DonPhillipe
New Member
- Joined
- Jul 13, 2020
- Messages
- 103
No offense but I'm looking only for someone who has spent a lot of time observing their cell voltages and hopefully during a period of 3 days or so in a 12V configuration. (In other words tapping into practice over theory.) I have two of these 12V systems set up separately, each on a 200a JBD BMS and the two banks are built from cells from 2 different vendors. One bank seems well matched, with voltage that slowly drops and uniformly from a hard-charge of 14.2V (cells normally gobble up a constant 50-60a flow until the demand just falls off to zero) and then once the JBD coulohm meter shows full, I disconnect them. These cells generally settle around 3.45V and all stay around this value while taking several days to slowly tick down lower, but the cells stay close in voltage.
On the second bank, I am interpreting this one as my "problem bank". But being inexperienced I think what I am now seeing is that contrary to what seems logical it's Ok for the cells to lose their original charge voltage much faster than the first bank and if so, the questions I have from this are:
a) is it OK that this group of cells deplete much faster than the other bank
b) is it OK that they deplete in voltage like shown in my chart below
I decided to just monitor my more rapid-discharging bank over a few days, then poll anyone here to see if this seems to be normal behavioir and thus not every bank is supposed to retain their "charge to" voltage once the initial charge voltage is cut??? (Guessing maybe this is why they call them 3.2V cells because once you charge them in the 3.5V range where my BMS shuts down passing any more charging current. I first thought this was severe internal resistance leaking but a chart I have since found indicates it may be normal???
I began with 4 "problem" cells that arrived as supposedly already top-balanced but unpacking them, they all read exactly 3.23 to 3.25V. I decided to put them on the 200aH BMS charging at 14.2V and they also absorbed around 50-60A of charge for nearly 2 hours but the BMS started tripping off on the second hour when the highest cell showed 3.64 and the lower cells were still in the area of 3.37V. From this I assumed they were not really top-balanced so rather than rewire them for a static voltage balance, I instead added a 5A active BMS and finally got them up to 3.54V and called it a day. At this point I removed the active BMS, plus removed the positive lead and continued simply to monitor cell voltages. From the equalized voltage of 3.54V (via the heavy hand of the 5A active BMS), the uniform charge appeared first to be stable but then within a half hour each cell began to show a surprisingly decreasing voltage level at mostly different change-rates.. I decided to just monitor the voltages over a 48 hr period and here is what I observed:
Cells connected in series, charged to 100% on the BMS coulomb counter, then the positive cables were removed from the battery bank. At full charge the active balancer was also removed:
(Hours after original 3.54 peak) (Cell 1 - 3 - 2 - 4) (BMS battery voltage display)
0 - 3.54, 3.54, 3.54, 3.54 - 14.1
3 - 3.50, 3.52, 3.51, 3.47 - 14.0
6 - 3.48, 3.50, 3.49, 3.45 - 13.9
8 - 3.47, 3.49, 3.48, 3.43 - 13.9
10 - 3.45, 3.48, 3.47, 3.42 - 13.8
13 - 3.45, 3.48, 3.47, 3.42 - 13.8
21 - 3.44, 3.47, 3.45, 3.40 - 13.8
24 - 3.44, 3.46, 3.45, 3.40 - 13.8
30 - 3.44, 3.46, 3.45, 3.40 - 13.8
35 - 3.42, 3.44, 3.43, 3.38 - 13.7
38 - 3.42, 3.44, 3.43, 3.38 - 13.7
49- 3.40, 3.41, 3.41, 3.37 - 13.6
55- 3.37, 3.36, 3.36, 3.36 - 13.5
58- 3.36, 3.35, 3.36, 3.35 - 13.4 (33F)
62- 3.39, 3.40, 3.40, 3.36 - 13.6 *1 (49F)
74- 3.38, 3.39, 3.39, 3.36 - 13.5 (36F)
78- 3.37, 3.38, 3.38, 3.35 - 13.5 (40F)
Normal???
*1 - No external power sources connected, no solar connected, no drain connected, positive disconnected with a battery switch and balane is turned off on the BMS; how the battery gained voltge during the past 8 hours I have not a clue (The temperature is at 39F when the reading 8 hours ago was at 49F)
On the second bank, I am interpreting this one as my "problem bank". But being inexperienced I think what I am now seeing is that contrary to what seems logical it's Ok for the cells to lose their original charge voltage much faster than the first bank and if so, the questions I have from this are:
a) is it OK that this group of cells deplete much faster than the other bank
b) is it OK that they deplete in voltage like shown in my chart below
I decided to just monitor my more rapid-discharging bank over a few days, then poll anyone here to see if this seems to be normal behavioir and thus not every bank is supposed to retain their "charge to" voltage once the initial charge voltage is cut??? (Guessing maybe this is why they call them 3.2V cells because once you charge them in the 3.5V range where my BMS shuts down passing any more charging current. I first thought this was severe internal resistance leaking but a chart I have since found indicates it may be normal???
I began with 4 "problem" cells that arrived as supposedly already top-balanced but unpacking them, they all read exactly 3.23 to 3.25V. I decided to put them on the 200aH BMS charging at 14.2V and they also absorbed around 50-60A of charge for nearly 2 hours but the BMS started tripping off on the second hour when the highest cell showed 3.64 and the lower cells were still in the area of 3.37V. From this I assumed they were not really top-balanced so rather than rewire them for a static voltage balance, I instead added a 5A active BMS and finally got them up to 3.54V and called it a day. At this point I removed the active BMS, plus removed the positive lead and continued simply to monitor cell voltages. From the equalized voltage of 3.54V (via the heavy hand of the 5A active BMS), the uniform charge appeared first to be stable but then within a half hour each cell began to show a surprisingly decreasing voltage level at mostly different change-rates.. I decided to just monitor the voltages over a 48 hr period and here is what I observed:
Cells connected in series, charged to 100% on the BMS coulomb counter, then the positive cables were removed from the battery bank. At full charge the active balancer was also removed:
(Hours after original 3.54 peak) (Cell 1 - 3 - 2 - 4) (BMS battery voltage display)
0 - 3.54, 3.54, 3.54, 3.54 - 14.1
3 - 3.50, 3.52, 3.51, 3.47 - 14.0
6 - 3.48, 3.50, 3.49, 3.45 - 13.9
8 - 3.47, 3.49, 3.48, 3.43 - 13.9
10 - 3.45, 3.48, 3.47, 3.42 - 13.8
13 - 3.45, 3.48, 3.47, 3.42 - 13.8
21 - 3.44, 3.47, 3.45, 3.40 - 13.8
24 - 3.44, 3.46, 3.45, 3.40 - 13.8
30 - 3.44, 3.46, 3.45, 3.40 - 13.8
35 - 3.42, 3.44, 3.43, 3.38 - 13.7
38 - 3.42, 3.44, 3.43, 3.38 - 13.7
49- 3.40, 3.41, 3.41, 3.37 - 13.6
55- 3.37, 3.36, 3.36, 3.36 - 13.5
58- 3.36, 3.35, 3.36, 3.35 - 13.4 (33F)
62- 3.39, 3.40, 3.40, 3.36 - 13.6 *1 (49F)
74- 3.38, 3.39, 3.39, 3.36 - 13.5 (36F)
78- 3.37, 3.38, 3.38, 3.35 - 13.5 (40F)
Normal???
*1 - No external power sources connected, no solar connected, no drain connected, positive disconnected with a battery switch and balane is turned off on the BMS; how the battery gained voltge during the past 8 hours I have not a clue (The temperature is at 39F when the reading 8 hours ago was at 49F)
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