DIY Simple Spot Welding Machine with 12V Battery | IRFZ44N

 

DIY Simple Spot Welding Machine with 12V Battery | IRFZ44N

DIY Simple Spot Welding Machine with 12V Battery (IRFZ44N Spot Welder)

Creating your own DIY Simple Spot Welding Machine is a great project for all kinds of electronic hobbyists, technicians and hobbyists working often with lithium ion battery packs. The spot welder can be used to connect nickel strips on 18650, 21700 and other rechargeable batteries without subjecting them to heat produced by a soldering iron.

 

The spot welder is based on a 12V lead-acid battery (40Ah to 120Ah) power supply and eight IRFZ44N MOSFETs paralleled for providing the required high current for spot welding. This is a simple and cheap project created from easily obtainable parts.

 

With proper construction, this DIY spot welder will be able to create good enough welds for assembling battery packs, power banks, DIY power tools, electric bikes, and any number of battery-operated projects.

Components Required

The following components are required to build this spot welding machine.

Component	Quantity
IRFZ44N MOSFET	8
10Ω Resistor	1
1kΩ Resistor	1
5408 Diode	1
Push Button Switch	1
12V Battery (40Ah–120Ah)	1
Thick Copper Wire	As Required
Copper Electrodes	2
Heat Sink	1 Large
PCB or Strip Board	1

Why Use Eight IRFZ44N MOSFETs?

Spot welding requires an extremely high current for only a short duration. A single MOSFET cannot safely handle this current.

Using eight IRFZ44N MOSFETs in parallel provides several advantages:

• Higher current capacity
• Reduced heating
• Lower resistance
• Improved efficiency
• Longer component life
• Better welding performance

Each MOSFET shares part of the total current, making the circuit much more reliable.

Circuit Working Principle

The way this DIY spot welding machine works is kinda straight forward, like it’s not doing anything too fancy. The 12V battery is the source of electricity, or well, that is where the power comes from.

 

For each IRFZ44N MOSFET, the gate is wired via a 10Ω resistor, mostly so the gate charging current doesn’t get too high and to avoid extra noise during switching , because that can be a thing. Also the MOSFET gate and source are tied together with a 1kΩ resistor, this one acts as a pull down resistor, so basically all MOSFETs stay off until the push button gets pressed.

 

The diode 5408 is there to protect the circuit from reverse polarity and it also lessens the effect of the voltage spike that happens when switching occurs.

 

When you press the push button, the voltage is sent to the gates of all MOSFETs at once, no delay or sorting. Then all eight MOSFETs turn on simultaneously, and then a low resistance path is formed between the battery and the welding probes.

 

Because of that sudden low resistance, a big current starts moving through the nickel strip but only for a very short time period. At the contact point, the electrical resistance causes heat, and that heat is what welds the strip to the battery terminal.

 

Right after you let go of the push button, the MOSFETs switch off immediately.

Recommended Battery

The performance of a spot welder depends heavily on the battery used.

Recommended battery specifications:

• Voltage: 12V
• Capacity: 40Ah to 120Ah
• Type: Lead-acid automotive battery or deep-cycle battery

A larger battery generally provides:

• Higher current output
• Better weld quality
• Less voltage drop
• More consistent welding

Avoid using small sealed batteries because they cannot supply sufficient current.

Choosing Welding Electrodes

Copper electrodes are recommended because they have:

• Excellent conductivity
• Low resistance
• Long service life
• Better heat transfer

Sharpen the electrode tips for accurate welding.

Maintain a small gap between the two electrodes during welding.

Importance of Thick Wires

Spot welding requires hundreds of amperes for a very short time.

Thin wires increase resistance and reduce welding performance.

Use heavy-gauge copper cable between:

• Battery
• MOSFET board
• Welding electrodes

Keep cables as short as possible.

***Diagram***

Heat Sink Installation

Although welding pulses are very short, the MOSFETs still generate heat.

Install all eight IRFZ44N MOSFETs on one large aluminum heat sink.

Use:

• Thermal paste
• Proper insulation if required
• Tight mounting screws

Adequate cooling greatly increases reliability.

Assembly Tips

Follow these practices for the best results:

• Keep PCB tracks wide for high current.
• Use thick solder on power connections.
• Keep wire lengths short.
• Ensure all MOSFETs are mounted firmly.
• Double-check gate resistor values.
• Verify battery polarity before connecting.
• Test using scrap nickel strips before welding battery packs.

Applications

A DIY spot welding machine has many practical uses.

Common applications include:

• Building 18650 battery packs
• Repairing lithium battery packs
• Electric bicycle battery assembly
• Solar energy storage batteries
• DIY UPS projects
• Portable power stations
• Power tool battery repairs
• Robotics projects
• RC battery packs

Advantages

This project offers several benefits:

• Low construction cost
• Easily available components
• Simple circuit design
• High current capability
• Portable operation
• Reliable performance
• Easy maintenance
• Suitable for beginners with electronics experience

Limitations

Although effective, this simple design also has some limitations.

• No adjustable welding pulse timer
• Manual operation using a push button
• Requires a high-current battery
• Not suitable for continuous industrial welding
• Welding quality depends on operator timing

Adding a timer circuit or microcontroller in the future can improve consistency.

Safety Precautions

Spot welding involves very high current.

Always observe these precautions:

• Wear protective safety glasses.
• Never short the battery terminals.
• Disconnect power before servicing the circuit.
• Use insulated handles on welding probes.
• Avoid welding near flammable materials.
• Ensure adequate ventilation.
• Keep children away from the work area.
• Check all wiring before connecting the battery.
• Never hold the push button longer than necessary.

Following these precautions will reduce the risk of damage and injury.

Troubleshooting

Weak Welds

Possible causes:

• Battery charge is low
• Thin power wires
• Loose connections
• Dirty nickel strip
• Poor electrode pressure

MOSFET Heating

Possible causes:

• Small heat sink
• Long welding pulse
• Poor solder joints
• Unequal MOSFET connections

No Welding

Check:

• Battery voltage
• Push button
• Gate resistors
• MOSFET orientation
• Electrode continuity

Frequently Asked Questions (FAQs)

Can I use fewer than eight IRFZ44N MOSFETs?

Yeah, you can use fewer than eight IRFZ44N MOSFETs, but the maximum current you can safely manage drops. With only a handful of them, the current sharing becomes less tidy and the reliability usually doesn’t feel as good. Using eight MOSFETs is basically the safer setup, it helps the load split more evenly and keeps things steadier.

 

Which battery is best, though?

A fully charged 12V lead-acid battery rated somewhere between 40Ah and 120Ah tends to give really solid performance, as in consistent output under load.

 

Can I weld 18650 battery packs?

Yes, and in fact this project is made for welding nickel strips onto 18650, 21700, and similar lithium-ion cells. So the intent is kinda directly aligned with that.

 

Why isn’t a soldering iron recommended?

Because too much heat from soldering can mess with lithium-ion batteries. Spot welding (on the other hand) delivers heat right where it matters at the weld point, and only for a very short moment. That brief pulse is usually what you want.

 

Why do gate resistors matter

The 10Ω resistors limit the gate current and also reduce switching noise, which helps the circuit behave cleaner. The 1kΩ resistors help keep the MOSFETs turned off whenever the push button isn’t being pressed, so you don’t get accidental conduction.

 

Is a heat sink necessary?

Yes, pretty much. Eight MOSFETs pushing high current will create heat, and a proper heat sink improves reliability. It also tends to extend the useful life of the components, so they don’t cook themselves.

 

Can I add a welding timer?

Yes. A timer circuit or even a small microcontroller can be added to create more consistent welding pulses, and that usually improves weld quality too.

Conclusion

So, a DIY Simple Spot Welding Machine , powered by a 12V battery, is actually a pretty affordable and reasonable project for anyone who builds or repairs lithium-ion battery packs. With eight IRFZ44N MOSFETs, a 10Ω resistor and a 1kΩ resistor, plus a 5408 diode and a push button, you can put together a compact spot welder that can do dependable welds for nickel strips, in a straightforward way.

 

That said, the results really depend on proper wiring, thick copper cables, a good heat sink, and yes, a decent 12V battery. If you do all of that, the machine should feel much more stable during use, and not like it is struggling. Also , make sure you stick to recommended safety practices, especially when you are dealing with high-current circuits. With careful assembly and a bit of proper testing, this DIY spot welder can turn into a handy piece in your electronics workshop.