The Arduino Spot Welder Mosfet Board just got updated to V3.3

The improvements in this new version are:

  • Much wider traces on the bottom of the pcb for the high current connection to the u-shaped aluminum part
  • Mosfet gate resistors directly on the mosfet board, very close to the mosfet gate pins
  • All 8 Pins of the female 8 pin header that connects the Arduino and mosfet board are now connected to each other, which eliminates contact problems.
  • compatible to all Spot Welder Arduino Boards V3 or later

Wider Traces

The hole for the middle pin of the mosfets legs has been removed from the mosfet board. The middle pin was not used anyway, because the current is transfered through the big top part of the mosfet that is screwed to the straight aluminum part.

This allowed to make the trace that has to transfer the high current from the outer pin of the mosfet to the u-shaped aluminum part much wider. The benefit of this is that the current can spread over a bigger area of the pcb that will make the pcb more robust to very high currents.

The pad for soldering the middle pin of the mosfets is still there but only at the top of the pcb. When building the mosfet board you can decide to simply cut off the middle mosfet pin or just shorten it a bit and solder it to the pad. This has no effect on functionality, its only an optical choice what look you like better. Prebuilt Kits will come with the midlle pin cut off.


Gate Resistors close to mosfet gates

Having the gate resitors very close to the mosfet gates prevents “swinging” in the gate voltage. That results in better mosfet switching synchronisation and less stress for the mosfets. It also made it possible to connect all 8 pins of the 8 pin female header together. This way it is no longer a problem if there is bad contact on one of the 8 pins of the header. All mosfets will always turn on or off exactley the same time.


What about the Arduinio Board ?

The Arduino Board does not need an update to be used with the new mosfet board. If you are going to populate the Arduino Board on your own you can use 30 Ohm resistors for R2 – R9 as before. Or if you dont have enough resistors simply bridge R2 – R9 with wire bridges like shown in the picture.

When populating R2 and R9 on the arduino board keep in mind that you need 8 additional 30 Ohm resistors for R2 – R9 on the mosfet board.

15 thoughts on “Mosfet Board V3.3 Update

  1. miguel.sepulve1 says:

    Congratulations for the streamlining of the MOSFET Board. Can it be made with 1oz layer or should be made with 2oz copper layer?

    • Marc Schoenfleisch says:

      I would recommend to use at least 2oz copper. The current through this thin copper layer is very high.

  2. sans says:

    KICAD R1 resistor in version 3.3 should be modified to 1Kom ?
    I see in other version is for 150 ohm resistor SMD 3521 2w
    However, version 3.3 was changed to 1206 1kom
    Is a bug?

    • Marc Schoenfleisch says:

      You can use a normal resistor with 1k no problem.
      The 150 ohm resistor is still in the design because in the earlier version of the welder an addidtional external protection diode was used.
      This required the resistor to have such a low value.

  3. wolverstom says:

    I have recieved my v3.3.4 kit and are searching for a car battery. The manual says 400 to 600 cca but;
    – is 300 also good enough?
    -and what happens to the board when it reaches max current?
    – what is the max current?

    Tom 🙂

    • Marc Schoenfleisch says:

      300A might not be enough current to get good welds.
      The best results are made with about 600A (CCA) car batterie size.
      The maximum i tested the welder with was a 800CCA battery. Higher current may damage the mosfets or the protection diodes on the mosfet board.

      • Mike says:

        Hey Marc,

        Let’s say I need just a bit more juice. I have a 900 CCA battery that I would like to use.

        If I damage a mosfet or the protection diodes, are they an easy replacement? Also, will my board start on fire or just shut down?

        • Marc Schoenfleisch says:

          Replacing the mosfets or diodes requires a powerful soldering iron, because the aluminum parts transfer the heat away very quickly.
          But other than that it is pretty easy to do.

          In case the mosfets fail only the legs should brake. They act kind of like a fuse then.
          If a diode fails it will eject smoke and a little very short explosion. But it will not set the board on fire.

          • Mike says:

            Thanks Marc! I might get a new mosfet board just in case on order and then report back.

          • Mike Deau says:

            Hey Marc,

            Three more things

            1) Can I just order a mosfet board? I did not see it on your website.
            2) Did you not test higher amps due to lack of a 900cca battery or is it that the electrical theory for the diodes that says they will not take it and it does not make sense to try?
            3) Can I upsize the fan/heatsinks to allow for more current?

            I am repairing Tesla Model S packs with new fuses and the connection to the bus bar is not going well @ 725 CCAs and 100ms.


            All for now.

          • Marc Schoenfleisch says:

            1.) Its possible to get as replacement part. Please contact via email

            2.) and 3.) The diodes and mosfets are already stressed out pretty much at 800A car battery.
            It may work with 900cca but will need good cooling and i dont know if lifetime of the mosftes / diodes is compromised then.

  4. Jens says:

    Hallo, brauche mal Eure Hilfe.
    Auf meinem Board ist eine Diode defekt. Bezeichnung 5PEQ9DHJV. Finde mit dieser Bezeichnung keinen Händler.
    Wer kann helfen bzw. welche Dioden anderer Bezeichnung würden funktionieren

    Danke für eure Hilfe

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