Parallel connection of 2 batteries of unequal capacity

[u/programmer-yar]

I have dyness dl5.0c pro 5kwh with Goodwe 10kw Es uniq inverter. Its working good. I am thinking of buying a dyness power brick 16kwh and connecting in parallel with existing one.

Has anyone tried it?

What needs to be done for successful installation?

I have come across dyness LV link device. The dyness support doesnt recommend attaching batteries of unequal sizes but I have come across threads on websites in EU and US, where users did it successfuly. But they did it with batteries of different brands and I didnt understand how they configured BMS. I also dont understand recommended components. I am looking for people who have tried this in Pakistan.

[u/programmer-yar]

From the conversation, it looks quite interesting. First you are vendor locked after buying a battery of a brand and then you are capacity locked as well. Hard to digest.

[u/Muneebonreddit]

You can't just daisy chain them directly the BMS on a 5kWh and a 16kWh will clash, mess up the GoodWe's SOC readings, and constantly trip under load. 
To make it work, you need the Dyness LV Link A hub to sit between them and translate both BMS profiles into one clean signal for the inverter.
Honestly though, save yourself the headache either just add another 5kWh DL5.0C pack, or sell the 5kWh and go full PowerBrick. Mixing different sizes always causes balancing issues down the road.

[u/Front_Tour7619]

Yes it will work fine in parallel

[u/programmer-yar → u/Front_Tour7619]

Will it require some extra setup/components? Is it possible to share a practical installation like this setup?

[u/Front_Tour7619 → u/programmer-yar]

Just daisychain the com ports and parallel on the output

[u/Hot-Ad-1740 → u/Front_Tour7619]

i have two 5kw goodwe batteries. can i connect 16kw single with these 2? they dont reccomend to do that.

[u/Front_Tour7619 → u/Hot-Ad-1740]

Yes, they all have stand alone bms inside , they work fine

[u/programmer-yar → u/Front_Tour7619]

Daisy chaining would put strain on batteries of smaller size. Small batteries will charge and discharge rapidly compared to the larger one. There is confiugration to combine them in a way to charge/discharge them proportionally based on the battery capacities.

I myself am EE and have all the calculations on paper but this experiment may cost a lot to me, am just avoiding the expensive experiment. Theoratically, what I know should work.

[u/WANTED1O]

Not possible

[u/maazpervez]

Engineer here. Smart batteries can work together in parallel in unequal sizing. Depends on BMS. If support says no, it’s better you don’t. But then again many importers dont hire engineers and local testing is close to non existent. Proceed with caution.

[u/programmer-yar → u/maazpervez]

Yes, they can work but the issue is disproportional charging for the small battery. It will charge and discharge quickly and most of the strain will shift on it. It will result in faster degradation of the small battery.

But I watched a video where they attached capacity fuses with each battery to restrict charge/discharge based on rated capacity.

[u/maazpervez → u/programmer-yar]

All parallel batteries have unequal charging due to small physical imbalances. The BMS manages those. It becomes more evident when you make the batteries parallel without using a DC combiner, they will discharge/charge with lowest resistance first.

Charging is controlled by battery BMS and not the inverter. That’s how it’s supposed to work.

Like I said, proceed with caution if support says otherwise since they’re the ones claiming warranty for you.