Build a high precision circuit for charging/discharging Li-ion batteries

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Project Budget
€30 - €250 EUR
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Project Description

I'd like to build a high precision circuit for charging/discharging Li-ion batteries with the ability to monitor current, capacity, voltage, and temperature versus time. The circuit should have the following characteristics:

1) Ideally powered from the 5 V pin on a Raspberry Pi (this is somewhat negotiable)

2) Can charge a battery to 4.5 V and discharge to 2.5 V (discharge to 0 V is better)

3) Have constant current (CC) and constant voltage (CV) mode capabilities where the circuit switches from CC to CV at a programmable user defined voltage. For example, the circuit would do constant current charging to 4.2 V, then hold at 4.2 V for a period of time, then discharge to 3 V, and repeat. I suspect the circuit will look something like this : Figure 1 at [url removed, login to view], but it does not need to

4) Constant current is programmable (e.g. using a Raspberry Pi, python, i2c and a DAC). Ideally the DAC is an MCP4725 ([url removed, login to view])

5) Constant voltage is programmable (e.g. using a Raspberry Pi, python, i2c and a DAC). Ideally the DAC is an MCP4725.

6) In constant current mode the current does not vary by more than 0.1%

7) Current range of -100 to +100 mA. Being able to both sink and source current is important (e.g. discharge/charge)

8) In constant voltage mode the voltage does not vary by more than 1 mV

9) Programmable voltage range of 2.5 to 4.5 V (ideally 0 - 4.5 V)

10) All components can be tested on a bread board (e.g. no surface mount components unless they can be found on an inexpensive breakout board like the MCP4725: [url removed, login to view])

11) Voltage measurements (e.g. ADC) are made with an ADS1115 ([url removed, login to view])

12) Current measurements are also made with an ADS1115 across a shunt resistor with minimal resistance drift and low temperature co-efficient. Must be able to read negative and positive currents (e.g. charge/discharge currents). Shunt resistor should be in series with the battery immediately in front of, or behind.

13) To accomplish above accuracy I assume a voltage regulator/shunt is required

14) Complete bill of materials

15) Circuit diagram and PCB design done in ExpressPCB software ([url removed, login to view]) including a Raspberry Pi header with male/female pins (e.g. so the board can be mounted directly to a Raspberry Pi and all pins are still accessible). PCB layout should include mounting holes so the board can be secured to the Pi using standoffs. Also PCB should not be larger than the Raspberry Pi 3 board in width or length

16) Description of how the circuit operates

17) Reasonable amount of technical support during building/testing

Miles Stones:

1) Circuit Diagram (35%)

2) PCB Express design with BOM (35%)

3) Working circuit (bought, built and tested by me) (30%)

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