Power Supply:

The strength of the welds highly depends on the power supply of the spot welder. Your car battery or Lipo should be able to supply 400 – 600A current.

To get the best results it is recommended to use a 600A (CCA) car battery or a Lipo that can do that much current. (e.g. 3s 5000mAh 60-130C)

Nickel Strip:

Depending on what size nickel strip you are using you need to choose the right power source. Welding 0.1mm to 0.15mm nickel will work ok with a 400A current. But to get good welds on 0.2mm  or even thicker you need about 600A current.

Pressing Strength:

Its also important how hard you press the welding tips against the nickel while welding. You need to apply some pressure (about 1 kg). But dont push very hard because this will reduce the weld strength again.

By pressing hard once prior to welding, then holding the spot welding leads lightly, you should be able to get great bonds..

Most of the time when the oled display stays black its a problem of the Arduino Nano. The display will only turn on if it gets a valid signal.

First try to reupload the software to the Arduino Nano again. See the Tutorial

If this does not help it could also be a contact problem of the pin header of the display. Remove the 2 screws that hold the display in place and unplug it from the socket. Then plug it back in.

Should you have a spare Arduino laying arround (it does not have to ba an Arduino Nano) you can upload the Spot Welder Software to it and connect the display to it to confirm the display does work. This way you would now for sure the defective part is the Arduino Nano.

Otherwise the Arduino Nano or the display needs to be replaced.

Weld Mode Setting

First check if you set the welder to the right welding mode. If it is in manual mode it will not activate a weld pulse automatically. Only if the foot switch is pressed. If it is in auto mode you can not activate the weld pulse by pressing the foot switch. It will automatically be triggered when both welding tips touch the nickel strip.

Hardware Problem

If it only works in auto mode but not in manul mode the foot switch could be defective or connected wrong. Check the assmebly guide to see how the foot switch needs to be connected.

If it does not activate a pulse at all or instantly welds (short circuits) there is most likely a hardware defective on the welder. To find out which part it is you need a multimeter for some measurements.

Then you could do the folowing:

Check the voltage at pin D5 of the Arduino Nano. That should be 0V and only go up to 5V during a pulse activation.
If its always 5V its an indicator the Arduino Nano has failed.

Next check the voltage at the 8 pin header that connects the mosfet board and the arduino board.
There should be about 0V. If it always is 12V while there is 0V at Pin D5 of the Arduino Nano its an indicator that the MCP1407 mosfet driver has failed.

Another thing that could have failed is one of the 4 big protection diodes on the bottom of the mosfet board.
The damage of these is usually visible by cracks in the case of the diode or black burn marks arround the failed diode.
If these fail they tend to short out.

You can also measure the resistance between the 2 aluminum parts (with the welder switched off). That should then read about 1k Ohm or 150 Ohm on older welders.
If its close to zero it is most likely caused by a defective protection diode.

Weld Mode Setting

First check if you set the welder to the right welding mode. If it is in manual mode it will not activate a weld pulse automatically. Only if the foot switch is pressed. If it is in auto mode you can not activate the weld pulse by pressing the foot switch. It will automatically be triggered when both welding tips touch the nickel strip.

Hardware Problem

If it only works in auto mode but not in manul mode the foot switch could be defective or connected wrong. Check the assmebly guide to see how the foot switch needs to be connected.

If it does not activate a pulse at all or instantly welds (short circuits) there is most likely a hardware defective on the welder. To find out which part it is you need a multimeter for some measurements.

Then you could do the folowing:

Please take a look at the mosfet board and check if there is any visible damage to the 6 mosfets or the 3 diodes on the bottom of the board.Like cracks in the components housing or burn marks on and around the components.

If that looks good (no damage)  you can measure the resistance between the two aluminum parts. For this the mosfet board needs to be attached to the top half of the welder. It should be about 1000 Ohm.  If it’s only 1000Ohm when the welder is switched off, but 0 Ohm when the welder is switched on, it’s a problem of the control electronics. (Arduino Nano or Mosfet Driver Chip)

Check the voltage at pin D5 of the Arduino Nano. That should be 0V and only go up to 5V during a pulse activation. If it’s always 5V or even higher it’s an indicator the Arduino Nano has failed.

Next check the voltage at the 6 pin header that connects the mosfet board and the arduino board. There should be about 0V. If it always is 12V while there is 0V at Pin D5 of the Arduino Nano it’s an indicator that the MCP1407 mosfet driver has failed.

After many hundreds of welds the welding tips will wear out. You can “refresh” them pretty easily by sanding with sandpaper or a file. The tips should always look clean for best welding results. If there is to much “burnt stuff” on them it can cause bad electrical contact to the nickel strip.

If you damaged the tips so bad they can not be sanded anymore you need to replace them or get a new welding cable set. There is a Welding Tip Change Tutorial available.