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40 Amp MPPT Solar Charge Controller. Multiple solar charge controllers

40 Amp MPPT Solar Charge Controller. Multiple solar charge controllers

    Amp MPPT Solar Charge Controller

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    • Automatically detects 12V or 24V DC system voltages.
    • Compatible with various deep cycle battery options: Sealed, Gel, Flooded, and Lithium.
    • Innovative MPPT technology with high tracking efficiency up to 99% and peak conversion efficiency of 98%.
    • Electronic protection against reverse polarity, overcharging, over-discharging, overload, short-circuiting, and reverse current.
    • LCD screen and multiple LED indicators for displaying system operation information, customizable parameters, and error codes.
    • Features diverse load control; also capable of charging over-discharged lithium batteries.
    • Die-cast aluminum design allows for efficient heat dissipation.
    • RS232 port to communicate with BT-1 Bluetooth module.


    Rated Battery Current: 40A
    Rated Load Current: 20A
    Max. PV Input Short Current: 50A
    Max. Battery Voltage: 32V
    Max Solar Input Voltage: 100VDC
    Charge circuit voltage drop: ≤ 0.26V
    Discharge Circuit Voltage drop: ≤ 0.15V
    Working Temperature: -35°C to 45°C
    Max Terminal Size: 8AWG
    Rated Load Current: 10% to 90% NC
    Overall Dimension: 9.37 x 6.81 x 2.85 in
    Net Weight: 4.41 lb

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    Can I Use Two Solar Charge Controllers?

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    A charge controller performs several important functions in a solar system, such as overload and overcharge protection. But if you have a large array, can you use more than two charge controllers in one system? And will you need two battery banks?

    Two charge controllers can be used in one battery bank, but the solar panels must be in separate parallel arrays. The solar panels in each array must also be the same size.

    Can I Use Two Charge Controllers in One Battery Bank?

    Yes, you can use two or more controllers with a single battery bank. In fact that is how large solar arrays are usually set up to produce the best results. There are a few things that you have to remember before getting multiple controllers though.

    Charge controller capacity. MPPT and PWM controllers have a limit to how many watts it can handle. The capacity depends on the watts and the voltage. The following are common charge controller sizes and their watt capacities.

    • 15A up to 300W
    • 20A up to 480W
    • 30A up to 600W
    • 60A up to 720W at 12V / 1440W at 24V / 2880W at 48V

    These figures are only to give you a general idea. Newer controllers are more efficient and can handle more watts, amps and voltage than older models. Be sure to check the product manual to be certain. Depending on the design, the controller may be able to run handle more solar watts.

    For MPPT controllers, we like the Renogy Rover 3 30A which is compatible with AGM, gel and lithium batteries.

    The Renogy 30A Wanderer is our top pick for PWM solar controllers. It is cost effective and works with different solar panel and battery bank configurations.

    Each controller must have its own solar panel. The two solar panels must not be wired to each other, except only through the battery bank. Each controller will be plugged into the battery bank. Under this configuration, each charge controller will evaluate the battery voltage and determine how much current goes into their respective solar panels.

    Using two controllers (or more) with one battery bank is not uncommon. In fact it is standard practice in large scale arrays due to the way MPPT controllers work.

    Manufacturers – and solar power users – will also tell you not to use solar controllers to their limit. If your system is up to 480 watts already, you should get two 20A controllers. This is something you should do with solar panels, inverters, batteries and charge controllers.

    Every MPPT controller functions according to the battery voltage it is connected to. Each one runs independent of the other. These controllers will also rarely synchronize because of the varying wire lengths used for each battery and controller.

    The varying cable length means different voltage readings, affecting how the MPPT functions. The behavior of each controller will also vary depending on the manufacturer design.

    What Battery Types Can I Use?

    MPPT and PWM charge controllers work with different types of batteries like AGM, lithium, gel and others. However you should never mix two different battery types together.

    If you are going to use AGM, every battery in the bank has to be AGM. If it is lithium, do not use gel, FLA or SLA. These batteries have different properties and using them together can damage the system, controller or inverter if you have hooked one up.

    Lithium batteries have a superior discharge rate and a completely different chemical composition than lead acid batteries. Even lead acid batteries have different types like AGM and gel. Do not mix them together and always refer to your controller documentation for the best batteries to use.

    The charge controller settings may have to be adjusted depending on what type of battery you use. Can you use different types of batteries with separate solar arrays? Yes it is possible, but it really does not make sense since they have unique properties. It is better to use the same type for your entire system.

    Can I Use Multiple Charge Controllers with One Solar Panel?

    If you can use multiple solar controllers on one battery bank, can you do the same with a solar panel?

    You can use two charge controllers in one solar system, but each controller must have its own solar panel block or array. Theoretically you can connect two controllers in one array, but it could cause problems later on. If one controller can handle the array, do not add another.

    Two or more controllers in an array can cause confusion because both will think they are the “lead one”. Both will attempt to adjust the LMP and VMP, which can result in miscalculations and the output will be less than it can be.

    If the charge controller can handle the solar panel output, there is no need to add another one. But if your calculations show another is required, you should configure the solar panels into separate arrays and add a controller to each one.

    What Solar Panel Sizes Can I Use?

    You can use any solar panel size as long as the total output is within the controller capacity. However, the solar panels must all be the same size, otherwise the controller will defer to the smaller panel.

    For example, if you connect 2 x 200W and 1 x 150W solar panels in one array, the controller will rate all the panels as 150 watts. So make certain the panels have similar watt outputs.

    You can have solar arrays with different voltages however. Array 1 could have six 12V 100W solar panels and array 2 can have four 24V 100W solar panels. If you have MPPT controllers the panels can have varying voltages and the system will still produce optimum results.

    Parallel or Series Connection?

    In almost all cases you should use a parallel connection. There are instances where a series connection is better, but for two or more controllers, a parallel setup is the best.

    To set up a parallel connection, simply connect the positive to positive terminals and the negative to negative terminals. With a series you connect the positive to the negative.

    In a parallel configuration, the amps increase while the voltage remains the same. But in a series, the voltage goes up but the amps are unchanged. In our examples you want to get the maximum power so you should use a parallel configuration.

    Connecting your system in a series will boost the voltage and might make it harder for the controller to function. All the connections in a multiple controller setup has to be in parallel if you want to increase the amps.

    Can I Use Different Types of Charge Controllers Together?

    PWM controllers are best suited for small systems, while MPPT controllers are for large solar arrays. But can you use the two together in one system?

    Do not use PWM and MPPT charge controllers together in one system. These controllers have different properties and using them together can lead to a systems malfunction. At the very least you will not get the best results from your solar panel and batteries.

    An MPPT controller is more efficient than a PWM, and it can handle solar panels and batteries with different voltages. With a PWM the panels and battery voltages have to match. Imagine if you have an MPPT and PWM controller in one system, and there will be conflicts on how to adjust the voltage.

    What if you have two solar arrays wired together, can you use different controller types then? No, as long as the arrays are linked, it is still considered a single system. And there is a potential for conflict if you use different types of charge controllers.

    So if you are going to use an MPPT, use MPPT only. These can be different sizes but as long as they are the same type your system will be fine. Of course now the question becomes, how many charge controllers should you have?

    How Many Charge Controllers Do I Need?

    One question you should be asking of course is, do you even need more than one charge controller? Fortunately the answer is pretty easy to figure out.

    Total solar array watts / battery voltage 25% = charge controller size

    If you have a 4000 watt solar array running on 24V batteries:

    Your charge controller needs 207.5 amps or 210 amps rounded off.

    210 amps x 24V = 5040 watts

    A 60A charge controller can handle up to 2880 watts, so you need two 60A MPPT charge controllers to run a 4000 watt solar array.

    The battery size will depend on how much power you want to store. For a 4000 watt system you probably need a minimum one 24V 200ah battery, either one 200ah or two 100ah 24V will do.

    These are simple calculations, but they work with different types of solar charge controllers. Also note that MPPT charge controllers have a higher voltage capacity. Their other advantage is they can adjust the voltage output as required by the battery bank.


    Charge controllers are crucial parts in any solar system, so knowing how they function is crucial. If you have a small system, a single controller will be enough. but if your system is several thousand watts, two or more charge controllers are in order.

    Choosing the Right Solar Charge Controller/Regulator

    A solar charge controller (frequently called a regulator) is similar to a regular battery charger, i.e. it regulates the current flowing from the solar panel into the battery bank to avoid overcharging the batteries. (If you don’t need to understand the why’s, scroll to the end for a simple flow chart). As with a regular quality battery charger, various battery types are accommodated, the absorption voltage, float voltage can be selectable, and sometimes the time periods and/or the tail current are also selectable. They are especially suited for lithium-iron-phosphate batteries as once fully charged the controller then stays at the set float or holding voltage of around 13.6V (3.4V per cell) for the remainder of the day.

    The most common charge profile is the same basic sequence used on a quality mains charger, i.e. bulk mode absorption mode float mode. Entry into bulk charge mode occurs at:

    • sunrise in the morning
    • if the battery voltage drops below a defined voltage for more than a set time period, e.g. 5 seconds (re-entry)

    This re-entry into bulk mode works well with lead-acid batteries as the voltage drop and droop is worse than it is for lithium-based batteries which maintain a higher more stable voltage throughout the majority of the discharge cycle.

    Lithium batteries

    Lithium batteries (LiFePO4) do not benefit from re-entry into a bulk mode during the day as the internal impedance of the lithium batteries increases at high (and low) states of charge as indicated by the orange vertical lines in the chart below and it is only necessary to occasionally balance the cells which can only be done around the absorption voltage. A related reason is to avoid the Rapid and large variation in voltage that will occur in these regions as large loads are switched on and off.

    Lithium batteries do not have a defined “float voltage”, and therefore the “float voltage” of the controller should be set to be at or just below the “charge knee voltage” (as indicated in the chart below) of the LiFePO4 charge profile, i.e. 3.4V per cell or 13.6V for a 12V battery. The controller should hold this voltage for the remainder of the day after bulk charging the battery.

    The Difference Between PWM and MPPT Solar Charge Controllers

    The crux of the difference is:

    • With a PWM controller, the current is drawn out of the panel at just above the battery voltage, whereas
    • With an MPPT solar charge controller the current is drawn out of the panel at the panel “maximum power voltage” (think of an MPPT controller as being a “Smart DC-DC converter”)

    You often see slogans such as “you will get 20% or more energy harvesting from an MPPT controller”. This extra actually varies significantly and the following is a comparison assuming the panel is in full sun and the controller is in bulk charge mode. Ignoring voltage drops and using a simple panel and simple math as an example:

    Battery voltage = 13V (battery voltage can vary between say 10.8V fully discharged and 14.4V during absorption charge mode). At 13V the panel amps will be slightly higher than the maximum power amps, say 5.2A

    With a PWM controller, the power drawn from the panel is 5.2A 13V = 67.6 watts. This amount of power will be drawn regardless of the temperature of the panel, provided that the panel voltage remains above the battery voltage.

    With an MPPT controller the power from the panel is 5.0A 18V = 90 watts, i.e. 25% higher. However this is overly optimistic as the voltage drops as temperature increases; so assuming the panel temperature rises to say 30°C above the standard test conditions (STC) temperature of 25°C and the voltage drops by 4% for every 10°C, i.e. total of 12% then the power drawn by the MPPT will be 5A 15.84V = 79.2W i.e. 17.2% more power than the PWM controller.

    In summary, there is an increase in energy harvesting with the MPPT controllers, but the percentage increase in harvesting varies significantly over the course of a day.


    A PWM (pulse width modulation) controller can be thought of as an (electronic) switch between the solar panels and the battery:

    • The switch is ON when the charger mode is in bulk charge mode
    • The switch is “flicked” ON and OFF as needed (pulse width modulated) to hold the battery voltage at the absorption voltage
    • The switch is OFF at the end of absorption while the battery voltage drops to the float voltage
    • The switch is once again “flicked” ON and OFF as needed (pulse width modulated) to hold the battery voltage at the float voltage

    Note that when the switch is OFF the panel voltage will be at the open-circuit voltage (Voc) and when the switch is ON the panel voltage will be at the battery voltage voltage drops between the panel and the controller.

    The best panel match for a PWM controller:

    The best panel match for a PWM controller is a panel with a voltage that is just sufficiently above that required for charging the battery and taking temperature into account, typically, a panel with a Vmp (maximum power voltage) of around 18V to charge a 12V battery. These are frequently referred to as a 12V panel even though they have a Vmp of around 18V.


    The MPPT controller could be considered to be a “Smart DC-DC converter”, i.e. it drops the panel voltage (hence “house panels” could be used) down to the voltage required to charge the battery. The current is increased in the same ratio as the voltage is dropped (ignoring heating losses in the electronics), just like a conventional step-down DC-DC converter.

    The “Smart” element in the DC-DC converter is the monitoring of the maximum power point of the panel which will vary during the day with the sun strength and angle, panel temperature, shading, and panel(s) health. The “smarts” then adjust the input voltage of the DC-DC converter – in “engineering speak” it provides a matched load to the panel.

    The best panel match for an MPPT controller:

    • The panel open circuit voltage (Voc) must be under the permitted voltage.
    • The VOC must be above the “start voltage” for the controller to “kick in”
    • The maximum panel short circuit current (Isc) must be within the range specified
    • The maximum array wattage. some controllers allow this to be “over-sized”, e.g the Redarc Manager 30 is permitted to have up to 520W attached

    Choosing the Right Solar Controller/Regulator

    The PWM is a Good Low-Cost Option:

    f or solar panels with a maximum power voltage (Vmp) of up to 18V for charging a 12V battery (36V for 24V battery, etc).

    When the solar array voltage is substantially higher than the battery voltage e.g. using house panels, for charging 12V batteries

    An MPPT controller will yield higher returns compared with a PWM controller as the panel voltage increases. I.e. a 160W panel using 36 conventional monocrystalline cells with a maximum power amp of 8.4A will provide around 8.6A at 12V; while the 180W panel having 4 more cells will provide the same amperage but 4 additional cells increases the panel voltage by 2V. A PWM controller will not harvest any additional energy, but an MPPT controller will harvest an additional 11.1% (4 / 36) from the 180W panel.

    For the same principle, all panels using SunPower cells with more than 32 cells require an MPPT charge controller otherwise a PWM controller will harvest the same energy from 36, 40, 44 cell panels as it does from a 32 cell panel.

    Solar Charge Controller Features and Options

    Boost MPPT Controllers

    “Boost” MPPT charge controllers allow batteries to be charged that has a higher voltage than the panel.

    Combined MPPT and DC-DC Chargers

    The MPPT function is a natural adjunct to the DC-DC charger function and there are several quality brands that provide this with more under development. A single unit can be used by itself, as it automatically switches between alternator charging and solar charging. For larger systems, our favoured arrangement is to use a separate MPPT controller for the fixed roof-mounted panels and use the combined MPPT/DC-DC with portable panels. In this case, an Anderson connector is placed on the exterior of an RV which is then wired to the solar input of the MPPT/DC-DC unit.

    Note that the battery capacity must be sufficient so that the combined charging current from simultaneous charging from the alternator and the roof solar panels does not exceed the manufacturer’s recommended maximum charging current.

    Cheaper Options

    Cheap controllers may be marked as an MPPT but testing has shown that some are in fact PWM controllers. Cheap controllers may not have the over-voltage battery protection which could result in the battery being overcharged with potential damage to the battery; caution is recommended. Normally, due to the increased circuitry, MPPT solar charge controllers will be physically larger than PWM solar charge controllers.

    Multiple Solar Chargers

    Properly wired, it is possible to add multiple solar chargers (any combination of type and rating) to charge a battery. Proper wiring means that each solar charger is wired separately and directly to the battery terminals. This ideal case means that each controller will “see” the battery voltage and is unaffected by the current flow coming from other charge controllers. This situation is no different from charging a battery from the grid/generator at the same time as charging from solar. With modern controllers, the current will not flow backwards from the battery to the controller (excepting a very small quiescent current).

    MoonRay 320 Solar Charge Controller

    Performance MPPT. – Peak performance in all conditions. – Minimal self-consumption (14mA).

    Shadow Optimized. Unrivaled output in shaded and low light conditions.

    Optimized for ONE to many solar panels in parallel. – No limitations when using single solar panels. – Avoid sensitive serial installations and enjoy the full potential of solar panels in parallel. – Cluster many MoonRay for an optimized big size array.

    SUNBEAMsystem Multi Connect App – Connect via the bluetooth dongle with full info at your hand. – Direct connection to multiple MoonRay’s for big solar arrays. – Connect and network with other SUNBEAMsystem units.

    In stock (can be backordered)




    The new MoonRay MPPT solar charge controllers are truly optimized for use on yachts and RVs. MoonRay outperforms other MPPT charge controllers. Tested in both perfect as well as ‘real-life’ weather conditions. It’s performance outshines others in clouded or partial shadowing conditions.

    The MoonRay is optimized for a typical installation on a boat or motorhome. Often, with a single solar panel or a couple of solar panels connected in parallel. Charging one or several 12V batteries.

    Thanks to its versatility it is also possible to use many MoonRay’s together. Controlling groups of solar panels. This makes it possible to optimize each group. So you can make groups according to the ever-changing conditions on a moving platform. Thanks to the Multi Connect App it is possible to collect information from all the controllers as they were one.

    If you intend to connect your Moonray MPPT charge controller to a 24V system, note that you´ll need to use two or more solar panels connected in series.

    PWM vs MPPT Charge Controllers: What’s the Difference?

    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.

    In this guide, I’ll break down the differences between PWM and MPPT charge controllers.

    And I won’t just talk about price and efficiency. I’m going in depth to help you understand when you should choose a PWM or MPPT.

    I’ll also show you the results of a real-world PWM vs MPPT test I did.

    PWM vs MPPT Comparison Table

    Pros – Cheap (but can lead to increased wiring and equipment costs)– All you need for some small solar power systems – Efficient (~95% conversion efficiency)– Higher current and PV voltage limits– features (e.g. Bluetooth, custom charging profiles)– Usually better build quality
    Cons – Less efficient (~75% conversion efficiency)– Lower current and PV voltage limits– Usually fewer features than MPPT charge controllers– Usually worse build quality – Expensive– Overkill for some small solar power systems
    Best for – Small solar power systems (300-400W or less)– When PV voltage is close to battery voltage – Larger solar power systems (400W)– When mounting space is limited– When conversion efficiency is a top priority– When series connecting solar panels
    My favorites – Renogy Wanderer 30A– Renogy Wanderer 10A– Morningstar SunSaver – Victron SmartSolar MPPT 100/30– Renogy Rover 40A– EPEver Tracer 4215BN
    Full review Best PWM Charge Controllers Best MPPT Charge Controllers

    4 Main Differences

    • MPPT charge controllers are more efficient than PWM charge controllers. The rule of thumb conversion efficiencies are about 75% for PWMs and 95% for MPPTs.
    • PWM charge controllers are cheaper than MPPT charge controllers. Many popular PWMs retail for 20-50, while MPPTs start at around 100.
    • When connecting multiple solar panels together, PWM charge controllers usually require you to wire them in parallel. Most MPPT charge controllers have high enough PV voltage limits that you can wire them in series. Parallel wiring increases current (amperage), which can require thicker wire and equipment with higher current ratings.
    • PWM charge controllers are often best suited for smaller solar arrays of 300-400 watts or less. MPPT charge controllers are often best suited for larger solar arrays of 400 watts or more. MPPTs start to make more sense the greater the size of the solar array.

    PWM vs MPPT: How to Choose

    Here are the main considerations when deciding between a PWM or MPPT charge controller.

    Conversion Efficiency

    PWM charge controllers have a rule of thumb conversion efficiency of 75%. If you don’t need to squeeze every possible watt out of your solar panels, a PWM is probably all you need.

    MPPT charge controllers have a rule of thumb conversion efficiency of 95%. When conversion efficiency is a top priority, an MPPT is often the best option.

    Note: As you’ll see from the results of my real-world test, these conversion efficiencies don’t always hold true. But they’re helpful for conveying average expected efficiency across a number of different scenarios.


    PWM charge controllers are cheap. You can find many budget PWMs online for 15-25, though caveat emptor definitely applies when buying one of these. Higher quality ones start around 40-50.

    However, the sticker price of a PWM charge controller can be misleading, because — depending on how you build your system — using one can lead to greater downstream costs. For instance, if you want to use multiple solar panels with a PWM, you’ll likely have to wire them in parallel which can lead to increased wire and equipment costs.

    MPPT charge controllers are expensive. It’s hard to find one for less than 100. Many popular options fall in the 150-200 price range.

    Solar Array Size

    PWM charge controllers often have low current and PV voltage ratings, making them best suited for solar arrays of around 300-400 watts or less. For instance, it’s common to see PWM charge controllers with max PV voltages of 25-50 volts (usually 1-2 100W 12V solar panels wired in series), and current ratings of 10-30 amps (usually 2-4 100W 12V solar panels wired in parallel).

    MPPT charge controllers are often suited for larger solar arrays, such as 500-1000 watts. This is because they tend to have higher current and PV voltage ratings, such as 30-40 amps and 100-150 volts.

    Tip: Use our maximum open circuit voltage calculator to find the maximum voltage of your solar array. Pick a charge controller with a PV voltage limit that is greater than this number.

    PV Voltage vs Battery Voltage

    PWM charge controllers work best when the incoming PV voltage (i.e. solar panel voltage) is close to the battery voltage. The ideal setup with many PWMs is with a 12V solar array and 12V battery. The greater the difference between PV voltage and battery voltage, the less efficient a PWM charge controller will be.

    MPPT charge controllers work well regardless of the difference between PV voltage and battery voltage. For example, with an MPPT, you could efficiently charge a 12V battery with a 36V solar array.

    Note: For both types of charge controllers, PV voltage needs to be greater than the battery voltage in order for the battery to charge. The only exception is if you’re using a boost MPPT charge controller, which is capable of boosting the incoming PV voltage to match the battery’s voltage. There is no such thing as a boost PWM charge controller.

    Where You Live

    PWM charge controllers perform about the same as MPPTs in subtropical to tropical climates, unless you have lots of panels connected in series.

    MPPT charge controllers perform better in cold to temperate climates.

    Series vs Parallel Connections

    PWM charge controllers: When wiring multiple solar panels to a PWM, you’ll usually have to wire them in parallel. This is because many PWMs have low PV voltage limits (e.g. 25V or 50V), which is enough for only one or two 12V solar panels in series.

    MPPT charge controllers: MPPTs almost always have higher PV voltage limits than PWMs, letting you wire more panels in series. For example, a common PV voltage limit for MPPTs is 100 volts. Many popular 12V 100W solar panels have an open circuit voltage (Voc) of around 22V, so you could connect up to 4 of them in series without exceeding this limit. Series wiring keeps current low, saving you money on wiring and equipment costs.

    Note: Series wiring isn’t always the best option, though. For instance, parallel wiring is advantageous when the panels spend a lot of time in mixed light conditions. For a full tutorial and breakdown of series vs parallel wiring, check out my guide on how to wire solar panels in series and parallel.

    mppt, solar, charge, controller

    Mounting Space

    PWM charge controllers are better suited for when you have lots of roof or mounting space.

    MPPT charge controllers are best when roof or mounting space is limited. Because they’re more efficient, they’ll extract the maximum amount of solar energy from a limited space.

    Battery Type

    PWM charge controllers: Many PWMs are only compatible with lead acid batteries (sealed, gel, flooded, AGM).

    If a PWM is compatible with lithium (LiFePO4) batteries, it tends not to treat them as well as an MPPT would. Why? Because it may not offer the option to connect a temperature sensor or battery voltage monitor (BVM) for improved temperature compensation and voltage readings. Others don’t have custom charging profiles, in case you want to customize the boost, float, and absorption voltages of your battery. And I’ve found in my testing that PWMs often have less accurate battery voltage readings, meaning they can chronically over charge or over discharge your battery, shortening its lifespan.

    MPPT charge controllers: Most of the MPPTs I’ve used work with lead acid and lithium (LiFePO4) batteries, or at least offer the ability to create custom charging profiles.

    MPPTs usually have the option to connect a temperature sensor and battery voltage monitor. I’ve also found their battery voltage readings to be more accurate. If you’re using expensive batteries that you want to last as long as possible, I’d recommend an MPPT.

    Distance from Charge Controller to Battery

    PWM charge controllers: If your PWM is forcing you to wire solar panels in parallel and increase wire gauge as a result, longer wire runs can increase wiring costs substantially.

    MPPT charge controllers: MPPTs let your wire more solar panels in series which keeps PV current low and allows you to use smaller wire gauge.

    PWM vs MPPT Test Results

    The rule of thumb conversion efficiencies for PWM and MPPT charge controllers are averages. They try to capture the average conversion efficiencies across temperature ranges, weather conditions, solar array voltages and other conditions.

    Simply put, it’s rare that the 75% and 95% efficiency numbers will hold true for your particular situation.

    To illustrate this, I connected a PWM and MPPT charge controller each to a 100W 12V solar panel and 12V 100Ah LiFePO4 battery. Then I placed the solar panels outside and monitored each charge controller’s output over the course of a day with a watt meter.

    9AM output – full shade 2.1 W 1.4 W
    11AM output – full sun 65.8 W 73.4 W
    12PM output – full sun 70.8 W 75.9 W
    1PM output – full sun 72.0 W 73.9 W
    2PM output – full sun 67.7 W 69.1 W
    3PM output – half shade 4.3 W 4.6 W
    4PM output – full shade 3.4 W 2.9 W
    Peak current 5.41 A 5.85 A
    Peak output 72.3 W 76.2 W
    Total power output 284.4 Wh 292.2 Wh

    Note: This test was conducted on a sunny day in mid April in Alabama.


    • The PWM charge controller output a total of 284.4 watt hours, while the MPPT charge controller output at total of 292.2 watt hours. That’s a difference of only 7.8 watt hours. If we assume the MPPT operated at a 95% conversion efficiency, then each solar panel generated around 307.5 watt hours (292.2 ÷ 95% = 307.5). This would mean the PWM operated at 92.5% conversion efficiency (284.4 ÷ 307.5 = 92.5%).
    • In full shade, the PWM actually slightly outperformed the MPPT.
    • The MPPT’s output seemed to be affected by heat more than the PWM’s. This isn’t really captured in the numbers, but as I watched each charge controller’s output over the course of the day, the MPPT’s seemed to slowly drop as the day (and panels) heated up. This is in line with the finding that, in hotter climates, MPPTs perform similarly to PWMs.

    What Is a PWM Charge Controller?

    PWM solar charge controllers use a method called pulse width modulation (PWM) to reduce solar panel voltage to the right level for safely charging the battery.

    Pulse width modulation is like turning a switch on and off at an extremely fast rate. By adjusting (or ‘modulating’) how long the switch stays on and off, you can in essence adjust the output of the solar panel.

    You can actually see pulse width modulation in action using lights. To illustrate it, I set up two LEDs and programmed them to turn on and off very quickly. The LED on the left was programmed to be on for 5 milliseconds and off for 10 milliseconds. The LED on the right was programmed to be on for 15 milliseconds and off for 5 milliseconds.

    To the human eye, both lights appear to be constantly on. However, as you can see in the photo, the light on the left is much dimmer than the light on the right.

    This is pulse width modulation in action. By adjusting how long a switch stays on and off, you can affect the average output. In this case, the more time the light spent turned off, the dimmer it appeared.

    Now consider PWM in the context of solar panels. A solar panel’s output is constantly changing depending on how sunny it is. So the voltage and current need to be regulated to safely charge the battery. Because, for example, if the solar panel’s voltage gets too high, it could damage the battery.

    So, PWM charge controllers are essentially turning the solar panels on and off very quickly to regulate their output.

    This helps us understand why it’s important for your battery and solar panel to have similar voltages when using a PWM charge controller. If the solar panel voltage is much greater than the battery voltage, the solar panels will spend much more time ‘turned off,’ greatly reducing how much power they can generate.

    Best PWM Charge Controllers

    After testing some of the best PWM charge controllers on the market, here are my recommendations:

    What Is an MPPT Charge Controller?

    MPPT solar charge controllers use a method called maximum power point tracking (MPPT) to harvest the maximum power from the solar array. They use more sophisticated technology, and are thus more expensive.

    Essentially, they are always ‘tracking’ at what point along the IV curve the solar panel output is greatest. This point of max power is, unsurprisingly, called the maximum power point.

    Once an MPPT has found the maximum power point, it collects all that solar energy and then steps the voltage down to match the voltage of your battery bank while boosting the current to make up for the lower voltage. The result is minimal conversion losses.

    Best MPPT Charge Controllers

    After testing some of the best MPPT charge controllers on the market, here are my recommendations:

    • Top Pick:Victron SmartSolar MPPT 100/30
    • Budget Pick:Renogy Rover 40A
    • Honorable Mention:EPEver Tracer 4215BN

    The Bottom Line

    The main differences between PWM and MPPT charge controllers are cost and conversion efficiency. PWM charge controllers are cheap and inefficient, while MPPT charge controllers are efficient but pricey. The rule of thumb conversion efficiencies are 75% for PWM and 95% for MPPT.

    In reality, though, these conversion efficiencies will likely not hold true for your specific situation. As happened during my real world test, a PWM may actually perform better than expected.

    And I think the general claim of “PWM is cheap and MPPT is expensive” is also a bit misleading. PWM charge controllers are often only compatible with 12V and 24V solar arrays and battery banks. To connect multiple solar panels to a PWM, you’ll usually have to wire them in parallel, which requires buying branch connectors and can also result in higher wire and equipment costs, especially in systems with long wire runs.

    Personally, here’s how I’d decide which controller to get for my next solar project:

    I’d use PWM charge controllers when building a solar power system of 300-400 watts or less, where I don’t need to squeeze out every watt from my panels.

    In any other situation, I’d use an MPPT charge controller. I’d even consider an MPPT from the start if I knew I’d probably expand my solar array later on. They’re so much more versatile and feature-rich that you can add many more panels before having to upgrade.

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