Proper process for balancing two Dyness batteries

Hanno Labuschagne said:
Thanks, appreciate the feedback. Just to be clear: Would there not be cases where the newer battery's SoC drops below its minimum rated depth-of-discharge if I set the minimum overall charge across the entire bank to 20%?

Or would the BMS stop drawing from the newer battery entirely once it reaches its 10% minimum and use only the older battery?
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No because its voltage based (they are always the same voltage), so at higher voltages the lower resistance battery takes more load then when it gets emptier, its resistance increases to a stage where its higher than the high resistance battery allowing the high resistance battery to catch up. I would go to 15% or even 11% and worry about it in 16 years, then just add a third battery.
 
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Is the newer battery not perhaps the version 2 of the DL5.0C and the older battery the version 1?

Maybe get in touch with Dyness to get them on the same firmware?

Have you checked that they are both set to the same capacity in the BMS. Different capacity settings for the same make and model is not uncommon.

If it appears that SOC is drifting further apart based on the SOC lights then the most logical answer would be SOC counter not resetting to 100%.

There can be lots of other reasons (like low SOH on one battery) but you would need access to the BMS and it's data to determine this. A 100ah battery with an 80% SOH will act like a 80ah battery and reports it SOC based on a full capacity of 80ah. It will therefore discharge "faster" when only considering SOC.
 
Koosvanwyk said:
Is the newer battery not perhaps the version 2 of the DL5.0C and the older battery the version 1?

Maybe get in touch with Dyness to get them on the same firmware?

Have you checked that they are both set to the same capacity in the BMS. Different capacity settings for the same make and model is not uncommon.

If it appears that SOC is drifting further apart based on the SOC lights then the most logical answer would be SOC counter not resetting to 100%.

There can be lots of other reasons (like low SOH on one battery) but you would need access to the BMS and it's data to determine this. A 100ah battery with an 80% SOH will act like a 80ah battery and reports it SOC based on a full capacity of 80ah. It will therefore discharge "faster" when only considering SOC.
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We are getting 9kWh which is to spec. They are not drifting apart, the one is just lagging behind the other but then catches up.

All is good imho.
 
Hanno Labuschagne said:
So update after maintaining 100% SoC for 24 hours...The newer (left) battery still discharges significantly faster than the older (right) one, when looking at the light indicators at least.

Gap widens over time.

5 to 4 lights drop: Happens at 80% overall SoC. Older battery only drops to 4 at 77% overall SoC.

4 to 3 drop: Happens at 63% overall SoC. Older battery only drops to 3 lights at 54% overall SoC.

3 to 2 drop: Happens at 45% overall SoC. Older battery only drops to 2 at some point after 34% overall.

2 to 1 drop: Happens at 28% overall SoC. Older battery does not drop to one light all the way down to 11% overall SoC.

Haven't gotten around to testing voltages yet, but at this point I think my installer needs to come and test themselves.

It is worth noting that I previously had another issue with the batteries not taking all the available charge that I detailed in another thread. This only started happening after we added the second battery:
Hanno Labuschagne

Thread 'Strange issue with solar power production'

Hi everyone

I noticed a strange problem with our solar power system's production in Pretoria today (29 May 2025). The specs are as follows:
  • 6 x 545W JA Solar panels
  • 5kW Deye hybrid inverter
  • 2 x 5.12kWh Dyness DL5.0C batteries
Early on in the day, I noticed that solar production was picking up slower than in the past few days despite clear skies and similar irradiance.

By 11:35, just as our 3kW geyser turned on, the peak generation was only at 2.06kW, despite the battery still being far from full. Yesterday at the same time it was 2.68kW. See images below for comparison...

That issue (largely) went away after I changed my minimum SoC from 15% to 20%.

I am a bit worried about what is happening with the newer battery when the overall SoC is under 20%

There seems to be a nearly 10% difference between the two...it is getting awfully close to the absolute minimum 10% SoC each day.

Also had a rare sudden 4% SoC drop around 20% but figured that may just have been an issue with logger.
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The soc the j verter reports is combjned ie the master battery uses the soc of the slave and itslef and reports the avg as the total SOC

Each bms will however use its lights as the inducator of ts own soc so those lights will work according to % you listed

What is the charge amps in battery serting on jnverter

And if you tap

Li bms you get info so you can see coms is working correct


Is the coms working correctly
 
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leon.davibe said:
The soc the j verter reports is combjned ie the master battery uses the soc of the slave and itslef and reports the avg as the total SOC

Each bms will however use its lights as the inducator of ts own soc so those lights will work according to % you listed

What is the charge amps in battery serting on jnverter

And if you tap

Li bms you get info so you can see coms is working correct


Isbthe coms working correctly
Click to expand...
What is the problem with 8.9kWh from 89% capacity?
 
Freedomwon allow 10% SoC differences when mixing batches of batteries. Internal resistances differ, it's probably fine.
You could get solar assistant cables, connected directly to both batteries, to monitor them individually and graph how they differ.
 
wingnut771 said:
No because its voltage based (they are always the same voltage), so at higher voltages the lower resistance battery takes more load then when it gets emptier, its resistance increases to a stage where its higher than the high resistance battery allowing the high resistance battery to catch up. I would go to 15% or even 11% and worry about it in 16 years, then just add a third battery.
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Another way and more accurately describes it is the voltage on the fast left battery drops ever so slightly (lower soc) causing the potential to move to the slow right battery that has an ever so slightly higher voltage (higher soc) which causes it to catch up.
 
abc98 said:
Freedomwon allow 10% SoC differences when mixing batches of batteries. Internal resistances differ, it's probably fine.
You could get solar assistant cables, connected directly to both batteries, to monitor them individually and graph how they differ.
Click to expand...
Just get a cheap multimeter and you'll see the voltages are the same. I agree, its probably fine, there is no problem with 9kWh consumed.
 
Hanno Labuschagne said:
Thanks, appreciate the feedback. Just to be clear: Would there not be cases where the newer battery's SoC drops below its minimum rated depth-of-discharge if I set the minimum overall charge across the entire bank to 20%?

Or would the BMS stop drawing from the newer battery entirely once it reaches its 10% minimum and use only the older battery?
Click to expand...

BMS will always take precedence while the inverter is in lithium mode.

Only time this would change is if you ran the inverter on AGM mode which bypasses the BMS.
 
SauRoNZA said:
BMS will always take precedence while the inverter is in lithium mode.

Only time this would change is if you ran the inverter on AGM mode which bypasses the BMS.
Click to expand...
but the BMS has its own internal cut off? with 2 batteries in parallel with 2 bms' not aware of each other will still bottom out together.
 
SauRoNZA said:
BMS will always take precedence while the inverter is in lithium mode.

Only time this would change is if you ran the inverter on AGM mode which bypasses the BMS.
Click to expand...
How would the batteries BMS know the inverter is set to lithium mode?
 
SauRoNZA said:
Because that’s the only mode that communicates with the BMS.

AGM doesn’t.
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So then the batteries BMS should take over, cause it's not being told how to on the system anymore?
 
wingnut771 said:
but the BMS has its own internal cut off? with 2 batteries in parallel with 2 bms' not aware of each other will still bottom out together.
Click to expand...

Exactly. So it won’t go below its minimum DOD, doesn’t matter if they are aware of each other or not.

They are aware of each other as they’ll all be connected to each other.
 
SauRoNZA said:
Exactly. So it won’t go below its minimum DOD, doesn’t matter if they are aware of each other or not.

They are aware of each other as they’ll all be connected to each other.
Click to expand...
What are we arguing about here?
 
Lupus said:
So then the batteries BMS should take over, cause it's not being told how to on the system anymore?
Click to expand...

Other way round really. In AGM it goes into dumb mode and just does what it’s told without caring.

In Lithium mode they fight with each other and the BMW wins.

I’ve never tried to run it completely dead in AGM mode so chances are there is a secondary BMS protection, but I could definitely run it was lower in AGM than on Lithium mode.
 
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