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but isn't it just simply the fact that most of the cells that have blow up, haven't been equalised first, the last 3 sets i seen go bang, i asked the people involved and all said equalise is that really necessary,?? well yeah. i never had one go bang yet, discharge then equalise before you charge, problem solved

Quote:

Originally Posted by neiloliver (Post 69456)

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

Now this is a piece of advise that I am going to follow as it is from someone that knows what he is talking about Cheers Neil.

as i said equalise and u should be OK, thanks Neil great piece of info

Quote:

Originally Posted by mark christopher (Post 69488)

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?

Steady tiger... I don't remember saying I followed the advice, I remember saying that I had received conflicting advice.

I follow Neil's advice. I have never had a cell go, or lose power, or anything else, since I started using IBs two years ago. I think Neil's right, but my note was simply pointing out that things stated on here as being gospel are not, and that advice one receives conflicts.

Quote:

Originally Posted by josh_smaxx (Post 69275)

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.

And they were GP3700's not IB's

Quote:

Originally Posted by Alan1467 (Post 69523)

And they were GP3700's not IB's

Well that says its not only IB's that go bang.

having seen a lipo go up, and an ib the lipo is way less violent and danjerous than a nimh

Isn't it so that we have been blowing up cells since about the time RC started?
NEVER have any federation stopped it though, before now, when some jerks in the Norwegian federation did it.
No investigation into what actually happened when cells blew up last weekend in Norway. And of course no reaction what so ever before these incidents happened "at home"...

Reading the explanations in this thread regarding these newer cells I think it is obvious that these so called explosions must have come from some kind of abuse. I mean, have anyone ever soldered tabs to cells without ever overheating a cell...

When reading the panic actions and statements that the Nor. federation has published, I think that their next move can not be anything else than to force their clubs to have people overseeing/managing all cell charging that will have to take place in a designated area well separated from pit/racing area. Probably on the clubs owns chargers that have to be exactly the same chargers with a maximum possible charge rate of 1C...
Next step after that will then be that the fed. people can stop working and go home, since there will be no more racers and no more clubs...

Ive had a set of Epic3800's go, had a bit of warning so chucked them into long grass.

What I tend to do now, is leave my cells with whatever is left from a race in then either in the morning of the night I am racing or the evening before the day I am racing I will discharge, allow to cool, equalise, cool and partial charge my IB4200's to 3000mah at home - then when I go to the track I peak the cells for racing with.

Is this a bad way of doing it? :confused:

My IB4200's seem to have deteriorated in performance faster than any other cells I have ever had.

They don't like being re-peaked Chris, as they don't actually 'peak' very well the second time, causing overcharge as Neil said.

I tend to not re-peak, but if I do (because the cells have been charged too soon before I race) I just put 200 seconds into them and cut off the charge myself.

Discharge, equalise and charge on the day would be my suggestion Chris.

G

Well I don't peak them on the 1st charge, just do a partial - come off cool and keep it to 5amp at home, this is what I am confused with, as its only the 2nd charge I let the peak detection cut in.

I find it more convenient this way, but if it is wrong - yeh I'll discharge, equalise and charge at the track - although the 1st pack i charge will get charged from storeage so I don't get a little behind..... I'd then rotate which pack I charge first, so I have no 1 pack which is abused, all of them will be in turn.

Chris

the ideal method from what i've been told by those that know is

discharge, equalise and immediatly charge never re peak once charged
if being stored between meetings leave 1/4 to 1/2 charge in
if not being used cycle cells 1/mth also discharge and put in 1/4 to 1/2 charge weekly

also storage conditions have a big effect if kept in a cold place the cells will hold more of the storage charge than if kept somewhere hot

Quote:

Originally Posted by mark christopher (Post 69525)

having seen a lipo go up, and an ib the lipo is way less violent and danjerous than a nimh

Me also,Lipo cells seem to burst into flames but nimh packs EXPLODE.

Yeh, cause flames aren't dangerous are they? :eh?:

G

Quote:

Originally Posted by Northy (Post 69640)

Yeh, cause flames aren't dangerous are they? :eh?:

G

wont do as much damage as exploding bits of metal tho!

Even if some kid has them on charge in the garage, or on his bedroom floor? :confused:

G

I agree Mark, but both choices aren't particularly nice.

The question is, do we have an issue with safety? Will the BRCA intervenene ? To be honest, right now, I am just taking good notice of all good advice to do what I can to avoid a potential explosion.

Is Lipo charging covered on house insurance? :confused:

G

Well, general "Battery charging" would be considered safer than various other things done in the house I hope.... who'd give them the nitty gritty on "I was charging Lipo at 20amps and set the cutoff wrong", not me.

Chris

I was just point out why I though an 'on fire' lipo would be worse than an exploding nimh, but I agree, both are bad.

G