New DIYish battery build

Batteries
61

Still lots of work to do, but the battery is at least connected:

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Still no electronics, so relying on initial top balance, and the rather conservative protection on the other battery.

So far, one ‘interesting’ thing has reared its head. The internal resistance of this battery is much bigger than the old bank (probably due to 4 BMS charge/discharge switches in series). This means that under heavy load, the old bank delivers far more than its share of the current (about 75% of the total instead of the predicted 65%). And then when the imbalance gets too high the new bank delivers far more to catch up - to the extent that when load is removed, the old bank actually recharges from the new one…

Far from ideal, but the numbers are within acceptable limits. Discharged at 6kW for 2 hours and some the two inverter feed lines got up to 40°C and stable, and everything else fairly cool. No batteries warmed up measurably. Settled at a 50/50 current split near the end, with only a small balancing charge at the end when loads were removed.

So it looks like this will probably be an ‘OK’ experiment. Far from perfect, but it will do the job.

2 Likes
62

First full day of sunlight with the balancer fully hooked up, and it got a chance to work:

VestBank_CellV_0 = 3.532   
VestBank_CellV_1 = 3.531 
VestBank_CellV_2 = 3.532         
VestBank_CellV_3 = 3.534     
VestBank_CellV_4 = 3.530          
VestBank_CellV_5 = 3.529 
VestBank_CellV_6 = 3.529
VestBank_CellV_7 = 3.531
VestBank_CellV_8 = 3.532      
VestBank_CellV_9 = 3.528      
VestBank_CellV_10 = 3.530      
VestBank_CellV_11 = 3.530                 
VestBank_CellV_12 = 3.530                 
VestBank_CellV_13 = 3.531         
VestBank_CellV_14 = 3.531 
VestBank_CellV_15 = 3.531

(Serial logging is also better formatted for parsing and dumping into InfluxDB.)

One more check on the long list of todos, but progress is being made, and it is still looking like this setup will actually work.

63

And logging to InfluxDB working:

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  1. Still some work to do to chase down glitches.
  2. Those cheapie cells are obviously not well matched.
  3. The cheapie BMSs don’t seem to coulomb count too well.
64

One thing about these Champion/Vestwoods batteries:

The cells are not well matched at all, but it has a very strong balancer to get them back together when fully charged.