On_The_Road
New Member
- Joined
- Mar 27, 2020
- Messages
- 102
I am trying to figure out why Cell 4 is falling so far behind at the very end of charging. Deltas under 8mv until the very last Ahs to go then it ends up at 200mv at absorb which is set to 14.00. If I discharge after the charge the deltas come down below 10mv quickly.
Two 280AH packs 4S. Cells from 18650 Battery Store
Top balanced as per this PDF https://diysolarforum.com/resources...ls-using-a-low-cost-benchtop-power-supply.65/
Two Overkill 120A BMSs
Polished and cleaned all contacts
All BMS voltages verified with a voltmeter
Using 45in lbs for the bolts on the battery.
2/0 positive wires / double 2awg negative wires all crimped with a 5 ton hydraulic hand crimp tool. Copper wire.
I did discharge it yesterday and it seemed well behaved at the end and the capacity seems right (See attached pictures). During that discharge I was pulling 180A at times and the deltas stayed under 8mv.
Cell #4 on each pack is where the positive battery cables land and those are the cells that seem to fall behind the furthest. It almost seems like Cell #4 in each pack stops charging 3.38v while the other cells keep on going.
Suggestions so far.....Swap Cell #4 to a different position on each pack to see if it follows the cell. If it does follow the cell top balance again.
Could it be the fact that the battery terminals that have my positive wires have less surface area contact with the lugs than a battery terminal with a bus bar on them?
Just looking for any additional suggestions before I take it all apart and try the above? I can't help but think it's something with my setup as it's the same cell in each pack falling behind. I have ordered some silver paste and I will give that a try on all of the contact points.
Thank you
Two 280AH packs 4S. Cells from 18650 Battery Store
Top balanced as per this PDF https://diysolarforum.com/resources...ls-using-a-low-cost-benchtop-power-supply.65/
Two Overkill 120A BMSs
Polished and cleaned all contacts
All BMS voltages verified with a voltmeter
Using 45in lbs for the bolts on the battery.
2/0 positive wires / double 2awg negative wires all crimped with a 5 ton hydraulic hand crimp tool. Copper wire.
I did discharge it yesterday and it seemed well behaved at the end and the capacity seems right (See attached pictures). During that discharge I was pulling 180A at times and the deltas stayed under 8mv.
Cell #4 on each pack is where the positive battery cables land and those are the cells that seem to fall behind the furthest. It almost seems like Cell #4 in each pack stops charging 3.38v while the other cells keep on going.
Suggestions so far.....Swap Cell #4 to a different position on each pack to see if it follows the cell. If it does follow the cell top balance again.
Could it be the fact that the battery terminals that have my positive wires have less surface area contact with the lugs than a battery terminal with a bus bar on them?
Just looking for any additional suggestions before I take it all apart and try the above? I can't help but think it's something with my setup as it's the same cell in each pack falling behind. I have ordered some silver paste and I will give that a try on all of the contact points.
Thank you
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