sunlight (irradiance) landing on a solar panel throughout the day, the panel voltage and current continuously vary. In order to generate the most power, an MPPT sweeps through the panel voltage to find the sweet spot or the best combination of voltage and current to produce the maximum power. The MPPT continually tracks and adjusts the PV voltage to generate the most power, no matter what time of day or weather conditions. Using this clever technology, the operating efficiency greatly increases, and the energy generated can be up to 30% more compared to a PWM charge controller.

    PWM Vs MPPT Example

    In the example below, a common 60 cell (24V) solar panel with an operating voltage of 32V (Vmp) is connected to a 12V battery bank using both a PWM and an MPPT charge controller. Using the PWM controller, the panel voltage must drop to match the battery voltage and so the power output is reduced dramatically. With an MPPT charge controller, the panel can operate at its maximum power point and in turn can generate much more power.

    Best MPPT solar charge controllers

    See our detailed review of the best mid-level MPPT solar charge controllers used for small scale off-grid systems up to 40A. click on the summary table below. Also see our review of the most powerful, high-performance MPPT solar charge controllers used for professional large-scale off-grid systems here.

    Battery Voltage options

    Unlike battery inverters, most MPPT solar charge controllers can be used with a range of different battery voltages. For example, most smaller 10A to 30A charge controllers can be used to charge either a 12V or 24V battery, while most larger capacity, or higher input voltage charge controllers, are designed to be used on 24V or 48V battery systems. A select few, such as the Victron 150V range, can even be used on all battery voltages from 12V to 48V. There are also several high voltage solar charge controllers, such as those from AERL and IMARK which can be used on 120V battery banks.

    Besides the current (A) rating, the maximum solar array size that can be connected to a solar charge controller is also limited by the battery voltage. As highlighted in the following diagram, using a 24V battery enables much more solar power to be connected to a 20A solar charge controller compared to a 12V battery.

    Based on Ohm’s law and the power equation, higher battery voltages enable more solar panels to be connected. This is due to the simple formula. Power = Voltage x Current (P=VI). For example 20A x 12.5V = 250W, while 20A x 25V = 500W. Therefore, using a 20A controller with a higher 24V volt battery, as opposed to a 12V battery, will allow double the amount of solar to be connected.

    • 20A MPPT with a 12V battery = 260W max Solar recommended
    • 20A MPPT with a 24V battery = 520W max Solar recommended
    • 20A MPPT with a 48V battery = 1040W max Solar recommended

    Note, oversizing the solar array is allowed by some manufacturers to ensure an MPPT solar charge controller operates at the maximum output charge current, provided the maximum input voltage and current are not exceeded! See more in the oversizing solar section below.

    Solar panel Voltage Explained

    All solar panels have two voltage ratings which are determined under standard test conditions (STC) based on a cell temperature of 25°C. The first is the maximum power voltage (Vmp) which is the operating voltage of the panel. The Vmp will drop significantly at high temperatures and will vary slightly depending on the amount of sunlight. In order for the MPPT to function correctly, the panel operating voltage (Vmp) must always be several volts higher than the battery charge voltage under all conditions, including high temperatures. see more information about voltage drop and temperature below.

    The second is the open-circuit voltage (Voc) which is always higher than the Vmp. The Voc is reached when the panel is in an open-circuit condition, such as when a system is switched off, or when a battery is fully charged, and no more power is needed. The Voc also decreases at higher temperatures, but, more importantly, increases at lower temperatures.

    Battery Voltage Vs Panel Voltage

    For an MPPT charge controller to work correctly under all conditions, the solar panel operating voltage (Vmp), or string voltage (if the panels are connected in series) should be at least 5V to 8V higher than the battery charge (absorption) voltage. For example, most 12V batteries have an absorption voltage of 14 to 15V, so the Vmp should be a minimum of 20V to 23V, taking into account the voltage drop in higher temperatures. Note, on average, the real-world panel operating voltage is around 3V lower than the optimum panel voltage (Vmp). The String Voltage Calculator will help you quickly determine the solar string voltage by using the historical temperature data for your location.

    12V Batteries

    In the case of 12V batteries, the panel voltage drop due to high temperature is generally not a problem since even smaller (12V) solar panels have a Vmp in the 20V to 22V range, which is much higher than the typical 12V battery charge (absorption) voltage of 14V. Also, common 60-cell (24V) solar panels are not a problem as they operate in the 30V to 40V range, which is much higher.

    24V Batteries

    In the case of 24V batteries, there is no issue when a string of 2 or more panels is connected in series, but there is a problem when only one solar panel is connected. Most common (24V) 60-cell solar panels have a Vmp of 32V to 36V. While this is higher than the battery charging voltage of around 28V, the problem occurs on a very hot day when the panel temperature increases and the panel Vmp can drop by up to 6V. This large voltage drop can result in the solar voltage dropping below the battery charge voltage, thus preventing it from fully charging. A way to get around this when using only one panel is to use a larger, higher voltage 72-cell or 96-cell panel.

    48V Batteries

    When charging 48V batteries, the system will need a string of at least 2 panels in series but will perform much better with 3 or more panels in series, depending on the maximum voltage of the charge controller. Since most 48V solar charge controllers have a max voltage (Voc) of 150V, this generally allows a string of 3 panels to be connected in series. The higher voltage 250V charge controllers can have strings of 5 or more panels which is much more efficient on larger solar arrays as it reduces the number of strings in parallel and, in turn, lowers the current.

    Note: Multiple panels connected in series can produce dangerous levels of voltage and must be installed by a qualified electrical professional and meet all local standards and regulations.

    Solar panel voltage Vs Temperature

    The power output of a solar panel can vary significantly depending on the temperature and weather conditions. A solar panel’s power rating (W) is measured under Standard Test Conditions (STC) at a cell temperature of 25°C and an irradiance level of 1000W/m2. However, during sunny weather, solar panels slowly heat up, and the internal cell temperature will generally increase by at least 25°C above the ambient air temperature; this results in increased internal resistance and a reduced voltage (Vmp). The amount of voltage drop is calculated using the voltage temperature co-efficient listed on the solar panel datasheet. Use this Solar Voltage Calculator to determine string voltages at various temperatures.

    Both the Vmp and Voc of a solar panel will decrease during hot sunny weather as the cell temperature increases. During very hot days, with little wind to disperse heat, the panel temperature can rise as high as 80°C when mounted on a dark-coloured rooftop. On the other hand, in cold weather, the operating voltage of the solar panel can increase significantly, up to 5V or even higher in freezing temperatures. Voltage rise must be taken into account as it could result in the Voc of the solar array going above the maximum voltage limit of the solar charge controller and damaging the unit.

    Panel Voltage Vs Cell Temperature graph notes:

    • STC = Standard test conditions. 25°C (77°F)
    • NOCT = Nominal operating cell temperature. 45°C (113°F)
    • (^) High cell temp = Typical cell temperature during hot summer weather. 65°C (149°F)
    • (#) Maximum operating temp = Maximum panel operating temperature during extremely high temperatures mounted on a dark rooftop. 85°C (185°F)

    Voltage increase in cold weather

    Example: A Victron 100/50 MPPT solar charge controller has a maximum solar open-circuit voltage (Voc) of 100V and a maximum charging current of 50 Amps. If you use 2 x 300W solar panels with 46 Voc in series, you have a total of 92V. This seems ok, as it is below the 100V maximum. However, the panel voltage will increase beyond the listed Voc at STC in cold conditions below 25°C cell temperature. The voltage increase is calculated using the solar panel’s voltage temperature coefficient, typically 0.3% for every degree below STC (25°C). As a rough guide, for temperatures down to.10°C, you can generally add 5V to the panel Voc which equates to a Voc of 51V. In this case, you would have a combined Voc of 102V. This is now greater than the max 100V Victron 100/50 input voltage limit and could damage the MPPT and void your warranty.

    Solution: There are two ways to get around this issue:

    • Select a different MPPT solar charge controller with a higher input voltage rating, such as the Victron 150/45 with a 150V input voltage limit.
    • Connect the panels in parallel instead of in series. The maximum voltage will now be 46V 5V = 51 Voc. Note this will only work if you use a 12V or 24V battery system; it’s unsuitable for a 48V system as the voltage is too low. Also note, in parallel the solar input current will double, so the solar cable should be rated accordingly.

    Note: Assuming you are using a 12V battery and 2 x 300W panels, the MPPT charger controller output current will be roughly: 600W / 12V = 50A max. So you should use a 50A MPPT solar charge controller.

    Guide only. Use the new String Voltage Calculator to determine panel voltages accurately.

    Basic guide

    The charge controller Amp (A) rating should be 10 to 20% of the battery Amp/hour (Ah) rating. For example, a 100Ah 12V lead-acid battery will need a 10A to 20A solar charge controller. A 150W to 200W solar panel will be able to generate the 10A charge current needed for a 100Ah battery to reach the adsorption charge voltage provided it is orientated correctly and not shaded. Note: Always refer to the battery manufacturer’s specifications.

    Advanced Guide to off-grid solar systems

    Before selecting an MPPT solar charge controller and purchasing panels, batteries or inverters, you should understand the basics of sizing an off-grid solar power system. The general steps are as follows:

    • Estimate the loads. how much energy you use per day in Ah or Wh
    • Battery capacity. determine the battery size needed in Ah or Wh
    • Solar size. determine how many solar panel/s you need to charge the battery (W)
    • Choose the MPPT Solar Charge Controller/s to suit the system (A)
    • Choose an appropriately sized inverter to suit the load.

    Estimate the loads

    The first step is to determine what loads or appliances you will be running and for how long? This is calculated by. the power rating of the appliance (W) multiplied by the average runtime (hr). Alternatively, use the average current draw (A) multiplied by average runtime (hr).

    • Energy required in Watt hours (Wh) = Power (W) x Time (hrs)
    • Energy required in Amp hours (Ah) = Amps (A) x Time (hrs)

    Once this is calculated for each appliance or device, then the total energy requirement per day can be determined as shown in the attached load table.

    Sizing the Battery

    The total load in Ah or Wh load is used to size the battery. Lead-acid batteries are sized in Ah while lithium batteries are sized in either Wh or Ah. The allowable daily depth of discharge (DOD) is very different for lead-acid and lithium, see more details about lead-acid Vs lithium batteries. In general, lead-acid batteries should not be discharged below 70% SoC (State of Charge) on a daily basis, while Lithium (LFP) batteries can be discharged down to 20% SoC on a daily basis. Note: Lead-acid (AGM or GEL) batteries can be deeply discharged, but this will severely reduce the life of the battery if done regularly.

    For example: If you have a 30Ah daily load, you will need a minimum 100Ah lead-acid battery or a 40Ah lithium battery. However, taking into account poor weather, you will generally require at least two days of autonomy. so this equates to a 200Ah lead-acid battery or an 80Ah lithium. Depending on your application, location, and time of year, you may even require 3 or 4 days of autonomy.

    Sizing the Solar

    The solar size (W) should be large enough to fully charge the battery on a typical sunny day in your location. There are many variables to consider including panel orientation, time of year shading issues. This is actually quite complex, but one way to simplify things it to roughly work out how many watts are required to produce 20% of the battery capacity in Amps. Oversizing the solar array is also allowed by some manufacturers to help overcome some of the losses. Note that you can use our free solar design calculator to help estimate the solar generation for different solar panel tilt angles and orientations.

    Solar sizing Example: Based on the 20% rule, A 12V, 200Ah battery will need up to 40Amps of charge. If we are using a common 250W solar panel, then we can do a basic voltage and current conversion:

    Using the equation (P/V = I) then 250W / 12V battery = 20.8A

    In this case, to achieve a 40A charge we would need at least 2 x 250W panels. Remember there are several loss factors to take into account so slightly oversizing the solar is a common practice. See more about oversizing solar below.

    Solar Charge controller Sizing (A)

    The MPPT solar charge controller size should be roughly matched to the solar size. A simple way to work this out is using the power formula:

    Power (W) = Voltage x Current or (P = VI)

    If we know the total solar power in watts (W) and the battery voltage (V), then to work out the maximum current (I) in Amps we re-arrange this to work out the current. so we use the rearranged formula:

    Current (A) = Power (W) / Voltage or (I = P/V)

    For example: if we have 2 x 200W solar panels and a 12V battery, then the maximum current = 400W/12V = 33Amps. In this example, we could use either a 30A or 35A MPPT solar charge controller.

    Selecting a battery inverter

    Battery inverters are available in a wide range of sizes determined by the inverter’s continuous power rating measured in kW (or kVA). importantly, inverters are designed to operate with only one battery voltage which is typically 12V, 24V or 48V. Note that you cannot use a 24V inverter with a lower 12V or higher 48V battery system. Pro-tip, it’s more efficient to use a higher battery voltage.

    Besides the battery voltage, the next key criteria for selecting a battery inverter are the average continuous AC load (demand) and short-duration peak loads. Due to temperature de-rating in hot environments, the inverter should be sized slightly higher than the load or power demand of the appliances it will be powering. Whether the loads are inductive or resistive is also very important and must be taken into account. Resistive loads such as electric kettles or toasters are very simple to power, while inductive loads like water pumps and compressors put more stress on the inverter. In regards to peak loads, most battery inverters can handle surge loads up to 2 x the continuous rating.

    Inverter sizing example:

    • Average continuous loads = 120W (fridge) 40W (lights) TV (150W) = 310W
    • High or surge loads = 2200W (electric kettle) toaster (800W) = 3000W Considering the above loads, a 2400W inverter (with 4800 peak output) would be adequate for the smaller continuous loads and easily power the short-duration peak loads.

    ATTENTION SOLAR DESIGNERS. Learn more about selecting off-grid inverters and sizing solar systems in our advanced technical off-grid system design guide.

    MPPT Solar Oversizing

    Due to the various losses in a solar system, it is common practice to oversize the solar array to enable the system to generate more power during bad weather and under various conditions, such as high temperatures where power derating can occur. The main loss factors include. poor weather (low irradiation), dust and dirt, shading, poor orientation, and cell temperature de-rating. Learn more about solar panel efficiency and cell temperature de-rating here. These loss factors combined can reduce power output significantly. For example, a 300W solar panel will generally produce 240W to 270W on a hot summer day due to the high-temperature power de-rating. Depending on your location, reduced performance will also occur in winter due to low solar irradiance. For these reasons, oversizing the solar array beyond the manufacturers ‘recommended or nominal value’ will help generate more power in unfavourable conditions.

    Oversizing by 150% (Nominal rating x 1.5) is possible on many professional MPPT solar charge controllers and will not damage the unit. However, many cheaper MPPT charge controllers are not designed to operate at full power for a prolonged amount of time, as this can damage the controller. Therefore, it is essential to check whether the manufacturer allows oversizing. Morningstar and Victron Energy allow oversizing well beyond the nominal values listed on the datasheets as long as you don’t exceed the input voltage and current limits. Victron MPPT controllers have been successfully used with 200% solar oversizing without any issues. However, the higher the oversizing, the longer the controller will operate at full power and the more heat it will generate. Without adequate ventilation, excess heat may result in the controller overheating and derating power or, in a worst-case scenario, complete shutdown or even permanent damage. Therefore always ensure adequate clearance around the controller according to the manufacturer’s specifications, and add fan-forced ventilation if required.

    Warning. you must NEVER exceed the maximum INPUT voltage (Voc) or maximum input current rating of the solar charge controller!

    IMPORTANT. Oversizing solar is only allowed on some MPPT solar charge controllers, such as those from Victron Energy, Morningstar and EPever. Oversizing on other models could void your warranty and result in damage or serious injury to persons or property. always ensure the manufacturer allows oversizing and never exceed the maximum input voltage or current limits.

    about Solar Sizing

    As previously mentioned, all solar charge controllers are limited by the maximum input voltage (V. Volts) and maximum charge current (A – Amps). The maximum voltage determines how many panels can be attached (in series), and the current rating will determine the maximum charge current and, in turn, what size battery can be charged.

    As described in the guide earlier, the solar array should be able to generate close to the charge current of the controller, which should be sized correctly to match the battery. Another example: a 200Ah 12V battery would require a 20A solar charge controller and a 250W solar panel to generate close to 20A. (Using the formula P/V = I, then we have 250W / 12V = 20A).

    As shown above, a 20A Victron 100/20 MPPT solar charge controller together with a 12V battery can be charged with a 290W ‘nominal’ solar panel. Due to the losses described previously, it could also be used with a larger ‘oversized’ 300W to 330W panel. The same 20A Victron charge controller used with a 48V battery can be installed with a much larger solar array with a nominal size of 1160W.

    Compared to the Victron MPPT charge controller above, the Rover series from Renogy does not allow solar oversizing. The Rover spec sheet states the ‘Max. Solar input power’ as above (not the nominal input power). Oversizing the Rover series will void the warranty. Below is a simple guide to selecting a solar array to match various size batteries using the Rover series MPPT charge controllers.

    20A Solar Charge Controller. 50Ah to 150Ah battery

    • 20A/100V MPPT. 12V battery = 250W Solar (1 x 260W panels)
    • 20A/100V MPPT. 24V battery = 520W Solar (2 x 260W panels)
    • 40A/100V MPPT. 12V battery = 520W Solar (2 x 260W panels)
    • 40A/100V MPPT. 24V battery = 1040W Solar (4 x 260W panels)
    lithium, battery, solar, charge

    Remember that only selected manufacturers allow the solar array to be oversized, as long as you do not exceed the charge controller’s max voltage or current rating. always refer to manufacturers’ specifications and guidelines.

    solar charge controller Price guide

    The older, simple PWM, or pulse width modulation, charge controllers are the cheapest type available and cost as little as 40 for a 10A unit. In contrast, the more efficient MPPT charge controllers will cost anywhere from 80 to 2500, depending on the voltage and current (A) rating. All solar charge controllers are sized according to the charge current, which ranges from 10A up to 100A. Cost is directly proportional to the charge current and maximum voltage (Voc), with the higher voltage and current controllers being the most expensive.

    A general guide to the cost of different size solar charge controllers:

    • PWM 100V Solar controllers up to 20A. 40 to 120
    • MPPT 100V Solar controllers up to 20A. 90 to 200
    • MPPT 150V Solar controllers up to 40A. 200 to 400
    • MPPT 150V Solar controllers up to 60A. 400 to 800
    • MPPT 250V Solar controllers up to 80A. 800 to 1200
    • MPPT 300V Solar controllers up to 100A. 900 to 1500
    • MPPT 600V Solar controllers up to 100A. 1600 to 2800

    About the Author

    Jason Svarc is a CEC-accredited off-grid solar power system specialist who has been designing and building off-grid power systems since 2010. During this time, he also taught the stand-alone power systems design course at Swinburne University (Tafe). Living in an off-grid home for over 12 years and having designed, installed and monitored dozens of off-grid systems, he has gained vast experience and knowledge of what is required to build reliable, high-performance off-grid solar systems.


    This is to be used as a guide only. Before making any purchases or undertaking any solar/battery related installations or modifications, you must refer to all manufacturer’s specifications and installation manuals. All work must be done by a qualified person.

    Leave a Reply

    Your email address will not be published. Required fields are marked *