31-10-2016, 10:00 AM
Nick Wrote:(31-10-2016, 02:50 AM)Refugee Wrote: I am working on a way of safely charging dodgy Li-Iron batteries and will start a new thread when I have sorted it out with or without the fireworks.
Testing so far has come up with a dodgy battery that charged without exploding a few times before it began to de-laminate internally causing it to bulge and become difficult to insert into the device.
The chemistry of Lithium-based batteries is complex and quick to anger - really, you should not under any circumstances attempt to resurrect suspect units - it's just dangerous - a false economy.
As the charging profile is complex, subtle (must be exact), dangerous (if you get it wrong) and generally requires sensor feedback, e.g. thermistors buried in the pile, several of the standard chip manufacturers produce ranges of cheap ICs that do all this for you. Phone batteries have exactly this - they are not just a LiPo stack.
When I say dodgy I mean fake CE mark as opposed to the real thing. It is a camera battery. I bought a battery from the web and it performed well to start with. After about 100 charge cycles using the camera charger and then first the capacity began to fade. Next the thickness of the pack began to increase so that it got more difficult ti fin into the camera and even worst get it out again. I would at this stage assume that the layers inside are de-laminating and making the cell thicker and reducing the capacity and increasing the current density in what remains intact within the cell.
No wonder they call it thermal runaway.
I have since bought another aftermarket battery with a real CE mark that has proved to be a lot better than both the original one and the fake. The one from the camera manufacturer was priced at just under half the price of a new camera so was clearly a trip to the bin with the camera if it fails in any way. The fake was £10 and the real CE mark aftermarket one was £15. In my opinion the price of an extra battery should not be more than 20% of the cost of a new product in order to keep the public safe. Product reviews should be snubbed if they do not quote the price of an extra battery and the publishers put under pressure to include this important information. The product cost £99 so £15 was OK.
What I was looking at is to estimate the remaining capacity of the cell by whatever means by putting it through a charge cycle with a fixed discharge current and a timer and then pensioning the cell to a low current application such as a weather station or fire alarm.
I agree that using them back in whatever they were sold for is a false economy and if the battery has a bit of extra space to bulge in the equipment dangerous as well. I would indeed ban equipment with loose fitting batteries that do not need to be removed for charging. Equipment needs a battery compartment with a cut out if the pack begins to expand especially in the charger.
Can all readers please refrain from debating brand names and save me the trouble of photoshpping the name of the original battery.
I like the burn in the wheelie-bin logo on the fake battery with the little chimney on the top. What a lot of melted plastic that would make. I have never seen a wheelie burn in bin on sale but round steel ones can be bought.
https://www.google.co.uk/search?q=burn+bins&ie=utf-8&oe=utf-8&gws_rd=cr&ei=URUXWIPrH-XYgAa4i72IDg
