Battery management system calculator

Two sums behind a BMS: how long passive balancing takes, and whether the BMS current limit or the inverter limits charge power.

Read this first. Every default is an invented placeholder, not a product's data, except that the 30 A per unit and 51.2 V in part 2 are the Sunsynk L3.0 sheet's (v.7) recommended current and nominal voltage. Read real limits from the maker's documents. Use a dot for decimals; "10,000" is read as ten thousand. Part 1 assumes one cell bleeds the whole time and ignores charging current and temperature. Part 2 assumes units share current equally at the stated voltage.

1. Passive balancing time

Cell capacity (Ah) Imbalance (% of capacity) Bleed current (mA) Cell voltage while bleeding (V) Hours a day the pack sits in the balancing window

Result	Value
Charge to remove (capacity × imbalance)	-
Hours of bleeding (Ah ÷ bleed current)	-
Days at the window you entered	-
Heat in the bleed resistor (V × current)	-
Energy dissipated (Ah × V, approximate)	-

2. Who limits charge power: the current limit or the inverter?

Battery units in parallel (whole number) Current limit per unit (A) Pack voltage (V) Inverter charge limit (W)

Result	Value
Power the current limit allows (units × V × A)	-
Charge power allowed (the smaller of the two)	-
Which limit binds	-
Units needed before the inverter binds	-

The limit a BMS reports can be lower than a sheet value and can fall with temperature and state of charge, so this is the best case.

Method: balancing hours = charge difference in Ah ÷ bleed current in A. Charge power = the smaller of (units × volts × amps) and the inverter limit.