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Li-Poly?

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things

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hi all, i have a very small lightweight battery out of a remote control plane. it is covered in foil stuff, and has a little circuit attached. i presume it is a li-poly battery, as that is what it said on the packaging. i am trying to run an led of it, and it does work, but then the output stops. if i hook the led directly to the battery(before the circuit) it works fine. my question is, what does this circuit do? can i remove it? and why does the output stop after about 10 seconds? i will try to get a pic now.
thanks
 
heres a pic bat.jpg
 
i have just been doing a bit of reading, and have found that these batteries require very strict charging? and they can explode if shorted or overcharge. i certainly don't want it to blow up. so i'm guessing the little circuit on top is a charge circuit? and i want to leave it on there, but for some reason, the output stops after a while? i have heard that they don't like being fully discharged, so maybe the little circuit is stoping the battery from doing that?
 
sorry for all the posts, but here is a close up of the circuit. i just can't make out the numbers, but if anyone reconises these chips/circuit and knows what it's for, will be greatly appreciated!cir.JPG
 
If you want a answer fast maybe ask this question on a RC airplane site. There is a good chance you can get info on its care and feeding from these people.

I assume you have read the wikipedia stuff on them.

Have you tried to charge the cell?
 
i hooked it up to a small solar panel once, but htat's about it. i have been watching some vids of these things exploding, and i DEFINATELY don't want it to happen. so maybe i should just stay away from these things, they look VERY dangerous?
 
That little circuit is probably a battery protection circuit to prevent it from blowing up so don't even consider removing it.

What's that black blob on the battery?

Is it just glue or has the battery leaked?
 
the blob looks like glue.

you'll need a proper li+ charger. You can buy them, they are very expensive, or you can build one easy enough. Maxim makes some chips that are very easy to use for charging single cells, which is what you have.

The MAX1555 is a very easy linear charger, which you can power from USB or an AC-DC adapter.

The MAX1811 is another usb/ac powered charger, which can provide more current - unless you know what the ratings on your battery are, you might not want to go crazy with charging current.
 
LiPo's are safe, you just need to use a proper charger and make sure not to over-discharge. I work with them at work and have a programmable charger that cost $100 but is very nice. You can get cheaper chargers that are OK for $30 or so. I think Groupner makes one.

Never charge to more than 4.2V, and never go below 3.0V. They have a very flat discharge curve, staying around 3.7 for most of their charge life.

They are neat little things, right now I'm working on a project with a 150mAH single cell that will do 10C continuous discharge. Nifty.

Oh, and I have no idea what that board is. Might be protection circuitry, but who knows. I would remove it. Make your own protection ckt so you are sure what it does, if you feel you need one. Also, does the cell pack seem puffed out at all to you? Or is it flat?

Oh, and don't connect the LED straight to the leads. That could be very bad. If it's forward voltage is much less than the battery voltage, you will dump a LOT of current through the LED and it would be bad for the battery.
 
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The little circuit probably detected the battery voltage becoming too low and cutoff your LED. When the voltage of a Li-Po battery gets less than about 3V then it is ruined.

The little circuit also might be a charger circuit to cutoff the charging when the cell is fully charged.
 
thanks for all the answers! that black stuff is just glue. no, the package doesn't seem puffed. and i think audioguru is on the right track about the led turning off. i hooked my multimeter to the battery when the led was on, and it read about 3 volts, then it slowly discharged to about 2.6 volts, then it cut off. i'm pretty sure this circuit is for charging, because inside the RC plane, there is one little circuit that it was hooked up to, and it had inductors and all those rf related components, so that would be the rf side of things. i wired it up to a 4 volt solar panel through the 2 wires, and it seemed to charge. if only i could read the numbers/writing on the chips, then i could look up the data sheet.

thanks
 
Well if it is engaging you might already have limited the life of the battery. Going below 3V really shortens the lifespan. But yeah, if you can get part #'s you might not have to buy a charger.
 
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