Solar Charger and Adjustable Power Supply

In this instructable I am going to show you how to build a Solar Charger in a very simple way, so that it will be easy and affordable for anyone to build its own one.

We are going to use solar panels as our source of energy, to be able to use this device anywhere. We will use some Li-ion batteries to store the solar energy when it is available, so that we can use it at every time, not only when it is sunny.

The device will have 2 outputs:

One constant 5 V output, max 1A.
One adjustable output between 1.25 V and 24 V, max 3 A or 15 W.

This way, we will be able to easily charge any USB device with the 5 V output and we will also be able to adjust the output to the Voltage needed by other devices.

The main objectives of the design are simplicity, affordability and usefulness, so that anyone could get a similar project properly working on its house.

Let's start!

Step 1: Materials

To make this project, we will need the following components:

2x 6V 4.5W Solar Panel
2x 1N4007 diode
1x TP4056 + protection module
2x 18650 Li ion battery
1x 3.7 to 5 V boost converter
1x USB female connector
1x LM2577 Buck Boost Converter
1x Voltmeter/Ammeter 0-100V 0-10A
2x Panel switches
1x 10K potentiometer
1x 21mm Jack connector (or which you prefer)
Some terminal block connectors
Some wire
Some cardboard or some wood

All the documentation I have found about these components will be posted at the end of the instructable.

Step 2: The Circuit

As it is shown in the pictures, the schematic is not very complex.

We connect both Solar Panels in parallel with its corresponding diode so that we get an output from them of 6V and 9W (1.5 A max theoretically).

We take this power input and connect it to the TP4056 Lithium batteries charge regulator. This module has a protection circuit too, to prevent our batteries from overcharge and overdischarge. We will talk about that later.

We connect the batteries in parallel, so that we add their capacities, not their voltages, and we connect the 'pack' to the TP4056 module.

At the output of the TP4056 we connect the 3.7 to 5 V boost converter, the LM2577 module and the power wires of the voltmeter/ammeter module. We will also put a switch before the 5V boost converter and other one before the LM2577 module and voltmeter/ammeter power wires.

We finally connect the connectors (despite the redundancy) where we will plug our devices to be powered and charged.

This circuit can be simply modified to our needs. For example, we could add another 5V boost converter, so that we could have 2 USB 5V ports. We could, of course, use other modules which were able to output 5V 2A. We could add more solar panels, use other batteries configuration, etc.

The circuit has 3 main parts, in which we can act separately:

Power input: This includes the solar panels or any power source from we are going to power our project. We can add more solar panels, use different kinds of them, connect them in other configurations, etc. The only thing we have to be worried about is that at the output of this part, we need between 5 and 6 volts. If we have less, the batteries may not be charged. If we have more, we may burn the TP4056 module and even damage the batteries. For this reason, if we use other configurations or other voltage solar panels, we might need a regulator. Depending on how you decide to mount that, you will have to decide what regulator fits best.
Charging module and batteries: Here is where the energy is stored to be ready to use it when we need it. We will have to think about what use of this device are we going to do, so that the batteries have enough capacity to satisfy our needs. We can add more batteries in parallel to raise capacity, or we can even change the type of battery to other voltages or other chemicals, but then, we will have to change the charger too, according to the new design.
Output line: Here we have the 3.7V line which outputs from the battery through the TP4056+protection module. We have to connect here the devices we need to get the energy in the appropriate format. This is the most simple part to be modified, as we only have to think how to get the output we need from the 3.7V we have. As I said before, I have put one 5V boost converter and a LM2577 buck boost module, but you can connect here the modules you want or that you consider you need.

Step 3: Power Source: Solar Panels

Let's start building this from the Solar Panels.

Electrical part

We just have to take our solar panels, connect each one to a diode, and then connect them in parallel, as shown in the schematic. I have made this with a protoboard, but in the future I will make a small PCB in which I will be able to connect up to 4 panels (for example)

You can make your own PCB or directly solder the diodes and wires. But be careful to not produce a shortcircuit if the wires or the soldering is not properly insulated.

Mechanical part

We are going to build a small stand for our solar panels. This part is very user-adjustable, and you can build it as you prefer. I am going to show you my design, but, again, you can modify it and make your own stand.

I have made this of cardboard as it is really easy to work with. There is nothing special on it, as it is shown in the pictures. I did not make any plan of this, because I didn't know what piece of cardboard I was going to find to make this. But it is so simple, that it is not necessary.

The stand puts the panels at 30º from the horizontal. This is not a random number. My location is around 40ºN , and this device is specially designed (in my case) for being used in summer, so the Sun will be even more perpendicular. That is why I picked that value. In any case, you can choose the angle you like, and it will probably possible to adjust it when you put it into work.

We can sum up this just saying that we have to try to get our solar panels surface perpendicular to the Sun's rays.

Step 4: Charging Module and Batteries

Now we have the power source ready, and we have a 5.5~6V input. It is time to store all that energy if we are not consuming it in this moment.

I have used a TP4056 module, which is able to charge a Lithium battery at a maximum current of 1 A. I will upload some datasheets and documentation about this at the end of the instructable. I will just say that it is possible to change and adjust that charging maximum limit current by changing the value of a resistor in the PCB if it were needed. It is all specified in the documentation, and you can also find a lot of information about that on the Internet.

The module that I have picked includes also a protection circuit. Be careful: NOT ALL the TP4056 modulesINCLUDES this PROTECTION. I think this is very important, as you will probably don't want your batteries to die due to an over-discharge, or to explode due to an over charge.

This module is there to prevent this two problems. On the one hand, it disconnects the battery from the load circuit, the output of the module, if its voltage falls under 2.4V to prevent over-discharge. On the other hand, it disconnects the battery too if its voltage raises above 4.2V to prevent overcharge.

Anyway, it is a good advice to never leave alone without some supervision a battery while charging. Not only in this project. Safety MUST always be the maximum priority.

So we now just have to connect the 3.7V batteries we need in parallel to add their capacities, and connect them to the proper contacts of the TP4056+protection module. I made my own battery holder, as I didn't have any one at home for this kind of battery.

I made it with some cardboard, and a can. As shown in the pictures, I just measured the space I was going to need and cut the cardboard. Then I cut the can, and sanded it to remove the protecting enamel and the paint over the metal, because otherwise it wouldn't conduct electricity. Finally, I made a small hole in the metal, and soldered the wires.

CAUTION: All the batteries which we connect in parallel must be equally charged. This means they must to have the same voltage. Otherwise there will be an uncontrolled current from the most charged battery to the lowest, which could be enough dangerous to seriously damage the batteries and even a risk of fire. This could happen if the difference between them is very big. For this reason, I recommend to charge all the batteries before connect them, so that we can be sure that they are very approximately equally charged and there is not that risk.

We connect the output 3.7V line wires to the respective contacts too, and we are ready to next step.

Step 5: Output Modules

We have the 3.7V line coming from the batteries ready. But at the output of the device we probably won't want 3.7V, so we have to add some output modules to transform that energy to the format we need.

In my case, I will need a 5V output to charge any USB device, so I connect a 3.7 to 5V step up module, max 1A to satisfy that need. I will also connect it through a switch, so I can switch it off when it is not on use, and save battery. I recommend to do this with all output modules you use, to save battery when they are not in use, and to have more control and safety over them.

I will probably also need other voltages for other devices: 6V for a battery charger, 9V for a lamp, 12V for whatever... So I decide to connect too another output module and this will be an adjustable LM2577 buck boost converter. Again with a switch.

This module is, as I have already said a hundred times, a buck boost module. This means I can reach any value above or below the input voltage, between 1.25 and 24V, with a max of 3A or 15W (because I am not using any heatsink, if not, we could get more power -but not more current-).

I have to make a modification of the module. As I will want to change the output value, I think it is interesting to replace the potentiometer soldered in the board by a panel potentiometer. To do this, I just have to desolder the potentiometer that came with the module, and solder 3 wires for the new one. Later, I will put that potentiometer with the switches and the voltmeter/ammeter in the frontal of the box that I will make.

Again, I remind you that you can connect the output modules you want or you consider you need.

Step 6: Voltmeter-Ammeter

As I have an adjustable output module, I think it will be really interesting for the project that it has a built-in voltmeter to adjust it, and an ammeter to control the power limits.

I found this module and it seems to fit perfectly in the project. Here I have shown you how it is connected, in the pictured above.

Just a note: I have connected the power wires together with the LM2577 input, so that when I switch off the module, the voltmeter-ammeter switch off too. This seems very obvious, as we only need it to work with the module, but I remind you just in case you didn't realize.

This step hasn't got anything more. It was just to show the connections and to explain its use.

Step 7: The Box

Now we have all our electronics ready, but a little messy and unprotected.

It's time to build a simple box to contain all the electronics, and where to mount all the panel controls: switches, potentiometer, voltmeter-ammeter, and the connectors, of course.

We can build it of cardboard or of wood. It hasn't got much complexity, and, once again, you can make your own design as you prefer, so that it fits the best to your needs.

Step 8: Ready to Work! Some Uses and Notes. Problems and Solutions.

We have our project ready to work!

Look for a sunny and safe place, and put the solar panels properly oriented.

When needed, connect the devices you want to power to the appropriate connector, and switch on the output.

To operate the adjustable output:

Make sure nothing is connected to the output.
Switch on the module (the voltmeter should switch on too, remember).
Adjust the output voltage value.
Connect the device.
Check that the output never exceed 3A or 15W (remember that the 15 W is because we are not using any heatsink).
When you have finished, disconnect the device and switch off the output.

Possible problems and some solutions:

My batteries never get charged.

Verify with a multimeter that the input voltage to the TP4056 coming from the Solar Panels is between 5 and 6 volts. DISCONNECT the wire and verify too what current do you have in short circuit coming from the solar panels. Maybe you are not getting enough power from your solar panels due to insufficient light or small panels.

My batteries seem to be disconnected from the circuit, but all connections are right

Verify with a multimeter the voltage of the batteries. If they are dead or overcharged, the protection circuit probably has disconnected them. If they are over discharged, try to charge them in a properly charger at home. Keep an eye on them while charging.

The adjustable output doesn't raise as much as I need.

This can happen due to different causes. Maybe you are requesting more power than the one the batteries can supply. Maybe the module is not able to get enough voltage for your need from just 3.7 V. You will probably need to analyze where the problem is (as there could be many factors), and redesign the project.

My voltmeter-ammeter doesn't turn on, but the batteries are charged.

Verify the connections. If still doesn't turn on, maybe it needs more voltage to power up. A solution could be to connect its power wires to the 5V output, but then you will need to switch on the 5V output to make it work, and always you use the 5V output, the voltmeter will be on. Another solution could be to install another 3.7 to 5 V boost converter inside the box, just to power this device, and connect it where the voltmeter were originally powered from.

My voltmeter-ammeter turns on and measure Volts, but not Amps, and there is not output current.

Verify the connections. You may have misconnected the negative (red and blue) wires. (See the schematic previously shown)

As a general advise, always keep an eye on the device, and specially in the first uses on the temperature of the components. If you consider your box gets too warm, add ventilation holes.

Remember, SAFETY HAS TO BE THE MAXIMUN PRIORITY.

Step 9: Documentation and Datasheets

Here you have some information about the components used in this instructable. I recommend you to read it if you want to make modifications or if you are not sure about any aspect.

TP4056 + protection

I recommend the video I have put above too. It is not mine, but I found a lot of information on it.

LM2577
About the voltmeter/ammeter, I didn't find any reliable documentation, but I have already posted the connection diagram, which I found a bit difficult to find.

Step 10: Possible Future Improvements and Variations

Microcontroller:

For sure, many of you have been thinking while you were reading this instructable that this could be much more cool with an Arduino or any other microcontroller. It is true, with a microcontroller we could do much more things. We could get much more data about the working of the device. We could regulate the charge (no more need of TP4056), make it more intelligent, and even adapt it to other kind of batteries, like Lead Acid. It is all true, but it is also more complex.

As I said at the beginning, I wanted to make this simple, so that it could be easy for anyone to make its own one without much difficulties and so that they can understand what are they doing.

With an Arduino we could make a PWM charger for Lead Acid batteries. Someone could even think in a MPPT one, but that all is much more complex and difficult.

Maybe in the future I make another instructable about something of that. Or maybe not. But in any case, this is not that Instructable.

Other kinds of batteries

Yes, another "easy" variation of this instructable is to use other kind of storage. This can vary from a 7.4V lithium battery (for example), to a completely different kind of battery like lead acid or Ni-MH.

Of course it is possible to do that, but you will have to search for information, redesign the circuit, find an appropriate charger, and probably change the Solar Panels configuration. But if you have worked with that before, you may not have much problem.

Solar tracking PV stands

An interesting improvement, but much more complex design of the stand is needed, and may not be efficient for this small power installation. It should need some sensors, actuators and a microcontroller, although with an easy program.

We may talk about this in the future.