FNIRSI SWM-10 Spot Welder Review

Lithium-Ion battery packs that use 18650 cells are quite popular in a variety of applications. You can find them in laptops (at least in older models), power tools, and some portable devices such as tire inflators and vacuum cleaners. If you want to build your own 18650 battery pack or repair an existing one, you will need a Spot Welding Machine to weld nickel strips to the battery terminals. While there are some DIY spot welding machines (using super capacitors or capacitor banks), they are nowhere close to a proper commercial welder. Spot Welding Machines are expensive devices. Or that’s what I thought until I came across the FNIRSI SWM-10 Spot Welder (Welding Machine).

You might have seen YouTube videos where people build 18650 battery packs by soldering wires directly to the battery terminals. This is very wrong and dangerous. Even I once did the same thing. But instead of soldering wires directly to the battery, I used these SMD 18650 holders and soldered wires to the terminals of those holders.

Ever since I got the FNIRSI SWM-10 Spot Welder, I have been using it regularly to weld nickel strips to 18650 cells and build/repair battery packs. This tool is not meant for professional situations but rather for occasional users, DIYers, and hobbyists. I would like to express my personal experiences in this FNIRSI SWM-10 Spot Welder Review.

This post contains affiliate links. For more Information, see our disclosure here.

What’s in the Box?

FNIRSI does an excellent job at packaging (both in terms of the box as well as the packing inside it). The box has a nice print of the product on the front and some basic features and specifications on the back.

Coming to the contents, we get the main unit i.e., the FNIRSI SWM-10 Spot Welder, a multilingual user manual, a couple of welding cables (probes), USB A-to-C cable, a strip of nickel, and two spare electrodes.

I will talk more about the design of the FNIRSI SWM-10 Spot Welding Machine and some accessories in the next section.

Design of FNIRSI SWM-10 Spot Welder

At first glance, the FNIRSI SWM-10 Spot Welder looks like an oversized power bank (it is actually one, I will explain about that later). On the front, the main centerpiece is the tiny multicolor LCD. Just right to this display, there are two arrow buttons (up and down) and one multi-function action button. There are three indicator LEDs (Blue, Yellow, and Green) to the left screen. I will explain the elements of the display and the operations of the buttons in the next section. Just above the LCD, there are two slots to insert the welding cables.

If you turn your attention to the top edge of the device, you will find the main power button, USB-A Port, USB-C Port, and a reset hole.

The back of the unit has a very useful kick stand. There is nothing else on the unit worth mentioning.

The welding machine came with two good quality welding cables. They are 8 AWG cables with connectors on one end and electrode tips on the other. Both ends of the cables are neatly protected with silicone caps. The electrodes, after welding for some time, will become black (due to an oxide layer). They gave a couple of spare electrodes in the box.

Coming to the nickel strip they gave, looks like it is of 0.1mm thickness. I have some spare nickel strips and I will use both these strips to demonstrate the welding capabilities of SWM-10.

As per the specifications, the FNIRSI SWM-10 Spot Welder is capable of handling nickel strips of thickness 0.1mm to 0.25mm.

User Interface and Controls

To power on (or off) the SWM-10 unit, we have to long press the main power button.

Display

The first thing that comes on the display after boot-up is the main welding interface. There are a lot of things here to discuss. I’ve labeled all the different parameters that the LCD shows in the welding interface. Here’s the meaning of those parameters:

• Welding Status Indicator: It is normally green (meaning the unit is ready for welding). When we make the two electrodes come in contact with the welding object, it becomes yellow. It becomes red when the machine applies the welding pulse on the object. 
• Battery Voltage: Numerical indication of the current battery voltage.
• On-board Temperature: Displays the temperature of the on-board temperature sensor.
• Volume: Indicates the volume of the beeper.
• Battery Level Indicator: Graphical representation of the remaining battery level.
• Preheat Timer: The amount of time the device preheats the electrodes.
• Main Welding Pulse Timer: The duration of the actual welding pulse.
• Interval Timer: The time gap between preheating and actual welding pulses.
• Number of Welding Pulses: The number of times the device applies welding pulses.
• Welding Current: Inrush Welding Current of each welding pulse.
• Welding Count (since power-on): Number of times the device applied welding pulses since the boot-up.
• Warning Indicator: Indicates a warning if there is an over temperature (OTP), battery low voltage (UVLO), or short circuit between electrodes (SHORT).

If you short-press the main power button (after powering it on), the display changes to the charging and discharging page of the battery. The USB-C port is for charging the battery and the right side of the display (under ‘C’) shows the charging voltage, current, and power.

There is also a USB-A port on the device, using which you can charge external devices (use the FNIRSI SWM-10 as essentially a power bank). The left side shows the discharging parameters.

Basic Adjustments

The four main parameters that we can adjust with the FNIRSI SWM-10 Spot Welder are:

• Preheat Time
• Pulse Time
• Interval Time
• No. of Pulses

But what exactly are these? Let me take you through them one by one.

Spot welding involves applying a huge amount of current (at relatively low voltage) between the two electrodes. If we apply this current directly on cold electrodes and the welding object, the outcome may not be fruitful. Hence, most spot welding machines preheat the electrodes (after squeezing them on the target) to prepare the surface (slightly increase the temperature of the surface, clean any contamination, and properly seat the objects).

The recommended wave in SWM-10 is 2ms and you can adjust between 1ms and 10ms.

If you press the action button (the one below the arrow keys with yellow ring), the control moves to the next parameter. This button also acts as a confirm button. The next parameter on the screen is the Pulse Time.

This is the duration for which the device applies the high current pulse on the target through the electrodes. You can adjust the length of the welding pulse between 1ms and 30ms.

The next parameter is the Interval Time, which is the delay between the preheating of the electrodes and the actual welding pulse. This time is important as you don’t want to overheat the electrodes. With a proper time gap between preheating and the welding pulses, the chances of a successful weld are much higher. You can set a maximum interval of 20ms.

Last but not least, there is the option to select the number of welding pulses that the FNIRSI Spot Welder applies. The default is 1 but you can set up to 5 pulses.

Settings

Long press (press and hold) the action button for a couple of seconds to bring up the Settings menu. Here’s everything you can adjust/configure in the settings interface:

• Welding Delay: This is the delay between the Spot Welding Machine detecting the electrodes coming in contact with the nickel strip and applying the welding pulse. Default is 0.8 s.
• Interval Delay: The time gap between two consecutive welding pulses (in case you set more than one welding pulse). Out of the factory, the value is 0.5s. But as soon as you try to adjust it, the value becomes 0.8s (adjustable up to 1.2s).
• Auto Off: The amount of time the device waits after the last user action before shutting it off. Default is 60 min.
• Screen Brightness: Pretty self-explanatory. Allows you to adjust the brightness of the LCD.
• Volume: Set the volume of the beeper (not that it is high).
• Language: Choose between Chinese and English.
• Screen Reverse: You can flip the screen 180°, if you want.
• Overheating Warning: Set the temperature at which the Over Temperature warning kicks in. Default is 65℃ (adjustable between 50-75℃ in increments of 5℃).
• Undervoltage Warning: Set the low voltage limit of the battery for the undervoltage warning. Default is 3.7V and adjustable up to 4V. 
• Factory resetting: Again, self-explanatory. Reset all the values and parameters to the factory settings.

Indicator LEDs

Just left to the display, the unit has three LEDs in blue, yellow and green. The blue LED comes on when you discharge the unit (use it as a power bank). When the battery voltage drops significantly, it starts blinking.

The yellow LED corresponds to the welding indicator on the LCD. It turns on when the unit detects the two electrodes are in contact with the strips/surface (the welding indicator on the LCD will also become yellow).

When you charge the unit, the green LED starts flashing. It becomes steady when the battery is full.

Welding Performance

I started the welding tests on the FNIRSI SWM-10 Spot Welding Machine with a full charge (4.2V). I had only 0.1mm nickel strips. With this strip, I found that the following parameters are perfect:

• Preheat Time: 2ms
• Pulse Time: 8ms
• Interval: 10ms
• No. of Pulses: 1 or 2

With these settings, I gently touched the electrodes to the nickel strip (without too much pressure, this is important) and the welding was perfect. If I increase the pulse time above 10ms, the welding will be too deep and make a hole in the strip.

I did not have some thicker nickel strips. So, I got creative and used two strips to weld to a battery (which is a dud). This time, I increased the preheat time to 5ms, pulse time to 12ms, interval still at 10ms, and number pulses to 2.

You have to experiment a little with different-sized nickel strips and these timing parameters and make a note of the best combinations. For best welding results, place the electrodes as vertically as possible (avoid placing them at an angle).

The unit displays the welding current on the LCD and most of the time it was in the 550 – 700A range. After welding just over 50 times, the voltage dropped to 4.1V, which is very good. You will feel a lot more comfortable after the initial learning phase and finish the welding job in a few welding pulses. The sparks will definitely startle you and use a wooden plank as a surface.

I wish the electrode cable was a bit longer as I felt I was dragging the unit every now and then. Overall, an easy device to work with and the results are better than what I expected.

Charging and Discharging (as Power Bank)

As per the specs, the FNIRSI SWM-10 Spot Welding Machine has a 5,000 mAh battery. Someone on YouTube did a complete teardown of the unit to reveal that FNIRSI is using two lithium polymer pouch cells in parallel (each with approximately 2,500 mAh capacity). I have tested both the charging and discharging characteristics of the SWM-10. Here are my observations.

First, I discharged the battery of SWM-10 using a constant current (initially 1.5A, and then 1A after a while) load. Out of the box, the voltage was 3.9V. During the discharge process, we can see the charge/discharge interface display the output voltage, current, and power. While the “A” part of the screen is active, the display still shows ‘Charging’ even though we are discharging the battery.

At around 3.68V, the low battery warning indicator became active and when the voltage fell to 3.56V, a “Battery Low” pop-up appeared. I continued discharging until the voltage dropped to 3.4V and the unit shut off.

The unit can easily deliver 5V@2A without any issues (heating or otherwise). Only problem is the USB cable that came in the box is straight garbage (charge/discharge current won’t go past 400mA). Use a better cable instead. 

To charge the device, I connected a regular 5V⎓2A USB power supply and monitored the charge voltage and current using the FNIRSI FNB58 USB Tester. It took just over 3 hours to fully charge the battery (to 4.2V). As per FNB58, the battery capacity came around 4650 mAh and the energy was around 24 Wh. Pretty reasonable, I guess. 

The good thing about using the SWM-10 as a power bank is that you can discharge the battery to a safe voltage for storage. I connected a constant current load that drew 400mA to bring the voltage to 3.76V for storing the unit.

Specifications

• Model: FNIRSI SWM-10
• Battery Capacity: 5,000 mAh
• Battery Charge Parameters: 5V/2.1A
• Battery Discharge Parameters: 5V/2.1A
• Supported Welding Materials: Nickel Sheet, Iron Sheet, Stainless Steel Sheet
• Welding Material Thickness: 0.1 – 0.25mm
• Maximum Welding Current: 1,200 A

Price

I bought the FNIRSI SWM-10 Spot Welder from Banggood for ₹3,000 (about $35) including shipping. For this price and the performance it offers, I feel it is a steal. Instead of going the DIY route (with capacitors) or purchasing spot welder units that require external batteries (car batteries), you could invest in this unit and build or repair 18650 battery packs with ease. 

Conclusion

So, what are my final thoughts on the FNIRSI SWM-10 Spot Welding Machine? It is definitely an affordable way to properly spot weld nickel strips to 18650 cells. The build quality is decent and the welding quality is very good.

There is a bit of a learning curve in terms of understanding the different timing parameters and properly optimizing the settings depending on the material you are working with. However, if you frequently work with 18650 batteries and battery packs (I do, both professionally and personally), then spending some time with the unit to fine tune it is worth it.