DIY Arduino Based Battery Spot Welder (OPEN SOURCE)

Note:- The Entire Project is OPEN SOURCE including code, necessary files for PCB fabrication and 3D files for Making your enclosures.

Spot welding is basically shorting a very high current source on the surface for a brief period. A huge amount of current flows through the surface metal, which causes the metal to get super hot at the contact point of the electrodes and fuse with one Another. It is a crucial technique used in the manufacturing of e-bike battery packs. Soldering or using other welding techniques can be dangerous and cause damage to the battery cells. Spot welding ensures that the individual cells are securely welded together without damaging them.

Spot welder is a Must Have tool for a Battery Nerd.

But What I have seen is, getting a good Spot welder is a difficult task as the market is crowded with cheap Chinese welders that are unreliable in most cases, So, I challenged myself to create a Spot Welder completely from Scratch and the primary focus during my build design process was make it as DIY-Friendly as possible.

So, the Key Highlights are:

1. Uses Arduino pro mini which is a common microcontroller board and can be purchased from any hobby Stores
2. Primarily uses Group of Mosfets as a switch but, if you don't have power MOSFETs at your spare,
3. Motorbike Starter relays or Car Starter relays can also be used instead of the Mosfets.

Above mentioned are good options for Battery Spot welding which means a Battery is used as a Current source and the weld is made by sorting out the positive and Negative for a short-predefined period of time. This makes the Welder extremely portable if you have a Lipo battery of at least 5000MAH with 60C discharge ratings. If you have a battery with a lower 'C' rating, you can use a higher-capacity cell. 10000Mah battery with '30C' discharge rating will perform same as 5000Mah battery with '60C' rating.

It also has a small onboard relay which you can use to connect the primary side of the Hacked-Microwave Oven transformer to make a fixed Desktop Spot welding Station.

Reminder:- If you want to support this project, You can buymeacoffee or join me on Patreon.

Bill Of Materials

1. Arduino Pro Mini 5V :- 1Pcs, Amazon
2. 0.96 inch White Oled :- 1Pcs, Amazon
3. Rotatory Encoder Module :- 1Pcs, Amazon
4. 2 Pin Terminal Block :- 2Pcs, Amazon
5. 8AWG or 10AWG Wire :- 2Mtr
6. Barallel Jack Connector :- 2Pcs, Amazon
7. 5V relay :- 1Pcs
8. 5V Buzzer :- 1pcs
9. BC547 NPN BJT transistor :- 1Pcs
10. IRFZ44N Mosfet :- 1pcs
11. AMS1117-5V voltage Regulator :- 1Pcs
12. Any N-Channel Mosfet of TO-220-3 package with >=150 Drain to source current. MPG200N08 or HY4008P :- 6Pcs.
13. PC817 Optocupler :- 3Pcs
14. 0603 2 Ohm resistor :- 6Pcs
15. 0603 220 Ohm resistor :- 6pcs
16. 0603 10K resistor :- 3Pcs
17. 0603 100Ohm Resistor:- :- 1pcs
18. 0603 20K Resistor :- 1Pcs
19. 0603 4.7K Resistor :- 1Pcs
20. 0603 1K Resistor :- 1Pcs
21. SS56 Schottkey Diode :- 9Pcs
22. 1uF 0608 ceramic Capacitor :- 3pcs
23. 35V 680uF capacitor :- 1pcs
24. 10V 220uF capacitor :- 1Pcs

Tools Required

1. Soldering Iron
2. Tweezers
3. Screwdrivers

I hope If that you have already watched the Video, If not, watch it from Here.

So there are Key 4 Main Parts,

Current Source

As explained earlier, the current source provides a huge amount of current to weld the metals. The Current source can be anything, Your automotive Battery, Lipo Battery, High Current Transformer, Capacitor Bank or other.

Wires and Electrodes

The wires carry current from the source to the electrodes. The copper electrodes make contact with the surface and surfaces are welded on the contact point of the electrodes. Electrodes can be as simple as copper nails.

High-Current Switch

The wires and electrodes are not directly connected to the current source as this could cause an unintentional short circuit. Therefore, a High-current switch is used to only connect electrodes to the current source when needed during welding.

Microcontroller Unit

Spot welding is a very fast welding process, the switch has to be opened and closed with millisecond accuracy. Achieving such Accuracy with humans is next to impossible so, an Arduino microcontroller will be used to open and close the switch.

Apart from Switching, the microcontroller also,

1. Takes pulse input from humans
2. Displays info on the screen
3. Footswitch Trigger Input
4. Battery low-voltage protection and such.

I have already done the Heavy Lifting of designing the Circuit Diagram for you. Although the Circuit may look Complicated, It is actually very simple. Few might have already got afraid by looking at the long Bill of Materials but gathering them all is not mandatory. You may notice that the circuit diagram is also distributed into Blocks and each block has a different colour, Here is what they all mean.

• Red Rectangles

The components that are in the red rectangles must be present in the PCB to function this Board Properly. It Includes a microcontroller unit, power regulator unit, footswitch and display.

• Green Rectangles

The components in Green rectangles are for High-Current Switching Part. As mentioned earlier, the spot welder supports either group of MOSFETs, automotive relay, or 5V relay as switches in its 3 different modes. However, populating every component is not mandatory. If you have MOSFETs, you can populate Mosfet Switching Circuitry Block and others can be left empty.

If you have an automotive starter relay and don't have MOSFETs then, you can also skip adding Mosfets. For the Green rectangles, you have the option. You may populate only one type that you use or do it all for future-proofing, it's up to you.

• Purple Rectangles

These are Indication components. The buzzer sounds at the time of welding and the Led blinks. These can also be ignored for simple assembly but are recommended.

The Process of Ordering From JLCPCB

The Gerber Files can be Downloaded From Here. Click Here

The drive link not only contains the Gerber, But it also contains the Circuit Diagram, Board SVG Image and Assembly Drawing. The PCB is a 4 Layer Design so, it cannot be manufactured by Home CNC or by Toner transfer Method.

You can Use PCB manufacturing Service Provided by JLCPCB. I have never used other pcb assembly services so, I cannot say anything about others but JLCPCB always sends very high-quality PCB at very low Cost.

1. Go to the website, JLCPCB.
2. Click on Order Now. (Top Right side)
3. Upload Gerber Files. (First download Gerbers from the given link)
4. Choose Color. (White and Black are my personal favourite)
5. Add to Cart then go to my cart section.
6. Select the PCB you want to order and Click on "Proceed to Checkout"
7. Add your shipping Info.
8. Pay your order. (Coupons can be applied here)

Then wait 7-10 days to receive the Package From JLCPCB.

SMD ASSEMBLY

After Receiving the PCB from JLCPCB, You need to download the Assembly Image and circuit diagram of the PCB. This will help to know which component goes where on the PCB. You can directly download the Images here or you can also find these files in the drive Link I shared Earlier.

Prepare your Soldering iron and start by soldering 0603 small SMD components. Then you can solder big SMD diodes and finally, at Last, solder the Arduino and Display.

It will take around 45 minutes, so after that Only thing remaining is Coding the Arduino Pro Mini.

Making Electrodes

• You also need to make Electrodes and battery connector wires. To make electrodes, you can use a thick(3-4mm) Solid copper rod and grind on one side to make a pencil-like end.
• Then solder thick 10AWG or thicker wire on the electrodes with a powerful soldering iron or a Blow Torch.
• Crimp Some connectors at the end which you should bolt on to the PCB.

Uploading code is very easy, Download the "Poudell_Spot_Welder.bin" or hex file code from the Drive link, and Upload it to the Arduino Pro mini.

Get the code from the Github: - Click here

Remember that you need additional Hardware called a USB-Ttl converter to upload code to your Arduino Pro mini. Watch this video to learn about this, Click Here.

If You Followed the Instructions very Carefully then, By this Step, you will have a ready Spot Welder ready to do it's first-ever test weld. At your First test weld, try it in a safe place with a Fire suppression system. Dealing with Batteries and High-power electronics may cause damage to life and property.

I am there to help you if you encounter any problems on your way.

Thank you for reading this long article. Feel free to check out my YouTube channel for more awesome projects: Amateur Inventor - YouTube

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