Hangshun HK32F103 supercapacitor spot welding machine with main chip

1. Project background

The idea of ​​making my own 18650 lithium battery spot welder has been around for a long time. Every time I see others making it, I get excited, but I always hesitate to do it myself due to various reasons. Now with the help of the activities organized by Hangshun and Lichuang Make it happen.

The main protagonist is the 2.7v 3000F supercapacitor, 2 in series to 5.4v, you can consider adding 2 in parallel.

2. Function introduction

1. Use HK32F103C8T6 as the main chip

2. Dual-channel XL4501E1 is used as a constant current and constant voltage source to charge the capacitor. The design current is about 8A.

3. The BW6101 supercapacitor protection chip provides a balanced charging function for the capacitor, and the overvoltage alarm signal is provided to the MCU to ensure charging safety.

4. The parallel array of 32 IRL3713S MOS tubes provides strong protection for high current discharge of capacitors.

5. EG2131 tube driver chip ensures that charging and discharging will not be turned on at the same time.

6. The main chip also has another voltage detection and temperature detection

7. Use the control and display method of rotary encoder + OLED (the situation will be simplified according to the time progress)

8. Automatic/manual welding mode, pulse number, time and other settings

3. Detailed circuit description

3.1 Power supply part

Since the voltage of the two strings of capacitors has exceeded 5v, 12v is used for power supply. Since the charging current is relatively large, it is recommended to use a power supply of 12v3A or above.

12v is reduced to 5v through 78L05, and then reduced to 3.3v through 1117 to power the main control.

3.2 Capacitor charging constant current and constant voltage

Use the XL4501E1 chip constant current and constant voltage output to charge the capacitor, the FB constant voltage detection value is 1.25v, and the CS constant current voltage detection value is 0.11V

3.3 Capacitor voltage equalization protection

Use the BW6101 supercapacitor dedicated voltage equalizing chip, set the voltage to 2.7v, and turn on the voltage equalizing circuit when it exceeds 2.65v. The 0.5Ω 20w cement resistor can shunt about 5A of current.

Exceeding 2.75v turns on the alarm light and gives a high level signal to the MCU. It can be seen that the 2-way protection OV is in front of the resistor and the other is after the resistor so that the MCU can directly obtain the signal without adding a voltage dividing resistor, and it will not obtain the critical voltage of 5.5v.

3.4 Voltage detection

This circuit is simple. The voltage dividing resistor can also be unchanged, but it needs to be converted. It is worth mentioning that GND enters the negative electrode of the capacitor through the charge control MOS tube in the reverse direction, so the reverse voltage drop of the MOS tube is about 0.7v (not yet practical testing)

3.5 Test lead short circuit detection

In the actual circuit, Pen- is connected to the negative electrode of the test lead. After the test lead is short-circuited, it goes directly to the positive electrode of the capacitor. In fact, it is equivalent to the voltage detection circuit above.

3.6 Display and control

The above is a rotary encoder circuit, which can be controlled by rotating left and right and clicking. The display uses 0.96-inch OLED interface I2C.

4. Physical picture

Display capacitor voltage, detect capacitor temperature, MOS tube temperature

Dynamic charging symbols will be displayed when charging, and the rotary encoder is used for menu selection and setting of various parameters.