Arduino-based N-channel charger and discharge tester for 18650/21700 (or any other type) Li-ion batteries.
The project uses INA3221 current/voltage monitors, TP5100 charge modules and 16×2 LCD display to visualize current status in real-time. Each channel is controlled independently via a MOSFET-based discharge load.
Features:
- 4 fully independent measurement channels (expandable)
- Convenient control of the charge/discharge mode via a physical switch
- Automatic start of the charging or discharging cycle upon battery installation
- Automatic cut-off when battery is fully charged or discharged to certain value (default 2.8V)
- Real-time measurement of battery's voltage, current and capacity
- Measurement of battery internal resistance using the voltage drop under load method (DC)
- Uses very cheap N-channel logical gate MOSFET (AO3400 in SOT-23 package)
- Max charge current: 2A (depends on TP5100 module)
- Max discharge current: ~1.6A (depends on load resistance)
It can be easily expanded to support an arbitrary number of batteries: each INA module handles up to three independent channels. I2C expanders can be used to accommodate a larger number of INA modules. Be sure that your power unit and wires is capable of N-Amps output current to power-up all charging modules!
It is also possible to replace the TP5100 modules with standard TP4056 ones; this results in a lower maximum charging current and longer charging times, but provides more stable voltage.
| Ref. | Pts | Type | Comment |
|---|---|---|---|
| Arduino | 1 | Arduino Nano | Rev. 3.0 used |
| M2, M3 | 2 | INA3221 module | isolated channels version only |
| M4–M7 | 4 | TP5100 module | 2A charge current |
| M1 | 1 | LM2596 DC-DC converter | stable 5V power supply to the logic circuitry |
| LCD | 1 | LCD with I²C-bus | 1602 LCD or your choice |
| Q1–Q4 | 4 | AO3400 MOSFET | alt name: A09T, SOT-23 |
| R2-R4, R9-R13 | 8 | 220 Ω resistor | LED and Arduino pins protection |
| R5-R8 | 4 | 10 kΩ resistor | MOSFET pull-down |
| R14-R17 | 4 | 2.7 Ω power resistor | Discharge load resistor, 5-10W rated |
| LED1–LED4 | 4 | 3-5mm LED | Discharge load indication |
| S1–S4 | 4 | SPDT switch | 2A constant load capable |
| BAT1–BAT4 | 4 | battery holder | pay close attention to the polarity |
| V1 | 1 | power unit / input | 6-18V, 5+A (min 60W total power) |
Not listed:
- LCD channel switch button (not shown on the diagrams, add it to any arduino pin of your choice)
- 12-24V fan (for cooling load resistors and TP5100)
- Heatsink (a standard 70x22mm SSD heatsink is ideal for four TP5100 modules, place it UNDER the modules via heat-resistant isolation tape)
- Additional capacitors (ceramic and/or electrolytic) at the TP5100 input and at the fan input (to reduce voltage drops)
- Connection wires
- Open stand or case
You must use an INA3221 module with independent channels (there should be no electrical continuity between the IN+ pins).
Active cooling is required for prolonged operation: the TP5100, load resistors, and MOSFETs will generate significant heat.
Never leave batteries unattended while charging or discharging!