Quote:
Originally Posted by Danny
Useful to be reminded that Lipos need a fairly large amount of respect with the way they are charged and stored. Someones already asked what the charger was and id be interested to know more bout the routines of these failed Lipos, like what kind of amps/C were they being charged at usually? What % was left in them during storage? And what approximate temperature were they stored at and for how long?
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In the two LiPo fires I have sat next to
the charge rates were close to 1C. The issue with chargers is that some may default to an NiMh program when switched off, or disconnected inadvertently (power loss, fuse blown, etc.)
The temperature and storage state are not relevant to the issues. It is what has happened inside the cell that allows the anode and cathode the touch and short out. This can be caused by the growth of crystals known as dendrites. This is most common if a deep discharge happens, but age also comes into it. Dendrites are hard metal crystals that bridge the anode and cathode causing a short.
The most common fault is that during manufacturing the chemical parts of the manufacture are not easy to control. For any number of reasons there can be a fault inherent to the cell and there is nothing you can do about it. once the separators (about 70 microns thick, or half the thickness of a human hair) are hot and start to melt, there is nothing you can do to stop the inevitable.
In any given week over 1000 people are racing LiPo in the UK - it is probably five times that across the world? They charge their cells four times, say. That's 20,000 charges a week, over a million a year. I think I may be conservative on that, but if it's about right then we have maybe five or seven incidents factually recorded over three years - or about a one in 400,000 chance it might be you. I suspect the odds are longer than that.
Sensible precautions are the order of the day. Trying to find the exact conditions that lead to a failure is futile - the source of the faults that lead to catastrophic failure are seeded in the manufacturing process and you have no idea if they are there or not.
1C charge and discharge, store between 5C and 30C in a sack and/or metal container (steel is best) at the recommended storage charge - good advice to follow. HTH
