Solar MPPT Charger for 24/7 IOT devices
An inexpensive charge controller and 2A 5V power supply designed to supply remote power for devices ranging from Arduino to Pi 3 class.
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This project was created on 09/19/2018 and last updated 2 months ago.
Description
Feedback from an earlier project, the Solar Pi Platter, showed me there was interest in a Smart charger/power supply for single-board computer devices operating 24/7 from solar power. This project documents my efforts to bring this charger to the maker/hobby market, including the decisions behind its features and some of the stuff I learned along the way that might be useful to other people designing their own systems.
Cost was the primary design factor which led me to a firmware-controlled approach (instead of using a dedicated IC). The availability of inexpensive 12V AGM or LiFePO4 batteries (e.g. UPS batteries) and 36-cell (12V) solar panels, as well as the battery’s operation over an extended temperature range led to their choice as the power elements.
There are a lot of chargers like this one, including some very cheap units from China, so I am taking advantage of the micro-controller to provide a good set of features and a lot of software support.
Details
I did a lot of online research when I started this project and pored over earlier efforts by Julian Ilett, Debasish Dutta, Lukas Fässler, kjoehass and Ant. I appreciate their efforts to document their work and their great designs, and sometimes failures. It’s in that spirit that I’ve created this project entry. The actual technical documentation is in my github repository. Currently it has supporting documentation and software.
The MPPT Solar Charger is a combination solar battery charger and 5V power supply. It manages charging a 12V AGM lead acid or LiFePO4 battery from common 36-cell 12V solar panels. It provides 5V power output at up to 2A for systems that include sensors or communication radios (although designed for average power consumption of 500 mA or less). Optimal charging is provided through a dynamic perturb-and-observe maximum power-point transfer converter (MPPT) and a 3-stage (BULK, ABSORPTION, FLOAT) charging algorithm. A removable temperature sensor provides temperature compensation. Operation is plugplay although additional information and configuration may be obtained through a digital interface.
- Optimized for commonly available batteries in the 7-18 AHr range and solar panels in the 10-35 Watt range (larger panels will work)
- Reverse Polarity protected solar panel input with press-to-open terminal block
- Fused battery input with press-to-open terminal block
- Maximum 2A at 5V output on USB Type A power output jack and solder header
- Automatic low-battery disconnect and auto-restart on recharged battery
- Temperature compensation sensor with internal sensor fallback
- Status LED indicating charge and power conditions, fault information
- I2C interface for detailed operation condition readout and configuration parameter access
- Configurable battery charge parameters
- Status signals for Night detection and pre-power-down alert
- Night-only operating mode (switch 5V output on only at night)
- Watchdog functionality to power-cycle connected device if it crashes
Software support for the MPPT Solar Charger includes an arduino library (which also compiles on Raspberry Pi), a daemon program designed to run on the Pi enabling other software to communicate with the charger and also to log data, a desktop application for monitoring and graphing log data. Eventually I’d like to also add a simple web-server to allow easy remote access.
I envision this device being useful for all manner of remote sensing or monitor applications, or for remote webcams, or even to power a set of garden lights or provide solar USB charging power.
Files
prototype_system.zip
Zip Archive. 54.92 kB. 09/21/2018 at 16:07
Project Logs
FW 2.0 update instructions
A quick log entry to note that I added instructions to the repo detailing how to update firmware using a Silicon Labs USB Debug Adapter.
New firmware supports LiFeP04 batteries
I’m happy to announce that I just finished testing a new release of the firmware that supports 4-cell LiFePO4 batteries. Although these batteries can’t charge in environments as cold as lead acid batteries can (min of 0°C instead of.20°C), and are more expensive they have much longer life spans and can take many more charge/discharge cycles. They’re much lighter too! The new firmware version 2.0 supports LiFePO4 batteries by detecting a jumper soldered between two previously unused test points on the top of the PCB. Adding support was a little tricky as I am almost out of flash storage on the EFM8 micro-controller. With the new LiFePO4 features below I now have something like a whopping 40-50 bytes of unused flash!
- Float/Bulk initial charge state threshold set to 13.2V
- Bulk Voltage set to 14.4V
- Power On charge voltage set to 13.6V
- Temperature Compensation disabled
- Charge temperature range between 0°C and 50°C
The github repo has been updated and I also updated the mppt_dashboard app using the current version of Xojo, signing the OS X version and extending the current range on the graph from 0. 2000 mA to 0. 2500 mA.
Future orders from my tindie store will have the new firmware. I’ll think about how I could create a simple way for people to update their existing firmware if they want. Please contact me if you are interested in this.
Coda
The Crowd Supply boards have [finally] been delivered after various hangups with their distribution partner. The board is available from tindie as well. The manufacturing partner is setup so if there is demand I can make more. I wish I could say my experience with Crowd Supply had been better. Birthing this board with them was painful. I certainly appreciate some of the people there I worked with. This project is pretty small potatoes for them and I’m sure that with limited staff they had to prioritize and I got the short end of the stick. I am a typical engineer and not great with the self-promotion and marketing. My biggest disappointment was that for the additional percentage I gave them I was hoping to have gotten better exposure. Onwards and upwards. I still think this is a great little device and I’ll continue to try to find places where it helps people. I also hope anyone who read this set of articles found something helpful in them.
Finally.
It has been a long arduous task to get here but I finally have some production boards. After slow progress with Crowd Supply, I got caught up in the trade-war between the US and China and my parts were stuck in customs. 600USD to get 2100 worth of parts out. Ouch. This is partly my responsibility though because my Contract Manufacturer told me to use FedEx to ship parts to him but the cost was so much more (hundreds more) than USPS that I went the cheaper route. He said there would have been no import levied had I used FedEx. Later we learned that using his FedEx account would be cheaper than paying in the US. These are strange times we live in. I received a total of 50 untested boards from the CM that I used to validate test manufacturing test fixture. I didn’t want to ship a test fixture to the CM that didn’t work when exposed to a larger variety of boards. But it works fine and all 50 boards were tested, programmed and calibrated.
Now the test fixture will go to China and I should receive completed board assemblies in the future. Or ship them to Crowd Supply for distribution there. Yeah!
In celebration I’m making the initial production run available to the tindie customers who have been patiently waiting. Thank you.
Firmware on github
New Feature With firmware v1.2, the watchdog functionality has been extended to allow a new capability. A new 16-bit unsigned register called WDPWROFF is added that controls the length of time power is disabled when the watchdog timer expires. It specifies time in units of seconds allowing power to be disabled for up to 65535 seconds (18 hours, 12 minutes, 15 seconds). This means that the watchdog function can also be used to switch off power for a period of time, for example to turn off the user’s system overnight. The default value of WDPWROFF is 10 seconds like the previous firmware versions and the default value is restored every time the watchdog timer expires or is disabled.
Documentation and the arduino library have been updated. Firmware Release The v1.2 firmware source has also been uploaded to github. This is the intended production release code. I used Silicon Lab’s Simplicity Studio as the IDE and compilation environment. This code runs on the EFM8SB10F8 micro-controller and currently requires 7904 bytes (almost full!) and uses 140 bytes of xdata memory and 86.1 bytes of data memory. Campaign Status The Crowd Supply campaign is almost finished. The parts are in China but unfortunately being held in customs. My Contract Manufacturer is attempting to get them released. I am exploring some options in case this becomes a long-term problem.
Campaign launched
It has taken far longer than I hoped but the crowd funding campaign has finally launched at Crowd Supply. I have parts for 250 boards in my possession and will be sending them to my CM in China this week. This was a worry because of ongoing parts shortages. The plan is to build an initial run of 50 boards and send them to me for testing on the manufacturing test fixture to work out any remaining issues with it. Then the fixture will go to the CM for use on the remainder of the boards. After the campaign ends I will write-up my experiences with this crowd funding effort.
Slow progress. but a new name
Introducing makerPower MPPT Solar Charger Engaging with Crowd Supply has been interesting. They see this device from a fresh perspective and that has resulted in some changes. One is the name. To me Solar MPPT Charger (or MPPT Solar Charger as I changed to over time) made a lot of sense since it describes what the device does fairly succinctly. Of course from the perspective of a product to be searched for and found by prospective buyers, its generic nature it is almost useless. They suggested a picking a new name. They would brainstorm and I would brainstorm. Lots of ideas revolved around words like Pi and Solar and Sun were proposed. Although this device is very well paired with Raspberry Pi SBCs I don’t want to limit its appeal to just those devices so I proposed makerPower as either a stand-alone name or in conjunction with MPPT Solar Charger. Slowly I have been updating various references.
- Board only (along with a 6-pin header and spare fuse).
- Board plus 4-wire female-female cable for 5VI2C connection and 2-wire battery cable with spade connectors.
- Board plus cables 9 Ah battery 35W solar panel.
I guess I already knew that making a system easy to put together will make it easier to buy but it is a pain to source all the other parts. I have huge numbers of tabs open to Alibaba, AliExpress and Global Sources product pages and feel almost paralyzed by the choices and possible risks. Boulder CO USA feels very far away from these choices.
Test Fixture
The test fixtures are ready to go. It tests, programs and calibrates a charger in about 8 seconds per board. The printer prints out a failure record that also identifies the parts of the circuit being tested to help a technician fix failing boards. The idea is that the print-out will accompany any board that fails to the bone pile and eventually repair bench.
Coding was reasonably straight-forward and I 3D printed some components to make testing efficient (and to hold a photo-transistor for the charger LED verification). The big issue I had was the resistance of solder flux. These boards were hand-built by yours truly. I use a little flux to help reflow the SMT parts and this caused a lot of problems. I clean my boards using pure isopropyl alcohol and/or a quick soapy wash using a soft toothbrush, rinse and dry. However I still had problems making the two test fixture accurately measure voltages from the device-under-test (DUT).
The test fixture measures voltages using the Teensy 3.5’s ADC and an external precision 1.25 V reference. Higher voltages from the DUT are scaled using a voltage divider made up of two precision resistors. These resistors had to be fairly high resistance to not impact the circuitry under test.
Unfortunately flux under the resistors and between the soldered headers on the teensy and testfixture added measurable resistance and threw the resistance ratio off. The boards looked clean to me but still didn’t measure correctly. It took a while before I found every source of error and managed to clean it up.
The test fixture also sports a simple command interface to enable manual control of the test fixture or running of individual tests. The command interface is not used during normal operation (no computer is connected to the test fixture).
Pre-production units!
The last couple of weeks have been productive. I executed the final firmware validation testing and released v1.0, and completed the user manual and uploaded that to the github repository. The manufacturing programming/test fixture is also up and running. This project is ready to go! Edit: I’ve also now listed them on tindie. Edit 2: The day after I put them on tindie I heard from Crowdsupply that they were interested in running this device as a crowd-funding campaign. I had originally submitted it to them in the fall of 2018. One of their requirements is that the device not be for sale anywhere else until the campaign ends. So I have temporarily taken it down from tindie and here. If you think you might be a good beta customer then let me know. it may be possible for you to get a board if you will commit to sharing information about its use.
Quickie: working on manufacturing fixture
- Arduino library for the test fixture hardware itself
- Silicon Labs C2 programmer for the Teensy
- Hex File utilities
- Simple display support for the cap touch control LCD screen
- A custom test firmware to first program on the Charger’s SI EFM8 micro-controller to allow detailed testing and calibration
And finally I have gotten them all stitched together along with a test sequencer and am writing test code. It’s tedious because for every test I have to figure out what’s right and what the limits for valid measurements may be. But I see the light at the end of the tunnel now.
Some winter testing data
Two systems have been braving the [not so bad] Colorado winters for a couple of months now with good success while my progress on the test fixture has been very slow due to other project commitments. The system above the house with the 25 watt panel with no obstructions has remained up pretty much non-stop with only a couple of low-battery shut-downs. I even try to run the Christmas lights on it most nights for an hour or two. The system near the house, sitting on the ground in the trees, with a 40 watt panel and oldish battery, has gone down with a low-battery four times since Christmas and rebooted, if only for part of a day the next day in all cases. Both systems require about 2.6-2.9 AH per day and seem to be able to remain operational even in mostly overcast days when panel production is pretty low. Snow on the panels is the worst and results in almost no solar production at all. The graph below shows a typical overcast week with low production that resulted in a low-battery shutdown. The X-axis shows days. As you can see the charge cycle was often not able to complete the Bulk charging phase (terminated with the battery reaches the higher threshold value). Zooming in on a typical low-production day shows the system barely holding its own during the day (X-axis in units of hours). However a sunny day can produce a lot of power as shown below where the system (40 watt panel) started off shut-down and was able to fully charge the battery in about four hours. This graph shows the system limiting current taken from the panel to 2A. The step in the battery and threshold voltage at about hour 1056 is the transition from Absorption charge to Float charge when the battery was fully charged. The MPPT algorithm holds the panel voltage lower when it can’t supply enough current (for example the system in Bulk charge phase but there isn’t much light) and it lets it float higher when limiting solar input (for example when in Absorption charge phase and the buck is limiting). This makes sense and looking over days of output shows the algorithm behaving. Now to finish the test fixture and start building this damn thing.
How to Make a Solar Powered Raspberry Pi
Did you know that you can use a solar panel to power a Raspberry Pi? Think of the possibilities. A solar powered weather station. An autonomous vehicle that never needs to be charged. A camera that can record images in remote places for months without human intervention.
In this tutorial, we will build a project that uses a solar panel to power a Raspberry Pi.
In How to Power Your Raspberry Pi With a Battery, we explained that the best Raspberry Pi to use for low power projects like this one is the Raspberry Pi Zero, due to it’s very low power consumption compared to the Raspberry Pi 4. We also saw how to how to calculate the expected battery life and discussed how to determine the correct battery size for a Raspberry Pi Zero. I recommend taking a look at that article before building this project.
How to Choose a Solar Panel
To power a Raspberry Pi, the solar panel needs to output at least 5V. The wattage and current ratings of the solar panel will determine how fast the battery charges. This means a 2W solar panel can charge a battery twice as fast as a 1W solar panel.
The Battery Charge Controller
The voltage and current output by the solar panel will vary greatly depending on the amount of light hitting it. These voltage and current fluctuations could damage the Raspberry Pi.
A battery charge controller will prevent this from happening by supplying a constant voltage and current to the Raspberry Pi, while at the same time providing the correct voltage and current to safely charge the battery.
Now that you are familiar with what’s required to power a Raspberry Pi with a solar panel, let’s look at three possible ways to use a solar panel to power the Raspberry Pi.
TP4056 Charge Controller
This setup uses a TP4056 charge controller to power the Raspberry Pi and charge a 3.7V lithium battery. The TP4056 charge controller’s input pins are connected to the output of the solar panel. The OUT and OUT- pins are connected to the 5V and ground pins on the Raspberry Pi, and the B and B- pins are connected to the battery:
This setup has one problem though. The TP4056 charger controller only outputs 3.7V. To power the Raspberry Pi effectively, we need a 5V power supply.
TP4056 and a DC/DC Converter
The solution to this is to use a DC/DC converter to increase the 3.7V to 5V. All we need to do is insert a 3.7V to 5V DC/DC converter between the output of the charge controller and the Raspberry Pi’s power pins like this:
With this setup, you can be sure your Raspberry Pi will be operating at the correct voltage.
Adafruit’s PowerBoost Module
This setup uses the PowerBoost 1000 charge controller from Adafruit. This module works like a battery charge controller and a DC/DC converter in one. With this module there is there is no need for a separate charge controller and DC/DC converter – they are all contained in one module.
This circuit will provide a constant 5V to the Raspberry Pi and supply the battery with the correct current and voltage for a safe charge:
Hope this article has inspired you to take your projects off the grid with a solar powered Raspberry Pi! Be sure to leave a comment below if you have questions about anything!
Solar Info: The Down Low on Everything Up High
Rain or shine we get a huge number of calls about solar power each day. We’ll attempt to answer the questions asked most often so we can save you a phone call.
Before we get started, you should know that solar power is not the cure-all for replacing spent energy. For example, some people are trying to recharge batteries for a trolling motor, boat, RV, house, electric scooter, backwoods cabin, etc., and they want it done in very short time, usually in just a few days. Assume you take a discharged 100-amp hour battery and charge it with a 30-watt solar panel under ideal summertime light conditions. After a full week, the battery will be just about fully charged. Using this example, you can see that it will take at least 100 watts of solar power to recharge a 100-amp hour battery in a few days.
Also, keep in mind that it takes direct sunshine on the surface of the panel to produce the maximum-rated power of a solar panel. Conditions such as an overcast sky, shadows, improper mounting angle, equatorial direction or short winter days will reduce the actual solar panel output to below the rated values.
VOLTAGE RATING
Most solar chargers are designed for 12 VDC, but we do have limited availability on a 24-volt panel. Typically, when 24 volts or greater is needed, solar panels may be wired in series, or we can special order solar panels that are made to deliver more DC Volts such as 24V, 36V, 48V etc.
CONTROLLERS
Anytime you use a panel that is over 5 watts rated output, we recommend using a solar charge controller. Actually, a charge controller is a good idea in a majority of applications, as it can provide several benefits such as preventing overcharge, improving charge quality, and preventing battery discharge in low or no-light conditions. Some solar panels are made with blocking diodes pre-installed that prevent battery discharge during low or no-light conditions. In most cases where a 6-watt or larger solar panel is installed, the use of a charger controller is highly recommended. In a nutshell, a solar charge controller acts like an on and off switch, allowing power to pass when the battery needs it and cutting it off when the battery is fully charged. Something to be aware of when selecting a controller is that they are typically rated in amps, while photovoltaic panels are typically rated in watts. That means a solar charge controller such as the Morning Star SS6L, 6-amp controller will work with nearly every panel we sell, right up to about 70 watts.
POWER RATING WATTS AND AMPS
Solar panel manufacturers rate solar output in watts. As a rule of thumb, a rating of 15 watts delivers about 3,600 coulombs (1 AH) per hour of direct sunlight. As an example, the Pulse Tech SP-7 panel can output.33AH per hour of direct sunlight. This is a very popular panel for maintaining single and dual batteries for stand-by and storage applications.
HOW DO I FIGURE SOLAR PANEL SIZE
The first thing to remember about solar power is that it is all a matter of numbers. The power you require vs. the power the panel can put out. Before you can even get started when purchasing a panel, you need to know how many amp hours or watts you’ll need to produce in a set period of time. This figure could be measured in hours or days. Since there are 24 hours in a day, we suggest you use that as a baseline. First, determine your total electrical consumption in that time period. Then figure the amount of direct sunlight the solar panel will receive in that time period and come up with a total amount of watt hours needed. You should always err on the side of caution and over-estimate your power needs. Typically we see an average of 4 hours of usable sunlight in the winter, and 6 hours of usable sunlight in summer. Granted, there are exceptions to these averages, but erring on the side of caution creates a more reliable solar system. These averages also help compensate for variables like shade, clouds, panel angle, etc. Once you have a good handle on your power requirements, I suggest you go to our Solar Calculator.
OUTPUT CONDITIONS
Solar panel ratings are calculated in bright direct sunlight. Conditions such as indirect sunlight, overcast and partial shade conditions will decrease the output. We always recommend over-sizing the size of your solar array, as these conditions occur often. Also, remember that the length of daylight in summer vs. winter can make an impact.
One of the biggest errors commonly seen is when a solar array is designed in summer using summer daylight hours, but then it’s also used in the winter. The first complaint is often related to the batteries no longer holding up under load. This is a gradual process that begins when you lose daylight hours, and you start taking the battery pack beyond a 50% depth of discharge. When this happens, the batteries start to sulfate at a much quicker rate, and begin to no longer hold under load. As you can imagine, this is an expensive mistake! The solution generally involves more panels and new batteries with a higher Amp/Hr reserve. Therefore, we advise our customers to be conservative when accounting for daylight hours. Also, if you plan to utilize a solar array year-round, then you need to factor in your daily solar input for winter.
OPERATING A DEVICE DIRECTLY FROM A SOLAR PANEL BATTERY CHARGER
We carry several foldable/portable solar panels for backpacking that come with a female cigarette lighter adapter. This adapter allows you to power 12v accessories that commonly use a 12v DC plug. In order to connect directly to a panel, the device cannot be sensitive to voltage variation—otherwise they may shut down. To solve this problem, it’s best to use a small battery as a storage vessel for energy that will provide constant source of stable, reliable power. To do this, we recommend using a solar charge controller, Y-connector with a battery inline on one leg, and the female cigarette socket on the other leg.
ARE SOLAR PANELS WEATHER PROOF
Nearly all solar panels are designed for outdoor installation, as this is where they will receive the best, most direct exposure to sunlight. Remember that anything less than that will cause the panel to produce less than its full-rated power.
DO I HAVE TO MAINTAIN SOLAR PANELS
A periodic inspection to remove dirt, debris and check electrical connections is all that is needed. Keeping the panel clear of snow and debris will allow for better results.
HOW LONG DO SOLAR PANELS LAST
Performance from a solar panel will vary, but in most cases guaranteed power output life expectancy is between 3 and 25 years. This guaranteed life expectancy rating is usually 80% of the published rating of the solar panel. Of course, this will vary from manufacturer to manufacturer, and as always, you typically get what you pay for. Watch out for those cheap panels made in Paki-china-nam-istan.
USE OF A POWER INVERTER
Many folks use a DC to AC power inverter to convert 12 VDC to 110 VAC. Since they change power from one form to another, inverters are power-gobbling monsters and should be avoided when possible. If you have a choice of a 12-volt, DC-powered device or 110-volt AC device, go with the 12-volt DC device. There are DC devices on the market that either step down or step up DC power, and these also use significantly more power.
DC to AC via an Inverter Formula Examples
This “rule of thumb” is intended as a general guide for estimating the DC amps required operating a DC to AC power inverter. Since the calculations yield approximate values, an appropriate safety factor should be considered when designing and specifying system components, such as wire, size and length. This basically means “oversize your system.”
12-Volt DC Systems
Formula: 12-volt inverters require approximately ten 10 amps DC input for each 100 watts output power used to operate an AC load.
Example: How many DC amps will a 12-volt inverter require to operate three 500-watt quartz lights, or a 1500-watt electric heater?
- 1) Total watts = 1500
- 2) 1500 watts/100 (from formula) = 15
- 3) 15 X 10 amps (from formula) = 150 amps.
This is the DC current the inverter will use to operate the 1500-watt load. Note: If these 150 amps are drawn from the battery for one hour, 150 amp hours of battery power will be used.
To support 150 amp hours of battery power, 300 amps of battery capacity should be used for maximum battery life and performance.
24-Volt DC Systems
Formula: 24-volt inverters require approximately 5 amps DC input for each 100 watts output power used to operate an AC load.
Example: How many DC amps will a 24-volt inverter require to operate three 500-watt quartz lights, or a 1500-watt electric heater?
- 1) Total watts = 1500
- 2) 1500 watts/100 (from formula) = 15
- 3) 15 X 5 amps (from formula) = 75 amps.
This is the DC current the inverter will use to operate the 1500-watt load. Note: If these 75 amps are drawn from the battery for one hour, 75 amp hours of battery power will be used.
To support 75 amp hours of battery power, 150 amps of battery capacity should be used for maximum battery life and performance.
Ready to harness the power of the sun? Shop for a solar charger and accessories.
Whether you need a solar battery charger for boat, solar trickle charger for car battery, or a solar ac charger, we have the right chargers for any application.
Will a 5W Solar Panel Charge a 12V Battery?
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.
Yes, a 5W solar panel can charge a 12V battery.
In fact, I recently did it myself:
Then, after doing it, I saw that Google isn’t exactly giving the best answer to this question:
And I decided to write this article to set the record straight.
So, once again, for the people in the back:
Yes, you can charge a 12V battery with a 5W solar panel. You just need to make sure it’s a 12V solar panel. Anything less, such as a 6V or 9V solar panel, won’t work.
Materials Tools
Materials
- Newpowa 5W 12V solar panel
- 12V PWM solar charge controller
- 12V battery (I used a 12V 33Ah battery)
- Wires, connectors, and fuses (I used the NOCO GC018)
Tools
- Wire cutter
- Wire stripper
- Screwdriver
Step 1: Connect the 12V Battery to the Solar Charge Controller
Connecting a battery to a solar charge controller requires wires, wire connectors, and an inline fuse.
You can use your own wire and connectors, or you can buy some to make the process a little easier. I ended up buying something called the NOCO GC018. It’s a 12V plug adapter that comes with an inline fuse and ring terminals — the right kind for my 12V battery.
To start, I cut the 12V plug off the NOCO GC018 with my wire cutter.
Then I just pulled the wires apart a little bit and stripped the ends. (I’ll be sticking the stripped ends in the charge controller’s terminals.)
Now my wires are ready. I can connect them to the battery terminals using the ring terminals. And I can connect them to the charge controller terminals using a screwdriver.
I first connected the positive and negative wires to their respective battery terminals. Like so:
Then I used a screwdriver (a precision screwdriver, in my case) to connect the stripped wire ends to the charge controller’s battery terminals. My controller’s terminals have a battery icon on them, as well as a plus and minus, to help me know where each wire goes.
When all the wires were connected, my charge controller turned on to indicate that it was properly connected to the 12V battery.
Consult your charge controller’s manual for instructions on how to program it for your battery type. Mine defaults to sealed lead acid batteries, which is the battery type I was using.
Step 2: Connect the 5W Solar Panel to the Solar Charge Controller
My 5W solar panel came with wires that had stripped ends. This made it simple to connect it to my charge controller.
I simply connected the positive and negative solar wires to their respective terminals on my charge controller. Once again, the terminals have a solar panel icon on them and are marked for positive and negative which makes it easy.
Now your solar panel is connected…
Here’s how mine turned out:
That’s really all there is to it.
However, because my solar panel was inside, at this point it wasn’t getting enough sunlight to actually charge the battery.
Step 3: Test Your 5W Solar 12V Battery Charger
You’ve effectively just built a 5W solar 12V battery charger. Not bad!
To test mine, I took everything outside (making sure no wires got disconnected in the process) and put the solar panel in direct sunlight.
I then cycled through the system specs on my charge controller until I got to the PV current display.
It indicated that my 5W solar panel was charging my 12V battery at a rate of 0.2 amps:
There you go — proof that a 5W solar panel can charge a 12V battery.
I can now just leave my charging setup outside in direct sunlight. The panel will continue to charge the battery as I go about my day.
The charge controller has overcharge protection, meaning it will stop the charging once the battery is full.
W Solar 12V Battery Charger Wiring Diagram
Here’s the circuit diagram for using a 5W solar panel to charge a 12V battery:
And here’s what I call the “real-world wiring diagram”, which shows what it looks like in real life:
Notes about this wiring diagram:
- Safety best practices are to place a fuse between the charge controller and both battery and solar panel. (However, for this project, because my solar panel is so small, I left out the fuse between the solar panel and charge controller.)
- For most charge controllers, you connect the battery first and then the solar panel. Consult your controller’s manual for the manufacturer’s recommended connection order.
- Make sure to get a 12V 5W solar panel. If it is a lower voltage 5W panel (like 6V or 9V) it won’t work with a 12V charge controller.
- Make sure your charge controller is compatible with your battery’s chemistry. For example, some charge controllers only work with lead acid batteries. Others work with lead acid and lithium batteries.
- I recommend a PWM charge controller for this project because they’re cheap, and because the PV voltage likely won’t get high enough for an MPPT charge controller. For an MPPT controller to work, the PV voltage usually has to be 4 or 5 volts above the battery voltage.
Tip: This circuit diagram would work for many other solar panel sizes (e.g. 10W, 20W, 50W, 80W, 100W) as long as it’s a 12V solar panel and you use the appropriate wire gauge and fuse size for the current.
How Long Does It Take to Charge a 12V Battery with a 5W Solar Panel?
According to our solar panel charge time calculator, it takes around 107.3 peak sun hours for a 5W solar panel to fully charge a 50Ah 12V lead acid battery using a PWM charge controller.
And here are the estimated charge times for 5 other common solar panel sizes:
- 10W solar panel: 54.1 peak sun hours
- 20W solar panel: 27.6 peak sun hours
- 50W solar panel: 11.6 peak sun hours
- 80W solar panel: 7.6 peak sun hours
- 100W solar panel: 6.3 peak sun hours
Of course, these estimated charge times vary depending on factors such as battery capacity and battery type.
What Size Solar Panel Do You Need to Charge a 12V Battery?
You can charge a 12V battery with many different solar panel sizes.
Knowing this, the question then becomes:
“How fast do I want to solar charge my 12V battery?”
Based on the above charge times, we can draw some conclusions:
5W and 10W solar panels are good for slow, trickle charging 12V batteries. They’re a good size solar panel for maintaining a 12V battery’s charge, and will slowly charge it up over the course of weeks — maybe even months depending on the weather and size of the battery.
20W and 50W solar panels are good for fast charging small 12V batteries. For example, a 20W solar panel can charge a 20Ah 12V battery in around 17 hours of direct sunlight. A 50W panel can do it in around 8 hours.
80W and 100W solar panels are good for fast charging large 12V and car batteries. If it’s a 50Ah battery, they can fully charge it in around 12 hours or less of direct sunlight.
For more help on finding the right size solar panel for your solar charging setup, check out my post on what size solar panel will charge a 12V battery quickly.
Tip: You can reduce these charge times further by upgrading from a PWM to an MPPT charge controller. MPPT charge controllers are much more efficient, but they’re also much more expensive.
DIY Solar Charging Projects You Can Build Now
Like I said, you just built a solar 12V battery charger.
You connected a solar panel to a battery via a charge controller. And the solar panel is now charging that battery.
Using what you just learned, you can build even more solar chargers.
Here are some ideas for your next project:
DIY Solar Car Battery Charger
Car batteries are also 12V batteries. So, using the same solar panel and charge controller, I was able to make a solar car battery charger.
Solar Ebike Battery Charger
You’re also just a few parts away from solar charging an electric bike. Don’t be fooled by how complex it looks — you just need a bigger solar panel and a small inverter.