TL;DR another Bluenova 8Ah battery, about 2 years in service appears to have about 7Ah capacity retained. No capacity test was done when new. Methodology still questionable.
This is the second of four 8Ah Bluenova batteries I received March 2020.
Received at 13.19V.
Charged once only to 14.2V beginning of August 2020 and installed in a Centurion D3 Gate motor. PSU appears to charge to 13.53V (probably limited somewhere between 700mA to 1A). Gate is not overly heavy or big - maximum current around 4A-5A (not sustained) during open/close (average probably around 1.5A). This gate motor is not connected to any alternate AC source, so the battery was fully exposed to all load shedding since August 2020. Unlike an alarm the current draw would be very low though during a power outage - unless the gate was opened or closed during this time (I have no idea how many open/close cycles were completed). The D3 also uses the battery as primary power source (no battery = no gate operation even with AC connected). Battery would have been exposed to temperatures ranging between very occasional <5 ā and very occasional > 35ā. Average likely around 20ā.
Battery was removed from the D3 and the battery case opened. About 60 minutes after removal, without any additional charging, the battery was discharged with an approximate 1.5A load, and then charged to 14.40V limited to 1.5A. Current was checked with a clamp meter and continuously measured with a PZEM-015 battery meter (the 100A shunt of the meter is problematic with the small current on this battery). Voltage was checked and recorded for the individual cell pairs using the balance leads. Discharge was terminated before the BMS would disconnect on low voltage. Charge was terminated when total voltage was 14.40V and three of the four balancing load resistors were being kept in circuit but the voltage of the one 'low" cell appeared to no longer increase. By increasing the voltage of the charge source to 14.68 volt the final cell also reached 3.6V while the other three cells hovered around 3.73V. It is unlikely that forcing the low cell to 3.6V added more than about 30mAh to that cell.
Discharge
No Load
Start
60min
120min
180min
240min
270min
280min
+45min
Cell1 (V)
3,340
3,257
3,228
3,208
3,187
3,112
2,977
2,724
2,911
Cell2 (V)
3,408
3,258
3,233
3,212
3,191
3,122
3,027
2,850
3,008
Cell3 (V)
3,353
3,252
3,230
3,211
3,189
3,116
3,007
2,762
2,950
Cell4 (V)
3,435
3,254
3,234
3,130
3,192
3,220
3,039
2,844
3,105
Total (V)
13,52
12,97
12,90
12,81
12,73
12,43
11,97
11,03
11,88
Clamp (A)
1,53
1,53
1,52
1,53
1,56
1,58
1,80
Shunt (A)
1,08
1,01
1,05
1,05
1,10
1,18
1,42
Shunt Tot (Ah)
1,08
2,11
3,19
4,27
4,80
5,07
Charge
Start
60min
120min
180min
240min
270min
290min
+12h
Cell1 (V)
2,911
3,346
3,368
3,399
3,418
3,448
3,418
3,323
Cell2 (V)
3,008
3,349
3,366
3,397
3,417
3,457
3,673
3,323
Cell3 (V)
2,950
3,346
3,366
3,397
3,416
3,455
3,603
3,323
Cell4 (V)
3,105
3,350
3,367
0,399
3,418
3,460
3,734
3,323
Total (V)
11,88
13,41
13,48
13,60
13,68
13,84
14,40
13,28
Clamp (A)
Clamp
1,53
1,53
1,53
1,53
1,54
Shunt (A)
Shunt
1,43
1,43
1,43
1,43
1,43
Shunt Tot (Ah)
Shunt Tot
1,46
2,91
4,32
5,82
6,51
6,75
Allowing for the ~40% low reading of the meter during discharge and the ~4% low reading during charging, I get to around 7Ah out and 7Ah in. (apologies to the actuaries and math geeks ).
So, two batteries with an initial assumed capacity of 8Ah, that spent nearly 24 months at a float type voltage of around 13.5V, one being subjected to very little discharge and the other experiencing short multiple discharges almost every day, appear to now have a capacity of around 7Ah.
Some pics of an 8Ah Bluenova for the curious (I did not completely dismantle it since it still needs to earn itās keep):
Case open, BMS on top (can also see the grey rubber-like compound that fills the bottom 1/4-1/3 and keeps the cells from going anywhere). Terminal leads marked as 14AWG 200ā rated silicone insulated wire (think is good for about 40A?). MOSFETās = CRSS052N08N. Could not identify any other significant components.
High temp (65ā) cut-off switches in the goo. Dug them out and tested them in hot water, one prevents high temp charge, and the other high temp discharge. No low temp protection that I could identify.
Underside of the BMS PCB with balancing circuit populated. The astute might notice the slight brown tinge to the solder joints of B1 and B2ā¦I shorted the balance leads by accident. At least it cleaned some flux residue as wellā¦:
Your last pic showing the discharge resistors is interesting. Not all of the resistors are switched on which is good. It means that the balancer is correcting the high voltage cells. When all the resistors are off or on then no balancing is possible. (If they are all on then it could indicate too high float voltage)
PS: You donāt need the thermal camera or meter to check if they are on. You can feel the higher temp with your fingerā¦)
Balancer chips will typically interleave the switching so that no two adjacent cells are bypassed simultaneously, or at least so that not all of them are on at the same time. But at high voltages in a balanced battery I can well imagine that all of them are working half of the time as they try to keep things under control. Though ideally the protection FET should activate before you get there, right?
Good day Mariusm, I have successfully converted, 60v,72v UPSāes to Lifepo4 cells between 5 and 15 ah for less than R8k
96v UPSāe tend to be slightly more expensive since you need a 32s BMS and they are not exactly as widespread as 12v components.
you get what you pay for, Bluenova vs Securiprod vs Vestwoods
cannot even compare the bmsāes of these units as the BN bms is 4 notches above the other one and three above the securiprod, so is the overall construction only BN uses cell holders.
Now, does anybody have a Freedom won 7Ah battery?
With these devices, the adjacent channels are completely unaware of each other. They simply switch on the FET based on cell voltage. (And only switch on above 3.6V typically).
The odds of all of the balancers being on simultaneously is rather low though. The bypass turns on when two conditions are met, if I assume a left to right flow for the sake of the example, 1) the cell to the left has a voltage higher than some threshold, and 2) the cell to the right is lower than the cell on the left by some delta.
Then the bypass turns on and some charge bypasses the cell on the left.
For the balancer on the cell 2-to-3 junction to also be on, that cell also has to be higher than the threshold, and cell 3 needs to be lower.
And this would have to go down to the last cell, like a pipe organ division. And then, I suppose, if the current flowing by having all of them on doesnāt blow anything up (how could it, it is designed to sit across a 3.3V-ish cell)ā¦ you would simply not fix the āproblemā.
Aaah ok I get it. Individual chips. I was more thinking of single-chip solutions that balance a whole bank. like the BQ series made by Texas Instruments (which I believe is used by Pylontech). In a solution like that, you can interleave the switches.
To some extent the odds are probably still low for all the balancers to be on simultaneously for any significant time but not because of any comparitor rather due to the nature of the variance between cells and components.
Right, I asked the question here because I knew of someone who connected 4 x 12v BN batteries in series for 48v.
He sent me this picture that is one of his batteries: Note: maybe they since changed the BMS, as these cells have been running on a 48v 2.4kva APC for Ā±2 years. Every few months he recharges the cells individually for proper balancing.
).
