Li-ion cells
- Thread starter BillC
- Start date
Hi Denys not sure what the battery was from. It is sitting on 20.8 volts. I brought it up from 18.5 volts over a couple of hours. It has been sitting idle for about four years. If it is OK it would have dangerous power if short circuited etc. The battery is completely open so it needs some sort of plastic case to make it a bit safer. It could be good for a farm buggy, could sneak up on the sheep!! I have a number of dc motors which might suit. I have run out of voltage with the power supply I was using for charging, I will look for one with a higher variable voltage. And monitor the current when charging. I might seek more advice on Sat,.
You should be able to calculate the overall pack voltage by tracing the way they are connected, I imagine it's some series parallel combination, once you determine which cells are in parallel, you can charge each lot of parallel cells separately, nominally 4.2V times the number of cells in series.
But there is a hidden gotcha, if you have a shorted cell in the pack the voltage across the remaining good cells will be too high, so you need to check each cell individually to make sure they are charging equally. Sort of a manual balance charger.
But there is a hidden gotcha, if you have a shorted cell in the pack the voltage across the remaining good cells will be too high, so you need to check each cell individually to make sure they are charging equally. Sort of a manual balance charger.
VK2RK
Active member
Lithium Ion Battery 18650 Series battery
Nominal Voltage is typically 3.7 V The voltage at the end of discharging is 2.75 V to 3.2 V per cell, depending on the discharge rate and temperature.
Best to not fully discharge as it reduces cell life
The fully charged voltage is 4.2 V
The pack voltage is dependent on how its wired, can be 12, 24, or 48 nominal
When series connecting balancing must be employed to insure that all cells charge evenly, ignoring this will reduce the life of the cells having uneven charges, same deal as when placing sealed lead acid batteries, not doing so full charge of the individual components in the string will not be achieved.
With lithium, when top of charge is reached (4.2 V per cell) the charge must be turned off, ignoring this will reduce the life of the cells
Thus a 12 Volt pack end of charge is when the pack reaches 16.8 V
24 Volt pack reaches 33.6 V
48 Volt pack reaches 67.2 V
Charging requires smart charging with constant current and constant voltage ramping up to the Maximum Voltage in steps..
Most simply use constant current, if the charge current is not a fast charge the process will achieve a full charge with no determent to the cell.
No maintenance charge is used with lithium, doing so damages the cells
Self discharge does take place and usually the charge is resumed when the cell drops below the top charge back to the top and turned off
All above is only valid if the cells are balanced, thus cell balancing is most important if used in series parallel strings
When dealing with a second hand pack, one must insure no uneven temperature across the cells is present, any high temperatures cells is indicative of a faulty cell.
Caveat - DONT JUST PUT A CHARGER ACROSS THE PACK
Measure each cell, group cells of similar voltage, top balance them (Connect in parallel) charge to 4.2Volts
Let them rest if good the self discharge will be even, discard those that took a nose dive
Once you have graded the cells, wire them in the required string voltage pack
Parallel the strings for the required current handling
Then you can ignore all of above and live life dangerously.
Note there exists different chemistries for lithium, the most common cell chemistries are lithium cobalt oxide (LCO), lithium nickel cobalt aluminium oxide (NCA), lithium nickel manganese cobalt oxide (NMC), and lithium iron phosphate (LFP).
Thus the bottom and top voltages will vary slightly
For instance lithium-polymer battery cell nominal voltage is 3.7V and 3.2V for Lithium-Iron-Phosphate
If available consulting manufacturer data sheet is good practice with this kind of technology.
Hope this helps
Nominal Voltage is typically 3.7 V The voltage at the end of discharging is 2.75 V to 3.2 V per cell, depending on the discharge rate and temperature.
Best to not fully discharge as it reduces cell life
The fully charged voltage is 4.2 V
The pack voltage is dependent on how its wired, can be 12, 24, or 48 nominal
When series connecting balancing must be employed to insure that all cells charge evenly, ignoring this will reduce the life of the cells having uneven charges, same deal as when placing sealed lead acid batteries, not doing so full charge of the individual components in the string will not be achieved.
With lithium, when top of charge is reached (4.2 V per cell) the charge must be turned off, ignoring this will reduce the life of the cells
Thus a 12 Volt pack end of charge is when the pack reaches 16.8 V
24 Volt pack reaches 33.6 V
48 Volt pack reaches 67.2 V
Charging requires smart charging with constant current and constant voltage ramping up to the Maximum Voltage in steps..
Most simply use constant current, if the charge current is not a fast charge the process will achieve a full charge with no determent to the cell.
No maintenance charge is used with lithium, doing so damages the cells
Self discharge does take place and usually the charge is resumed when the cell drops below the top charge back to the top and turned off
All above is only valid if the cells are balanced, thus cell balancing is most important if used in series parallel strings
When dealing with a second hand pack, one must insure no uneven temperature across the cells is present, any high temperatures cells is indicative of a faulty cell.
Caveat - DONT JUST PUT A CHARGER ACROSS THE PACK
Measure each cell, group cells of similar voltage, top balance them (Connect in parallel) charge to 4.2Volts
Let them rest if good the self discharge will be even, discard those that took a nose dive
Once you have graded the cells, wire them in the required string voltage pack
Parallel the strings for the required current handling
Then you can ignore all of above and live life dangerously.
Note there exists different chemistries for lithium, the most common cell chemistries are lithium cobalt oxide (LCO), lithium nickel cobalt aluminium oxide (NCA), lithium nickel manganese cobalt oxide (NMC), and lithium iron phosphate (LFP).
Thus the bottom and top voltages will vary slightly
For instance lithium-polymer battery cell nominal voltage is 3.7V and 3.2V for Lithium-Iron-Phosphate
If available consulting manufacturer data sheet is good practice with this kind of technology.
Hope this helps
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