I am attempting to build an Arduino solar circuit that can utilize solar power by day to operate and to charge a LiPo battery backpack, and then at night automatically uses the power from the LiPo battery. Is there any way to do this? The switch for LiPo battery backpacks are hardware switches. Or is there a better way to do this? Essentially, I want to charge LiPo batteries and then discharge them without having to manually do anything.
The problem with using LiPo's is they are very sensitive to being overcharged, undercharged, shorted, overheated, punctured etc, so you will need a little charger for the LiPo to be safe.
As for getting it to turn on at night, you could have something senses when the voltage being generated by the solar panel drops below a certain level, it switches to the battery. That's how the typical garden solar lights work using minimal components.
You had a question in there... "is there a better way to do this?"
Is this a mobile application?
If it is not, then there IS a better way.
Just not as glamorous as LiPoly.
No, not mobile, just small scale.
Whatever it is has to fit into a 2.5"x1.5"x3-4" space, battery and all. It's enclosed so it doesn't need to be visible.
Certainly this is something that the Arduino could handle, but be aware that some of the Arduino software tasks will have to handle the battery management. I would recommend that you first research on Li-Po battery useage. You have to make sure you don’t over-charge, you have to disconnect the battery when cell voltage drops too low.
It’s all possible, automatically, but your choice of Li-Po battery means you have to do your homework well or a fire hazard is a real possiblity.
Doesn't have to be lipo. Just has to be small. Lipo was inexpensive when I was looking it up.
I would recommend using a dedicated charger IC then... unless you're OK with blowing a lot of fuses and ruining several battery packs while debugging your code and circuitry :-[
LiPoly requires a charging circuit that can operate in two modes... constant current at the beginning of the charge cycle, and constant voltage at the end.
At the beginning of the charge cycle you use a constant current (specified by the manufacturer). That current is maintained until the cell voltage rises to 4.2 volts.
The charger then switches to constant voltage mode, holding the cell voltage at 4.2 volts, until the charging current falls to 10% of the original rate.
Not as simple as just connecting a solar cell and a diode!
“Not as simple as just connecting a solar cell and a diode!”
Where would someone (like me) get information on this type of setup - or do you have any recommendations for circuits to power a small Arduino circuit requiring less than 500mW?
I have a 1W solar charger but not sure what combination of pieces should be used to manufacture the final product. I’m sure this is basic electronics to some, but I am bewildered when it comes to this.
If there’s a beginner tutorial out there I’ll go and have a read as well.
I suggest you buy one of the "garden solar light" (like this one http://www.amazon.com/Moonrays-91225-Powered-Plastic-10-Pack/dp/B0024NK0P6/ref=sr_1_1?ie=UTF8&s=home-garden&qid=1257414688&sr=8-1) (they sell for $3 a piece at homedepot), take it apart and adapt it to your Arduino needs. You would need a step-up converter from the 1.2V-2.5V of the rechargeable (NiCd) battery inside. For higher current you can always scale up (more solar cells, more batteries).
Thanks - will have a look at one of those. Sounds like a good cheap real-life tutorial.
Still interested in the diode option…
Nuelectronics have a LiPo based 5v power pack designed for Arduinos.
The pack can accept charging from a solar cell or USB cable.
About US$22. They are in the UK, but they ship worldwide, and you can pay in any currency via PayPal or credit card.
The best bit: The board incorporates the charging control and discharge limiting circuitry.
(And my only connection is "happy customer".)
Also, I've just added a page to the playground for information about ways of powering Arduino projects....
This problem sounds complicated,why not buy a solar battery charger?it's so easy,and it is absolutely useful,besides batteries,it can also charge cell phones,laptops,cameras etc.