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Table of Contents


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Parts

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PartDescriptionLink
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 SwitchAC 250V 10A SPDT NO NC Plastic Momentary Power Foot Pedal Switch BlackAmazon
Sonoff SVWireless Smart Switch Sonoff SV
Aligator Clamps

Battery Terminal Connector

Bolts/Nuts

Probes

Wire



Relay



Schematic - Push Button Fire

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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.

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I programmed the SONOFF micro-controller (ESP8266) to open the relay for a number of microseconds in order to perform the weld.

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  • 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



Revised Build 

I revised the build to allow the weld time to be configurable via a web ui running on the microcontroller.


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Observations

With my batter fully charged, a 25ms 30 ms weld did a good job most of the time. For some welds, I increased the weld time to 50ms.