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Author Topic: Rechargeable battery for Arduino project: which one?  (Read 730 times)
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Hi, All -

I'm working on an Arduino project that will be powered more or less like a cordless phone: drop it in a cradle and it'll charge, but pick it up and it'll run off the batteries.

To do this, I bought an Adafruit USB/DC LiPo charger and a 2200mAh LiPo battery. Seemed like it'd work on paper... I don't have a lot of experience with LiPos, though, and since this project will be a gift, I'm a little concerned about safety. I don't want to inadvertently start a fire with a LiPo if I can help it.

I recently learned that it's possible to use off-the-shelf NiMH batteries for a similar purpose instead:
http://tomtor.blogspot.com/2012/09/solar-powered-arduino-and-attiny.html

So... two questions.

1) Am I being overly-paranoid about the safety of LiPo batteries given that I have the Adafruit-made charger?

2) Would NiMH batteries be simpler/easier to work with? Seemed like the schematic in the link above called for a pretty minimal setup, and I could swap out the solar panel in that project with a 5v source.

thanks,
David
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The NiMH is not easier, there is no charge limiting. That is not good.

Adafruit uses a special chip to control the charging. That is the only way to do right.
And I haven't seen anything bad designed by Adafruit, so I trust them they did it well.
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Thanks, Erdin-

I figured I was just being a little over-cautious. Do you think it matters what kind of enclosure the LiPo/charger circuit is in (as long as it's not a conductive material)? Apologies if these are obvious questions, but I'm very new to working with LiPo batteries.

David
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For indoors use ? Just any plastic box, or even a wooden box.
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Hi, Erdin -

I'm planning to have the LiPo, charger, and arduino inside a glass jar—a hole drilled in the bottom will connect the assembly to the power supply. Do you think ventilation will be an issue? The top will be closed, but not hermetically sealed shut since it's essentially another piece of glass loosely sitting on top of the main body.

thanks,
David
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For clarification, it's this jar:

http://www.amazon.com/gp/product/B0001BMYH0/ref=oh_details_o07_s01_i01?ie=UTF8&psc=1

Without a rubber seal, the glass top shuts loosely.
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I think the ventilation is not a problem. I don't know what components are used that create heat, but I think it is okay. Glass transfers heat from the inside to the outside.

Do you want to use it outdoors ? Moisture could be a problem. If damp air gets in and condensates to the glass, the dry air gets out  and you build up water at the bottom.
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Nope - just using it indoors, so moisture shouldn't be a problem.

I appreciate the advice - I think all the RC Car/Plane forums I've found made me nervous about LiPos, but then again, I'm not charging/discharging at even close to the same rates as they are.

FYI, this is for a variation on a friend's "whisper jar" project:

http://www.rosenthalproductions.com/projects/whisper-jars

...mine won't record audio, though, just play it back. I'm planning to give it to my sister as a wedding present, so it'll play a randomly selected toast or speech from her wedding whenever it's opened. Since I want her to be able to pick it up and use it whenever she wants,I'm keeping the LiPo/Charger inside it, and supplying power through the jar bottom with a hacked Duracell Powermat (http://www.amazon.com/Duracell-Powermat-CSA4B1-24-Hour-System/dp/B0082YVBO0).

The whole electronics assembly is built, and seems to work so far... I just wanted to double-check the safety concerns.
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