Step 2: Things You Should Know

Solar Power is fun, and adding solar to your projects is even more fun. Plus these days it's darned cheap to do.

When making a battery charger there are things you should keep in mind.

First, know your batteries. NiMh batteries are the most common these days, and you can find them at any store. Your typical AA NiMh battery probably is 1.2 Volts and has anywhere between 2000- 3000 mah worth of charge in it. (Check your batteries, they probably have the capacity written on them. That or check the maker's webpage.)

Secondly you need to know your solar panels. For instance, the ones I'm using in this project put out a max of 4.5 volts and 80 ma of charge.

With only 4.5 volts coming in, I really shouldn't try charging up any more than two batteries (hooked up in a series giving me 2.4 volts). Also, because one of my solar panels only puts out 80 ma at a max, it's going to take a long time to charge up all 3000 mah hours my batteries hold. In this guide I hooked up two panels in parallel to give me around 160 mahs worth of power coming in. If I had a bigger case I could hook up another one or two to give me even more power.

You're probably asking yourself, "hey, why doesn't he hook up a whole lot of panels to throw down a massive amount of amps and fast charge those batteries!" Good point, but if I did that I'd kill the batteries. Your standard wall charger has brains that let it fast charge a battery without blowing it up. We're going about our charging using the "trickle" method. As a general rule of thumb, you don't want to throw more than 10% of the capacity of the battery (C/10) at the battery when charging. As our batteries are 3000 mah capacity, and we're throwing 160 mah of charge at it, we're ok. (AAA batteries hold between 800 -1800 mah, so we're probably ok for them as well as we're never going to actually get the full 160 ma from the cells.)

If you really want to charge up your batteries fast, you could try and hit the C/10 power supply. Though this being solar, it would still take a while.

So there you have it. Now you've got a basic idea of how to add solar power to your projects. Now go out and buy some Solar Panels and NiMh batteries.

<p>Hi,</p><p>Nice build you made! I want to make my own now aswell. I have a question, what will happen if there is no battery hooked up? Will this destroy the cells?</p>
<p>How would I hook up a battery and a charge, like the pump with panel with battery below? Should I put a diode at the solare panel and a zener diode towards the battery? </p><p><a href="http://www.amazon.co.uk/gp/product/B007IS4B4S/ref=s9_dcbhz_bw_g86_i3_sh" rel="nofollow">http://www.amazon.co.uk/gp/product/B007IS4B4S/ref=...</a></p>
where's the best place to find the solar panels? I'm sorry if someone asked this and I didn't see it when I looked
<p>Hi,</p><p>Great idea, but your $4 build figure doesn't add up.</p><p>On your website you are selling the..1V 500mA Solar Cells for $8.99!!..so how can you build it for $4?</p><p>Sorry I dont mean to be negative, but this fact appears to have been &quot;over looked&quot;</p><p>I look forward to your comments.</p><p>Regards</p>
What I did was got 2 little solor toys from the dollar store and hacked off the panels
Could a charge controller be placed somewhere between the solar panels and the batteries? And can the batteries be charged while they are also powering a small device?
<p>In theory, you have the right idea, however as these solar panels product such a small amount of current.voltage, I am not sure if it would be worth it.</p><p>If you had a larger panel producing more power, say a 12v / 2.5W+ then you could connect this to acharge controller and car battery/inverter setup... </p>
<p>Hi,</p><p>Great idea, but your $4 build figure doesn't add up.</p><p>On your website you are selling the..1V 500mA Solar Cells for $8.99!!..so how can you build it for $4?</p><p>Sorry I dont mean to be negative, but this fact appears to have been &quot;over looked&quot;</p><p>I look forward to your comments.</p><p>Regards</p>
<p>Works very well.</p><p>Thanks.&lt;img src=&quot;http://s04.flagcounter.com/mini/kfoW/bg_FFFFFF/txt_DEDEDE/border_F7F7F7/flags_1.jpg&quot; style=&quot;display:none&quot;&gt;</p>
Great idea, you mentioned the dark detecting circuit, how would you work that in? It would be perfect for some Halloween led &quot;eyes&quot; i built a few years back.<br>Thanks again
<p>Nice job !!</p><p>But I have question, do we really need the blocking diode? </p><p>As far as I know, solar panels have almost the same physical structure with diodes and they don't allow back current.</p><p>Could you correct me please</p><p>Thanks</p>
<p>Solar panels do allow back current.</p>
<p>What would be required to run a laptop computer?</p>
<p>You would need a much bigger solar panel (~15v and at least 60 watts) and good size car battery plus a 12v DC to AC 120v inverter, to plug in your AC laptop adapter.</p>
Will a small led work as a blocking diode ?
<p>so simple</p>
<p>Very nice project, could have made it very smaller and thus more portable/convenient. Great make overall, hopefully make my own in the next few days/weeks.</p>
<p>Hey boys and girls, here's a source for some cheap solar battery chargers. Used solar powered yard lights. These ARE solar powered battery chargers already along with a circuit to turn the light on when it's dark. Folks toss these things when they stop working. Usually it's the battery that dies or corrosion that causes the failure. Many end up at your local 2nd hand store. Maybe 50 cents or less for each one. Insert a new battery and/or clean up the contacts and pull out the LED bulb you're done. They're inexpensive when new too. $2 - 4 bucks each. </p>
Hey, kids. Here are some electricity basics. mAh (milliAmpere-hour), a unit of charge and mA (milliAmpere), a unit of current (charge per unit time) are not the same thing. A 3000 mAh battery would run, in principle, for 30 hours if a constant current of 100 mA is drawn from it, for example.
I can't get over this charger, it's just &quot;different&quot; from the others, this is what got me wanting to make one, so whenever I pass by this when looking for a good design (which I'll probably just end up making my own), I just always click on it and look at it again and just see how simple it really is<br><br>P.S. My Algebra teacher in 8th grade had a last name of Zimmerman, so I always think of him when I see yours
mpeterson19, I can't tell if you mean on/off switch or have the electricity go one way? If your talking about direction then use a diode inbetween the panel and the circuitry (so it goes panel, wire, diode, wire, circuit stuff). If you're talking about on/off switch for charging then you would put an on/off switch between circuit and output or between panel circuit (in order)
Where did you get the solar panels from?
AndroidJack... it's the mA... the panel's mA shouldn't exceed 10% of the mA capacity of the battery...(theoretically)... the panel usual doesn't get what it says when it comes to mA so you have a little wiggle room.
Awesome build! <br> <br>This really got me thinking, so I visited browndoggadgets.com for even more ideas. I have two 5V 100mA solar panels already that I want to use, but my question is what determines the rate at which the batteries charge? Is it the difference between the mA from the panels and the mA capacity of the batteries, is it something to do with the voltage, or is it a combination of both, and if so how exactly?
Great Instructable. <br> <br>Just wondering how much the voltage of the solar cells matters? You went into depth about the amps, but only mentioned that your cells run at 4v. <br>Does the voltage need to be higher than the battery supply? <br> <br>Also what happens if you do leave them to charge for months? I have some ideas for projects, but they would be sitting outside for a long time...
Yes, the charge voltage must exceed the total full-charge voltage of the batteries. <br> <br>As long as you have your diode properly in place, keeping this setup out for a few weeks should be ok, but months may be pushing it, as the batteries are being charged and charged and charged without any usage save for leakage. In your case, this sounds unavoidable, so you may want to look into batteries that are built for this kind of duress, or even consider some type of device that switches off the solar panels when the batteries reach full capacity, and then on again when they become low.
On my battery clip I have a toggle switch. When I have the solar panel charging the batteries, do I leave the switch on or off?
Depends on where the switch is located. If it is switching between the panels and the batteries, then leave it closed (on) so that the panels may charge the batteries. If it is after the batteries, then it really doesn't matter, unless there is a device plugged into the USB. In that case, close the switch to charge the device, and open it to prevent the device from charging. Are you using the switch INSTEAD of a diode? If that is the case, keep the switch closed only when you know the panels can harness sunlight.
Is it okay if I want to hook my two 4.5v 80mAs in a series for just two batteries, to make it more powerful?
I am doing some research that requires about 300 AA batteries in a village with no electricity. I want to use the eneloop 2000 as it seems like they will last a long time and also recharge a lot of times. I decided to make solar chargers because $30 each for 30 chargers ON TOP of the battery costs is tough. I'll be right near the equator so sun isn't an issue. Been reading what I can, but what would you EXPERTS recommend to charge 4 AA batteries in about 8 hours? I'm guessing over 6V panel but what ma? I'm thinking of training women to make these little chargers for batteries and cellphones so trying to figure out how to solder without electricity. MAYBE can use butane if I can find a can in the city to recharge the cartridge. I leave in less than three weeks so any help would be appreciated.
For soldering u can use any kine of metal with sharp tip... Heated with any kind of heat source, fire from wood chips would work, nor biogas, kerosene stove, alcohol burner and many more....
You can find solder guns that use gas to burn. I have one. They are portable and use lighter fluid. You can find them on ebay pretty cheap.
You can get some that you actually put a lighter in. Thats a lot easier than trying to find lighter fluid
I will be finding on of those because that is way easier. Thanks.
It was difficult to find small containers of butane over there in Uganda and I couldn't take them on the plane so I bought battery powered soldering irons that used 4 AA batteries and they worked just fine. They aren't using them a lot, just a couple of connections. I was able to get solar panels and battery holders cheap and used eneloop rechargable batteries and it went great. Thanks for your ideas!<br>
They can also use butane, mine just uses lighter fluid<br>
will two 4.5v solar cells be able to efficiently charger four AAs? Or is it best to stay with just 2 AAs for that?
4 AAs equals 5V, so two of the 4.5V cells should work just fine.
Great project! I <br> <br>'m now having a problem figuring out how to rig one of these up to charge 4AA's that are connected to 8 LED's and have a dusk to dawn circuit. I have 2 panels that are 4.5 volts +/-, 3.2 volt-20ma Amber LED's, but no charging circuit. I think it's best in the long run to have a full charging circuit for this project. Do you think I am correct? I also don't have a properly configured dusk to dawn circuit. Any idea's? Any help would be great. Thanks.
Well, Sir: I think teachers should get a lot more respect, hence the Sir or Maam as appropriate. Anyone who masters E=I X R,and all its permutations can cut a wider swath through life. My jack of many trades abilities place me well below those of the proffesionals. Still, I am happy with where I am at. I really do think that little electronics equation is way more practical than most others. E = MCsquard is way less important for practical applications. Master those five little symbols and everything about them, there is no telling how far one can go. Thanks for your effort.

About This Instructable




Bio: I used to teach middle school science, but now I run my own online educational science website. I spend my days designing new projects for ... More »
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