Hi all,

I'm sitting with the issue of unequal charge on my 3 x Dyness BX51100's. This morning the SoC level reported by my inverter was 30%, 1 LED on the master(+/- 20%), 3 LEDs (+/-60%) on slave 1 and 2 LEDs (+/-40%) on slave 2. How would I go about in equalising the charge/discharge on all 3? Should I remove comms, charge each one on it's own to 100% and then reapply comms? I only started experiencing this issue after I changed the comms cables to the correct ones to correct max charge & discharge currents on the BMS. Prior to this, the inverter only allowed 50A max charge/discharge currents and not 50A x N, where N is number of batteries.

Deye 8kW inverter

3 x Dyness BX51100, parallelled on a busbar

14 x 550W JA Solar panels

 

Edited May 7, 20242 yr by GGinelli

2 hours ago, GGinelli said:

Hi all,

I'm sitting with the issue of unequal charge on my 3 x Dyness BX51100's. This morning the SoC level reported by my inverter was 30%, 1 LED on the master(+/- 20%), 3 LEDs (+/-60%) on slave 1 and 2 LEDs (+/-40%) on slave 2. How would I go about in equalising the charge/discharge on all 3? Should I remove comms, charge each one on it's own to 100% and then reapply comms? I only started experiencing this issue after I changed the comms cables to the correct ones to correct max charge & discharge currents on the BMS. Prior to this, the inverter only allowed 50A max charge/discharge currents and not 50A x N, where N is number of batteries.

Deye 8kW inverter

3 x Dyness BX51100, parallelled on a busbar

14 x 550W JA Solar panels

 

Normally if the inverter only allowed 50A charging it might be set up to do so as if there was only 1 battery and not 3.

Personally now that we don't have LS I would charge one by 1 and disconnect each one as it reaches 100% to charge the next one. Only then connect all 3.

Remember to set the maximum charge/discharge to 50A when only 1 connected. Then back to 150A when all 3 are connected. 

Then do a discharge and see if they discharge at the same rate. 

Was given different instructions by my battery OEM.
Discharge each battery as individual Master to shutdown, one after the other.
Then reconnect the BMS comms between the batteries and set your Master and slaves as per the manual.
Now charge the batteries in parallel to full. That should sort the balance issue

On 2024/05/07 at 3:05 PM, GGinelli said:

I'm sitting with the issue of unequal charge on my 3 x Dyness BX51100's.

As I have written in other posts, I have 4 LEOCH 48100TB packs with uneven internal resistance. In particular the last one purchased has significantly lower resistance that results in higher charge and discharge currents. The BMS report SoC accordingly, however the newest one reports havoc.

However I observed that parallel connected packs equalize themselves when reaching full charge. This is a natural phenomena given by the physics of the batteries. That is as long as there is no fault in any cell. So don't worry, just charge them all together to bulk charge voltage and then lover to floating voltage. The correctly set inverters do it themselves. Don't get disturbed by the BMS SoC reporting. I trust the battery voltage more than the BMS. (Read "Are BMS reliable?")

On 2024/05/10 at 10:39 AM, Beat said:

 Don't get disturbed by the BMS SoC reporting. I trust the battery voltage more than the BMS. (Read "Are BMS reliable?")

BMS reporting is very hit-or-miss.

The factory-supplied firmware of my Hubble AM5's (2 in parallel) used to report the lowest battery SOC when charging, and the highest SOC when discharging. That was beyond useless and caused unwanted charging every time the inverter trickle-charged the battery to maintain a given SOC whilst on-grid (since suddenly it'd drop to the lower SOC from the higher one!)

After a firmware update the behavior is much improved; I've tested and the master battery now reports SOC as an average for the two batteries’ reported SOC. Far more useful.

I've also tested a run-down to 0% (I typically cycle to 15% daily) and it all worked as expected, with the Maximum Discharge Current reported by the BMS to the inverter dropping to single-battery levels when the first battery depleted (which occurred about 5 minutes before the second one hit 0Ah).

 

To the point of the OP: I also notice discrepancies of SOC between the two batteries, up to around 10%; so to an extent it's normal. Just check that the wiring connecting the batteries is uniform (same gauge and same length) since otherwise the wiring path to one battery may provide more resistance than the next which can affect charge/discharge rates to that battery.

 

Edited May 12, 20242 yr by JayMardern

5 hours ago, JayMardern said:

Just check that the wiring connecting the batteries is uniform (same gauge and same length)

Thanks you for all your reporting. However the differences of internal resistance between packs are likely to be far greater than differences in lead lengths. My newest pack is wired at the end of the packs wiring, has the longest leads, yet draws the highest currents due to its lower internal resistance.

Just some feedback on this matter...

After having the batteries in for a month and more imbalance between the three, I decided to book them back in at the after sales service department. They had the batteries for almost a month and had to change the signal board (BMS) on one or two of the batteries.

From what I understand, the BMS is supposed to work out the imbalance by itself. I received the batteries a few days ago and are monitoring them now.