Parts
| Part | Description | Link |
|---|---|---|
| Starter Relay | High Current Starter Relay 500 AMP DC 12V 4 Pin SPST Car Auto Start Contactor Double Batteries Isolator Control On/Off Switch | Amazon |
| Momentary Pedal Switch | AC 250V 10A SPDT NO NC Plastic Momentary Power Foot Pedal Switch Black | Amazon |
| Sonoff SV | Wireless Smart Switch | Sonoff SV |
| Aligator Clamps | ||
| Battery Terminal Connector | ||
| Bolts/Nuts | ||
| Probes | ||
| Wire |
Relay
Schematic - Push Button Fire
Schematic - Microcontroller
The Build
I ended up using a Sonoff SV since it had everything I needed. Instead of having to use a transistor to switch the 12v, I used the build in relay. The Sonoff SV also has 3 GPIOs available which I used for a RGB LED. It also exposes the GPIO-0 (button) which I used for the foot pedal. The foot pedal made things so much easier.
I originally powered the SONOFF SV off of the battery but found that it would cause the SONOFF to reboot sometimes. So, I ended up powered it with a dedicated 12V 2A power supply.
I programmed the SONOFF micro-controller (ESP8266) to open the relay for a number of microseconds in order to perform the weld.
The time required to weld really depends on your battery source. I noticed that when the battery was running low, it took more time to get a good weld.
Originally I programmed the micro-controller to perform the following tasks:
- welding would be performed using 1 of 4 durations (25, 50, 75, 100ms)
- pressing the foot pedal quickly would send 12v to the solenoid for the currently set duration.
- pressing the foot pedal for at least 2s would switch to the next duration.
- each duration had an associated color (LED):
- blue - 25ms
- green - 50ms
- orange - 75ms
- red - 100ms
Later, I made the weld time configurable via the web ui.
Revised Pictures
Observations
With my batter fully charged, a 25ms weld did a good job most of the time. For some welds, I increased the weld time to 50ms.