Choosing the Right Solar Charge Controller/Regulator
A solar charge controller (frequently called a regulator) is similar to a regular battery charger, i.e. it regulates the current flowing from the solar panel into the battery bank to avoid overcharging the batteries. (If you don’t need to understand the why’s, scroll to the end for a simple flow chart). As with a regular quality battery charger, various battery types are accommodated, the absorption voltage, float voltage can be selectable, and sometimes the time periods and/or the tail current are also selectable. They are especially suited for lithium-iron-phosphate batteries as once fully charged the controller then stays at the set float or holding voltage of around 13.6V (3.4V per cell) for the remainder of the day.
The most common charge profile is the same basic sequence used on a quality mains charger, i.e. bulk mode absorption mode float mode. Entry into bulk charge mode occurs at:
- sunrise in the morning
- if the battery voltage drops below a defined voltage for more than a set time period, e.g. 5 seconds (re-entry)
This re-entry into bulk mode works well with lead-acid batteries as the voltage drop and droop is worse than it is for lithium-based batteries which maintain a higher more stable voltage throughout the majority of the discharge cycle.
Lithium batteries (LiFePO4) do not benefit from re-entry into a bulk mode during the day as the internal impedance of the lithium batteries increases at high (and low) states of charge as indicated by the orange vertical lines in the chart below and it is only necessary to occasionally balance the cells which can only be done around the absorption voltage. A related reason is to avoid the Rapid and large variation in voltage that will occur in these regions as large loads are switched on and off.
Lithium batteries do not have a defined “float voltage”, and therefore the “float voltage” of the controller should be set to be at or just below the “charge knee voltage” (as indicated in the chart below) of the LiFePO4 charge profile, i.e. 3.4V per cell or 13.6V for a 12V battery. The controller should hold this voltage for the remainder of the day after bulk charging the battery.
The Difference Between PWM and MPPT Solar Charge Controllers
The crux of the difference is:
- With a PWM controller, the current is drawn out of the panel at just above the battery voltage, whereas
- With an MPPT solar charge controller the current is drawn out of the panel at the panel “maximum power voltage” (think of an MPPT controller as being a “Smart DC-DC converter”)
You often see slogans such as “you will get 20% or more energy harvesting from an MPPT controller”. This extra actually varies significantly and the following is a comparison assuming the panel is in full sun and the controller is in bulk charge mode. Ignoring voltage drops and using a simple panel and simple math as an example:
Battery voltage = 13V (battery voltage can vary between say 10.8V fully discharged and 14.4V during absorption charge mode). At 13V the panel amps will be slightly higher than the maximum power amps, say 5.2A
With a PWM controller, the power drawn from the panel is 5.2A 13V = 67.6 watts. This amount of power will be drawn regardless of the temperature of the panel, provided that the panel voltage remains above the battery voltage.
With an MPPT controller the power from the panel is 5.0A 18V = 90 watts, i.e. 25% higher. However this is overly optimistic as the voltage drops as temperature increases; so assuming the panel temperature rises to say 30°C above the standard test conditions (STC) temperature of 25°C and the voltage drops by 4% for every 10°C, i.e. total of 12% then the power drawn by the MPPT will be 5A 15.84V = 79.2W i.e. 17.2% more power than the PWM controller.
In summary, there is an increase in energy harvesting with the MPPT controllers, but the percentage increase in harvesting varies significantly over the course of a day.
A PWM (pulse width modulation) controller can be thought of as an (electronic) switch between the solar panels and the battery:
- The switch is ON when the charger mode is in bulk charge mode
- The switch is “flicked” ON and OFF as needed (pulse width modulated) to hold the battery voltage at the absorption voltage
- The switch is OFF at the end of absorption while the battery voltage drops to the float voltage
- The switch is once again “flicked” ON and OFF as needed (pulse width modulated) to hold the battery voltage at the float voltage
Note that when the switch is OFF the panel voltage will be at the open-circuit voltage (Voc) and when the switch is ON the panel voltage will be at the battery voltage voltage drops between the panel and the controller.
The best panel match for a PWM controller:
The best panel match for a PWM controller is a panel with a voltage that is just sufficiently above that required for charging the battery and taking temperature into account, typically, a panel with a Vmp (maximum power voltage) of around 18V to charge a 12V battery. These are frequently referred to as a 12V panel even though they have a Vmp of around 18V.
The MPPT controller could be considered to be a “Smart DC-DC converter”, i.e. it drops the panel voltage (hence “house panels” could be used) down to the voltage required to charge the battery. The current is increased in the same ratio as the voltage is dropped (ignoring heating losses in the electronics), just like a conventional step-down DC-DC converter.
The “Smart” element in the DC-DC converter is the monitoring of the maximum power point of the panel which will vary during the day with the sun strength and angle, panel temperature, shading, and panel(s) health. The “smarts” then adjust the input voltage of the DC-DC converter – in “engineering speak” it provides a matched load to the panel.
The best panel match for an MPPT controller:
- The panel open circuit voltage (Voc) must be under the permitted voltage.
- The VOC must be above the “start voltage” for the controller to “kick in”
- The maximum panel short circuit current (Isc) must be within the range specified
- The maximum array wattage. some controllers allow this to be “over-sized”, e.g the Redarc Manager 30 is permitted to have up to 520W attached
Choosing the Right Solar Controller/Regulator
The PWM is a Good Low-Cost Option:
f or solar panels with a maximum power voltage (Vmp) of up to 18V for charging a 12V battery (36V for 24V battery, etc).
When the solar array voltage is substantially higher than the battery voltage e.g. using house panels, for charging 12V batteries
An MPPT controller will yield higher returns compared with a PWM controller as the panel voltage increases. I.e. a 160W panel using 36 conventional monocrystalline cells with a maximum power amp of 8.4A will provide around 8.6A at 12V; while the 180W panel having 4 more cells will provide the same amperage but 4 additional cells increases the panel voltage by 2V. A PWM controller will not harvest any additional energy, but an MPPT controller will harvest an additional 11.1% (4 / 36) from the 180W panel.
For the same principle, all panels using SunPower cells with more than 32 cells require an MPPT charge controller otherwise a PWM controller will harvest the same energy from 36, 40, 44 cell panels as it does from a 32 cell panel.
Solar Charge Controller Features and Options
Boost MPPT Controllers
“Boost” MPPT charge controllers allow batteries to be charged that has a higher voltage than the panel.
Combined MPPT and DC-DC Chargers
The MPPT function is a natural adjunct to the DC-DC charger function and there are several quality brands that provide this with more under development. A single unit can be used by itself, as it automatically switches between alternator charging and solar charging. For larger systems, our favoured arrangement is to use a separate MPPT controller for the fixed roof-mounted panels and use the combined MPPT/DC-DC with portable panels. In this case, an Anderson connector is placed on the exterior of an RV which is then wired to the solar input of the MPPT/DC-DC unit.
Note that the battery capacity must be sufficient so that the combined charging current from simultaneous charging from the alternator and the roof solar panels does not exceed the manufacturer’s recommended maximum charging current.
Cheap controllers may be marked as an MPPT but testing has shown that some are in fact PWM controllers. Cheap controllers may not have the over-voltage battery protection which could result in the battery being overcharged with potential damage to the battery; caution is recommended. Normally, due to the increased circuitry, MPPT solar charge controllers will be physically larger than PWM solar charge controllers.
Multiple Solar Chargers
Properly wired, it is possible to add multiple solar chargers (any combination of type and rating) to charge a battery. Proper wiring means that each solar charger is wired separately and directly to the battery terminals. This ideal case means that each controller will “see” the battery voltage and is unaffected by the current flow coming from other charge controllers. This situation is no different from charging a battery from the grid/generator at the same time as charging from solar. With modern controllers, the current will not flow backwards from the battery to the controller (excepting a very small quiescent current).
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.
January 7, 2022 Jason Svarc
Best mid-range MPPT solar charge controllers up to 40A
In this article, we review six of the most popular, mid-level MPPT solar charge controllers commonly used for small scale solar power systems up to 2kW. These are more affordable, lower voltage (100-150V) units, which are generally designed for 12V or 24V battery systems, although several can be used on 48V batteries. A number of these charge controllers also feature inbuilt load control terminals for basic DC lighting and other loads.
In this review, we don’t list simple PWM controllers used for DC lighting and basic systems since there are many sites already covering these entry-level PWM controllers. For high-performance MPPT solar charge controllers with higher input voltages up to 300V and current ratings from 60A to 100A, see our high-power MPPT solar charge controllers review.
What is a solar charge controller?
A solar charge controller, also known as a solar regulator, is a battery charge regulator connected between the solar array and battery. Its job is to regulate the solar output to ensure the battery is charged correctly and not overcharged. DC coupled solar charge controllers been around for decades and are used in most small scale off-grid solar power systems.
Top 6 Solar Charge Controllers
Mid-level solar controllers up to 40A
Smaller capacity MPPT solar charge controllers with a current rating from 20A to 40A are used for many different applications including off-grid cabins and homes, RV’s, boats, caravans, telecommunications and remote site backup. These mid-range MPPT solar charge controllers are available from many different manufacturers, but this review will FOCUS on the most popular and best quality charge controllers from the most reputable manufacturers which have been on the market for several years.
|1||Victron SmartSolar MPPT||35 A||150V||12V 24V 36V 48V||350 to 480|
|2||EPever TRIRON Series||40 A||150V||12V 24V||150 to 250|
|3||Morningstar ProStar MPPT||40 A||120V||12V 24V||460 to 540|
|4||EPever XTRA Series||40 A||150V||12V 24V 36V 48V||130 to 190|
|5||Renogy Rover||40 A||100V||12V 24V||150 to 190|
|6||EPever BN Series||40 A||150V||12V 24V||170 to 250|
In this review, we rank the various charge controllers according to a number of important criteria including build quality, MPPT tracking speed, battery voltage range, operating temperature range (heat dissipation), monitoring, real-world performance and price. In our reviews, we generally rank performance and quality over affordability, so in this case, we rate the unit price lower than other criteria. This may come across as bias towards the more expensive models, but based on real-world results, testing and performance monitoring, the higher-end controllers have proven to out-perform the cheaper models.
Read more about selecting and correct sizing a solar charge controller in the MPPT solar charge controllers explained article.
Victron Energy is considered a world leader in power electronics and specialise in manufacturing equipment required for off-grid and stand-alone power systems including, inverters, batteries, chargers, monitors and of course, solar charge controllers. Based in the Netherlands, Victron manufacture many products in India and have become well known for producing quality, reliable off-grid battery inverter/chargers and a wide range of quality MPPT solar charge controllers.
Victron offer a huge range of solar charge controllers, from small 10A PWM models, to high-performance 100A MPPT varieties with high voltage inputs up to 250V. The MPPT 150V models appear very simple in design, and may not have a display or load control terminals like many others, however, where Victron out performs the competition is in MPPT tracking performance, communications and monitoring.
Victron have by far the most advanced system monitoring with inbuilt Bluetooth connection offering easy programming and configuration, plus remote firmware updates which add extra features and options. The display-less design may not please all users, but the fast, accurate MPPT tracking, high build quality, and V.E. Smart networking options are stand-out features.
Smartsolar MPPT 150V 35A
- Fast MPP Tracking
- 150V max Voc
- 12V, 24V or 48V batteries
- Compatible with LiFePO4 Lithium batteries
- Very advanced monitoring app
- Wide operating temperature up to 60°C
- Inbuilt temp sensor
- Optional wireless battery sensor
- Easy remote firmware updates
- 5 Year warranty
See the detailed Victron Energy Review
EPever TRIRON Series
EPever was founded in 2007 and has grown rapidly to become one of the largest Chinese manufacturers of cost-effective power products including a wide range of MPPT solar charge controllers. The Triron series is the next evolution to the well-known Tracer series of MPPT’s.
The TRIRON series from EPever is a much more advanced and user-friendly version of the original AN series of charge controllers. The TRIRON controllers have a unique swappable display module as well as a swappable interface module with an RS485 communication option that can be used for a number of different applications. Note, maximum PV voltage is either 100V or 150V depending on the model. The 5 button display module is very easy to use and provide all the important information you need about the PV, battery and load. Wireless access is available via the eBox-BLE Bluetooth adapter or the Wi-Fi adapter is available for remote monitoring.
TRIRON Series MPPT 150V 40A
- Fast MPP Tracking
- 150V max Voltage Voc (TRIRON 3215N 4215N)
- Easy to use with a large clear display
- Compatible with Lead-acid and Lithium batteries
- 40A Load control
- Swappable display and interface modules
- RS485 Interface for communications and remote control
- USB Port and relay control options
- Optional Temp sensor
Morningstar Prostar MPPT
Morningstar are a well-established company based in the US with 25 years of experience in engineering and manufacturing high-performance solar charge controllers. Morningstar is widely recognized as developing some of the best quality products on the market with high levels of protection against extreme environments, lightning surges and high operating temperatures.
The Prostar range of MPPT charge controllers are available in 25A and 40A versions with a 120V input voltage limit. The extremely fast MPP tracking can perform a full voltage sweep in less than 1 second using the Trakstar technology. The device features good size terminals protected under a front cover, including load control output terminals rated up to 30A, plus a clear backlit LCD display and can easily programmed using the 4 large buttons. However, the very high price tag means the Prostar MPPT series is out of reach for many users.
Prostar MPPT 120V 40A
- Very fast MPP Tracking
- 120V max Voc
- Compatible with LiFePO4 Lithium batteries
- Wide operating temp up to 60°C
- 30A Load control
- High surge protection
- Optional Battery sensor
- 5 Year warranty
EPever XTRA Series
EPever, also known as EPsolar, was founded in 2007 in Beijing, China and has grown rapidly to become one of the largest manufacturers of cost-effective solar power products including a wide range of MPPT charge controllers. The XTRA series of MPPT’s released in early 2018, have only recently become more popular due to the low cost, easy setup, and lithium battery compatibility.
The XTRA series is available in 10 different options with 3 display types, current ratings from 10 to 40A, battery voltages from 12V to 48V, and input voltage limit up to 150V. In comparison to the older AN series which had a 100V input limit, the XTRA series features lithium battery compatibility and a higher input 150V voltage (Voc) on the 30 and 40A models, plus a modern look and concealed screw terminals. Note, the two-button version with LCD is basically the older AN series controller in a modern package.
XTRA Series MPPT 40A
- Good MPP Tracking
- Three display options with a clear simple LCD
- Compatible with most Lithium LiFePO4 batteries
- 40A Load control
- Optional MT50 display
- Optional Temp sensor
- Optional Wi-Fi and Bluetooth module
- Low cost
5. Renogy Rover
Renogy, founded in the US in 2014, recently became a very popular choice for solar enthusiasts across the world due to the low-cost, easy setup and good MPPT tracking. Renogy manufacture a wide range of affordable inverters, DC converters and solar charge controllers in China.
The Rover series from Renogy is a feature packed MPPT controller with a clear inbuilt display, plus a low-cost (optional) Bluetooth adapter which provides a great, easy to use interface with many configuration options. Load control terminals are built-in, although the output is limited to 20A. The overall build quality is quite good, however there are some area’s which could be improved, most notably the cable terminals which are far too small for a 40A controller.
Rover MPPT 100V 40A
- Good MPP Tracking
- Clear Simple display
- Compatible with Lithium (12.8V LiFePO4)
- 20A Load control
- Advanced Bluetooth app and user settings
- Temp sensor included
- Low cost
6. Outback BN series by EPever
The Outback Power Flexmax40 is made by EPever and is commonly known as the Tracer BN series which is a well known affordable MPPT controller.
EPever one of the leading manufacturers of cost-effective power products including a wide range of solar charge controllers. The well-known Tracer and TRIRON series of MPPT’s are a very popular choice for solar enthusiasts across the world due to the easy setup, good MPPT tracking, and low cost.
The first generation AN series is the best-known MPPT in the range, being a low-cost 100V unit with an inbuilt display. However, the BN series is the more expensive higher-performance version with many extra features including a 150V input voltage limit, heavy-duty robust design, large heatsink, and huge input terminals which can accept a cable size up to 50mm2 (1 AWG).
The obvious feature lacking from the BN series is the display. However, monitoring and configuration is available via the additional remote MT50 display which features a good clear LCD screen showing all the basic information required. Wireless access is also available via the eBox-BLE Bluetooth adapter.
Tracer BN Series MPPT 150V 40A
- Very large screw terminals
- Large heatsink and wide operating temperature range
- 12V, 24V batteries
- 150V max Voc
- Wide MPP voltage range
- 20A Load control
- Remote MT50 display with settings and load control
- Optional Temp sensor
RV Solar Power Kits and AGM Batteries
A full selection of complete RV solar power systems with AGM batteries for the house battery bank.
Complete power kits for your RV include an Inverter Charger, solar array for charging your RVs house battery bank. In this group of products, we include AGM batteries. These Absorbed Glass Mat (AGM) batteries are second to only the lithium kits. AGM batteries can be more affordable, but they do require larger banks and more weight. The warranty on AGM batteries is also much less than their lithium counterparts.
Inverter Chargers for easy power
Go Power IC-3000 Inverter Charger Inverter chargers like the IC-3000 pictured include several components in one unit. A true sine wave power inverter, a transfer switch, and a battery charger. With these three items in one unit, there is greater control over the entire inverter and battery charging system.
We carry Inverter Chargers in both 2000 and 3000 watt configurations.
Larger solar arrays
Newer RVs require larger arrays to power the items on board. Everything from TVs to residential refrigerators are power hungry devices. These devices will drain your battery bank, but a good solar array can work to create a charging balance.
This is a great entry levelf Go Power’s Inverter Charger Kit. They offer the Elite and Extreme kits. These have different amounts of solar and also different size Inverter units.
The Go Power! Elite Solar Kit. IC-2000. 380 Watts of solar
We have found these kits contain much of what you need for getting going with off-grid solar and inverter power. We have also added lithium battery and sealant as well
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What Kind of Batteries Do You Use for Solar Panels?
You can use any kind of batteries with solar panels. Solar panels don’t care what batteries they are charging, and batteries don’t care what solar panels are being used. You can use lithium-phosphate batteries, lithium-ion batteries, lead-acid batteries, flooded cell or AGM. What matters the most is the solar charge controller.
What Kind of Batteries Do You Use for Solar Panels?
Most boondockers use lead-acid batteries with their solar panels. Specifically, they use flooded-cell batteries (the kind you pour water into) because these batteries are cheap enough to replace every 12 to 24 months.
All batteries have to be replaced at some point, and thus the cheaper the better. If you buy expensive batteries, then you will want to spend more time (and money) managing those batteries to maximize their life span. On the other hand, if you’re the type who’d rather “set it and forget it”, using cheap, flooded cell batteries are your best option.
- A 12 volt, deep cycle, 100 AH flooded cell battery will cost 120.00 on average.
- A 12 volt, deep cycle, 100 AH AGM battery will cost 250.00 on average.
- A 12 volt, 100 AH lithium phosphate battery will cost between 800.00 to 1,000.00.
The only real advantage of the AGM battery is that it does not produce any toxic fumes. Thus, it can be stored inside your living space. AGM batteries are popular with van dwellers for this reason. AGM batteries also charge more quickly, and they also get about 50% more life span.
Lithium phosphate batteries have their advantage in much lighter weight, about 30 pounds versus 60 pounds for flooded cell or AGM, and being able to sustain voltage all the way down to 0% state of charge. However, lithium batteries are very sensitive to cold; they cannot be recharged once temperature reaches 32 degrees F.
Tip: Many boondockers buy their batteries from Costco. Costco sells batteries made by Interstate. Costco sells these batteries cheaper than any other store, and gives you a 12 month warranty, with no questions asked. This means, you can return the batteries in the 11th month, and get a new set for free.
What Matters the Most is the Solar Charge Controller
It doesn’t really matter what solar panels you have nor what batteries you have. What matters is that you have a good solar charge controller to marry the two together.
The solar charge controller is a device that sits between your solar panels and your batteries. The controller makes sure your batteries don’t get “over charged”. Charging your batteries too much causes them to overheat and catch on fire.
A controller also decides how to charge your batteries properly by changing the flow of amps and voltage rate based on the battery manufacturer’s recommended specifications.
The industry is filled with cheap, Chinese-made solar charge controllers. This is where you don’t want to go cheap. Spend the extra money to get a high quality solar charge controller.
How to Find a Good Solar Charge Controller
- A good solar charge controller is programmable to accommodate any brand or type of battery. Make sure it will let you adjust the amperage and voltage for a battery’s “bulk”, “absorption”, and “float” modes.
- Solar charge controllers come in “MPPT” and “PWM” varieties. The “MPPT” is the more popular with boondockers because it allows solar panels to deliver their maximum power possible.
- Solar charge controllers made by “Victron Energy” are the most popular with full time boondockers due to their programmability and high quality standards. Their Blue Solar 100 | 50 MPPT (see it on Amazon) is the best selling controller, and probably the most respected controller among boondockers.
It Also Depends on How Much Battery Power You Want
If you want to run your air conditioning and refrigerator from solar and battery, and be able to do so for at least eight (8) hours a day, then you will want Lithium Phosphate batteries instead. The reason why is because air conditioners are huge electricity hogs, and being able to run one or two units for eight hours a day, will demand an awful lot of power. Refrigerators are electricity hogs only because they need to cycle on and off 24 hours a day, but are still not as bad as air conditioning units.
You could still do it with lead acid batteries but you will need as many as 20 to 24 of these batteries. Each 100AH, deep cycle, lead acid battery will weigh about 60 pounds. Thus 20 to 24 of those batteries will add almost between 1,200 to 1,500 pounds to your trailer or motorhome.
Meanwhile, a similar sized lithium phosphate battery is like having two flooded cell batteries because it can sustain voltage down to 0% state of charge, compared to 50% for a flooded cell. Thus, you’d only need 10 to 12 of these batteries to run both air conditioning and refrigerator for eight (8) hours a day. Lithium batteries are also lighter in weight, about 30 pounds total. Hence, you’re only adding 300 to 360 pounds to your trailer or motorhome.
You will also need at least 1,200 watts of solar on the roof to recharge those batteries. The more solar, the better.
What if I Don’t Need to Run My Air Conditioning and Refrigerator From Battery?
Then you probably don’t need lithium phosphate batteries. If you can use your generator to run the air conditioning, and propane for your refrigerator and heating, then getting four (4) flooded cell, 100 AH, lead acid batteries will do just fine. With that setup, you can add a 2,000 watt inverter and still be able to run your microwave oven, coffee maker, and (possibly) a toaster oven or small hair dryer.
You will want at least 600 watts of solar panels on the roof to keep those batteries recharged.
Read About Solar Panels and Batteries for Boondocking