Battery Charge Controller
For many people, building their own solar panel system and living off-grid is becoming a reality instead of a dream. Connecting the solar panels directly to a single battery or bank of batteries for charging may work, but is not a good idea. What’s needed is a battery charge controller to safely charge and discharge your deep cycle battery for a longer lifespan.
A standard 12 volt solar panel which can be used to recharge a battery, could actually be putting out nearly 20 volts at full sun, much more voltage than the battery needs. This difference in voltage between the required 12 volts need for the battery and actual 20 volts being generated by the solar panel translates into a greater current flow into the battery.
This results in too much unregulated solar generated current overcharging the battery which could cause the electrolyte solution within the batteries to overheat and evaporate off, resulting in a much shortened battery life and ultimately, complete battery failure.
Then the quality of the charging current will directly affect the life of any connected deep cycle battery, so it is extremely important to protect batteries of a solar charging system from being overcharged, or even undercharged, and we can do just that using a battery charge regulation device called a Battery Charge Controller.
A battery charge controller, also known as a battery voltage regulator, is an electronic device used in off-grid systems and grid-tie systems with battery backup. The charge controller regulates the constantly changing output voltage and current from a solar panel due the angle of the sun and matches it too the needs of the batteries being charged.
The charge controller does this by controlling the flow of electrical power from the charging source to the battery at a relatively constant and controlled value.
Thus maintaining the battery at its highest possible state of charge while protecting it from being overcharged by the source and from becoming over-discharged by the connected load. Since batteries like a steady charge within a relatively narrow range, the fluctuations in output voltage and current must be tightly controlled.
Solar Battery Charge Controller
Then the most important functions of battery charge controllers used in an alternative energy system are:
- Prevents Battery Over-charging: This is too limit the energy supplied to the battery by the charging device when the battery becomes fully charged.
- Prevents Battery Over-discharging: Automatically disconnect the battery from its electrical loads when the battery reaches a low state of charge.
- Provides Load Control Functions: Automatically connect and disconnect the electrical load at a specified time, for example operating a lighting load from sunset to sunrise.
Solar panels produce direct or DC current, meaning the solar electricity generated by the photovoltaic panels flows in only one direction only. So in order to charge a battery, a solar panel must be at a higher voltage than the battery being charged. In other words, the voltage of the panel must be greater than the opposing voltage of the battery under charge, in order to produce a positive current flow into the battery.
When using alternative energy sources such as solar panels, wind turbines and even hydro generators, you will get fluctuations in output power. A charge controller is normally placed between the charging device and the battery bank and monitors the incoming voltage from these charging devices regulating the amount of DC electricity flowing from the power source to the batteries, a DC motor, or a DC pump.
The charge controller turns-off the circuit current when the batteries are fully charged and their terminal voltage is above a certain value, usually about 14.2 Volts for a 12 volt battery. This protects the batteries from damage because it doesn’t allow them to become over-charged which would lower the life of expensive batteries. To ensure proper charging of the battery, the regulator maintains knowledge of the state of charge (SoC) of the battery. This state of charge is estimated based on the actual voltage of the battery.
During periods of below average insolation and/or during periods of excessive electrical load usage, the energy produced by the photovoltaic panel may not be sufficient enough to keep the battery fully recharged.
When the batteries terminal voltage starts to drop below a certain value, usually about 11.5 Volts, the controller closes the circuit to allow current from the charging device to recharge the battery bank again.
In most cases a charge controller is an essential requirement in any stand-alone PV system and should be sized according to the voltages and currents expected during normal operation. Understanding your batteries and their charging requirements is also a must for any battery based solar system.
Any battery charge controller must be compatible with both the voltage of the battery bank and the rated amperage of the charging device system. But it must also be sized to handle expected peak or surge conditions from the generating source or required by the electrical loads that may be connected to the controller.
There are some very sophisticated charge controllers available today. Advanced charge controllers use pulse-width modulation, or PWM. Pulse width modulation is a process that ensures efficient charging and long battery life. However, the more advanced and expensive controllers use maximum power point tracking, or MPPT.
Maximum power point tracking maximizes the charging amps into the battery by lowering the output voltage allowing them to easily adapt to different battery and solar panel combinations such as 24v, 36v, 48v, etc. These controllers use DC-DC converters to match the voltage and use digital circuitry to measure actual parameters many times a second to adjust the output current accordingly. Most MPPT solar panel controllers come with digital displays and built-in computer interfaces for better monitoring and control.
Choosing the Right Solar Charge Controller
We have seen that the primary function of a Battery Charge Controller is to regulate the power passing from the generating device, be it a solar panel or wind turbine to the batteries. They assist in properly maintaining the solar power system batteries by preventing them from being overcharged or undercharged, thus offering long life to batteries.
The solar current being regulated by a battery charge controller not only charges batteries but can also be passed to inverters for converting the direct DC current to alternating AC current to supply the utility grid.
For many people who want to live “off grid”, a charge controller is a valuable piece of equipment as part of a solar panel or wind turbine power system. You will find numerous charge controllers manufactures online, but choosing the right one can sometimes be quite confusing and to add to your worries they are not cheap either, so finding a good quality solar charge regulator really matters.
It’s best not to go for those low quality cheaper ones, as they may actually harm the battery life and increase your overall expense in the long run. For a little peace of mind then why not Click Here and check out some of the better battery charge controllers available from Amazon and learn more about the different types of solar charge controllers available as part of your solar power system helping you to save money and the environment.
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Комментарии и мнения владельцев already about “ Battery Charge Controller ”
Hi. Im considering a combination of wind and solar power generation for my boat kept on mooring. I think a combination would be good as Scotland not blessed with lots of sun and my mooring is a bit sheltered with harbour wall. Can i plug output from 2amp wind turbine into a Renogy mppt regulator (20 amp), would it manage the power to my batteries in same way as with a solar panel?
MPPT controllers have been used for photovoltaic (solar) power for a long time, but can also be used for wind turbines. In real life the wind speed is not constant, but changes continuously, thus the ideal rotor RPM for maximum torque will also change. What is important to remember is that there is an optimum RPM for each wind speed, and that is where we want to run the wind turbine to achieve MPPT. However, to work properly the controller needs an MPPT power curve that is specific for the wind turbine that you want to hook up to the controller. So check the MPPT’s manual if you can connect it to a wind turbine. If not, then it is not advisable since unlike PV, a wind turbine can output much higher open circuit input voltages (Voc) when it is not loaded up or your batteries are full.
I have a 730 W, 76 V solar panels system charging 24 V battery set up using a Morning Star MPPT charge controller in an OFF GRID set up. Which is the best suited APC or LUMINOUS UPS/Inverter that is solar compatible that can be used.
Hello, I have read your site with interest. We have a large dwelling with a business operating from it. Our standing load without all onsite is around 4KW This is a combination of servers and IT equipment, freezers, fridges etc. When all onsite with heating lighting TV’s etc. this can reach 10KW our energy costs are spiralling out of control. We have a large paddock approx 50m from the nearest 240V electrical connection into the site wiring that is in a barn. We are looking at taking a step into solar. Our initial aim is to simply power the office load using purely solar Generated energy whenever it is operating and obviously use the grid for any shortfall. We know the property will consume all of the power generated. We had a couple of thoughts. 1) Simple system. Setup an array that can generate approx 3KW and connect it to a Solar inverter and simply connect that into the property wiring system as an input. Whatever it produces should be consumed first before we need to get energy from the grid. Is this assumption correct assuming we have a local load at or exceeding the solar-generated capacity? 2) As an expansion of 1) above. We would look to build a larger array and connect that to a battery bank (this looks like the black magic area) that has enough capacity to provide a stable supply to an inverter that would then be connected as before into the property wiring systems that would provide a variable load of between 4 and 10KW we have seen peaks of 12KW on our monitor that is clamped onto the incoming 100A 240V Grid connection. How would we size the array and battery system and corresponding Invertor etc. Are higher voltage panels better than lower voltage panels? Are higher string voltages better than lower voltages from a power conversion point of view. e.g. is it more efficient to convert from 48V to 240V rather than 12 or 24V to 240V If I have a string of 24V 1000Ah made up of a series connected 2 x parallel 12V strings of 5 x 12V 200Ah batteries giving me 24V 1000Ah of capacity or in theory 24KWh what size inverter would I need to provide power into the property and would my system use the power I have before going to the grid? I am sure some of these questions are a bit basic but we are very DIY-orientated people and want to build this ourselves. Any help in understanding this would be great. I am sure there is much left out of my note. Like cable sizing etc. Logically I think we know what we think is happening, but, that doesn’t make it so! Like will we consume all we have before taking anything from the grid? I apologise for any typos or grammer. Cheers Tony
There are a number of good points raised here, and we will attempt to answer them. Firstly, an inverter fed grid-connected, or grid-tied system is basically a bunch of solar panels (or turbines) connected to a single inverter (or a collection of small inverters) feeding power directly to the utility grid. Generally, PV inverters operate as current sources injecting electric current into the utility grid in-phase with the grid voltage. It is commonly assumed that ALL the power generated by the PV panels (array) is consumed at the point of generation but this is not always the case. Power consumed is both active (real) and reactive. PV panels generate active power only. If your average power consumption is, for example, 10kWh per day, and you generate 12kWh for the 4 hours of full sun that day, then some of the inverters output power maybe autoconsumed and some may flow into the utility grid. Equally 100% inverter current may flow into the grid and you may consume 100% from the grid, just slowing down your energy meter in the process. On average PV panels generate maximum power for 4 to 5 hours of full sun per day as they do not consistently generate power 24 hours per day at their nominal output wattage rating. Oversizing an inverter by having more DC input power than the inverters AC output power, may increase power output in lower light conditions, thus extending the 5 hours. As would solar tracking. Connecting a battery bank would allow for more autonomy but at a cost and an increased array size, as now the array has to charge batteries for 5 hours plus feed the grid. Then the size and type of grid-connected system would ultimately depend on how many hours of autonomy you require and how much you are willing to pay upfront. Higher string voltages are better providing everything stays within tolerance at worst case conditions. As P = VI, a higher voltage (V) means a lower current (I) for a given power (P) and therefore smaller diameter cabling so cheaper. PV panel voltage depends on the wattage (100W or 400W) of the panel. Higher PV wattages means physically bigger panels, which means more m 2 of installation area.
the article states the controller should stop charging a 12V battery at approx 14.2V, what about 6 volt batteries – same?
No of course not. A single 3-cell 6 volt rechargeable battery should have a fully charged terminal voltage of about 6.35 volts. To correctly charge a wet battery, the output voltage of the charging system needs to be slightly higher than the batteries fully charged terminal voltage, to ensure that the charging current flows in the direction from charger to battery. A constant voltage equal to between 2.35 to 2.45 volts per cell is recommended for charging storage batteries. Thus for a 12 volt, 6-cell battery this is between 14.1 and 14.7 volts, so the charge controller should stop charging the battery once this voltage level is reached, or switch to a low current float charge. For a 6 volt, 3-cell battery this voltage level is between 7.05 and 7.35 volts.
Steps to Determine if Your Solar-Charged Power Supply Has a Problem
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Are you having communication problems or seeing readings you don’t trust? Is it possible your solar-charged power supply is the cause? How can you find out for sure?
As we mentioned in the “6 Steps to Determine if Your Data Logger Needs Repairing” blog article, many data acquisition system failures are caused by problems with the power supply. These may include issues with batteries, charge regulators, or charging sources. In this article, we’ll look at seven steps to help you find out if your solar-charged power supply has a problem.
Before we get started, you will need to have these tools handy:
- Good digital multimeter (DMM)
- Small (2.5 mm) flat-bladed screwdriver
- Pair of wire strippers
Most of the steps outlined here involve direct current (dc) or voltage measurements on different parts of your power system. To measure the dc voltage, set your DMM to the 20 Vdc range with the red probe firmly in the mAVΩ socket and the black probe firmly in the COM socket. During testing, you will touch the red probe to one of the following: the terminal screw labeled 12V. or the bare end of a red wire. In contrast, you will touch the black probe to one of these: the terminal screw labeled G., or the bare end of a black wire.
#1. Test the data logger POWER IN
You can check whether the data logger is getting power from the power supply by following these steps:
- Measure the voltage on the power input terminals of the data logger. Most Campbell Scientific data loggers have a green plug that connects to a socket labeled POWER IN.
- If your data logger does not have the two-pin connector, you will need to trace the wires from the battery to the data logger and make the measurements there.
- Touch the black probe to the terminal screw labeled G or Battery
- If the voltage reads greater than 11 V, the test is successful, and your data logger is receiving enough power.
- If the voltage reads less than 11 V, there is likely an issue with your power supply. Work through the following steps to find out where it is failing.
#2. Ensure the power supply is turned on
You might be surprised how common it is for someone to turn off the power to a data logger for some reason and then forget to turn it back on later. (For more information on this subject, read the “Troubleshooting Best Practices for Data Acquisition Systems” blog article.)
- If the power switch is in the Off position, move it to the On position, and repeat step #1.
- If the power switch is already in the On position, proceed to step #3.
#3. Measure the voltage on the power supply
If you look at your power supply, do you see multiple terminals labeled 12V and G? Just pick one of each terminal type to use.
Measure the voltage between the 12 volt and ground terminals on your power supply. If you measure more than 11 V on the power regulator, but less than 11 V on the data logger, check the wires that connect them.
- If you find a loose wire, turn off the power before reconnecting it.
- If you find good electrical connections on the wires, move on to step #4.
#4. Check the voltage on the battery
At this step in the process, your measurements have been less than 11 V for both the data logger and the power supply. The next step is to test the battery voltage with the black probe on the negative (-) terminal and the red probe on the positive terminal.
- If the voltage reads greater than 11 V, the battery is OK, but the power supply needs to be returned for repair. Contact Campbell Scientific for a Return Material Authorization (RMA).
- If the voltage reads less than 11 V, disconnect the battery.
#5. Without a battery attached, check the voltage on the power supply
With the battery disconnected, you can recheck the voltage on the power supply using step #3 as a guide.
- If the voltage between 12V and G reads 13 to 14 V, the battery needs to be replaced.
Now check the voltage on the two charge terminals of the power supply. These are both labeled CHG, but it doesn’t matter which color probe you put on which terminal.
- If the voltage on the charge terminals reads more than 17 V, the power supply needs to be returned for repair. Contact Campbell Scientific for a Return Material Authorization (RMA).
#6. Measure the voltage on the solar panel
Now it’s time to disconnect the solar panel from the power supply. You can measure the panel’s voltage by touching the probes to the ends of the panel’s bare wires. Be sure to do this test during the day at a time when the solar panel is not covered or in the shade. With the red probe touching the red wire, and the black probe touching the black wire, measure the voltage.
- If the voltage on the solar panel reads less than 17 V when the panel is in full sun, the solar panel needs to be replaced.
#7. Test the current of the solar panel
For this last step, set your DMM to measure amps so that you can measure the current coming from the solar panel.
Tip: To avoid sparking, it’s good practice to temporarily cover the solar panel with a cloth or something similar.
Measure the current by following these steps:
Move the red lead on the DMM to the 10ADC socket, and set the range to 10 A.
- When the panel is in the sun, if the measurement of the current from the solar panel is close to the maximum output current, but the voltage on the 12V and G terminals from step #5 is less than 13 to 14 V, then the power supply should be returned for repair. Contact Campbell Scientific for a Return Material Authorization (RMA).
- If the measurement of the current from the solar panel isn’t realistic, either the solar panel or the wires connecting the solar panel to the power supply may be damaged.
Testing Data Loggers with Built-in Power Supplies
Some Campbell Scientific data loggers have their power supply built into a rechargeable battery base. For this type of data logger, before you can perform steps #5 and #6, you will need to disconnect the battery by separating the data logger module from the base. (For more details, see your data logger manual.)
To find a power supply problem, we start at the data logger and test each part of the system back to the charging source. After you perform these steps, contact Campbell Scientific if you find any of the conditions outlined below:
The voltage from the power supply is less than 11 V with the battery attached, but the voltage increases to 13 to 14 V when the battery is disconnected.
The battery needs to be replaced.
The battery voltage is more than 11 V, but the voltage from the power supply is less than 11 V.
The power supply needs to be repaired.
The voltage on the charge terminals is more than 17 V, but the voltage between 12V and G on the power supply is outside the range of 13 to 14 V.
The power supply needs to be repaired.
The current output from the solar panel is realistic, but the voltage between 12V and G on the power supply is outside the range of 13 to 14 V.
The power supply needs to be repaired.
When the solar panel is in the sun, the solar panel voltage is considerably less than 17 V.
The solar panel is defective or damaged.
When the solar panel is in the sun, the solar panel current is not close to its maximum output current.
The solar panel is defective or damaged.
If your solar-charged power supply has a condition that hasn’t been covered in this article, or if you have a question, post your comment below.
About the Author
Jason Ritter was a Senior Support and Implementation Engineer at Campbell Scientific, Inc. He worked with customers to help them make the best measurement possible. Jason was a longtime fan of Campbell Scientific, having been a customer for ten years before joining the company as an application engineer. He also held the positions of soil scientist, soils product manager, soils market manager, and product group manager.
Комментарии и мнения владельцев
djtire | 11/24/2015 at 12:23 PM
It is also possible that a sensor that is using the 12V or SW12 may be causing the problem. If battery is good, the charging source is good, and the charge controller is good, but the system seems to be having power issues it could be a sensor or sensor cable issue.
We recently had a client who’s datalogger would power up, appear fine for about a short period and then disconnect from the PC he was using to communicate with it. After several times of rebooting the power and trying to maintain communication without success, he call us. We went through the process described above and found everything was fine. Then we started to disconnect sensors that were using the 12V terminal, one by one. Sure enough, one of the sensor was the culprit. With the sensor disconnected everything returned to normal.
Notso | 11/24/2015 at 12:56 PM
Thanks. We discuss disconnecting powered sensors in the “6 Steps to Determine if Your Data Logger Needs Repairing” blog article. It’s a quick and easy way to determine if the problem is with the sensor or with the datalogger. I’m glad it worked for you.
Notso | 11/24/2015 at 01:29 PM
Another common power supply issue not mentioned in the article is when there is some data stored on the datalogger during daylight hours but long data gaps during the night and on cloudy days. This indicates that the solar panel provides enough current to keep the system running in sunlight but the battery can’t hold a charge and needs to be replaced. When this happens you might also see the system crash when a cell modem or radio powers on or when you try to connect with a computer.
Jessica-S | 06/13/2020 at 10:00 AM
I have solar panels on the roof of my box truck. They are connected to a battery which is connected to an invertor. I use the Victron connect 100/50 app to see my solar intake and battery power. On a normal sunny day I produce about 40w at any given time producing up to 1.5 kWh for the day. I took it in for an oil change and a fuse repair on the truck but after picking up the truck, my app is reading that I am producing 1w for the last 3 days. It is very sunny and the truck is parked in it normal spot in direct sunlight. The 12v battery reads as being at 13.7v and seems that the fridge has plenty of power to keep running. It appears I am collecting solar power based on much power my battery has and continues to power all of my things without issue for 3 days but am confused why the solar is only ready as producing 1w-10w for the day when it usually reads around 1.5 kWh. Any help would be greatly appreciated.
Notso | 06/17/2020 at 09:53 AM
Hi Jessica-S. I’m not familiar with the VictronConnect app, but the fact that your battery is still reading 13.7 volts while powering a fridge indicates that the system might be fine. However I would see what the battery voltage does when the sun isn’t shining because if it drops quickly that would indicate that during the day the fridge is running on solar power only because the battery can’t hold a charge. If the battery drops slowly at night, then my best guess is that the system is fine, but something has gone wrong with the software and it isn’t measuring correctly. In that case I recommend that you contact Victron and see if they can help. Good luck.
About PWM Solar Charge Controllers
The technology for solar photovoltaic battery charge controllers has advanced dramatically over the past five years. The most exciting new technology, PWM charging, has become very popular. Some frequently asked questions about PWM battery charging are addressed here.
What is PWM?
Pulse Width Modulation (PWM) is the most effective means to achieve constant voltage battery charging by switching the solar system controller’s power devices. When in PWM regulation, the current from the solar array tapers according to the battery’s condition and recharging needs.
Why is there so much excitement about PWM?
Charging a battery with a solar system is a unique and difficult challenge. In the old days, simple on-off regulators were used to limit battery outgassing when a solar panel produced excess energy. However, as solar systems matured it became clear how much these simple devices interfered with the charging process.
The history for on-off regulators has been early battery failures, increasing load disconnects, and growing user dissatisfaction. PWM has recently surfaced as the first significant advance in solar battery charging.
PWM solar chargers use technology similar to other modern high quality battery chargers. When a battery voltage reaches the regulation setpoint, the PWM algorithm slowly reduces the charging current to avoid heating and gassing of the battery, yet the charging continues to return the maximum amount of energy to the battery in the shortest time. The result is a higher charging efficiency, Rapid recharging, and a healthy battery at full capacity.
In addition, this new method of solar battery charging promises some very interesting and unique benefits from the PWM pulsing. These include:
- Ability to recover lost battery capacity and desulfate a battery.
- Dramatically increase the charge acceptance of the battery.
- Maintain high average battery capacities (90% to 95%) compared to on-off regulated state-of-charge levels that are typically 55% to 60%.
- Equalize drifting battery cells.
- Reduce battery heating and gassing.
- Automatically adjust for battery aging.
- Self-regulate for voltage drops and temperature effects in solar systems.
How does this technology help me?
The benefits noted above are technology driven. The more important question is how the PWM technology benefits the solar system user.
Jumping from a 1970’s technology into the new millennium offers:
- Longer battery life:
- Reducing the costs of the solar system
- Reducing battery disposal problems
- Increasing the reliability of the solar system
- Reducing load disconnects
- Opportunity to reduce battery size to lower the system cost
- Get 20% to 30% more energy from your solar panels for charging
- Stop wasting the solar energy when the battery is only 50% charged
- Opportunity to reduce the size of the solar array to save costs
Are all of these benefits tested and proven?
A great deal of testing and data supports the benefits of PWM. information is attached that describes the technology and various studies.
Morningstar will continue our ongoing test programs to refine the PWM charging technology. Over time, each of these benefits will be improved and more clearly defined with numbers and graphs.
Are all PWM chargers the same?
Buyer beware! Many solar charge controllers that simply switch FETs differently than the on-off algorithm claim to be a PWM charger. Only a few controllers are actually using a Pulse Width Modulated (PWM) constant voltage charging algorithm. The rest are switching FETs with various algorithms that are cheaper and less effective.
Morningstar was awarded a patent in 1997 for a highly effective battery charging algorithm based on true PWM switching and constant voltage charging. All Morningstar products use this patented algorithm.
Ability to recover lost battery capacity
According to the Battery Council International, 84% of all lead acid-battery failures are due to sulfation. Sulfation is even more of a problem in solar systems, since opportunity charging differs significantly from traditional battery charging. The extended periods of undercharging common to solar systems causes grid corrosion, and the battery’s positive plates become coated with sulfate crystals.
Morningstar’s PWM pulse charging can deter the formation of sulfate deposits, help overcome the resistive barrier on the surface of the grids, and punch through the corrosion at the interface. In addition to improving charge acceptance and efficiency, there is strong evidence that this particular charging can recover capacity that has been lost in a solar battery over time. Some research results are summarized here.
A 1994 paper by CSIRO, a leading battery research group in Australia (reference 1), notes that pulsed-current charging (similar to Morningstar controllers) has the ability to recover the capacity of cycled cells. The sulfate crystallization process is slowed, and the inner corrosion layer becomes thinner and is divided into islands. The electrical resistance is reduced and capacity is improved. The paper;s conclusion is that pulse charging a cycled battery can evoke a recovery in battery capacity.
Another paper, a Sandia National Labs study in 1996 (reference 2, attached), summarizes testing of a VRLA battery that had permanently lost over 20% of its capacity. Conventional constant voltage charging could not recover the lost capacity. Then the battery was charged with a Morningstar SunSaver controller, and ;much of the battery capacity has been recovered.
Finally, Morningstar has been testing for capacity recovery. An attached graph (reference 3, attached) shows how a battery that was dead recovered much of its lost capacity after extended charging with a SunLight controller.
After the test was set-up, for 30 days the solar lighting system produced virtually no lighting since the system went directly into LVD each night. The battery was very old and about to be recycled. Then, the load began to turn on longer each night as shown on the graph. For the next 3 months the battery capacity steadily increased. This test and other capacity recovery tests are ongoing at Morningstar.
Increase battery charge acceptance
Charge acceptance is a term often used to describe the efficiency of recharging the battery. Since solar batteries are constantly recharging with a limited energy source (e.g. opportunity charging with available sunlight), a high charge acceptance is critical for required battery reserve capacity and system performance.
Solar PV systems have a history of problems due to poor battery charge acceptance. For example, a study of four National Forest Service lighting systems (reference 4) using on-off shunt controllers clearly demonstrated the problems caused by low charge acceptance. The batteries remained at low charge states and went into LVD every night, but the battery typically accepted only about one-half the available solar energy the next day during charging. One system only accepted 10% of the energy available from the array between 11:00 AM and 3:00 PM!
After extensive study, it was determined that ;the problem is in control strategy, not in the battery. Further, the battery was capable of accepting that charge, but it wasn’t being charged. Later a system similar in all respects except using a constant voltage charge controller was studied. In this case, the battery is being maintained in an excellent state of charge.
A later study specific to Morningstar’s PWM constant voltage charging by Sandia (reference 2, attached) found that the SunSaver’s increased charge acceptance is due to the PWM charge algorithm. Tests showed that the SunSaver provided 2 to 8% more overcharge compared to a conventional DC constant voltage charger.
A number of tests and studies have demonstrated that Morningstar;s PWM algorithm provides superior battery charge acceptance. An attached graph (reference 5, attached) compares the recharging ability of a Morningstar SunSaver PWM controller with a leading on-off regulator. This study, done by Morningstar, is a side-by-side test with identical test conditions. The PWM controller put 20% to 30% more of the energy generated by the solar array into the battery than the on-off regulator.
Maintain high average battery capacities
A high battery state-of-charge (SOC) is important for battery health and for maintaining the reserve storage capacity so critical for solar system reliability. An FSEC Test Report (reference 6) noted that ;the life of a lead-acid battery is proportional to the average state-of-charge, and that a battery maintained above 90% SOC can provide two or three times more charge/discharge cycles than a battery allowed to reach 50% SOC before recharging.
However, as noted in the previous section, many solar controllers interfere with the recharging of the battery. The FSEC study noted at the end of the report that the most significant conclusion is that some controllers did not maintain the battery SOC at a high level, even when loads were disconnected.
In addition, a comprehensive 23 month study of SOC factors was reported by Sandia in 1994 (reference 7, page 940, attached). It was learned that the regulation setpoint has little effect on long-term SOC levels, but the reconnect voltage is strongly correlated to SOC. Five on-off regulators and two quasi constant voltage regulators were tested (Morningstar controllers were not developed when this test started). A summary of the SOC results follows:
- 3 on-off regulators with typical hysteresis averaged between 55% and 60% SOC over the 23 month period
- 2 on-off regulators with tighter hysteresis (risking global instability) averaged about 70% SOC
- The 2 constant voltage controllers with hysteresis of 0.3 and 0.1 volts averaged close to 90% SOC (note that Morningstar controllers have a hysteresis of about 0.020 volts)
Sandia concluded that the number of times a system cycles off and on during a day in regulation has a much stronger impact on battery state-of-charge than other factors within any one cycle. Morningstar’s PWM will cycle in regulation 300 times per second.
It would be expected that batteries charged with Morningstar’s PWM algorithm will maintain a very high average battery state-of-charge in a typical solar system. In addition to providing a greater reserve capacity for the system, the life of the battery will be significantly increased according to many reports and studies.
Equalize drifting battery cells
Individual battery cells may increasingly vary in charge resistance over time. An uneven acceptance of charge can lead to significant capacity deterioration in weaker cells. Equalization is a process to overcome such unbalanced cells.
The increased charge acceptance and capacity recovery capabilities of PWM pulse charging will also occur at lower charging voltages. Morningstar’s PWM pulse charging will hold the individual battery cells in better balance where equalization charges are not practical in a solar system.
testing will be done to study the potential benefits is this area.
Reduce battery heating and gassing
Clearly battery heating/gassing and charge efficiency go hand in hand. A reduction in transient gassing is a characteristic of pulse charging. PWM will complete the recharging job more quickly and more efficiently, thereby minimizing heating and gassing.
The ionic transport in the battery electrolyte is more efficient with PWM. After a charge pulse, some areas at the plates become nearly depleted of ions, whereas other areas are at a surplus. During the off-time between charge pulses, the ionic diffusion continues to equalize the concentration for the next charge pulse.
In addition, because the pulse is so short, there is less time for a gas bubble to build up. The gassing is even less likely to occur with the down pulse, since this pulse apparently helps to break up the precursor to a gas bubble which is likely a cluster of ions.
Automatically adjust for battery aging
As batteries cycle and get older, they become more resistant to recharging. This is primarily due to the sulfate crystals that make the plates less conductive and slow the electro-chemical conversion. However, age does not affect PWM constant voltage charging.
The PWM constant voltage charging will always adjust in regulation to the battery’s needs. The battery will optimize the current tapering according to its internal resistance, recharging needs, and age. The only net effect of age with PWM charging is that gassing may begin earlier.
Self-regulate for voltage drops and temperature effects
With PWM constant voltage charging, the critical finishing charge will taper per the equation I = Ae.t. This provides a self-regulating final charge that follows the general shape of this equation.
As such, external system factors such as voltage drops in the system wires will not distort the critical final charging stage. The voltage drop with tapered charging current will be small fractions of a volt. In contrast, an on-off regulator will turn on full current with the full voltage drop throughout the recharging cycle (one reason for the very poor charge efficiency common to on-off regulators).
Because Morningstar controllers are all series designs, the FET switches are mostly off during the final charging stages. This minimizes heating effects from the controller, such as when they are placed inside enclosures. In contrast, the shunt designs will reach maximum heating in the final charging stage since the shunt FETs are switching almost fully on.
In summary, the PWM constant voltage series charge controller will provide the recharging current according to what the battery needs and takes from the controller. This is in contrast to simple on-off regulators that impose an external control of the recharging process which is generally not responsive to the battery’s particular needs.
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January 7, 2022 Jason Svarc
Best mid-range MPPT solar charge controllers up to 40A
In this article, we review six of the most popular, mid-level MPPT solar charge controllers commonly used for small scale solar power systems up to 2kW. These are more affordable, lower voltage (100-150V) units, which are generally designed for 12V or 24V battery systems, although several can be used on 48V batteries. A number of these charge controllers also feature inbuilt load control terminals for basic DC lighting and other loads.
In this review, we don’t list simple PWM controllers used for DC lighting and basic systems since there are many sites already covering these entry-level PWM controllers. For high-performance MPPT solar charge controllers with higher input voltages up to 300V and current ratings from 60A to 100A, see our high-power MPPT solar charge controllers review.
What is a solar charge controller?
A solar charge controller, also known as a solar regulator, is a battery charge regulator connected between the solar array and battery. Its job is to regulate the solar output to ensure the battery is charged correctly and not overcharged. DC coupled solar charge controllers been around for decades and are used in most small scale off-grid solar power systems.
Top 6 Solar Charge Controllers
Mid-level solar controllers up to 40A
Smaller capacity MPPT solar charge controllers with a current rating from 20A to 40A are used for many different applications including off-grid cabins and homes, RV’s, boats, caravans, telecommunications and remote site backup. These mid-range MPPT solar charge controllers are available from many different manufacturers, but this review will FOCUS on the most popular and best quality charge controllers from the most reputable manufacturers which have been on the market for several years.
|1||Victron SmartSolar MPPT||35 A||150V||12V 24V 36V 48V||350 to 480|
|2||EPever TRIRON Series||40 A||150V||12V 24V||150 to 250|
|3||Morningstar ProStar MPPT||40 A||120V||12V 24V||460 to 540|
|4||EPever XTRA Series||40 A||150V||12V 24V 36V 48V||130 to 190|
|5||Renogy Rover||40 A||100V||12V 24V||150 to 190|
|6||EPever BN Series||40 A||150V||12V 24V||170 to 250|
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