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 you 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.
Your'e probably asking yourself, "hey, why doesn't he hook up a whole lot of panels to thrown 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 probabl 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 awhile.
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.
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 you 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.
Your'e probably asking yourself, "hey, why doesn't he hook up a whole lot of panels to thrown 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 probabl 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 awhile.
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.
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Your charger circuit here will have the desired effect, and for the batteries you mention, the issues with milliamps should not be a concern. The kind of series (blocking) diode is not a big deal either, since the forward drop will not matter. You may use any garden variety silicon diode, and worst case is that the diode will fail (without damaging anything else) and you are out a penny. Just be sure to pick a diode that will allow the max current from the solar cell, in your case, 80 mA, which is 0.08 Amps.
Good luck, and always, safety first. It's a great habit to have.
Now, if you have a silicone diode with about 0.6V forward drop, you have to produce 3V. If you have a schottky diode with 0.3V drop you only need to produce 2.7V.
3/2.7 = 1.11, an 11% efficiency increase. More importantly, during periods of less sunlight your cells may not even be able to get the voltage up to 3V at a meaningful charge current so that extra 0.3V margin could allow for charging for more hours per day too.
"One or Two Solar Panels rated 4 Volts or above"
If the 4-volt requirement is no longer true, then yes, it does matter.
I really shouldn't be writing instructables at 1 a.m. anymore.
Thanks!
The biggest tragedy would be for someone to have a great idea and not share it.
Say we have two AA batteries in series Then wired in parallel to another set.
That's about 2.4-2.8v at like...4000Mah.
What if we used a cell that is 6v @330Mah? The Mah is cool but what about voltage? If anybody could help I would be really grateful.
Also, you shouldn't charge NiMH above 30 C or 86 F so if it is getting really hot, like in a car in the sunlight, you will have a lower capacity from that charge.
Again, good luck, and keep experimenting!
kz1o