Made my own battery

[Nikmish]

My son's battery was almost gone, lasted only about 20min, so i build a new one out of used laptop battery cells - so far so good!
24v ~10ha

It's twice lighter too...

 

[Lucky7]

Now that's cool.

 

[itsid]

I hope you levelled the cells overnight.

And since those look to be lithium cells, I hope you added at least two thermal fuses to that contraption.

It's your son, so I do not think you'd want him anywhere near even the smallest lithium fire.

'sid

PS honestly.. one burning cell can scare a fully grown fireman when not in gear!

 

[ghost civic]

low voltage detection?

 

[machinist@large]

low voltage detection?

Thermal detection; I.E. did a cell start to go up in flame's. Lithium is pretty flammable, and usually requires specialist gear to contain and extinguish the fire. And while they might be available in the consumer market, I haven't yet heard of any home fire extinguisher rated for that....

 

[Nikmish]

you got me all worried now :\

I do charge with balance charger and have one fuse in the circuit, but that's it...

 

[itsid]

lithium cells are a ..

nice powerful, lightweight, and ohhh fancy...
all true, all good;
but they are dangerously fancy, since the people who DO know how to use them properly usually do not use them at all, for exactly those safety issues...
one false move and all that's left for you to do is RUN FORREST, RUN!!!!
Don't try to rescue anything, just get away as fast and far as possible.

now that being said.
You do not have thermal fuses installed..
Do so NOW!

Your laptop batteries had them for sure (I know no laptop with lithium cells that doesn't, at least none that can be legally bought in europe! who knows about them us'icans *shrugs*)
a small tube usually in a heatshrink, that stuck right between the cells, with two wires attached.

just wire that inline with the cells, I'd say for a pack that big, four of those
(one on each corner of the innermost 2x2 grid) should do.
That way you'll have the excessive heat under control (if done properly of course)

levelling (balancing) can NOT be done with a charger; never.
they do try, and they sort of work... IF the cells were perfectly balanced before connecting the grid.

So, no..
But since you'll have to cut some leads anyways to install the fuses...
here's what to do:
connect all cells in parallel, best with a freshly polished copper bar (as big and beefy as you can) then let it sit for a day or two.. if you can, make that a week just to be sure.
Now get your charger and charge them to about 30% individually.
(that's lithium cells sweet spot IIRC)
now reconnect them as before and again let them balance each other for at least a day.

If you got this far, it doesn't harm to grab a multimeter and measure each and every cell;
they should have the exact same voltage reading, if one doesn't.. do not use it!
(that's the one that'll break first.. and by braking I meant overheating, cracking, burning... uaaaaahhhhh)

Yes, lithium cells are great
but this is what happens if they break mechanically:
http://www.youtube.com/watch?v=gisdMQbtJqk

or electrically:
http://www.youtube.com/watch?v=HCGtRgBUHX8

'sid

 

[Lucky7]

Oh ****. Sid' your making me scared to use my computer.

 

[itsid]

I said it before, I'll say it again.
lithium cells are fine if treated correctly, but puncturing the cell or overloading/shorting a cell is not good advice.

Laptop manufacturers do their best to make them as safe as possible;
and they ask you to not buy cheap chinese laptop batteries for that very reason;
one failure and you should run
(personally I do not own a class D fire extinguisher... or could use it properly if I had one)

original battery? you're good, every once so often touch it.. if it's too hot to touch, shut down the computer and let it cool down (or remove the battery and use the powersupply) to let it cool.
normally the thermo fuse should kick in at around 60-80° C (whatever that is in Frankenfurters)
And most are one shots.. once triggered they need to be replaced (you need to replace the battery) mostly still being alive and well thanks to that fuse

But thruth is: they only protect you from shorts (overheat) failures.. you could still puncture your laptop batteries into runaway mode


'sid

 

[ghost civic]

while it is true there are cautions to take with Lipo batteries, I think they get a bad rap. I mean, there are things you can do to a lead acid or SLA battery that can cause disaster as well.
Ways to make lipo's dangerous:
Puncture a cell: This is why to race a RC truck it must use a Hardcased lipo pack.

Short the lipo: Pretty obvious, no battery likes to be shorted. But lipos will swell until they burst, then you get flames.

Over discharge them: Draining a cell below 2.8v damages it. Go much lower, and the cell wont except a charge anymore. This however will not result in a fire. without a charge, you can puncture the cells and hardly even get a puff of smoke.

Exceed their specs: Just like with most batteries, if you demand too much amps from the pack it will cause heat to build up. Build up enough, the pack swells, bursts and you get flames. This has happened on some RC's that demanded more amps than the lipo was able to provide. Putting a 20c lipo in a 1/8 scale RC with a monster brushless motor is asking for flames. I knew a guy who lost his $600 practically new RC because he used lipo's that were not rated for the demand the truck put on them. Once you have flames shooting out of your RC, the RC is pretty much toast.

Overcharging: Again, no battery likes this. Charging on a proper charger is nessesary. For packs with more than 1 cell, you must balance the charge amongst the cells. Overcharging...such as putting a 12v battery to charge a lipo pack will result in a fire.

Several of they ways to kill a lipo apply to most batteries. The major difference is that the ways which cause the pack to swell and rupture can result in some pretty nasty flames. Even a smallish (5000mah 2cell) rc lipo can produce flames several feet in height.

I heard of a guy who had a NIMH battery in his RC. It somehow shorted itself...drove the rc off the shelf and onto the floor and burnt down his house. Lesson: NO battery should be treated carelessly!

edit: safest way to put out a lipo fire is with sand.

 

[itsid]

Haven't seen a NiMH burning on it's own;
heating up, gassing out.. yes... burning? Nope
unless of course it shorts and a spark ignites something else flammable.

But that doesn't mean it cannot happen, it only means never seen it, never heard of it myself.

'sid

PS that sand must be perfectly dry!! everything else means explosive evaporation.
wet sand would cause just a bigger boom
and it cannot be choked!! (lithium cells conveniently come with their own oxygen source to fuel the fire)

 

[ghost civic]

good point about the sand having to be dry.
I think the point of the sand is to slowly let out the gasses without them being able to ignite...at least that's my guess.

Ive had a softcased lipo fly out of a RC going 40 mph and skid/roll/bounce across the ground for a good distance. Pack was fine. Ive been using lipos for years...have yet to have one catch fire. Ive had a few go bad...either start to swell up and I know it is time to retire them or I have accidently drained them beyond 2.8v/cell.

That said, I know there is a difference between a 2 or 3 cell 5000mah lipo and the battery the OP made. One, Ive never used those type of cells and 2, Ive never had a pack with that many cells. If one of those cells for some reason ignited....you would have many more explosive fire balls, one after another until all the cells had ruptured. It wouldn't be pretty.

It would be VERY advisable to either charger that pack somewhere other than in your house, and certainly not to charge it unattended.

As a RC guy, I LOVE lipos. They have done a ton for the hobby. double the power, runtime and in a lighter package than comparable NIMH packs. It used to be a decent quality nimh would cost you $50 or more and get you maybe 20 minutes of runtime. Now a $25 lipo can do double that runtime.

 

[chancer]

So Sid, After doing all of the proper techniques you described in post 7 would You then allow your child to use the battery in his kart?

 

[ghost civic]

So Sid, After doing all of the proper techniques you described in post 7 would You then allow your child to use the battery in his kart?

I cant speak for Sid, but for myself...yes.
With proper wiring, fuses and a fire wall or metal case I would see little to no danger to my boy.

Even should a cell rupture, there should be plenty of time for your kid to get out of the kart. Any lipo Ive seen go up always emits smoke well before it bursts into flames.

 

[itsid]

So Sid, After doing all of the proper techniques you described in post 7 would You then allow your child to use the battery in his kart?

Well...
hard to tell honestly.

if my child is anything like me... nope!
if my child is anything like my wife? yepp!

A decent kid -told to take care- can and will be able to observe and detect any misbehaviour of the homemade batpack in time and is very well capable of getting out of the danger zone soon enough, and even prevent the pack from failing.

A rascal who wants to test each and every limit will ignore any parental advice as soon as the parent is out of sight.
crashing and rolling the kart.. going uphill at full throttle with seven of his closest friends... such kid get's a lead acid batpack

'sid

PS Oh and Eric.. post #7 is what I THINK is sufficient to prevent an electrical failure, could be I missed something important; plus I haven't even thought of mechanical protection yet