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  #21  
Old 03-12-2007
kyosho_greg
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Quote:
Originally Posted by SlowOne View Post
Batch number is on the IB shrink in black under the '4' of 4200. However, it isn't always on the cells with another matcher/distributor's shrink, and I don't know how to find it! Make sure you peel all the labels off your cells (from the matcher, etc.) before you give up the search.

No problems have been reported with those packs on public forums, so I'd not be concerned. For peace of mind, charge at 1C (so 3.6 amps for the Nosram cells, 3.7amps for sanyo, etc.) and allow the time it will take to get a full charge. Use a good delta-peak charger, or, if you have it, a thermal cut-off set to 40degC, and placed in one end of the stick pack.

There is a known problem with IB cells, but previous issues with NiCad/NiMh going back 30 years have been due to users abusing their cells. I would not worry about your cells if I were you.
thanks m8 ive seen a lot of exploshions at my club mainly li-po's
and my car even got set on fire bye some one using a lipo battary theres onw of are club on youtube search for flamin rc thanks very mutch not so scerd now bye :greg
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  #22  
Old 04-12-2007
kyosho-viking kyosho-viking is offline
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Norwegian federation finaly came to reason.

Under federation meeting november 18.th they came up with a solution the drivers agreed to.
Most of Jimmy's list are used, plus all chargers and powersupplies must be CE branded.

Heats are sat up with 75 min between them in races, to give charge time enough to everybody.

From April 1.st only EFRA listed batteries are alowed in races.
IB cells without or with unreadable batchnumbers are banned.
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  #23  
Old 05-12-2007
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That sounds like a very reasonable solution to the problem
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  #24  
Old 04-11-2008
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Jimmy,

As always the information supplied is great. Thanks.
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  #25  
Old 22-03-2009
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i use an army surplus grenade box for charging lipo cells, one of those would surely be of use in the case of exploding cells and would almost certainly contain quite a substantial explosion. box cost me a pound, fireproof stuffing gland on cable entry cost about 50 pence
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  #26  
Old 02-06-2015
Ivan Iland Ivan Iland is offline
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Confused I am newbie.sounds complicated
Quote:
Originally Posted by jimmy View Post
EXPLODING NiMH 23/43 CELLS


No doubt you will have read or heard the stories of batteries exploding and that the Norwegian Federation has temporarily suspended all electric racing. We have been monitoring these ‘incidents’ but obtaining hard facts is not easy, making it difficult to draw any meaningful conclusions.

Given that there are thousands of cells in circulation, such incidents have been exceedingly rare in the past. The only serious incident that has occurred to date in UK was when a receiver pack blew, that has permanently damaged a person’s eyesight. Although there will have been more injuries caused by scalpels or super glue in eyes than caused from exploding cells, you still need to take care!

The NiMh cells have a chemistry that allows the cell to 'self-discharge' over a relatively short period, (days as opposed to weeks). Lately, some of the 4200 cells seem to self-discharge more rapidly than other/previous versions. More importantly the amount each individual cell within a pack discharges varies (i.e. cell 1 might be .9v, cell 2 .8v, cell 3 .9v, cell 4 .7v, etc.)

If charged in this state, some chargers will not know when to stop the charge process, as some cells are demanding to continue with the charge, whilst others could be over charged. It is also important to control the delta peak (voltage drop-off after completed charge) to a low value when charging. Once the cell has achieved full charge, any further charging will produce gas. The cells have a pressure vent, but if that is blocked or not working, the gas pressure could cause an explosion.

High charge rates will also produce more gas and reduce the cell’s useful life. It is possible that internal gas pressure may cause distortion to some internal parts that could result in a short circuit within the cell. An internal short circuit combined with gas pressure is likely to be a 'big bang'.

Drivers need to recognise that the 'matchers' recommendations are intended to achieve maximum performance. It is the recommendation from the cell manufacturer that should be used.



Best Practice for use of NiMH cells.


1. Equalise cells before charging if they have been stored (with charge) for more than 2/3 days. If any of the cells in the pack show that they do not need to be equalised (i.e. the light does not show or goes out straight away) then remove the pack from the equaliser and charge for a short period (approx. 5 mins. should be adequate). Then carry out the equalising process.


2. Never exceed the manufacturers recommended fast charge rate. This should be 1C max., even if the manufacturer states higher. (C being rate of charge based on capacity of the cell, e.g. a 4200 mAh cell = 4.2 amps)


3. Disregard any charge rate recommendations by the 'matcher' if it is more than 1C.


4. Use a maximum Delta-Peak setting of 3mV per cell (6-cell pack = 3mV x 6 =0.018V).

5. Never repeak cells after main charge.


6. Use a temperature cut-out as an additional safety feature set at 42 deg. C max., located on the hottest cell (usually middle cell). If charging on a cold day then consider reducing this to around 35 deg. C.


7. Allow cells to fully cool to ambient temperature before further charges. Be aware the
centre of the cell cools slower than the outer casing. Do not put them in water to cool down; in an emergency cover the cells with a damp/wet cloth if you have to quickly cool them.



8. Store cells with some charge (30/50%).


BRCA Electric Board 16.11.07



UPDATE:


Updated news regarding NiMH 4200 cell faults.

The Intellect Battery Co. have now supplied the following cell Batch No's., which may contain cells that could explode when subjected to ‘race type’ conditions :-

ARAET, AZCWT, BNCWT, BNDST, BRAET, BZAWT.


We must stress that the Batch No's. detailed have been compiled only from returns by European customers to Intellect. There may be other batches that we have not yet been notified of. (So, do not assume that if a Batch No. is not detailed above, that it does not have any problem cells within it). Some EU drivers obtain cells directly from USA, etc. and it is possible that batches outside the EU could also be affected which have not been notified to us.

Intellect supply the same cell in 'Customer designed shrink'. Intellect has not confirmed if the same Batch Codes are used on these versions of cells. Most of the reports that have been received appear to be relating to cells in the Intellect shrink. Hopefully the above information will cover most of the problems.

BRCA Electric Board. 17.11.07
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  #27  
Old 02-06-2015
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Don't be. This thread is 7 years old. As far as I'm aware the only people that still use these are mardave type peeps. Everyone else saw the future and went lipo.
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  #28  
Old 02-06-2015
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The change in rules back then also meant the nimh cells that have been available since then have been considerably safer, as Intellect in particular could no longer bend the rules in producing race packs.

It's nothing to worry about these days.
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