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Hi Tommey
I have built a Lithium mountain bike before and had a range of about 10 miles that could get me to work over some of the biggest downland hills in the South East England.
Your solution for letting the pressure from the cell is very interesting and this actually shows how bad all manufacturers charge their batteries.
For safety a Lithium battery should never be allowed to over charge, or under charge or even have an excessive discharge current, any of these are potentially creating a bomb.
It's hard to believe, but all manufacturers i know charge their batteries in series and monitor the total voltage to get an average over charge voltage indication, the more complex systems do monitor the voltage across each cell but then only switch in a low wattage resistor to help slow the charge to that particular cell.
This is not a good design yet every Battery management system i have seen works this way.
Some don't even monitor the voltage across each cell, this leads to an in balance over a period of time where 1 cell could end up at 20% charge and the others varying up to full charge, the result during discharge is that once the 20% charged cell reaches it's 0% charge level then the whole battery shuts down, giving the wrong conclusion that the whole battery is faulty, and in actuality each cell just needs re balancing, but because there is no balancer built in then you need to buy a new battery.
There are some things that you need to monitor to be safe with these batteries.
Each cell must not go over it's maximun working voltage.
Each cell must not get over discharged by going under it's minimun cell voltage.
Cell temperature needs monitoring during charge and discharge to stop explosive pressures, hence the pressure cap design, these batteries are not batteries they are sticks of dynamite in an over pressure situation, sealed in a metal can.
There's only one way to safely charge a Lithium battery cell and that's to charge each cell singularly, monitoring temperature, and cell voltage.
To my knowledge there is no manufacturer that correctly implements this correct charge regime.
and on this basis there is one thing you would never do and that is to start using Lithium batteries in Aeroplanes LOL
There is one safe Lithium battery technology that is not dangerous and that is LIFEPO4 or Lithium / Ferric Phosphate Chemistry, these do not suffer the thermal runaway problems all the other chemistry's see.
If you love your life and your house there is only 1 safe way to charge your laptop/ mobile phone or anything that uses these Lithium cells and that is to charge in your shed or at least in a fireproof battery charge bag, which is designed for the worst case scenario.
The only thing that has saved many explosions is the pressure cap design, but the battery should never have got to an over charged state in the first place through bad Battery management design.
If a cell gets over charged then as you found the top shorts, if the cell gets over discharged then the crystalline structure of the cell gets damaged, you may be lucky if the under voltage is minimal, but generally when the under voltage state is reached then leakage in the cell tends to trickle discharge the cell over a short period of time, good cells have a very slow self discharge rate, cells that have been under voltage self discharge at varying rates, a really bad one will get hot due to the heating leakage current within the cell and can again become a ticking time bomb due to increase pressure due to excessive internal stress and heat.
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Topic: 60 miles per charge on a electric lithium power trike project (Read 7311 times)
