In this instructable I used 5 CHEAP solar lights. As I recall I bought them for $2 each at Wal*Mart over a year ago.
It would be hard to find the solar cells for that price let alone the whole light assembly etc.
Step 1: Let's get started
First I headed to the DOLLAR TREE dollar store where everything is a dollar, not $1,2,3.50 etc.
I was searching for a container that was in the experimenters budget along with one that had some qualities I was looking for.
this box has a 4 side snap feature. It is easy open/ easy close etc. The one thing I liked is the rubber seal built in the lid portion.
This should make things fairly water tight.
I may use this during emergency situations (preparedness). As a Ham Radio operator I need to be prepared to work emergency communications at some point. A solar charger for a cell phone or other device would be handy.
Step 2: Preparing the cell/battery combination
As you can see these lights were part of a July 4th celebration and thus they sold cheap the day after on clearance. you will notice I took a black sharpie marker and blotted out the stars on the side of the casings. Not that I am not patriotic but isn't the focus of this instructable.
The underside/base has three screws that need to be removed. I cut the RED and BLACK wires (positive and negative) on both the battery and solar cell right where they connect to the circuit board.
I am not one to throw things a way but in this case I tossed the circuit board and light assembly I have too much of this stuff hanging around :)
After the light assembly was removed I turned the cell upside down. I used a sharp paring knife to strip the wires about 1/3-1/2 inch long. BE CAREFUL KNIVES ARE SHARP!!!
You will want to join both red wires together as both black wires. this creates a parallel circuit between the solar cell and the Ni-Cad battery.
I created an extra red wire that I used to bridge from cell to cell thus allowing me to move and locate the cells in the box at will.
Step 3: Assembly
In this picture you can see the 5 cells soldered positive to negative in a series circuit.
Each battery is what is known as a 2/3 AA cell. They are 1.2 volts when charged. We should show a voltage of aproximately 6 volts or more. As you can see I had 6.25 volts with out the circuit loaded.
This voltage will give us enough voltage to regulate it down to somewhere between 4.8 and 5.2 volts. Most 5 volt devices charge at about 5 to 5.2 volts.
As some of you know a Zener diode can reduce the circuit voltage by .5 to 1 volt if placed in the circuit.
The second picture shows the zener diodes that I used. They show a voltage drop of about 1/2 volt each.
Using a voltage regulator such as a LM317 would be counter productive as losses would be too great.
I put 2 diodes in series and obtained approximately a 1 volt drop just what I was looking for.
As you can see the meter is reading 5.11 volts un-loaded, this should work very well.
My guess is that it will take a bit of time to charge a phone due to low amperage.
Step 4: Wire assembly
Here you can see all 5 cells in the container sitting loosely.
I chose to use a female USB cord end for connection.
The second picture shows the wiring of the USB cable. The red and black are obviously positive and negative. The green and white wires are not used. The green and white wires are for data transfer in a computer context.
I poked a hole in the side of the container end. After knotting and feeding the USB line through the side I tied another knot to secure it somewhat.
By using the female USB cord you can switch out all manner of other 5 volt accessory cords for different devices.
I will most likely use some clear silicone around the cable entry to as to keep it moisture resistant in bad climates.
Step 5: Securing the components
I believe a picture is definately worth a thousand words.
I hope the 6 pictures are of some assistance in knowing what I did to secure the solar cells in the container.
All I can say is that hot glue is my friend. I personally would use nothing else in this case. The time and frustration of other glues would be too much hassle.
You will notice I also attached the two zener diodes to the side of the center cell casing. I also used about one drop of glue per solder junction after carefully trimming the excess wire..
The hot glue really helps to secure the junctions on these very thin wires. Who knows how much rough use t his charger could get. Possibly tossed around a bit ?
Step 6: The final results
I was testing things out and realized I had glued the junction beyond the last diode :((
I had to do my voltage test at the center of the two diodes then subtract .5 volts for the last diode.
Basically I ended up with 5.09 volts DC.
You will see the micro USB charge cord from my cell phone. I was tired and thought I would hook up the phone and take a picture of it charging... YEAH RIGHT! It's hard to take a picture of a phone charging when you are using the same phone to take the pictures.
Time to go to sleep Bryan!!!!
I took 3 pictures of the container/enclosure so that you could see the seal and side lock assembly.
On the theoretical TOP/LID of the container I am going to hot glue some sort of non slip material. My hope is to be able to set this in a window sill, a dashboard of a vehicle, a picnic table and know that it won't slide off for any reason.
******* JUST A CONSTRUCTION NOTE *******
You might remember to have a moist (More wet than dry) sponge handy for the hot glue work.
First off hot glue is dangerous if handled carelessly.
CHILDREN SHOULD NEVER USE HOT GLUE UN-ASSISTED !!!
** When attaching the cell to the container I suggest this to make it easier.
be careful about getting hot glue over the solar cells. I doubt the glue would harm them but it would look messy.
After you squirt glue around the cell keep your finger on the shell of the cell/battery combo to keep it in position. then lift the container and set it on the moist sponge to absorb the excess heat from the glued union.
This cools things down safely and allows you to move forward quicker with out components accidently shifting out of place.
I hope you have received some creative ideas for your next project.