saftey

geekbait111 · Post by **geekbait111** » Wed Mar 15, 2006 5:33 pm

So I was wondering exactly how Li-Polies explode and how to prevent that. Because I know Li-Polies are super good but I don't want the same thing that happened to the GCp v. 1.5 and the housey thingy and Gamevelver to happen to me thanks.

daguuy · Post by **daguuy** » Wed Mar 15, 2006 5:45 pm

the battery site (i forgot the site address) has a section with lithium bateries that include a protection circuit, get some of those and you'll have nothing to worry about
EDIT: it's batteryspace.com
EDIT2: i found the page with the protected batteries but those aren't very high capacity so get some lipo batteries and a protection circuit

Post by **marshallh** » Wed Mar 15, 2006 5:51 pm

Best to buy a battery pack with the protection circuitry already built in, like a DVD player battery. You can get a Polaroid BT41 4200mAh 7.4v Li-Poly battery for about $60 if you froogle around. You can use any old wall wart to charge it, I can show you how.

What causes the explosion is when the cells get discharged beyond a safe limit (<~3v maybe timmeh87 can elaborate) and they explode the next time you charge them. They also explode if your charger doesn't stop charging when the batteries are "full".

geekbait111 · Post by **geekbait111** » Wed Mar 15, 2006 5:51 pm

Oh, yay!!! Thanks!!!
P.S Sorry about me being so stupid

.
edit: yah, how do you charge it with a wall wart, is there any risks like recharging it too much. By the way, is a Polaroid BT41 4200mAh 7.4v Li-Poly a DVD battery like http://www.walmart.com/catalog/product. ... id=2350787
that? Or something like it. But do you know if it still has the risk of the 3 volt thing or too much recharging risk (because it has-i think- the saftey feature)?

blackbox_dev · Post by **blackbox_dev** » Wed Mar 15, 2006 7:50 pm

Hmmm, I was wondering what the explosion "looked like".

Post by **Gamelver** » Wed Mar 15, 2006 9:59 pm

li-poly batteries can only go down to 2.7V, and up to 4.2V...any higher and BOOM!....no more portable

....I overcharged 'em, and they got to higher than 4.2V and so began the awful fire

.

timmeh87 · Post by **timmeh87** » Wed Mar 15, 2006 9:59 pm

theres 3 conditions that will get you some rupturing at least, probably fire

1) the undervoltage
2) the overvoltage
3) the overcurrent (in either direction)

so undervoltage has been discussed. basically, what ive heard is that once you get below "3.0v" they will start to grow large crystals when you charge them again. these crystals will tear through the layers inside the battery, and the outside one too. once these things are exposed to air, well, lithium is pretty reactive.

in practise the danger voltage is lower, maybe 2.3 or something. you also have to differentiate between load and no load. if you shut down when the votlage is 2.7v, the voltage will immedately jump back to about 3.5v, because the battery isnt under load anymore. when were talking about undervoltage, its the open-circuit (not loaded) voltage i think. at any rate, you shouldnt let them get below 3.0v under load, since they only have about 5% of their capacity left at this point anyways.

heres a graph that was generated this afternoon. green= volts, red= amps, blue= capacity.

you can see the jump in voltage after the load has been removed here. it dosent actually even jump past 3.0v in this case (it does on our other kind of cells... this is our first test with this kind, we probably brought this one a bit too low...). oh and the intial screwyness with the voltage? my freind was poking at the circuit while it was running

anyhow. that was a nice long explanation of condition 1).

so. overvoltage. you let the voltage get too high, the a'slpode. theres some videos of this on google video. its also what happened to gamelevelers portable gamecube. not pretty. max voltage is about 4.2v. 4.25v might be ok. if i ever measured one at 4.3v id immetately back away. thats about where they start exploding

and overcurrent. a portable shouldnt draw too much current, so theres two other ways this could happen - imporper charging, and short circuit.

so, how do you charge them? carefully. do you directly hook one up to a 9v wall wart? NO!. what about 5v? NO!!!

what we do is we hook them up to a constant currrent/constant voltage power supply. you set the voltage to a maximum to 4.2, hook up the battery, and then set the current maximum to whatever it is for your cells (1A is usually safe). so they will charge at the maximum current until they hit about 4v. then the potential difference isnt enough to charge them that fast, and the charging will taper off as they approach 4.2v. you should taper off the charging after 4v anways, so it all works out very nicely, and they stop charging on their own when they are done, and no potential difference exists (the power supply and the battery are at the same potential). id assume most "smart" lithium chargers work like this too. i reccomend getting one.

and i guess i should put a disclaimer here: im just a kid, i might not know exactly what im talking about, dont blow yourself up, yadda yadda.

Turbo Tax 1.0 · Post by **Turbo Tax 1.0** » Thu Mar 16, 2006 4:44 pm

buy a protection circuit from batteryspace.com they are pretty simple to wire up

Nicholai · Post by **Nicholai** » Thu Mar 16, 2006 7:57 pm

iam7805 wrote:Hmmm, I was wondering what the explosion "looked like".

Well, most start like this:

And end up like:

geekbait111 · Post by **geekbait111** » Thu Mar 16, 2006 9:08 pm

Oh, so in other words i should get a volt measure thingy and when charging make sure the charger is set to 1A about. Then I need to measure the voltage, when it gets to 4.2 V about I should stop charging it. And before charging them make sure that they aren't less than 3 V. So is that basically what this is whole forum is saying? And if I'm wrong (which I probably am) how do the batteries get to 4.2-3V??? Like from charging, too old/too much use, not enough use, or me being too stupid and they just don't like me, or something else.

timmeh87 · Post by **timmeh87** » Fri Mar 17, 2006 7:21 am

yeah, they change voltage as you charge them. go look at that green curve again. thats voltage, and it goes down as you discharge. it follows the same curve in reverse as it charges.

you could baby sit your charging with a multimeter, but it would be pretty boring if the battery takes like 3 hours to charge every time.

you really would be better off with a charger designed for your batteries. AND a protection circuit. theye like $15 and $5, respectively.

charger:
http://www.batteryspace.com/index.asp?P ... rodID=1268

protection:
http://www.batteryspace.com/index.asp?P ... rodID=2156

<edit. i was surfing batteryspace, and look what i found!
http://www.batteryspace.com/index.asp?P ... D=945&HS=1
these are the exact batteries we are currently testing for the car... we have a box of 20 of them. >

Turbo Tax 1.0 · Post by **Turbo Tax 1.0** » Fri Mar 17, 2006 8:37 am

they also sell premade battery packs on battery space with the circuit built in

blackbox_dev · Post by **blackbox_dev** » Fri Mar 17, 2006 9:24 am

Nicholai wrote:
iam7805 wrote:Hmmm, I was wondering what the explosion "looked like".

That looks pretty lethal.

I guess anyone would be pretty stupid if they didn't get a protection circuit for their Li-polys. (except for Gamelver, anyone who can finish a portable isnt stupid)

geekbait111 · Post by **geekbait111** » Fri Mar 17, 2006 3:41 pm

So... yah. DVD batteries have the protection circut thing. So what does the protection circuit actually do? Does it prevent it from exploding to a ceertant extant? or does it always protect it? Because that would be stupid if the DVD battery just exploded unexpected (like to a person who buys a portable DVD)

joevennix · Post by **joevennix** » Fri Mar 17, 2006 7:31 pm

The protection circuit keeps it from overcharging, or from running for too long.