Solar and batteries

[emmannuel]

So as I'm basically done with my robot I've started looking into other stuff I wanted to work/learn on.

I've always wanted to make a robot that would use solar but also store excess energy into batteries.  I know it doesn't sound very practical but I'm not trying to make a robot like the one I have now that can burn through the batteries faster than I'd like.  Luckily i use NiMH so it doesn't bother me to much.

I've tried to do the research and found products for sale that do what I want but they don't explain how I'd make my own

One thing I don't understand is how to charge a battery.  Do you just connect the battery to a higher voltage to charge it?

[Portugal]

Try to unmount a garden solar lamp and use it system, with boards and everything. I will try it.

[Commanderbob]

Be careful when charging batteries. To charge them you do just connect a higher voltage, but it should be monitored. Most NiMH batteries can handle 0.1C rate of charge forever as once they are charged they can vent it off as heat safely. That means if you have a 2000mAh NiMH battery you could charge it with 200mA of current and not monitor it charge rate. However it would take 10 hours for it to charge completely and some batteries can handle up to 4C when charging (15 min charge time), but most take around 1 hour (1C). If you need to charge it faster there are IC that are just for charging batteries. Like [url-http://www.maxim-ic.com/quick_view2.cfm/qv_pk/4788]this one[/url].
Justin

[emmannuel]

Thanks for the comments Justin that really clears up a some of the stuff I was wondering about.

I also was looking into a Solar fountain kit cause I wanted a solar panel and a pump for it anyways.  I was able to find it for under $40 on ebay thanks Portugal.

[Commanderbob]

Does it have batteries or just run the pump directly with the solar panel? My first electronics project was a solar iPod charger. Looking back on that now it was really easy, but it still took me a couple of weeks to take a 7805 regulator and two capacitors and get something that worked  . I did a lot of work with solar and batteries after that so I am glad to help.
Justin

[emmannuel]

Does it have batteries or just run the pump directly with the solar panel? My first electronics project was a solar iPod charger. Looking back on that now it was really easy, but it still took me a couple of weeks to take a 7805 regulator and two capacitors and get something that worked  . I did a lot of work with solar and batteries after that so I am glad to help.
Justin

Thats cool. Thanks.

I got a 2W solar panel that connects directly connects to the 6VDC pump. I wana make a circuit that can charge the batteries so that the pump could hopefully work at night as well.  I've been trying to find schematic or similar examples but not having much luck.

[Commanderbob]

If you want it to work at night there are a few things to consider first. 1) How long after light is not available does it need to work? 2) If the the pump takes 2W of power where are you going to get power to charger your batteries? A larger solar panel may be needed. I don't have much time now but if can answer those questions I'll see what I could come up with.
Justin

[Cotowar]

Don't know if it would work or not, but have you considered a DC/DC transformer and a DC generator, along with a second(possibly more) battery pack, and some kind of switching device in between that changes the power source based on current output? if you have room for something like this, I think I could help you, as it is how I was planning to power my android.

Let me know if its what you're looking for, if not, go with the solar.

[emmannuel]

Well I got the solar panel and pump and its a lot smaller than I thought it was going to be.  Which is great!

I've decided to change what I was originally wanted to do (hydroponics) to something that will be simpler and allow me to focus on learning about solar and batteries.  I was spending to much time figuring out hydroponics issues and not able to focus on what original goal of the project is.  This new project is more robotic too

The new project is a solar battery charger that properly aligns itself with the sun ever 15~30 min while there is sunlight.

I've drawn up a sketch of what it should be mechanically and should have a simple circuit up and more questions to ask later.
Greatest part of this project is I probably have all the parts but the wood to hold up the solar panel, the worm gear motor and minor electrical components I think.

I've already got an attiny26, NiMH batteries, mercury tilt switch, 5V voltage regulator, caps, LDRs, etc.  So I'm hoping I can spend less than $20 to finish all the bits and ends

I'm planning to get the http://www.pololu.com/catalog/product/73 as my worm gear box, and what ever else I need for my circuit.

PS:  My previous robot sneaked in my pic

[emmannuel]

So I have a much clearer view of what I want the bot to do now.

While not receiving sunlight the only thing getting powered will be the atmega8 from the batteries.

It would wake up every half and hour turn on the MOSFET to turn on the LDRs to check for sunlight if none go back to sleep.
If there is sunlight align the solar panel, then go back to sleep.

This idea should use very little power.

So I've made a schematic my problem is I still don't know how to charge the batteries while also allowing the batteries to be the power source.

I'd like to use a battery charger IC like http://focus.ti.com/docs/prod/folders/print/bq2000.html since its a simple to solder 8-DIP.

Suggestions (and criticism) are greatly appreciated!

[Admin]

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http://www.societyofrobots.com/robotforum/index.php?topic=4800.0