Instructables has quite a few guides on how to make Solar USB Chargers, including the very well done guide on how to combine a Lady Ada Minty Boost circuit with a solar + lithium ion battery. Great, but a bit expensive to make and not a very simple project for the weekend DIY person.
Well luckily for us I know how to make one for under $20 that is better in nearly every way and also completely fits into an Altoids Tin. Covert style.
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Signing UpStep 1What You Need
USB Charging Circuit
Solar Panel 4V or greater
AA Battery Holder
AA Rechargeable Batteries
1N914 Diode
Altoid Tin (or whatever)
Wire
Tools:
Soldering Iron
Solder
Tin Snips
Melt Glue Gun and Glue
Tape
Cost is less than $30. I can make one for under $10 when I buy parts in bulk. I have a kit available at my website BrownDogGadgets.com which has everything you need to make this project. Also, if you're lazy, I do sell made versions in a variety of tin styles.
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Well I recently tried with a new batch of these circuits and my iPhone 4 charged perfectly. Big surprise to me.
If you're going to be using this with only an iPad or iPhone you might want to use a different circuit. I have one that has a retractable iPhone/ iPod/ iPad cable on it, as opposed to a USB port. Handy.
For example, if i wire 2 packs of batteries, each cell with 1.2V and 2000mA together in parallel to make a combined total of 2.4V and 4000mA, should i buy a solar panel with a current output of 200mA or 400mA for best results?
Thanks!
Parallel = 1.2V at 4,000mah
Series = 2.4 at 2,000mah
10% of total capacity.
I've gone over 10% before, it really depends on your batteries and how trusting you are of them.
So in your case you'd want to use two battery packs, with a total of 4 batteries. Giving you 2.4V at 4,000mAh.
Go with the bigger cell. You'll never ever reach your max power for solar anyways.
will the 12v be sufficient? ... too much? will the 100ma allow me to charge the batteries in a reasonable amount of time given that it's solar trickle charge we're working with?
Meaning a 12V system should have at least 18V of solar panel in it.
So if you're doing 9.6V you should have at least 14-15V of power.
It sounds like I can't very well blow anything up with 12v so I'm going to proceed with wiring the mock up and testing on the next sunny day.
also I might add, the panel only puts out 100ma, and that for 2500mah batteries would take forever so i've got two panels. Should suffice. The idea is that i can strap the device atop my backpack while hiking, trickle charging as i do, and then flip open to reveal both panels when the opportunity presents itself.
I am looking to build a slightly different version of this instructable, but with supercapacitors instead, to make this "super-green". Do you know if it would be possible to just use supercapacitors to completely replace the batteries? Even if it would only work while in the sun, that would be fine with me... Any help would be great!
The only downside is that super caps cost a lot of money compared to just using some AAs. Plus because of how little power this thing uses a set of AA batteries would last a very very long time.
http://www.ladyada.net/make/mintyboost/changelog.html
Apple has apparently changed and rechanged their load protocal to make it difficult to charge. Adafruit has tried to keep up with it.
The ones I bought for the yard claim to be 4x bright. What would be the proper way to determine if I need 1 or 2 solar cells of these? Just test output of the panel with a voltmeter?
You'd still need to get all the other parts. AA holder, 2 AAs, diode, wires, charging circuit.
Plus you should really use a multimeter to figure out what the voltage of your solar cells is. You need a combination that is greater the 3V. The bigger the better.
Long story short you just need to find a newer charger that has this problem fixed.
Question: Do you know what kind of capacitors are on that circuit...just curious.
-Relient Owl
The caps just help the power flow more smoothly in the circuit. They're not for storing large amounts of power. That is why we have batteries in the circuit. Though some people have instead used some massive capacitors instead. They're nice, but cost an arm and a leg.
I don't understand two things:
1) i have a lithium batthery 3.7V 2800mAh with a internal circuit for the protection: can i use it in your circuit? I need an battery charching circuit for it? Can I disassemble something to use?
2) if i put in parallel a simple AA ni-mh battery, the 10% of their maximum limit for charging it from a panel will double it? So i have a solar panel that give me 700mA, so if i put in parallel a 2200mah battery to arrive at 6600mAh, is it sufficient?
Thanks a lot.
You would need a small changing circuit to handle your Li-ion pack. You can pick them up most anywhere. For instance I know adafruit.com has some that work well in similar circuits. Otherwise ebay is your friend.
I wouldn't try and take a li-ion charger out of something else. Just buy a small circuit from somewhere. Adafruit.com has directions on how to hook up a li-ion pack to a very similar circuit to the one I use in my project. Seriously check out her site.
Bye!!!!
Also, I saw a video on youtube and this guy used 4 AAA's. Which is better, AA's or AAA's?
Wall chargers step down voltage, we need to step it up. This means you need a little emergency USB charger that uses 2 AA batteries. It'll boost the voltage up to the right levels.
(Assuming they're completely dead, though you'll always need about 10% more time than needed to charge up NiMh in my experiences.)
You'll also need full sunlight. If it's a bit cloudy then charging will take longer.
If you want fast charging (like very fast) you're going to need a bigger solar cell or several small solar cell. Solar is great, but you have to know it's limitations.
Plus your batteries will never be 100% dead (well, usually) so you'll never need to charge them up all the way.
Shoot, I have a few hundred in my basement and I want more...