How to not start a fire

[Dillzio]

I have a very important tip and trick for anyone new to the hobby, or anyone who may have become so used to using lipos that they've become more complacent and less afraid than they should be.

If you connect a 3S lipo to your charger, and you accidentally have your charger set to 4S, the battery will catch fire. I've always known it, but now that I've experienced it for myself this fact of life has taken on a whole new meaning for me.

Sometimes you may be lucky enough to get an error message on your charger when such mistakes are made, but in some circumstances (such as when you're least expecting it) it is possible to starting a charging cycle with the charger set to 4S. This is because a 3S lipo flown down to a healthy 3.8v per cell still has enough voltage for the charger to think it's actually a dead flat 4S battery. In my case, it occurred because I connected a full 3S lipo and set it to discharge to storage voltage (3.8v per cell), but since it was set to 4S it ended up trying to charge my lipo up to 15.2v and it didn't like it.
I didn't have the balance lead connected, I'm not sure if that would have allowed my charger to detect the error or not.

So, lessons learned are as follows:
Always check and double check that you have selected the correct number of cells for your lipo. If you try to charge a 2S at 3S rates, or try to charge a 3S at 4S rates, you will start a fire. You only need a 0.1% failure rate and you will start a fire eventually (it took me 3 years)
Always have the balance connector connected to the charger, even if you're only discharging to storage voltage.
Always charge your lipos in a 'lipo safe' flameproof bag, and use a temperature probe if your charger supports that feature (all B6 charges do).
Never leave lipos to charge unattended (which is probably the main reason it only burnt the contents of one drawer, instead of the whole room)



This is what happens when a Lipo is left to charge in a drawer, without a flameproof lipo bag or a temperature probe connected - I mean who ever thinks to use the temperature probe when you're discharging a lipo for storage?

[Dillzio]

Didn't attach last time

Attachments:

[Dillzio]

And the casualty list:
1 3000mah 3s 20c Zippy flightmax battery
1 mini GPS tracker
1 turnigy/hobbywing esc programming card
Three keychain cameras I use for aerial photography
Two lipo testers
One Parallel charging adaptor I made myself
Two lipo battery testers
A bunch of melted connectors of different types
The bottom of one drawer (since replaced)

Plus now my room stinks badly of burnt plastic, I don't think I'll be sleeping in there tonight

[flydiver]

Ouch!
I hear that smell is pretty persistent. Good reason not to charge lipos in a living area even if it's a 'safe' one. Even a lipo sack will vent the smoke.

[Dillzio]

Very persistent indeed!
My room was basically uninhabitable yesterday and today it still smells, but it's no where near as bad so luckily, the pong seems to be clearing fairly quickly. I'll probably be able to do an insurance claim on the burnt items too, about $200 worth of electronics gear.

While a flaming lipo in a bag is still a very bad thing, it significantly limits the worst case scenario. I would say that if ever you charge lipos indoors (as I stubbornly insist upon doing) it should really be done in a sealed lipo bag with a temperature probe. The flaming lipo had actually burnt a hole in the bottom of the drawer, and was about to burn through to the next one. Had the battery been in a flameproof bag, this would not be possible. Sealed Lipo bags will also smother the battery of oxygen, making it smoke and smoulder but not burn. I also get the impression that the temperature probe that hooks up to the charger would be much more effective inside a bag since it attaches with a magnet, and lipos are not magnetic.

I'm not sure if a temperature probe would have detected the heat build up and cut off the charge cycle before the battery caught fire or not, but it would have been nice to have that last line of defence. At the very least it would beep loudly and warn you when the battery did get hot (as long as you have the buzzer turned on, which many people don't because it's quite loud, and sounds every time you finish the charge cycle).

I would be very interested to know if an overcharged lipo suddenly bursts into flames, or if it starts to get hot before it passes the point of no return. Anyone care to do some "field testing"?

[flydiver]

Not I said chicken little.

What kind of charger?
Neither of my main lipo chargers would allow me to hook a 3S and then charge it as 4S.
Well, maybe the AC-6 on non-balance mode (no balance taps plugged in) just might, but I've never tried it.
It's about impossible to do that with the FMA Cellpro.

[Dillzio]

If you hook a 3S battery with at least 3.8v per cell up to a charger without the balance port, the charger actually has no way of knowing if it's a 1/3 full 3S or a dead flat 4S

The charger was a Polimax B6, just like the other dozen clones of the same type

[toff]

Hi Dylan. First off, glad you and yours are safe after quite a nasty fire, bet that was a bit exciting at the time! ( and yes, that is english understatement at work). At least it was noticed and put out, rather than burning unchecked, which could have been infinetely worse.....
As far as I'm aware, over-charging degrades the seperator between the positive and negative cells, resulting in an intense short, which causes the fire. It also acts a little like white Phosphorus, in that the chemicals react in oxygen, and burn intensely in air.
You can also over-charge if using the Ni-Cd method for bring a 'dead' cell back - don't use a balance tap, charge directly, and watch the temps. Plenty of you-tube vids also show puffing before any fire, so there is some warning. Not much, but some.
And no, I'm not going to test it either.

[ginginho]

Only just seen this, been away for a while. Dillz although you've lost a fair amount you are relatively lucky, at least it didn't start a house fire. I'm surprised you could charge without the balance leads attached, my charger certainly won't allow that. I would suspect the charger would've complained if the balance was attached but I guess we'll never know for sure unless someone else suffers a similar fate as yourself.
I'm also quite surprised that you lost so much other stuff. Although we all get flippant about charging it's a bit daft having equipment that doesn't need to be in the vicinity so close that a fire will destroy that too. My workshop is always a tip but I always clear a space around the area where I charge, and place the charger and packs on an old ceramic floor tile. If the pack being charged isn't in a lipo bag (me being lazy) I cover it with an old pottery plant pot. If it burns it'll vent up out of the hole in the bottom of the pot and not sideways to cause collateral damage.

[flydiver]

The accucel-6 and assorted clones will all allow charging through the mains without balancing if you want.
There's also the possibility of putting it in the wrong function. Most people find the programming pretty acceptable but there are a large number of others that are utterly baffled by the setup and only bought the charger because everyone said it was great. There's a LONG (100+ pages) thread in RCGroups on just that one and most of it is repetitions of help to do the same basic charges over and over again.
A buddy of mine got one-completely flummoxed him. If you are really lousy on PC's, and poor with RC electronics you could find a charger like this pretty daunting.