Electronics > Projects, Designs, and Technical Stuff
Intelligent BMS (Battery Management System)
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JohnnyBerg:
The boards arrived today, at first sight they look ok.
ealex:
it looks interesting
how are you shifting the cell voltage to the MCU's adc ?

will you publish a schematic ?
JohnnyBerg:
There you go ;)

What this circuit does:
1. It ignores the first 2.5V of a cell as not being of interest.
2. It converts the cell voltage between 2.5 and 4.5 Volt to a current.
3. The current is then converted to a voltage, with 1.5 times amplification, giving a range of 0 to 3 Volt to the MCU.

Total current draw from a cell is < 50 uA

U6 = Output to MCU
B6 = Positive of cell 6
B5 = Positive of cell 5 = negative of cell 6

ealex:
nice - never thought of that.
i've tried with resistor dividers, but the errors stack up quickly -> i've decided to go with the BQ chips.
JohnnyBerg:

--- Quote from: ealex on November 22, 2019, 08:58:01 pm ---nice - never thought of that.
i've tried with resistor dividers, but the errors stack up quickly -> i've decided to go with the BQ chips.

--- End quote ---

Yaeh .. resistor dividers are a absolute no go. Not also do errors accumulate, resolution is lost also.

This circuit i.c.m. with a 12 bit ADC gives a resolution in the order of 500uV. And because the voltage does not change quickly, the MCU can do noise cancellation with a moving average.
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