Hello everyone, so i'm looking into starting to work with lithium batteries. There's a lot of warnings and hype about how dangerous they are, to be honest it has me a little worried about touching them lol, so i'm looking for project specific advice vs. the generalized replies to most other posts. I have several 3.7v 4000mAh li-poly batteries lying around picture below, that I've salvaged out of the leappad tablets my son has destroyed and id like to use them for a few projects. They have a 5 pin connector 2 red, 2 black, 1 white. From what I've read i feel comfortable assuming the white is a thermistor ? I can test both reds with both black and still get 3.7v. So first question is it safe to remove the black covering to see how everything is wired inside ? Or is it possible to do without removing the cover ? Next question would be, i have a cheapy lithium charging circuit from ebay that's rated at 5v 1a can i charge these batteries with that or should i look for something else ? I know that would leave my charge times at roughly 4 hours. One of the projects tho i was hoping to power the charge circuit from 2 5v 500mah(manufacturer rating i haven't tested i'm well aware its highly unlikely ill actually get that) solar panels ? i'm hoping its 2 single cells at 4000mah but i'm pretty sure its 2 cells at 2000mah.
Batteries like that look perfect for experiments like this: - YouTube
(29 second video showing a violent fire when the battery is stabbed with a knife.)
Lithium batteries are only safe with the correct charge AND discharge protection. If you don't know what the wires coming out of the battery do, then it's not safe. It's sad to see an otherwise perfectly good product go to landfill but the amount of time you'd spend working on it is absolutely going to cost more than a new battery that comes with a datasheet.
Open it up (carefully!) and see what's there. I'm sure it will be educational.
The battery could have double wires for positive (2xred) and negative (2xblack).
A 10k thermistor (battery temp) might be connected between the white wire and negative.
As mentioned, only use a proper LiPo charger.
Leo..
This is the Charge Circuit. I attempted to google a datasheet for the battery with no luck. To my understanding from reading adafruit and such 3.7v lithium's are "supposed" to charge to 4.2v which the circuit says it does, so im more curious as to the charging a 4amp battery with a 1amp charger, i did just notice it says adjustable so im going to read the datasheet when i find it. Videos like that are EXACTLY why i'm asking these questions before i touch them
I'm going to try the knife thing tomorrow on one of my many LiPo packs to see if I can duplicate that video. I bet I can't. I suspect the video is fake.I think this one is more realistic.
I've seen videos of people having to work very hard to get LiPo packs to burn. One person ended up pouring gasoline on the pack to get to burn since their other attempts to ignite it failed.
Of course LiPo cells can burn and should be treated carefully, but I see a lot people worry much too much about LiPo batteries. Most of us carry one around in our pocket all the time in our cell phones.
Don't throw away the black battery. Charge it and use it.
I think the charger you linked to would work, it will likely take a while to charge but I don't see any reason why it wouldn't work.
Charging single cell LiPo batteries is relatively easy. An inexpensive charger is fine for a single cell. Multiple cells require a bit more care.
Edit: I think I was too quick to call the other video a fake. I think there is likely a big difference in how LiPo cells react depending on their condition. The milder reaction occurred in older bloated packs. The very aggressive reaction occurred in a pack which looked new. As I think about this a bit more, I don't think the video was a fake but I still plan to try this for myself new freshly charged cell(on a smaller less expensive cell).
Well i was originally going to connect the 2 red wires to the out + and the 2 black wires to the out - ? But i'm guessing i should pull the black cover to see if there's one or two cells first ? Or could it maybe be a 1 red wire is intended as an input and the other an output kind of situation ? I did attempt to follow the traces on the original PCB but there were SO small and running under around and inside of almost everything.
MorganS:
Lithium batteries are only safe with the correct charge AND discharge protection.
LiPo cells in lots of consumer electronics have PCBs to protect a LiPo but but these PCBs are generally not present in LiPo packs used in RC aircraft.
I'm pretty sure as long as a LiPo cell isn't charged or discharged too fast, it will be fine.
I believe one of the purposes of the the protection circuits is to keep the cell from being discharged beyond a point which will damage the battery.
As I mentioned, RC packs generally don't have these circuits so it's common (and a very good idea) to use some sort of alarm to prevent a battery from being over discharged.
I have several of these and I think they work well.
The one above needs at least two cells to work but there are also single cell alarms.
I prefer LiPo cells without the extra PCB to prevent over discharge because these circuits can end up interfering with the charge process.
RC LiPo packs can generally be charged at 1C (at a rate which would fully charge the cell in one hour). Consumer electronics LiPo or Li-Ion cells are generally charged at about 0.5C (two hours to charge).
A LiPo shouldn't get warm as it's charged but RC packs are often warm after they been discharged quickly.
It's a good idea to use a charge bag when charging LiPo packs. Apparently they're great at containing the flames of a burning LiPo but the smoke will still come pouring out of the bag. If practical, it's a good idea to charge LiPo cells in a place where the smoke of a burning pack won't cause a big problem. Apparently the smoke smells awful.
I have scores of LiPo packs. I've never had one catch fire. I use a LiPo bag and I never leave the house while charging a pack. I also don't leave batteries charging while I sleep. It's not a good idea to charge NiMH or NiCd batteries unattended either.
K well ill definitely order a bag as soon as i can. Would monitoring the voltage with an arduino then tripping a relay to disconnect battery power work instead of the discharge alarm ? Or is the alarm meant to monitor current ?
cgroshko:
K well ill definitely order a bag as soon as i can. Would monitoring the voltage with an arduino then tripping a relay to disconnect battery power work instead of the discharge alarm ? Or is the alarm meant to monitor current ?
You just want to make sure the battery isn't discharged past a set value. The precise cutoff voltage depends on who you ask. I've read batteries last longer if you use a higher cutoff voltage than a lower one.
I think 3.0V is a common cutoff point but 3.3V is also common. I often recharge my LiPo cells once they're down to 3.5V. The main benefit of using a lower cutoff point is you get a longer runtime between charges.
I know there used to be concerns with some batteries about creating some sort of memory effect by not letting batteries discharge fully. I'm not sure how real this effect ever was but if such an effect exists it's not a problem for LiPo cells.
I've run into the memory problem with a few phones but from what I've learned i don't THINK its the discharge i think its from not charging them completely. Plug it in for 30 mins here and there eventually the battery only lasts 20 mins lol.
