MC800S module hub step-down board

PDF_MC800S Module Hub Step-Down Board.zip

Altium_MC800S Module Hub Step-Down Board.zip

PADS_MC800S Module Hub Step-Down Board.zip

BOM_MC800S Module Hub Step-Down Board.xlsx

91744

2-cell supercapacitor spot welding machine

This 2-cell supercapacitor spot welder has a built-in charging chip that allows for simultaneous use and charging. It has been tested and works well.

This is copied from https://oshwhub.com/sunshineyang1999/dian-han-ji.
The program hasn't been modified (I don't know how to modify it either; according to others, the source code is an intermediate product, missing some components, while the firmware is the finished product, capable of achieving the target function and very practical).
I personally think there's room for improvement: 1. The spot welding pulse step is 1ms; I think 0.1ms would be better. Capacitor spot welding machines generally only have two or three ms working pulses. 2. Actual pulse time measurement: The first pulse displayed value is 1ms less than the actual value, but the other times are accurate. Does anyone have the ability to modify the source code?
Instructions for use:
1. Long press the encoder to automatically turn the machine on and off. The shutdown circuit uses an SS8550 transistor, which completely shuts off the power. 1. Automatic shutdown after 6 minutes of inactivity. 2. Low voltage shutdown. 3. Automatic saving of parameter settings. 4. Dual pulse (4 pulses seem unnecessary). 5. Detection of whether the boost circuit is working properly (to prevent the boost circuit from failing due to insufficient drive voltage; as long as the voltage is boosted to 10V, the R8 tube can be fully turned on; the actual boost voltage is 14V). 6. The boost circuit only works when the spot welding pin is pressed against the nickel sheet. 7. Charged by two series of capacitors using a CN3125 chip, with built-in balancing and linear charging; the maximum charging current is 500mA (warm). It is recommended to work while plugged in, as it can work and charge simultaneously.
 
There are a total of 5 interfaces: A. First pulse time unit: milliseconds; B. Pulse interval time unit: milliseconds; C. Second pulse time unit: milliseconds; D. Welding delay detection unit: seconds; V. Supercapacitor voltage
calibration voltage: On the V interface, long press the encoder until the buzzer sounds, release, and rotate left or right to calibrate the voltage (by adjusting the internal voltage division ratio). Protection voltage setting: On the V interface (voltage display interface), directly rotate the encoder left or right to set the protection voltage. Other interfaces: short press the encoder to set parameters A, B, C, and D; long press to shut down. After setting the parameters and leaving it idle for a few seconds, it automatically returns to the C interface.
When the hardware switch is in the off position, it disconnects the power supply to the control board from the capacitor (the capacitor and charging chip are always connected). This state is used for charging when the capacitor voltage is very low. When the capacitor voltage is above 4V, this switch can be left on, and the automatic shutdown circuit will shut it off almost completely.
The red indicator light below shows that the capacitor is 90% charged; it only lights up when the capacitor voltage exceeds 4.5V and USB power is plugged in.
 
 
It also integrates a Type-C charging function with a charging current of 0.5A and a voltage of 5.04V. It uses balanced charging, as long as the capacitor differences are not significant. The measured voltage difference was 0.02V. It is not recommended to try charging the CN3125 with 1A; sufficient heatsinks are required. I've already burned out two due to poor heat dissipation. With 500mA, it will barely get hot.
The PCB is now smaller than before, and the layout is much better; it fits perfectly into a toothpick holder.
It can work when plugged in (recommended). The charging chip automatically shuts off during spot welding and automatically turns on after welding. It takes approximately 1-10 seconds to recover the energy from one spot welding operation.
The supercapacitor I used is approximately 300F 0.7MΩ, the copper busbar is 15x1mm, and the bonding wire is a single 10 square millimeter 25cm strand. I used 9 R8 capacitors. The total loop resistance (pin-to-pin) is 3.3MΩ, and the theoretical maximum current can reach approximately 1500A.
 
It's assembled into separate units; a suitable battery box would be ideal.
 
 
I used 9 tubes (one was sent incorrectly by the seller, and I couldn't wait for a replacement, so I'm using 9 for now), 5 on each side, which is sufficient. It can charge while welding. The 6-minute automatic shutdown/long press shutdown function also works. Of course, it cannot charge after shutdown. The maximum charging current is 1.2A, which makes the charging chip very hot; a heatsink on the back of the charging chip would probably be better.
I used 10 square millimeter standard wire, 25cm long per strand, and homemade soldering needles (made by stripping the insulation from 5 square millimeter wire). The total internal resistance of a single strand is 0.6mΩ, which is quite ideal; any thicker and it wouldn't be worth much. The capacitors were too small and light, and the wire was too stiff, so I had to press a book on top of the capacitors while working.
I soldered 0.05mm copper sheets, which were strong, and 0.12mm nickel steel sheets, which were also strong. The image below shows a 1ms-0.4ms-0.4ms soldering sequence; it sparked every time. I'm just starting out; I'll find the right pulse time parameters later.
The soldering needles are 5 square millimeter copper wire, which I filed myself, so they're not smooth enough. Round tips are used for high-current components, and pointed tips are used for low-current components.