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 [login to view URL], 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 ([login to view URL])
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: [login to view URL])
11) Voltage measurements (e.g. ADC) are made with an ADS1115 ([login to view URL])
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 ([login to view URL]) 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
1) Circuit Diagram (35%)
2) PCB Express design with BOM (35%)
3) Working circuit (bought, built and tested by me) (30%)
Hello. I'm an electrical engineer / PCB designer. You may check my qualificationin the profile. We can discuss any details in the chat (it will be a challenge to achieve desired tolerance). Will do my best. Viktor
Hello, Have a great day. we will ship you fully working hardware and we will take care of ROHS compliance. Please feel free to contact us. Best Regards, Shahbaz.