Audi E-tron battery into powerwall

[yabert]

Just to make sure that I understand you correctly - the orange lines you drew are for balancing the cells (if any imbalance occurs) and there won't really be any large currents passing by these cables?

Yes, it's only for the small imbalance of capacity / impedance between groupe of cells. With a conductor between each group of three 60Ah cells (so 180Ah), a new 360Ah cells is create.

Given the number of packs I have (27). Perhaps 12S 9P (1620Ah) would be more suitable? That would bring down the number of BMS's to 3.

3 BMS, why? If you decide to build one gigantic 1620Ah battery you only need one 12S BMS.
Based on the 60Ah cells, that will give you a 12S 21P battery.

 

[yabert]

You could maybe use the BMS wires (circle in blue) to put cells in parallel, but you will have to:

1-Know what is the max current those circuits can take.
2-Evaluate the risk and the consequences to pass too much current by those circuits. They are probably fuse on the PCB board.

 

[SwedishDIYer]

Yes, it's only for the small imbalance of capacity / impedance between groupe of cells. With a conductor between each group of three 60Ah cells (so 180Ah), a new 360Ah cells is create.

3 BMS, why? If you decide to build one gigantic 1620Ah battery you only need one 12S BMS.
Based on the 60Ah cells, that will give you a 12S 21P battery.

Yes, but I will have three of those gigantic batteries, a total of 4860Ah. One BMS each.

 

[yabert]

???
4860Ah x 44V = 214 kWh
You have 3 E-Tron batteries?

If you are lost, you can also start with battery cell. You have 324 cells in a 71 kWh battery. You need 12 cells in serie to have 44V and that let you 27 cells in parallel.
But Audi already connect 3 cells in parallel for you , so you have to group 9 of them to build a 44V 1620Ah battery - 12S 27P battery - or simply a super nice and high quality 71 kWh battery.

 

[SwedishDIYer]

Oh never mind ? You are of course correct. It’s too late in the evening for me now, I need to hit the bed ?

 

[ampsterdance]

Hey fellow Swede, how is the project going?

I'm running a Victron system with some used Nissan Leaf cells. Seeing the "Flying tools" channel on YouTube got me keen on getting a used EV battery and probably use it at 400v.

You mentioned wanting to do some price arbitrage. An interesting idea is to also sign up for virtual power plant type service, CheckWatt is the only one I know of. It seems to pay quite a lot, a 10 kW system would be estimated to pay around 35'k SEK, a 20 kW system about 70'k annually. It seems most of the inverters they support are for high voltage batteries, Victron is not on the list.
The Flying tools guy went with an Orion BMS, I guess the BMS cost can be easily offset by the gains one can have by this sort of service, and they even handle the automation.

Just a thought to consider.

 

[SwedishDIYer]

Hey fellow Swede, how is the project going?

I'm running a Victron system with some used Nissan Leaf cells. Seeing the "Flying tools" channel on YouTube got me keen on getting a used EV battery and probably use it at 400v.

You mentioned wanting to do some price arbitrage. An interesting idea is to also sign up for virtual power plant type service, CheckWatt is the only one I know of. It seems to pay quite a lot, a 10 kW system would be estimated to pay around 35'k SEK, a 20 kW system about 70'k annually. It seems most of the inverters they support are for high voltage batteries, Victron is not on the list.
The Flying tools guy went with an Orion BMS, I guess the BMS cost can be easily offset by the gains one can have by this sort of service, and they even handle the automation.

Just a thought to consider.

The project is now online and working! Still some stuff to do, casing for the batteries and some cable management.

CheckWatt is nice, but they have no support for Victron. Maybe in the future! For now I´ll just use Victrons Dynamic ESS, or perhaps this project that seems to be working well, https://gbbvictronweb.gbbsoft.pl/