The Version 3.2.1 Update introduces a weld pulse measurement feature.
This feature allows the Spot Welder to measure the voltage drop across the two welding cables and the Spot Welder itself. From that value it then calculates the Amps. If you are connecting the Spot Welder directly too the car battery and dont use the fuse on the positive welding cable side, the measured voltage will be exactley your car batteries voltage during the pulse.
How to activate this feature:
Please note this feature only works with V3.2 or later Spot Welders.
You need to follow almost all the steps in the software update tutorial for V3. Instead of V3 use the V3.2.1 Software. Just the Bootloader on the Arduino Nano does not need to be updated because it already has the Optiboot Bootloader on it if you purchased a V3.2 Kit.
Make sure you set the processor in the Arduino IDE to “ATmega328P OptiBoot” instead of “ATmega328P” . (See Step 1 and Step 4 of the “Updating the Arduino Nano Bootloader” Chapter in the Software Update tutorial) Steps 2 and 3 are not relevant for updating existing V3.2 Spot Welders.
Then it is pretty simple to use. The measurement will be displayed if you hold down the foot switch for more than 2 seconds after a pulse or if you leave the welding tips on the nickel strip for more than 2 seconds after a pulse. Too leave the measurement screen simply push the rotary encoder button.
Details and Tips
The Amp calculation works with a fixed system resistance value of 9mOhm because it is not possible for the Spot Welder to measure the resistance. This means that the Amp calculation will only be accurate if you are using the original welding cables and place the tips on the nickel strip about 1 cm apart.
If you put the welding tips very far apart, the real system resistance will be way higher than 9mOhm and the Spot Welder will calculate to high Amps.
Also make sure when using the Fuse that you connect the 12V power cable that goes to the Spot Welder to the welding cable side of the fuse. Connecting it to the other side or even directly to the car battery will change the voltage drop the Spot Welder measures and therefore create wrong Amp calculation results.
Hacking V3.1 or older Spot Welders to make the pulse measurement work
The pulse measurement only works on V3.2 or newer welders. There was a little change in the V3.2 pcb layout that connects the input voltage from the 12V input pad directly to the voltage measurement circuit on the pcb. In V3.1 or older the voltage was taken from behind the schottky diode. This voltage does not drop during the weld pulse because the shottky diode prevents this.
To enable the pulse measurement you need to do a little modificaton to the pcb.
First cut the pcb trace marked in red on the picture.
Next take a piece of thin wire and connect the 12V input pad to the left pad of R12.