Picture of Solarize your backpack and power all your gizmos
In this instructable I'll show you how to build a detachable solar panel and battery charger for your backpack. This can power or charge all your gadgets (cell phone, mp3 player...) while on the road. HAMs can use it to power small QRP transmitters and receivers on a field day etc.
I was inspired by the excellent instructable "Rain or shine solar charger" by Blondietheblond, but wanted to avoid sewing, since I don't have a machine. So this is the result.

Step 1: Gather the stuff you'll need:

Picture of Gather the stuff you'll need:
0) a backpack (duh):

Most backpacks have enough possibilities to attach stuff. Mine provided these ribbons on the back. No idea what they are supposed to be used for.

1) for the solar panel:

- 4 Encapsulated 2V/200mA solar panels (Velleman SOL4).
- Self adhesive pads for cable ties (3M Scotchlok Ab02).
- Nylon cable ties to fit the adhesive pads above.
- Velcro adjustable cable binders (Tesa 55236-00000, 12mmx20cm).
- Heat shrink tubing.
- Electric wire (capable of carying 0.5A is more than enough).
- Connector to go to the battery box.

2) for the charger/battery box:

Parts list for this is less critical, so improvise. There's an explanation with important details ahead.

- Small plastic project box.
- 4 AA-size NiMH batteries (GP 2700 series is ok, see further).
- Battery holder .
- Two 2-pin panel-mount connectors of some sort.
- Components (see further).

...and some tools:

- soldering iron.
- cutters.
- pliers.
- sharp knife.
- drill for making holes in the project box.
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jtbennett01199 months ago

I want to do this on my school backpack, so it must be durable. I am looking at the flexible solar panels from Silicon Solar. It looks like it would take more panels to reach your requirement of 800 mA. Is 800 necessary? Is there a better option for durable solar cells that are fairly accident proof for everyday use?

Ok I finally got the bank to build one of these, now i have a few noob questions for you here,
1. does this setup have a plugin for charging like via usb or anything? and if not could i add plugins and how easy would that be?
2. what would i have to to to make something like this that could charge a laptop?

basically i want to make something like this where i can carry my laptop, phone, mp3 player, and my psp and charge them. idk if its possible....HELP!!
Most likely you would not be able to charge a laptop because of the amount of power a laptop takes (over 50 watts). If you wanted USB plugs, you would just buy a 5v voltage regulator from somewhere like radioshack and a usb jack and wire it up to the battery. Most things like cell phones and mp3's can be charged by this, but it takes time.
lothar15114 years ago
Now thats a good idea!!!!!! haha thats my next project
nice aswoom tech..
gabe0094 years ago
Would look better if you incorporate the sun panles into the design of the backpack.
bikeboy5 years ago
I'm building solar charger circuit for GPS assisted trek in Spanish Pyrenees.
Made a "Mintyboost" circuit to keep pack of 3 1.2V AA's at 5V even when "drained" (To charge PDA and GPS receiver). Mintyboost IC steps up as low as 0.7V to 5V, so your circuit will be good addition if indeed deep discharging (0.7V) is not good for battery lifetime (although GP datasheet only mentions "prolonged charging time" after deep discharge).
If I understand your circuit, the lower transistor "opens" the NDS332P, which has a higher current capacity (?). But how much current would there be "lost" through the lower transistor? (after all, after Spain, i'll be back in cloudy Belgium... :)
Kajnjaps (author)  bikeboy5 years ago
Not much, more or less the battery voltage divided by 100k, since no (static) current flows through the gate of the mosfet.

lucidn7 years ago
Do you happen to have a larger version of the charge box schematic? It's a bit tough to understand.
Kajnjaps (author)  lucidn7 years ago
I'm sorry, I don't. It basically is a just schmitt trigger with two transistors. Let me know if you have a specific question I can help with.
lucidn Kajnjaps7 years ago
Here's a few questions How are the ND5332Ps hooked up? Does the gound refer to the ground of the battery, or the ground of the solar panels? And I'm a bit confused about how the panels are hooked up. And help would be much appreciated, as I'm designing a PCB for this.
Kajnjaps (author)  lucidn7 years ago
Hi Lucidn, the NDS332P (Fairchild Semiconductor) are in parallel, meaning gate to gate, source to source and drain to drain. You can always do this with mosfets to increase the current capability (note: don't do this with bipolar transistors, as they have a negative resistance temperature coefficient). The solar panels are in series so you end up with two wires, positive (red) and a negative (black) . The black wire is the ground for the system,so for batteries, the circuit and the solar panels. If you are going through the trouble of designing a pcb for this, it might be a good idea to include a variable resistor in series with the 1Mohm.
lucidn Kajnjaps7 years ago
Thanks, and I'll send you a jpg of the PCB once I'm done it. It shouldn't take me long.
Kajnjaps (author)  lucidn7 years ago
What program do you use to design the PCB? One more thing: you might want to use other mosfets as they will work well too, as long as they have sufficiently low turn on voltage. bye, K.
lucidn Kajnjaps7 years ago
Well after looking for a CAD program that's both free and for mac, I remembered I still had Appleworks, from before I upgraded to OSX. So I've been using that, designing the PCB and then shrinking it down to the right size.
Yenka is a good program and its free if you just want it for personal use. It's really an educational tool, but the electronics features allow you to design, test and create PCBs ready for manufacture for circuits. You can get it at www.yenka.com It has other things such as chemistry and physics and such, but the electronics stuff is what you might be interested in.
Kajnjaps (author)  lukaj20036 years ago
Thanks, I'll check it out!
lucidn lucidn7 years ago
Here's PCB, actual size. Unfortunately there's no guide to go with it, but it's not hard to figure out.
Solar Backpack PCB.pdf(792x792) 23 KB
add names of components!
ScubaSteve6 years ago
what about Lithium-Ion (Li-ON) batteries?
Kajnjaps (author)  ScubaSteve6 years ago
much more difficult to charge/discharge safely...
grundisimo6 years ago
you should get a patent on this.
Kajnjaps (author)  grundisimo6 years ago
I don't think it is patentable; there is no inventiveness in it.
Most patents are just a waste of money anyway.
This text http://www.tinaja.com/glib/casagpat.pdfopended my eyes about patents.
highly recommended reading.
McPie6 years ago
This is awesome! This is exactly what I was looking for!
Kajnjaps (author)  McPie6 years ago
Thanks, have fun!
You should have used flexible solar cells from Silicon Solar. They are so strong they can even be walked on! Great for your kind of project.
vtec2k76 years ago
What is the transistor you are using to the left of the 1Mohm resistor? I cant read your handwriting. I am returning to the semi-conductor scene after being out of the game since college 6 years ago. Is there anyway you can explain the parts needed exactly for this so i could build it. I need to get back into this and I think this project is the one for me. Sorry i know its asking alot because i know you have alot on your plate but it would be very much appreciated. Thank you sooooo much Dan M.
Kajnjaps (author)  vtec2k76 years ago
it's a BC547(B), common garden variety small signal transistor, you can replace it with almost anything.
the one that is labeled 4748? Its circled in red in the picture. I just cant read the writing above it. I just want to use the same exact parts as you so i know it will work. Also where is a good place to buy all this stuff? I found the solar panels for cheap but all these other components are going to be hard to find local because in New York they dont have these kinds of stores anymore. Only circuit city's and they suck.
edfel01 vtec2k76 years ago
Is there a radio shack?
Kajnjaps (author)  vtec2k76 years ago
sorry for the handwriting... Thats a 1N4148 diode, also quite common. There's a gazillion other types of diodes that should do the same. Funny, you're from THE New York and there's no electronics shop nearby. I live in some backward little town in some Euro country, that's probably smaller than most of you're landfills, and at least we have one shop where I can get parts.What is this world coming to... :-)
yeh this city has severely gone the way of the "Big Business". None of the big stores carry components anymore. Its purely a "if it doesnt work right just swap it out for a new board" mentality. So sad. Great instructable by the way. I have been checking out the site for so long and nothing except the bread making has been in my price range or great interest. This hit me right where i like it though so ill let you know how it goes.
vtec2k7 vtec2k76 years ago
also the Cap on the top left, is that a Polarized Cap or a trimmer?
Kajnjaps (author)  vtec2k76 years ago
100nF unpolarized, doesn't really matter, you could use polarized 1uF or something else, only there for "good practice".
edfel016 years ago
this is a really cool instructable
BrettAlive6 years ago
I am going to attempt to make this setup on my daypack/bike pack for charging my MP3 player, and integrate another Instructable for on-board lighting for night hiking or bicycling. I found the cells for 8 dollars American each. Good show mate. I like the project. -Brett
Kajnjaps (author)  BrettAlive6 years ago
Thanks! Post some pictures when you're done.
DIYDragon6 years ago
I need to get into soldering so I can start doing cool stuff like this.. neat instructable. Favorited. : )
Kajnjaps (author)  DIYDragon6 years ago
Thanks, one day, I should write an Instructable on getting started with electronics. I guess many people would like to learn, but get scared off by the 'difficult' theory. Also nowadays there is such an overwhelming amount of information available that newcomers don't know where to start. My advise: take one step at a time. Don't run off to build a time-vortex-black hole machine before you can , for instance, calculate the correct resistor to use for a LED.
Do you have an instructible for a time-vortex-black hole machine? I have been looking for one for some time... I would appreciate the beginner's guide too.
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