FNIRSI SWM-20 Portable Spot Welder
The FNIRSI SWM-20 is a portable spot welder built for UK hobbyists assembling 18650 battery packs, rebuilding e-bike batteries, and replacing cells in power tool packs. It delivers up to 1200A of welding current with dual-pulse technology, adjusts across 10,000+ levels for precise control on material from 0.1mm to 0.5mm thick, and runs on its own 5000mAh dual-cell battery for up to 1,500 welds per charge — no mains socket needed.
- 1200A peak welding current — enough for 0.5mm nickel strip on high-drain cells
- Dual-pulse technology — pre-pulse cleans the surface, main pulse welds — cleaner joints, less spatter
- 10,000+ adjustment levels — fine control for thin nickel strip through to stainless tab stock
- 1,500 welds per charge — dual A-grade 5000mAh cells power a full build session
- 2-in-1: welder + power bank — 5V/2.1A USB output when the pens are off
- 2.4″ TFT colour display — real-time current, pulse width, and cycle count on screen
- 8-in-1 safety protection — over-current, over-voltage, short circuit, over-temperature covered
- 12-month Kunkune warranty — covered if it fails in normal use
| Specification | Value |
|---|---|
| Max welding current | 1200A |
| Welding thickness | 0.1–0.5mm |
| Welding materials | Nickel, iron, stainless steel |
| Adjustment levels | 10,000+ |
| Preset levels | 4 combination presets |
| Battery capacity | 5000mAh (dual A-grade cells) |
| Welds per charge | Up to 1,500 |
| Charging input | 5V / 2.1A via USB-C |
| Power bank output | 5V / 2.1A |
| Display | 2.4″ TFT colour |
| Auto-shutdown | 0–99 minutes (adjustable) |
What is dual-pulse welding and why does it matter?
Dual-pulse spot welding fires two pulses in rapid sequence. The first pulse burns off surface oxidation and contamination; the second delivers the weld energy into clean metal. Single-pulse welders skip the pre-pulse, leaving oxidation between the strip and cell that weakens the joint and increases resistance. On the SWM-20, every weld starts clean automatically.
How much nickel strip can the SWM-20 weld?
The SWM-20 welds nickel strip, iron, and stainless steel from 0.1mm up to 0.5mm thickness. For standard 18650 battery pack builds, 0.1–0.2mm pure nickel strip is typical — the SWM-20 handles this comfortably on presets 1 or 2. Thicker 0.3–0.5mm stainless tab stock for high-drain applications needs levels 3 or 4 and benefits from the fine 10,000-level adjustment.
How many welds does the battery last?
Up to 1,500 welding cycles per charge from the dual 5000mAh A-grade cells. A typical 10S4P 18650 pack requires around 160–200 spot welds — the SWM-20 completes that in a single charge with capacity to spare. The battery charges via USB-C at 5V/2.1A and the unit doubles as a 5V/2.1A power bank when you’re not welding. Once your pack is assembled, the FNIRSI HRM-10 battery tester lets you verify cell voltage and internal resistance before sealing the pack.
How do I set the welding power on the SWM-20?
Rotate the knob to select one of 4 preset combination levels for quick setup, or hold the button to access fine-adjustment mode across 10,000+ increments. The 2.4″ TFT display shows current level, pulse count, and battery status in real time. Auto-shutdown activates after a user-set interval of 0–99 minutes to conserve the battery between work sessions.
Is the SWM-20 safe to use at home?
Yes. The 8-in-1 protection system monitors over-current, over-voltage, short circuit, over-temperature, reverse polarity, and excessive discharge in real time, cutting power if any threshold is exceeded. The pure copper welding pens are detachable and include replacement tips, so worn contacts don’t compromise safety. USB-C firmware upgrades let FNIRSI push safety and calibration patches after purchase.
Best for
DIY 18650 and 21700 battery pack assembly (pair with the FNIRSI HS-03 cordless soldering iron for lead and connector work), e-bike and e-scooter battery rebuilds, power tool battery cell replacement, lithium pack prototyping, RC car and drone battery construction, solar storage battery assembly, spot welding 0.1–0.3mm nickel strip, stainless tab welding on high-drain packs, and repair shops replacing cells in laptop and power bank batteries.
What’s In The Box
- FNIRSI SWM-20 spot welder
- Welding pens (pure copper)
- Replacement welding tips
- USB-C cable
- Nickel strip (sample)
- User manual
Why Kunkune
Shipped from our Oxfordshire warehouse via Royal Mail 1–2 day delivery. 12-month warranty on all FNIRSI products — if the SWM-20 fails in normal use, we’ll replace it. 60-day returns. No drama.
Buying in bulk? For orders of 10+ units or trade pricing, contact us for a custom quote.
Frequently Asked Questions — FNIRSI SWM-20
Can the SWM-20 weld stainless steel?
Yes — stainless steel up to 0.5mm. Use preset level 3 or 4 and fine-tune from there. Pure nickel strip welds on levels 1–2 for most standard battery pack builds.
Does the SWM-20 work as a power bank?
Yes. With the welding pens disconnected, the SWM-20 outputs 5V/2.1A from its USB-C port — enough to charge a phone or small device from its 5000mAh battery.
What is the difference between the 4 preset levels?
Each preset combines a pre-pulse duration and main pulse energy optimised for a thickness range. Level 1 suits 0.1mm nickel; level 4 suits 0.4–0.5mm stainless. The 10,000-level fine adjustment lets you dial in between presets for any material.
How long does the SWM-20 take to charge?
Charging via USB-C at 5V/2.1A. With a 5000mAh capacity, a full charge from flat takes approximately 2.5 hours on a 2A charger.
Are replacement welding tips available?
Yes — replacement tips are included in the box, and compatible tips for FNIRSI SWM-series welders are available separately. Tips are consumables and wear with use, particularly on stainless steel.
Can the SWM-20 weld aluminium?
No. Aluminium requires specialised resistance welding equipment — the SWM-20 is rated for nickel, iron, and stainless steel only. Using it on aluminium risks poor welds and potential tip damage.
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