That's what we are asking, the only explosion of a battery causing injuries I know about, is a 1/8th that blew up in the pit. they are still alowed.

But they seem to ignore everything.

Why not forbid ib4200 cells, we could still be racing other cells.

Northy beat me to it!!

Kyosho-viking - please refer your Association to an accident we had here. A young driver was badly injured when a battery accident happened right in their face as they were looking at... a Nitro car!! The battery was for powering the Nitro electrics.

I hope that you are protesting to your Association. This is a ridiculous over-reaction. If the concern is safety, then all RC racing should be stopped, as all RC racing is using NiMH batteries. I hope you can get this decision reversed.

Anyone imagine what would happen if the BRCA tried to do this? :p:p:p springs to mind...!!

Id really rather not think about that, after the tread about national tracks......


back on topic: Cells can be dangerous if abused, and lets face it everyone racing electric cars are abusing the cells by charging them at least 8 times the manufactures rated current. but we have all seen a LiPo explosion on youtube, they seem alot more likely and much, much more violent, a cell exploded at TRCC a week or so ago, the guy was sitting right next to it and it caused no injury that i know of, and i was there.

the BRCA have already voted to outlaw direct soldering onto batterys at the EFRA AGM (see the other thread with a link to the item in question) so if there is a "real" percieved risk they will act upon it!
hopefully not in such a knee jerk way :rolleyes:

You're have to drive over the border to Sweden to race! It's not that far, right?.. ;)

Seriously - sounds like a complete overreaction to me.

I spoke to the guy whose cells went bang shortly after it happened, he told me that it was two sets of cells that had touched each other & shorted causing the cells to go off, wasnt due to over-charging so accidents can happen with any cells if you are unfortunate.

deleted by me

Mmm, my friend did that a few weeks ago, it burnt through the wire though, gonna have to tell him to be more careful.

I've seen LiPo's explode in real life, and trust me : if safety is a major concern : LiPo's are NOT the way to go. It was an ugly sight.

The only serious injuries I've seen in RC was a broken leg for a marshall during an 1/8 IC track race and head injuries at a bigscale event (guy was taking pictures when one of those 30 lbs lawnmowers hit him).

yep Lithium cells can be very dangerous, very high power!

I work for Steatite and we do Li-poly packs, I never touch them, they are OK if handled properly. We have a battery bomb bunker, if any cells get warm they go in this bunker made of concrete and filled with sand, shut the lid and RUN!!

We need to see what comes back from the AGM and see if the BRCA (through Paul) have any plans to change things for next year, otherwise all we have is rumour and speculation. From my point of view, the cells are abused terribly and you can always make a cell or battery go through a rapid disassembly if abused 'in the right/wrong way'.. but the ease with which it now seems possible is alarming.

The problem with the newer breed of cells is that the Chinese manufacturers are trading safety for other performance traits such as capacity and voltage. To get these traits you need thinner canned walls (the cell can not handle pressure as well) and thinner seperators (the cells are more prone to internal shorts). You also need a near 1:1 match between the two electrodes to increase capacity and a near starved electrolyte system (to increase capacity and voltage but these do nothing for life).

You also need a good vent mechanism. Newer cells use rubber slug vents rather than spring vents and these are not as robust, they also distort or have their properties effected by external soldering. There can also be issues with cell seperator melting and blocking up the vents in the cell.

If this were the powertool market then none of the high capacity NiMH cells we use would get qualified, they are just too tempremental.

Sanyo got out of this game and basicaly handed it to the Chinese cell manufacturers which is a shame as Sanyo make the best NiMH cells full stop... but they top out now at 3000mAh or 2600mAh if you want a really good high drain NiMH cell that will last you for years....

If cells we used had to meet strict cycle life and safety tests we could go back to running 2600mAh NiMH Cs... but we might need to reduce the length of our races ;)

All of this is my personal view, nothing to do with my work* (*disclaimer as Snr Tech Manager for Chinese owned Battery Company).

In the mean time, stay safe.

N

So blow up then neil :D:p
:wtf:

A

Why ??? 15 years ago we still ran 5 min races on 1200 Batteries !!!!!!
THE GOOD OLD DAYS ... :D

exactly what I was thinking !
I started racing with those black Sanyo 1900SCRC's and we raced 5min too.

Laptimes in offroad haven't gone down that much since the NiCd era.
Onroad is a different matter of course.

we should all race with sanyo 3600 then we would all be happy resonable capacity and safe for all the people concerned.

A

but then, wouldn't people will just charge at a higher current to give them a competitive advantage? thus making them unstable too?

I wonder how much of an issue there would be if we all charged at 1C (i.e. 4.2A for 4200's), as per manufacturer recommendations? I wonder if the number of explosions would be the same?

I've witnessed some IB4200's explode, indoors, at a meeting early this year. Scary stuff, but then I've also seen people charge at 5.5A, then repeak at 7.5A, so its hardly surprising, as they are abused so much.

Eveyone in the know, knows you shouldn't re-peak 4200's. I personally charge them in enough time to just be cool or warm before i put them in the car.

If people are charging at >4A then there is a name for that.. its called natural selection ;)

I too remember the days of the N-1300SCR and KR-1800SCE etc... and yes we managed five minutes.. that last lap was somewhat fingers crossed though :)

Technical bit.. You know I mentioned the 1:1 match.. do you know what that is? I will explain if anyone is interested... All NiCd and NiMH cells have what is called an electrode match, it is the ratio between positive and negative electrodes. The negative electrode is ALWAYS larger than the positive. This is because a charging cell gives off oxygen gas from the positive electrode and this is recombined in the negative and keeps the cell in equilibrium (this is why you can trickle charge batteries in cordless screwdrivers, emergency lighting etc).. The problem with the match is that the capacity of the cell is driver by the shorter electrode, so a cell with long life that you can trickle charge needs a much longer negative electrode and this means low capacity. You can increase the capacity by having the electrodes similar lengths but this reduces the life and the cells ability to withstand overcharge abuse.. it also reduces the cycle life as the longer negative electrode is used as a reserve as it oxidises due to the oxygen in the system.

The faster the charge the more gas is generated, and this has to be combined.. if gas is generated faster than it can be combined then the cell pressure builds up and the cell has to vent. Venting is a safety measure and I am sure we have all heard it on old cells while charging. (a little fizzing sound) the problem with venting is that some electrolyte is lost and this dries out the cell, so a cell that has vented will quickly deteriorate. Of course if you are charging a fully charged cell at high rate then the gas cannot recombine fast enough and the cell vents... or explodes if there is an issue with the vent (sealed shut with solder, bent by abuse, blocked etc etc..).

Lastly, our hobby chargers terminate on what is called 'negative delta V' which is the roll over of voltage when the cell is fully charged, this phenomenon is caused by the recombination reaction and is handy because we can use it to stop our charging.. except that it does not happen instantaneously when repeaking a fully charged cell so you are pushing a fully charged cell further into overcharge by re-peaking. Couple this with the fact that the charger is not looking at each cell, it is looking at a six cell string and you have the problem of matching, where one lower capacity cell can be well into overcharge with it's pressure building up but your charger cannot detect it because the other five cells are masking the fall in voltage...

so..
only charge at 4A max
use a low -dV threshold (3mV/cell)
use a Max T temperature backup (45°C)
do not repeak
Always allow cells to cool before recharging
balance cells as often as you can on a discharger with a 0.9V cut-off

Why is this abuse never directed at the matchers who boast of the 'voltage enhancing' methods? Do we know what these methods are, and do we know that they do not have an impact on these occurences? We're beating ourselves with sticks, but has anyone actually taken a cell direct from China and tried it? I don't know if it is a factor, but why is it never discussed?

Neil's reminder on what you should do with the cells is timely - that's what is recommended. I am a little peeved that people ignoring this advice in the face of mounting evidence are putting my racing in jeopardy.

No. Sanyo cells could take anything you could throw at them. Back in the 1200 NiCad days, you could get a real fast run in Stock, by charging your cells direct from a 12v battery, without any problems! Even the 2400 cells were bombproof, and the set of 3000 (I think) Sanyo NiMh I have as a hack set on the bench for years still work fine - and they've been left flat, blitzed at 6A, and generally abused. I wouldn't dare do any of these things with IBs, and never have!! :o

Ah... So I should ignore the re-peaking advice I got from a well-known person who develops motors and cells for a well-known European company... And he also said charge them in time for them to stand for ten minutes before they're run, irrespective of temperature. Oh well, he's obviously not in the know...

Conflicting advice; it's a bugger...!

Er dont preach what you dont practice,manufactures recomend no repeak or using solder to join cells, so presume you do both........who is putting your racing in jepordey now?