0

Rechargeable battery question
Moderators: adafruit_support_bill, adafruit

Please be positive and constructive with your questions and comments.

Rechargeable battery question

by neojonas on Sun Mar 21, 2010 7:31 pm

I'm working on a robot that will roam around doing tasks and when it's batteries have gotten low enough it will seek out sun to charge it's batteries with solar. I've been doing a lot of research on which batteries to use and I'm trying to decide between NiMH and Lithium Ion. It seems NiMH are better if you can quick charge them, which I doubt I can do with solar. I'm guessing I'll be running less than 10% of the batteries current into it for charging. But it seems it's easy to build a charger for NiMH. Lithium Ion seems like this slow charger might work but I worry about the safety with Lithium Ion. I don't want any explosions or fire (at least not unwanted ones).

Has anyone tried to make something like this and what batteries have you found to be good for a rechargeable robot? Thanks for you help! I'm learning a lot from this forum.
neojonas
 
Posts: 5
Joined: Mon Mar 15, 2010 12:50 pm

Re: Rechargeable battery question

by franklin97355 on Sun Mar 21, 2010 9:33 pm

Stick with NiMH until you perfect your knowledge and design a charger and fireproof battery compartment. Start slow, build safe.

franklin97355
 
Posts: 21362
Joined: Mon Apr 21, 2008 2:33 pm
Location: Lacomb, OR.

Re: Rechargeable battery question

by Entropy on Mon Mar 22, 2010 10:27 am

How fast does the robot need to move?

At low speeds and many environments, the weight disadvantage of lead-acids goes away. Lead-acids are near the top in the energy per unit volume rankings, they're just awful as energy density per unit weight. They're also easier to charge - MUCH easier than Li-Ion, and quite a bit easier than NiMH. You just need a current-limited constant voltage charger. (Although for solar cells below a certain wattage, you can sometimes just floatcharge lead-acids directly from a solar cell w/o charge circuitry - for example a 5W cell floating a car battery. Any more wattage and you need a charge controller.)

I suggest looking into SLAs or gel cells (these are lead-acids that are much safer to handle than the "don't tip it or it'll spill" construction used for car batteries.)
Entropy
 
Posts: 472
Joined: Tue Jan 08, 2008 12:43 am
Location: Owego, NY USA

Re: Rechargeable battery question

by neojonas on Mon Mar 22, 2010 5:08 pm

Thanks for the tips. I think I'll stay away from Lithium until I get some more experience. I'll look into the lead acid batteries as well. Just need something that can slowly charge with solar. I see a lot of solar garden lights using NiMH so maybe I'll stick with those.
neojonas
 
Posts: 5
Joined: Mon Mar 15, 2010 12:50 pm

Please be positive and constructive with your questions and comments.