Hello,
I'm looking to built a Li-On battery to deliver 16.5V at 3A, based on 18650B cells.
For this purpose, I will create two pack of 6 cells in series and join the packs in parallel to have more current.
Now, i would like to find how to cut off the cell pack before it goes under 16.8V, while the included PCB off the cells would theoretically permit the pack to go down until 15V, and how to precisely transform the tension which will be between 16.8V (2.8V*6=16.8V) and 25.2V (4.2V*6=25.2V, at full charge each cell have 4.2V), to a constant 16.5V with safety.
Two work around :
First one :
The cut off from the PCB of the cell is 2.5V, i think put 7 cells in series (6*2.5V=15V less than the 16.5V needed) wouldn't be the best idea, because it save the cell to cut off before 2.5V (2.8V would give 2.8V*6=16.8V minimum, should be perfect including the margin error), and at full charge with 7 cells i would have 4.2V*7=29.4V, which make a lot to step down.
i'm looking to cut off the cells before it goes under 2.8V, in the pack it makes under 16.8V for 6 cells in series.
So, which module could regulate theses two pack to cut off before the tension drops to 16.8V ?
Second one :
-To transform the tension (16.8V-25.2V) to 16.5V precisely, I found this step down on ebay :
http://www.ebay.com/itm/5A-Adjustab...379067?hash=item5d5c9750fb:g:X70AAOSwEK9TzdA9,
what do you think about?
Should it be really precise during all the discharge, are I need to add an other component ?
Adding capacitor would be a great idea? Which capacitor I should buy, or how to calculate the capacity of the capacitor I need from my voltage and current input / output? (arround 3A / 16.8/25.2V input and 3A / 16.5V output)
About safety, which kind of module can protect the step down itself, to cut off if the voltage ascent to 16.7V or drop under 16V?
Many thanks for your helps
I'm looking to built a Li-On battery to deliver 16.5V at 3A, based on 18650B cells.
For this purpose, I will create two pack of 6 cells in series and join the packs in parallel to have more current.
Now, i would like to find how to cut off the cell pack before it goes under 16.8V, while the included PCB off the cells would theoretically permit the pack to go down until 15V, and how to precisely transform the tension which will be between 16.8V (2.8V*6=16.8V) and 25.2V (4.2V*6=25.2V, at full charge each cell have 4.2V), to a constant 16.5V with safety.
Two work around :
First one :
The cut off from the PCB of the cell is 2.5V, i think put 7 cells in series (6*2.5V=15V less than the 16.5V needed) wouldn't be the best idea, because it save the cell to cut off before 2.5V (2.8V would give 2.8V*6=16.8V minimum, should be perfect including the margin error), and at full charge with 7 cells i would have 4.2V*7=29.4V, which make a lot to step down.
i'm looking to cut off the cells before it goes under 2.8V, in the pack it makes under 16.8V for 6 cells in series.
So, which module could regulate theses two pack to cut off before the tension drops to 16.8V ?
Second one :
-To transform the tension (16.8V-25.2V) to 16.5V precisely, I found this step down on ebay :
http://www.ebay.com/itm/5A-Adjustab...379067?hash=item5d5c9750fb:g:X70AAOSwEK9TzdA9,
what do you think about?
Should it be really precise during all the discharge, are I need to add an other component ?
Adding capacitor would be a great idea? Which capacitor I should buy, or how to calculate the capacity of the capacitor I need from my voltage and current input / output? (arround 3A / 16.8/25.2V input and 3A / 16.5V output)
About safety, which kind of module can protect the step down itself, to cut off if the voltage ascent to 16.7V or drop under 16V?
Many thanks for your helps