A lengthy part of our process is measuring the AHr capacity of each cell ...It seems everybody does this , then writes the capacity to the nearest mAHr !! on the side of the cell , then puts them in bins for latter use .
We don't really need great accuracy in this, since some will divide all into 3 or 4 categories ... perhaps dumping any below 1AHr ... using 1 to1.5for one thing ....1.5 to 2 for another ... and over 2 for yet another ....
Perhaps most will just dump those below 1AHr and use those above 1 AHrin their firewall , so we don't need extreme accuracy in measuring the cell's capacity ....anyway capacitywill depend how low you discharge ...
I've been using this well knowndevice for discharge ....
I set it up with a resistor for 1A discharge
I put in a charged cell and it shows the open circuit voltage , press the left button and it starts discharge .. displaying dischargecurrent , voltage , and capacity , cycling through the three readings ..
I've noticed that if after 10 secs the voltage is below 3.65 then the cell will have a capacity at the end of the 1hr test , of below 1AHr .. a good cell will show 3.75 after 10 secs and an excellent cell 3.85 after 10 secs ...
So why go through the whole discharge cycle , and then have to charge the cell up again , when you can tell it's condition in 10 secs ??
I realise those who have been building powerwalls for some time may have spent a lot of effort , and in some cases $100's , in establishing capacity measuring set ups... they will be looking for reasons to justify what they have created....
But for beginners I think all that is needed is a 10 or 20 cell charging arrangement , using the charging modules (10 for $3) , and one discharger pictured above ...
There is great diversity among builders upon which capacity cells to put in packs , some only use above 2AHr ...others anything above 1AHr ... so this is not critical ....capacity testing really does not need to be accurate.
We don't really need great accuracy in this, since some will divide all into 3 or 4 categories ... perhaps dumping any below 1AHr ... using 1 to1.5for one thing ....1.5 to 2 for another ... and over 2 for yet another ....
Perhaps most will just dump those below 1AHr and use those above 1 AHrin their firewall , so we don't need extreme accuracy in measuring the cell's capacity ....anyway capacitywill depend how low you discharge ...
I've been using this well knowndevice for discharge ....
I set it up with a resistor for 1A discharge
I put in a charged cell and it shows the open circuit voltage , press the left button and it starts discharge .. displaying dischargecurrent , voltage , and capacity , cycling through the three readings ..
I've noticed that if after 10 secs the voltage is below 3.65 then the cell will have a capacity at the end of the 1hr test , of below 1AHr .. a good cell will show 3.75 after 10 secs and an excellent cell 3.85 after 10 secs ...
So why go through the whole discharge cycle , and then have to charge the cell up again , when you can tell it's condition in 10 secs ??
I realise those who have been building powerwalls for some time may have spent a lot of effort , and in some cases $100's , in establishing capacity measuring set ups... they will be looking for reasons to justify what they have created....
But for beginners I think all that is needed is a 10 or 20 cell charging arrangement , using the charging modules (10 for $3) , and one discharger pictured above ...
There is great diversity among builders upon which capacity cells to put in packs , some only use above 2AHr ...others anything above 1AHr ... so this is not critical ....capacity testing really does not need to be accurate.