The Complete Solar Chargers

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Solar Battery Charger With LM317T

Find out how to make a current controlled solar battery

charger using an LM317T

A small solar panel makes an excellent battery charger for AA and AAA rechargeable

batteries. Only a few components are required and construction is very simple making this aperfect first renewable energy project.

Rechargeable AA and AAA batteries have a voltage of around 1.2 Volts when fully charged.Therefore 2 in series gives a total of 2.4 Volts, 4 in series 4.8 Volts. Common solar panel outputvoltages are 3 Volts (for example the 3V 100ma solar panels (1) in the REUK Shop (2)), and 6volts - perfect for charging 2 or 4 batteries respectively.

The Limitations of a Basic Solar Charger

Details on making the simplest kind ofSolar Battery Charger(3) are available here.Unfortunately this set-up has one serious limitation - the solar panel has to be well matched tothe batteries to be charged or the batteries may be overcharged. If you later decide to chargebatteries with a different capacity, you would need to change the solar panel.

Current

Current is the most important factor in any battery charger. As long as the voltage of the solarpanel is greater than the total fully charged voltage of the batteries, the batteries will be charged .If the current is too little, the batteries will charge very slowly. If the current is too high thebatteries will be charged too fast, are at risk of being overcharged, may overheat, and have their

usable lifetime reduced. Therefore the next development step is to make a current limitedbattery charger.

Safe Battery Charging Current

Since we are still making a simple solar charger it will not automatically turn off when thebatteries are full. Therefore we need to keep the charging current low enough that it will notdamage the batteries even when they are fully charged. A current of around 10% of batterycapacity gives the right balance of charging speed and safety - for example, 2700mah AArechargeable batteries (4) should be charged with a current of 10% of 2700 = 270ma. To chargethe batteries faster a higher current could be used, but the chance of the batteries beingovercharged would increase.

Limiting Current with an LM317T

The LM317T(5) is a voltage regulator chip. It can also be used with a suitable resistor(6) toregulate current. Full details on how this works are available here in our guide to using theLM317T with LED lighting (7).

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The value of the resistor required is given by Ohm's Law (8) as 1.25V divided by the outputcurrent required. (The 1.25V is the regulated output from the LM317T'sADJoutput.) The higherthe input voltage and current, the more heat will be generated by the LM317T since the output

current is fixed and the extra power has to go somewhere. The LM317T will cope with currentsof up to 1.5 Amps and so will have no problem at all with small solar panels.

Choosing the Resistor for the LM317T Current Limiting

Circuit

Resistors are only available in certain values - e.g. 5.6 Ohms and 6.8 Ohms, but not 6.2 Ohms.Below is a table of available resistor values together with the output current generated if eachresistor is used in an LM317T current limiting circuit (R= resistance, I = current).

R (Ohms) 3.9 4.7 5.6 6.8 8.2 10 12 15 18 22 27 33

I (mA) 321 266 223 184 152 125 104.2 83.3 69.4 56.8 46.3 37.9

Therefore using the table above we can see that to charge 1000mah AAA rechargeable batteries(9) with a current of 100ma, a 12 Ohm resistor would be perfect. A 15 Ohm resistor wouldreduce the current and slow down charging, a 10 Ohm resistor would increase the current andspeed up charging.

Example Solar Battery Charger with LM317T

In this example we will make a solar charger using a 6 Volt 250ma Solar Panel to charge four800mah AAA batteries. The batteries can be put into a couple of 2 x AAA battery holders (10)and wired in series (link the positive output from one battery holder to the negative of the other).

This gives us 4 x 1.2 = 4.8 Volts with a capacity of 800mah - therefore we want a chargingcurrent of around 80ma. According to the table above, a 15 Ohm resistor gives a fixed currentof 83.3 milliamps which will be perfect.The power loss in the resistor is again given by Ohm's Lawas I * I * R = 0.0833 * 0.0833 * 15

= 0.10 Watts, therefore we can safely use a standard 0.25 Watt 15 Ohm resistor.

For testing the circuit photographed below was built using prototyping breadboard(11). The

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circuit is connected between the positive output of the solar panel and the one free positive leadof the battery holders.

A digital multimeter(12) has been used to measure the actual current output by the circuit - inthis case 84.1ma is a little higher than the expected 83.3ma since resistor values are not exact,and theADJvoltage output from the LM317T is not exactly 1.25 Volts.

Complete Current Limited Solar Battery Charger Circuit

The negative lead from the solar panel should be connected to the free negative input of the

battery holders. The positive lead from the solar panel is connected to the positive input of the

current limiting circuit, and the output from that circuit connected to the free positive lead of the

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battery holders.

You now have an improved solar charger which will send a fixed amount of current (sunlight

permitting) to the batteries. Charging from flat would take around 10 hours of sunlight in this

worked example and you do not need to worry about overcharging your batteries.

A final enhancement would be to incorporate a simple battery status monitor(13) using a Zener

diode (14) to light an LED when the battery voltage reaches the desired level.

Basic 4 AA Solar Battery Charger Plans

Make a simple solar charger for 4 AA rechargeable batteries

In this article you will find out how to make a very simple solar battery charger for 4 AArechargeable batteries using a small 6 Volt solar panel. A labelled photograph of the completedcharger is provided at the end of the article.

nb.An introduction to Solar Battery Charging(1) can be found by clicking here.

This Solar battery charger is built entirely from parts available in the REUK Shop (2). Here isthe parts list:

1 of4 x 2700mah AA Rechargeable Batteries(3).

1 of6V 250ma Solar Panel(4).2 of2 AA Battery Holder with Flying Leads(5).1 ofBlocking Diode(6).

Click here to put all of the necessary parts into your REUK Shop basket: Buy Solar ChargerKit(7) . (We will throw in some terminal strip (see later) forfree in case you are not planningon soldering the parts together.)

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The Solar Battery Charger Specifications

The long life rechargeable batteries used have a capacity of2,700mah - therefore a chargingcurrent of 10% of this (i.e. 270ma) is safe. The nominal voltage of each battery is 1.2V, so fourin series is 4.8V with a fully charged voltage of around 5.2V being normal. Therefore our 6 Volt250ma solar panel is perfectly rated to be used as a charger for these batteries.

In order to prevent stored power in the batteries being released through the solar panel duringthe night, a blocking diode is used. Placed in the postive line from the solar panel this onlyallows electricity to flow from the solar panel to the batteries and not from the batteries to thesolar panel.Up to 0.7 Volts from the solar panel are lost as heat in the diode as electricity flows from thepanel to the battery leaving us with a perfect charging voltage of around 5.30 Volts for thebatteries.

Putting the Solar Battery Charger Together

To keep things simple no soldering is required to built this solar battery charger. Insteadterminal strip is used to make the connections - only a small flat head screwdriver is required to

secure each wire/component in place.

First of all the fourbatteries are put into the two battery holders and then the holders are wiredtogether in series. To do this the positive lead from one battery holder is connected to thenegative from the other. The remaining free wires - one positive and one negative - are ourcharging inputs.

The ringed end of the blocking diode (pictured above) is then connected to the positive batteryinput (red), and the other end to the positive output from the solar panel (red). The negativeoutput from the solar panel (blue) is connected directly to the negative battery input (black) .

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Pictured above is the completed Solar Battery Charger. The voltage measured across the pointslabelledB and Cis the voltage coming in from the solar panel. The voltage measured across thepoints labelledB andA is the voltage of the batteries. (Note that during charging the batteryvoltage measured will be higher than the true voltage of the batteries. Cover the solar panel tomeasure the true battery voltage.)A suitable multimeter(8) is required to make these measurements.

Enhanced Solar Battery Charging

In this example the solar panel and batteries are perfectly matched; however this is not usually

the case. Here are a couple of links to related articles which will explain how to make more

advanced solar battery chargers:

Solar Battery Charging

Make a solar charger for NiCd and NiMH rechargeable AA,

AAA etc batteries

Building a Solar Battery Charger

Pictured above is a battery holder for one AA battery. These battery holders are available in arange of sizes from 1 AAA to 4 AA batteries. Use the one which is suitable for your needs. Thesize of the solar panel required depends on the number of batteries you intend to charge and ontheir capacities. Note that all batteries charged at the same time should have the same capacity.

Each rechargeable AA or AAA battery is rated at 1.2 volts and needs a charging voltage ofaround 1.3-1.4 volts to reach full capacity. Therefore if you want to charge 4 x AA batteries youwould need a 6 or 9 volt solar panel.

Select a Suitable Solar Panel

Ideally you should not charge a battery with more than 10% of its capacity as current - forexample, charge a 2,000mah capacity battery with a current of 200ma or lower. This isparticularly important when the batteries are nearing full charge and far less important when they

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are fully discharged. If you break the 10% rule then overcharging can occur damaging thebattery potentially beyond repair and generating heat.

Adiodeis used to prevent the batteries' charge being dissipated back through the solar panelwhen it is dark. A 1N5817 diode is perfect for the job as it only 0.2 volts is lost as the generatedelectricity passes through it. If you have aGermanium Diodethese are also excellent.

Putting Your Solar Battery Charger Together

Detailed instructions on putting together a simple solar charger like this are now available inour articleBasic 4 AA Solar Battery Charger Plans. These plans can be used for all solarbattery chargers whether you are making a 1 AAA battery charger or a 4 AA battery charger.

Solar Battery Charger EnhancementsThis very basic solar charger can be improved by adding a current limiting circuit. Click here to

find out how toMake a Solar Battery Charger with an LM317T. The LM317T is a cheap

electronic component (cost under 1) which can be used to regulate current. Therefore you can

safely charge batteries with a largersolar panel without the batteries overcharging or

overheating.

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iThis instructable will show you how to make your own solar battery charger from very simplecomponents. It is taken from my documentation provided with a kit I supply - you should easilybe able to source the same components yourself of course.

If you have any comments on how to improve the documentation then please do not hesitate tosay :)

Step 1The Components Needed

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iThe items shown in the image are contained in your kit. This page explains their uses. Your kitmay have a smaller/larger copper stripboard than this and may contain extra wire - I try to beefup the kit as time goes on.

The Copper Stripboard contains rows of copper tracks. Each track is electrically separate fromits neighbour. It contains holes for your components. The boards I supply are larger than needed,this will allow you to expand the system at some future date.

The Batter Holder ... errrr holds your batteries.... and comes with two pins, one for the positiveand one for the negative ends, they will be soldered into the stripboard.

100 Ohm resister - at one point this was needful in the kit as the LED couldn't cope with someof the voltages in the experiments - however the new LEDs do and the resistor is simply in therebecause it is advertised as such! Maybe you will have need of it when you expand the system.

LED - this is a high intensity light emitting diode. 3.2-3.6V forward voltage, with 10000mcd at20ma. A LED must be placed in the circuit the correct way around. The longer leg shouldreceive current from the positive terminal/direction.

1N5817 DIODE - this diode allows current to flow in only one direction - this prevents batterypower discharging through the solar panel at night. It drops about 0.2V from the system. Thisblocking diode also needs placing in the circuit in the correct orientation. The diode has acircular band across its barrel at one end of the diode. This should be closest to thenegative/ground.

Wires - Usually I include at least 4 wires - a black and red wire for the solar panel, a brown wireas a jumper and another wire for use in unsoldered testing.

Solar Panel - This image shows the back of the solar panel. On your solar panel in the centre ofthe left side and the right side you will see a small panel of smooth metal - this is the

negative/positive terminals. I have marked the positive side by adding black dots on that side.This solar panel will output a max of 3V at 150ma.

Warning - I suggest you read the whole document before making any experiments - informationis contained throughout the document which will improve your understanding of chargingbatteries using solar power.

HINT - you should probably purchase a multimeter and learn how to use it - this will tell youimportant information on typical voltages and currents you solar panel will produce in varyingweather situations.

Soldering

It is quite possible to use this kit without having to do any soldering at all - however at somepoint you will need to so I include both soldered and non soldered options.

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How I built a Solar iPhone Charger for under $50.

To see my personal site with these tutorials and news, please visithttp://www.BrennanZelener.com

I am not responsible for any damage that you may cause to your iPhone or any device that you use with

this charger. I can not stress the importance of checking your circuits with a multimeter enough, and I

can assure you that I've done so at every step in this build process. Your phone is a very expensive

device. Treat it like one!

Intro and Design:

Over the past month or so, I've been working on designs for a stationary solar iPhone charger. By

stationary I mean a charger that will be kept in a fairly permanent place. I bring mine with me if I'm

going to be camping or staying somewhere for a while, but it's really not meant to be portable.

This isn't only a solar iPhone charger. You can use it with any device that will charge via USB. I just

happen to use it to charge my iPhone. Also, this design doesn't include a battery in the circuit - which

means that you'll have to charge your iPhone when the sun is out and shining. I know it's a serious

inconvenience, but adding a battery makes the circuit much more complex - and is a bit more costly. I'll

be following up this design with an update on how to add a battery conveniently into this circuit.

The idea behind this panel is that it's simple (and cheap!). You don't have to have any prior circuit

knowledge,or familiarity with electronics. I'm really just stepping out of the novice stage as far as

soldering is concerned, so this is a great beginner project for just about anyone!

Step 1Tools and Materials

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As I say in the title, I built this charger for just a bit less than $50. That doesn't include the cost for tools

and a few of the materials that were salvaged, but if you spend enough time on eBay you should be able

to build yours for the same amount, if not less.

Let's take a look at what was used to build the panel.

Tools:

Soldering Iron w/ Solder and Flux

Needle Nose Pliers

Wire Cutters/Stripper

MultiMeter (IMPORTANT)

Materials and Prices:

Part/Material ------------------------------------- Source ----------------- Cost

10 Watt Solar Panel ----------------------------- eBay -------------------$41.45 w/ shipping

7805 5Volt Regulator ---------------------- RadioShack ------------- $1.59

iPhone/iPod Cable ------------------------------ eBay ------------------ $1.20

USB Extension Cable -------------------------- eBay ------------------ $3.00 w/ shipping

Red/Black small-guage wire --------------- On Hand --------------- Free

Electrical Tape --------------------------------- On Hand --------------- Free

Small Zip Tie ----------------------------------- On Hand --------------- Free

Step 2The Panel

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This Solar Panel is a 10W panel made by LaVie Solar. You can check out their website, but your cheapest

bet is to use eBay. Their eBay user ID is lavie-inc. I snagged a pretty great deal at $41.45. The panel has a

really sturdy build quality. It has an aluminum frame, and seems to be entirely weatherized. I wouldn't

have too much of a problem leaving it in the rain. Also, All of the wiring has been done for us which

saves a LOT of time. They even put a blocking diode into the connection on the back, so we don't have

to worry about that in our circuit.

The panel has an output rating of 21.6 Volts (Open Circuit) and .62Amps (Short Circuit). These are

optimal ratings, but when I tested my panel in direct sunlight, that's almost exactly what I got.

As far as efficiency goes, this is not the ideal panel to be using as a direct USB charger. We'll be loosing a

lot of energy as heat when we regulate the 20V output down to 5V to match USB standard. However,

using a larger panel means that there will be more current flowing even when there's not a lot of sun.

I've even seen my iPhone charging when the solar panel is in the shade!

Step 3The Simple Circuit

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After gathering all of the materials, I sat down and got to work.

I cut 2 pieces of Black wire and 2 pieces of Red Wire. The lengths were around 5-6 inches. Then, I cut a

little bit less than an inch off both ends of each wire.

With my black and red wires ready, I cut my USB extension cable in half and stripped the cut half of the

female end to expose all of the individual wires. There are 4 wires in all USB cables- Green, White, Red,

and Black. The Green and White wires are for data, so those are not needed. I snipped the Green and

White wires, along with all of shielding and fiber - leaving only the Red and Black wires coming out aboutan inch and a half from the USB cable. I stripped a little bit less than an inch off the Red and Black wires

on my USB extension.

Since the 5V regulator only has one Ground pin, I used the two black wires that I cut initially- to make

the soldering a little bit easier. I took both of my black wires, along with the black wire coming from my

USB extension, and twisted them all together carefully and securely. I put some solder on that

connection to make sure that all of the wires stayed together. Then, to keep things safe, I covered the 3-

way connection with electrical tape.

Once all of the wiring was prepped, it was time to put the 5V regulator into the equation. Solderingwires onto the tiny pins from the 5V regulator can be a task. I used a small Zip Tie to hold my wires to

the 5V regulator to make things much easier. It really helped - I was able to do pretty clean solder jobs

on each of the pins. Since neither of the red wires were connected to anything, it didn't matter which

ones I soldered to which pins. Just make sure you know that if your 5V regulator is laying flat, the input

pin is on the bottom, and the output pin is on the top!. I also bent the pins in opposite directions to keep

everything separate.

The fantastic part about this charger is that we're already done with our circuit. Once I was done

soldering to my 5V regulator, I connected the Red wire from the Output pin on the regulator - to the Red

wire coming from my USB extension cable. Now, I only had 2 wire ends left. A Red wire connecting tothe input pin on my 5V regulator, and a Black wire connecting to the regulator's Ground Pin and my USB

extension cable.

Step 4Connect the Circuit to the Panel

Since the LaVie Solar Panel has a pretty simple connection panel, pinching the Black and Red wires to

the right screws on the panel was easy!

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DIY Solar Backpack

With the help of some DIY-expert friends, reporter Jon Kalish was able to get this solar backpackconstructed for $40 -- far less than the $200 or so that similar backpacks cost in the store.

Courtesy of Dick Demenus

It sounds great, doesn't it? Powering your portable devices while you're on the move. But likemost things, building your own solar backpack involves some compromises.

The solar cell we chose to power our apparatus cost less than $30 and can deliver a maximum of100 milliamperes (mA) of current at 6 volts. That's when it's in full sunlight and aimed directly atthe sun. (To put that into perspective: A computer's USB port provides up to 500 mA.)

The time it takes to charge an iPod in an electrical outlet varies depending on the model, but fourhours is typical for an iPod Classic. To charge an iPod using a solar backpack it would take morethan a day at full sunlight.

Of course, you can always add another solar panel or two and linearly increase the current. Mostcommercial chargers use a different strategy that you can also adopt: They include rechargeablebatteries in the charger. This allows them to charge slowly over time and then quickly chargeyour device off the batteries.

Materials You'll Need

One used backpack A solar panel A voltage regulator A capacitor A USB extension cable with the male plug taken off Wire Solder Duct tape Double stick tape (the foam type is best) Two sheets of laminating film

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Tools You'll Need

A soldering iron Wire stripper Scissors A razor blade Hot glue A stapler

How To Do It

1. Expose the solder pads on the solar cell(left). Carefully scrape off a small (1/8-inchdiameter) patch of the insulating film on the edge contact strips.

2. Tin the pads. This is essentially priming the surface. Apply heat and solder quickly (be carefulbecause sustained heat can kill electronic devices) until the solder "wets." When this happens,

the ball of molten solder flattens out into a shiny film.

3. Begin to wire it up. Again, it is best to tin the leads before soldering. Since this is a very simplecircuit, we used a minimalist approach: Solder everything together and then smush it onto apiece of double-stick tape to hold it all together and keep it from shorting.

Solder two flexible wires (each about 3 inches long) to the ground and input

terminals of the voltage regulator (left). Then solder two more wires (each about 5 inches long)

to the ground and output terminals of the voltage regulators. These 5-inch wires will go through

a small hole you poke into the backpack with an Exacto knife.

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4. Weatherproof it. Lay down one sheet of laminating film and arrange your solar cell and circuiton it. Now apply the other sheet and trim the edges of the film, being careful to leave a 1-inch

border of just laminate around the perimeter of the entire circuit.

5. Stabilize it. Cover the perimeter of the laminate with duct tape or colored, 1.5-inch clothfurniture repair tape. The laminating film is too fragile for attachment so we need a strong,

flexible border that won't tear easily.

6. Poke the hole through the backpack with an Exacto knife and run the wires coming out of thecircuit through the hole.

7. Attach the solar panel circuit to the backpack (left). This turns out to be thetrickiest task. Good luck sewing it; and keep some band aids handy. We scrapped that approach.

Glue is too messy. Tape won't hold. Nuts and bolts...inelegant. Our solution: staples! If you have

access to a saddle stapler, all the better.

8. Wire the inside. Now it's time to connect the USB cable and the capacitor (it'sneeded to make the voltage regulator happy) to the circuit. Solder the 5-inch wires coming

through the hole in your backpack to the positive and negative terminals of the capacitor (left)and the USB extension cable. We put the capacitor on the inside because it's fat. We put the

other parts outside just to show off.

9. Secure the connection. Hot glue is a big disappointment as an adhesive. Besides the burns thatkeep on giving, it fails so often when you least expect it. One place it shines, though, is in

attaching to porous surfaces like fabric. It is also the poor man's molded plastic; squirt it on

generously, imbedding the capacitor, wire and cable. We added an optional strain relief with a

nut and bolt.

10.You're done. Like cooking, this is but one recipe. Experiment! That's the beauty of doing ityourself.