Homemade solar panel charger. Conclusion

Electronics Projects

Gadgets like phones, iPods, smartwatches, etc. have become an important part of our life. They all face one problem, and that is the need to charge after regular usage. It becomes a major concern when you are in a place where electricity is not available. One of the solutions to these kinds of problems is to depend on the renewal energy sources. There are different types of renewable energy sources like wind, tidal, solar, etc. In today’s project, we are going to use solar energy to charge our mobiles. To convert solar energy into electricity, we will need solar panels. We will see how a solar panel works and design a solar mobile phone charger circuit to charge our mobile phone as well as to protect the battery from overcharging.

Components Required

  • Solar panel (6V, 80mA) – 2
  • Micro USB cable.1
  • LM317 Voltage Regulator. 1
  • BC547 NPN Transistor.1
  • Small Breadboard
  • Potentiometer (10K)
  • 1N5819 Diodes. 2
  • Resistors 100 Ohms and 150 Ohms. 2
  • 5.6V 1N4734A Zener Diode. 1

Solar cells are usually made out of silicon wafers. The silicon atoms in the solar cells form 4 strong bonds with its neighboring silicon atoms. By having these strong bonds, the electrons will stay in one place, and no current flow is seen. These solar cells usually have two layers of semiconductors. The top layer of the solar cell is doped with phosphorous to convert it into an n-type semiconductor, and the lower layer is doped with boron to convert it into a p-type semiconductor. The N-type layer has excess electrons, and the p-type layer has extra holes. When light particles strike the solar cell, the photons present in the light will have enough energy to knock the electrons from their bond, leading it to move towards the N-side, and the hole (formed by the absence of an electron) will move towards the P-side. The movable electrons are then collected at the thin metal material present at the top of the solar cell. If an external circuit is connected to these metal materials, the electrons will flow into the external circuit and then reach the conductive aluminum sheet present at the back of the solar cell. The electron then settles in the hole which is present in the P-type layer of the solar cell. Each solar cell has a voltage of 0.5V to 0.6V. The solar cells are connected in series to get the required voltage. Usually, 12 solar cells connected in series are sufficient to charge a mobile phone. There are three types of solar panels. They are Monocrystalline, polycrystalline, and thin-film. In our project, we are going to use two 6V 80mA solar panels. We are connecting the two solar panels in series to get a voltage of 12V and 80mA. The below pic shows the single mini solar panel which can generate an output voltage of 6V with a max current of 80mA.

The below pic shows the series connection of two mini solar panels, which can generate an output of 12V with a max current of 80mA. You can increase the output current by connecting extra solar panels in parallel and each parallel connection must be having two solar panels connected in series to supply 12V. So to get an 800mA output current, you will be needing 20 solar panels.

LM317 Voltage regulator

LM317 is a variable voltage regulator. By using LM317, we can vary the voltage up to 37V with a max current of 1.5A. To get the variable output voltage, the below circuit is used.

The output voltage can be calculated by using the below formula:

Now, by varying the value of the resistor R2, you can vary the output voltage.

Note: Even though the output voltage is dependent on the external resistors connected to the LM317, the input voltage should be greater (minimum of 3V) than the desired output voltage.

USB cable

I have used an old USB to micro USB cable to charge the mobile phone with our solar mobile phone charger circuit. I have removed the USB, and now the cable contains a micro USB connector, which is used to connect to the mobile phone and 4 wires on the other end of the cable. The micro USB cable consists of 4 pins. Two for transferring power and another two for transferring data. The pinout of the micro USB cable needed for transferring power is shown below.

After knowing the pinout, it’s time to know the wires connected to these pins on the other end of the cable. To determine which wire is connected to which pin, I have used a multimeter in continuity mode. In this way, I found the wires needed to connect to the output of our circuit.

How to Build a Solar Charging Station Anywhere

One of the most amazing innovations in the last five years has not been a new invention as the perfection of existing technology. Solar panels, which were once the territory of only the very rich and very environmentally dedicated, have gotten smaller, more efficient, and more affordable, and you don’t even need to mount them on your roof. Many people still think that solar is in the realm of “Go Big or Go Home,” but we’re here to tell you that times have changed.

Building a Solar Charging Station

While you can start your adventures into solar power generation with a full rooftop-mounted and grid-connected installation, you can actually learn about solar and build yourself a disaster-ready power generation and charging station for less than 500 and a little elbow grease. With this simple and easy to connect contraption, you’ll be able to generate enough power to slowly charge an electric vehicle or keep several mobile devices powered for as long as the equipment lasts.

Building a solar charging station is surprisingly simple because the components are now very efficient. All you need is power generation, power conversion, power storage, and the cables in between. All the parts can be bought on Amazon from various manufacturers, so compare and amperage until you find the right combination for your budget and power generation needs.

  • Portable Solar Panels
  • You don’t need a professional to affix some weather-resistant solar panels to a sunny spot and draw power. You don’t even need a stable location. Portable solar panels can be mounted, unmounted, and moved at any time, wherever you happen to need solar power.
  • Solar Cables – One Red, One Black
  • These will connect the solar panels (which have matching leads) to the solar controller and inverter, which will regulate the energy from the solar panels and make them useful.
  • Solar Controller
  • The solar controller device is part of what makes solar power so much more accessible than it used to be. It’s essentially a specialized charge controller with a useful info display screen.
  • Inverter
  • The inverter is what turns the DC solar energy into AC device and appliance energy. They usually have at least one power socket and often have USB ports as well. Some inverters come with their own batteries.
  • Batteries
  • A deep supply of battery storage ensures that you don’t waste solar power and have plenty to last you through the night and on rainy days.
  • Battery Cables – One Red, One Black Per Battery
  • These will connect the batteries and the solar controller, allowing the controller to balance voltage between, serve power out of them, and prevent them from over-draining.

You can build your solar charging station on anything you want. For an electric car charge stop, you can put the panels on top of a carport and stow the rest of the equipment safely in a cabinet within. You can add them to a camp cabin or tent to power basic equipment like a camp stove or radio. With flexible panels, you can even stick them securely but temporarily to the top of your car, truck, or RV with 3-5lbs Command strips for convenient mobile device charging on road trips. The Command strips don’t damage the paint when removed, so you can experiment freely without having to make even semi-permanent alterations. Choose what you’ll mount the solar panels on and how you’ll protect the electrical equipment before getting started.

Step 1: Mount the Solar Panels

For a semi-permanent structural mount like on a shed or carport, use a metal frame and bolts to attach the solar panels to the roof of your structure. Make sure to use the right brackets and screws based on the type of roof you’re working with. Tents should rely on either foldable solar panels or those with holes so they can be tied to the top or sides. A car either permanently mounts them with a frame or temporarily mounts them with safe sticky strips.

Step 2: Emplace the Batteries

The batteries need to be in a safe, dry, moderately temperature-controlled, and stable position. Anywhere indoors is usually fine, but they need to be carefully secured in a vehicle and probably carried in a sealed box for camping.

Step 3: Place the Solar Controller

You’ll want the solar controller somewhere safe but easy to read, as it will tell you how much energy is being generated, how much is being drained, and approximately how full your collection of batteries is. Make sure it’s accessible before wiring and arrange your connections around where the solar controller needs to be.

Step 4: Connect Everything

Connect your solar panels and the solar controller with the solar power cables using parallel or serial wiring based on your amperage and voltage needs, then do the same for the batteries. If you need a converter from the batteries to the power ports you plan to use, connect this to the solar controller and its own cables.

Method 2: Make a Solar Battery USB Charger

Solar battery USB chargers are compatible with iPhones, tablets, mobile phones, lithium ion batteries and GPS devices. The difference between this charger and the one earlier is you wil be using a battery.

Required Materials

  • A portable solar panel
  • Battery holder (AAA or AA)
  • 1N914 blocking diode
  • 1/8 inch wire
  • 1/4 in. heat shrink tubing
  • Case for charger storage
  • USB charging circuit
  • Super glue
  • Wire stripper
  • Soldering iron


  • Solder the negative side (black) of the diode onto to the solar panel’s red wiring. It should be facing away from the solar panel.
  • Put heat shrink tubing on.
  • Solder some fresh wiring onto the diode’s positive side. Not a lot, just a few inches is fine.
  • Twist the battery holder’s negative wire (black) onto the solar panel’s black wiring. You should end up with parallel wires. The battery holder wiring and the panel should also have a connection newly opened. Repeat these steps for the red wire.
  • Get a USB charging circuit and find the and – signs. Get the solar battery / panel wiring you just made and solder them onto the circuit’s and – points. Do this slowly.
  • Glue everything inside a case. Sturdy tape will also do.
  • You’re done. All that’s left is to test the charger. Get some charged batteries, set them in the charger case and plug in your smartphone. If the charger isn’t working, there might be a problem with the soldering points. If it is charging, get some dead batteries and watch the charger restore them.

Tip: install a second solar panel and place a diode between the two. This will allow you to charge larger, more powerful devices and much faster too. By hooking up the black and red cables between the battery case and the panel, you’ll get a nice charging light.

Method 3: Make a Lithium Solar Battery Charger

As you might have guessed, this is for recharging lithium ion batteries. Most mobile phones today use lithium battery, a testament to its quality and dependability.

Required Materials

  • Super glue
  • Wire stripper
  • Soldering iron
  • Storage case for the charger
  • Battery holder (AAA or AA)
  • 1N914 blocking diode
  • Portable solar panel


  • Just like the previous method, start by soldering the diode’s negative side (black) onto the solar panel’s red wire (positive).
  • Apply the heat shrink on the battery holder wires.
  • Solder the battery’s negative wire on the solar panel black wire. For the red wire, Solder it onto the diode.
  • Put the system in a case or small tin box. Glue or tape everything.
  • Test the charger.

Pure Solar Battery Charger vs. Battery Solar Charger

Direct or pure solar USB chargers are very light and easy to make. Just strip a USB cable, stick to a solar panel and it’s good to go. The solar panel does the work of converting the sun’s energy.

The drawback is direct USB solar chargers do not generate a lot of power. They are also insufficient for devices that need a lot of amp power. Lastly, direct solar chargers depend entirely on the sun. If it’s cloudy or the sun’s intensity wanes off, so does the energy flow.

Battery based USB solar changers are not as portable, but they’re more practical. You can charge the panel during the day and at night plug in your phone.

Frequently Asked Questions

How Long Does it Take for a Solar Charger to Charge a Phone?

A few hours at least. Battery based USB chargers are faster, but even then expect to wait hours to get a full charge. it also depends on how much you used up your phone. The weather condition also plays a factor.

An iPhone comes with 3.7 volt battery (100 mA). With a 6.5 watt solar array (433 mA/hour) it will take 3 1/2 hours to charge the iPhone (0 battery to 100%). This assumes that the sun is at its peak for the entire 3 1/2 hours, however.

You can make things easier by not waiting for your phone to drop to 0% before charging. It also helps if you keep your solar charger charged up during the day so you can power up your phone at night. powerful solar chargers are becoming available with shorter charge times though. You can also try these tips to make phone charging faster.

How Can I Charge My Solar Battery without the Sun?

Artificial light sources like LED will charge the battery. However it is going to be a lot slower and isn’t practical. You are better off with the sun.

Do Solar Chargers Need Direct Sunlight?

Direct sunlight is not needed for solar chargers to work, but you will get the best results if the charger is directly exposed to the sun. In some cases it may not be possible to place the charger directly under sunlight, but as much as possible try to.

Will Solar Charge on Cloudy Days?

The charger will still charge, but it will be at a lower level and take longer. That’s why it is best to charge during daytime so you get the best results and faster too.

Why Isn’t My Solar Charger Working?

The most common reasons are:

  • Check the wire soldering for damage.
  • The solar panels are dirty.
  • The phone is damaged.
  • There is no sun.

Do Solar Phone Chargers Really Work?

Assuming you followed the instructions above, yes, they do work. As pointed out, an iPhone is better suited for a battery based solar charger than the direct type. but for Android and other types of phones, any of the methods above will do.

What Solar Panels Do I Choose?

Any type of portable solar panel will do. Just make sure it has the power needed to charge your phone (and whatever other device you want to charge). Even the cheap ones will do as long as they’re not damaged.

Soldering 101

After waiting for all the parts to show up at my door (and for Malcolm to get back from his honeymoon), we finally sat down last week to do this together. Here’s what we started with (taxes and shipping included, and we also had to sacrifice a Micro USB cable that was kicking around):

With all the parts gathered, it was time to assemble the MintyBoost. This little green circuit board, first designed way back in 2006, is meant to take in power from batteries or solar panels and boost power to the 5V that the iPhone is made to take. When it arrived in the mail, it was just a bunch of loose wires (I learned those were resistors and diodes), a female USB connector, and some padding. So, step one was to solder the resistors to the board.

I always say that soldering is a three-hand job, Malcolm first told me, as he produced a weird little holding device. And this, is called a ‘third hand.’

In front of us was a little stand with clips that I could secure my MintyBoost to as I worked on it. Malcolm showed me how to bend the resistor legs down and thread them through the board. Then, carefully, I’d touch the soldering iron to the filaments and, voilà, sleek tin would flow onto the little pads on the board.

It got easier as I worked on it—and I quickly learned what happens when you mis-solder something (hint: you need to remove it). A spool of copper strips was produced, and through a combination of pressing heat to one side, the solder would jump to the copper.

The MintyBoost is alive

Once we’d finished assembling the MintyBoost—following essentially the same soldering steps for the four resistors, one diode, and two capacitors—it was time to wire it up to the LiPoly board.

Now we have to do the ‘smoke test,’ Malcolm told me. That basically means, if you see smoke, unplug everything—you’ve done something wrong.

No smoke, no fire, and we were well on our way. It took probably less than a minute to twist the electrical wires and connect all three elements of this setup to each other. Officially, this combination was the MintyBoost connected to the LiPoly, which in turn also connected to the already-charged battery. The moment of truth arrived and—it worked! Eureka! In less than two hours we had successfully created a functioning triad.

But I’d forgotten to get an Altoids tin. OK, it didn’t have to be an Altoids tin. But I needed some sort of container to put the three electronic devices (the battery, the LiPoly converter, and the MintyBoost itself) into. So I ran a block down to the nearest liquor store to get an Altoids tin. Once I’d distributed the mints among the co-workers and had washed out the tin container, we needed to fix the cable feeding power out of the solar cell. Malcolm showed me how to take that Micro USB cable and splice it onto the cable coming out of the solar panel, so we could get power from the panel into the LiPoly charger, which would then feed power to the iPhone and to the battery.

And with that, it functioned, solar panel and all. Malcolm put the foam pads onto the two boards so they wouldn’t short in the Altoids tin, made a few cutouts for each port, and we were done.

And for my next trick.

All that’s left now is for me to adhere the boards and the battery to the Altoids tin; then I could easily keep the whole thing in my bag when I’m out and about. I also need to sort out how best to adhere it to my backpack if I want to mimic Martinet accurately; though maybe velcro strips or clasps of some kind will work fine.

So far, I haven’t had a chance to adequately test my MightyMintyBoost and see how many hours I need to leave it plugged in to fully charge my phone. In fact, after the first few days of trying to use the charger on my desk, it didn’t seem like it was fully getting adequate power. Frequently I’d get a Charging is not supported with this accessory error message on the phone, or it would alternate between charging and not.

So I rang up Jerome Kelty, a Colorado-based jeweler by trade and the author of that original Instructable. Kelty told me that I should use it primarily outside.

solar, panel, charger

Phase 2: Purchase Vehicle Chargers, Not Inverters

For large solar power projects, I am a firm believer in using high-quality DC to AC inverters which allow using standard 120-volt AC appliances and power tools. Inverters are becoming much more reliable and less expensive, which allows using your existing house wiring instead of having to rewire everything for DC. However, powering 120-volt AC power tools requires a 1,500 to 3,000-watt inverter and very heavy battery bank. Some small inverters costing less than 50 are now available to power your laptop computers and video devices while in your car or truck.

Unfortunately, many of these lower cost inverters do not generate the same waveform as the utility grid, which can cause problems with the more sensitive electronic devices you want to power. It is also true that many battery chargers for recharging power tools will have very poor charging performance when connected to a low-cost modified-wave 120-volt AC inverter. Most of these low-cost inverters also have a low power conversion efficiency, and can quickly drain your car or truck battery if the engine is off while powering any 120-volt AC device.

I was pleasantly surprised, however, to find that most manufacturers of battery-powered construction tools now offer a version of their power tool battery chargers in a 12-volt DC portable model, typically called a “vehicle charger.” Although harder to find and a little pricey at 65 to 95, these DC-to-DC chargers provide the ability to recharge your 12 to 24-volt battery-powered tools from a 12-volt battery without inverter or generator. Here are some examples from Bosch and DeWALT.

There are many advantages to using portable 12-volt power without the need for an AC inverter. Not only will this make all wiring easier and safer than dealing with 120 volts AC, but powering 12-volt DC devices directly from a 12-volt battery is much more efficient.

This can be a real advantage if your construction project or weekend retreat is located in an area where hauling generator fuel and equipment up a mountain trail is a major effort. Although this project was intended primarily for powering tools at a remote job site, you can also use this portable solar-power system during a power outage or when camping to recharge your cell phone or power a laptop computer, since most of these devices include charging adapters to fit a 12-volt DC vehicle auxiliary outlet.

Phase 3: Build the System

I designed this project to require a minimum number of parts and very few wiring connections. I selected a standard Group 31 RV/Marine battery which is designed for multiple deep charge/discharge cycles while still being reasonably priced. I also found an inexpensive plastic battery box, 10 amp in-line DC fuse, and female cigarette lighter receptacle (Here’s one with battery terminal attachments and fuse built in). I decided to use this type of power receptacle for this project since so many portable tools and electronic devices have charging adapters that fit this type of 12-volt DC receptacle. As shown in the photo, I mounted the cigarette lighter receptacle in the box cover and wired it through the fuse to the battery using #10 standard copper wire and crimp on ring terminals. The center post of the cigarette lighter receptacle is always connected the battery positive and the outer shell is always connected to the battery negative (-).

The Solar-Tech 85-watt solar module I selected for this project includes a full-size conduit box mounted on the back. (Note, we had trouble finding a model with attached conduit box, so you may have to improvise when attaching the charge controller. One option is to mount it inside the battery box, and purchase a cable that ends with male and female MC4 connectors (typical of most solar panels). Wire the bare end of the cable directly to the charge controller, and you can use a short, 2-conductor cable with ring terminal ends for quick connect and disconnect to the battery terminals using wing nuts. This also allows for quick disconnect near the panel.—Editor)

Also make sure the solar module is advertised for a nominal 12 volt charging voltage (17 volts peak), as manufacturers are increasing the physical size and wattage of their modules so fewer modules and wiring connections are needed for the same array total wattage. However, this increased module size also requires increasing the nominal voltage to 24 volts (35 volts peak) to keep current and wire size as small as possible, and this is too high for directly charging a 12-volt battery. While solar charge controllers are available to allow a mismatch between the solar array voltage and battery voltage so you could use a higher voltage solar module, these solar controllers tend to have a much higher cost and are too large to use in this very basic portable solar charging system.

I purchased a Morningstar SunKeeper-12 charge controller, which is designed to mount into the standard ½-inch knockout opening in the solar module’s conduit box and is suitable for mounting out in the weather. You can locate the solar charge controller on the conduit box attached to the back of the solar module, if you can find one with a conduit, (or follow the MC4 instructions detailed above).

Phase 4: Estimate Your Power Needs

Each tool charging cycle consumes an average of 7 amp-hours of battery capacity (7 amp charge rate for 1 hour). The Group 31 RV/Marine battery used for this project has 100 to 115 amp-hours of charge capacity, depending on price and brand. To avoid discharging this battery below 50% (which will help increase battery life), we will have approximately 50 amp-hours of useful charge capacity. This equals seven battery tool recharges (50 amp-hour/7 amp-hour) before the RV/Marine battery will need to be recharged. Of course, the actual number of tool recharges will depend on ambient temperature, battery age, and depth-of-discharge of the tool battery.

We estimated this Group 31 solar battery will require 50 amp-hours of solar charging to replace what the battery tool charging took away. Assuming we have an average of five hours of full sun per day, this will require a solar module capable of providing 5 amps of output to fully recharge this size battery in two days. (50 amp-hours/5 amps = 10 hours).

A typical 85-watt solar module designed to charge 12-volt batteries will typically have a peak output of 5.1 amps, so I selected an 85-watt module. This smaller wattage module is also fairly easy for one person to carry, while still large enough to provide a reasonable amount of solar power. Your solar module can be larger or smaller than my 85-watt module selection, which will reduce or increase the number of days it takes to fully recharge the RV/Marine battery.

I have also omitted solar and charging efficiency considerations to simplify our example calculation. I have also assumed a clear blue sky all day, no module shading, and proper module solar orientation. When these factors are taken into consideration, you will most likely only convert approximately 70% of any solar module’s nameplate output rating into useful battery charging. Do not be surprised if it actually takes a little longer to fully recharge the battery you select.

solar, panel, charger

Phase 5: Put it to Work

It feels really rewarding to build something off-grid in a remote area with the convenience of labor-saving power tools without having to deal with a noisy generator. It’s also nice to have a portable solar-charging system instead of having to keep your truck running while using a DC to AC inverter to power your tools and tool chargers. When not needed to recharge power tools at a job site, this portable solar-charging system can be used for camping or during emergency power outages. This solar module with built-in solar charge controller can even be used to recharge your RV camper batteries when dry camping.

While most major manufacturers of battery-powered hand tools offer an “in-vehicle” charger, these are not easy to find in your local retail store. If you cannot find them locally, there are several Internet sites that sell in-vehicle chargers. Order the charger that matches your brand of battery-powered tools, and be sure the charger matches the voltage and chemistry of your battery packs.

DeWALT #DC9319 7.2-volt to 18-volt vehicle charger:

Makita #DC18SE 18-volt/Lithium-ion vehicle charger:

Bosch #BC006 7.2-volt to 24-volt vehicle charger:

Milwaukee #M12 12-volt Lithium-ion wall and vehicle charger:Milwaukee #M18 18-volt Lithium-ion wall and vehicle charger: This is one of the few that is also an A/C charger, so it’s double-your-value.

Ryobi One 18-volt dual chemistry in-vehicle charger:

About the Author: Jeff Yago is a licensed professional engineer and certified energy manager with more than 30 years of experience in the energy conservation field. He has extensive solar and emergency preparedness experience, and has authored numerous articles and texts.

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