KWeld spot welder

I recently bought Kweld spot welder kit for all battery welding purposes. The old, transformer welder was not good and welds were not consistent and reliable. Worst issue with transformer welder was inability to weld thicker metal strips (0,3mm Ni).

The Kweld came with everything needed to start welding except power supply source. They offer supercap bank with charger or recommend some RC batteries. I had niether. The most suitable battery pack I have was 3S1P LiFePo pack with internal resistance of 5mΩ. Unfortuantely such source is not OK for kWeld.

I ordered 4 prismatic cells VDA2714897HE with the following specs:

  • Rated capacity: 50 Ah (0.5C / +25 ° C)
  • Rated voltage: 3.65 V
  • Energy: 182 Wh
  • Brand: YOULION
  • Weight: 830 g
  • Case material: aluminum
  • Operating voltage range: 2.75 V ~ 4.2 V
  • Maximum charging voltage: 4.2 V
  • Standard charging current: 50 A / 1C
  • Maximum continuous discharge current: 150 A / 3C
  • Maximum discharge current: 300 A / 6C (30 seconds)
  • Self-discharge rate: ≤ 3% / month
  • Internal resistance: ≤ 1 mΩ
  • Number of cycles / service life:> 1600
  • Operating temperature / charging: 0 ° C ~ 45 ° C
  • Working temperature / discharge: -30 ° C ~ 50 ° C
  • Storage temperature: -20 ° C ~ 45 ° C
  • Dimensions (W × H × D): 148 × 97 × 27 mm

The cells were arranged in 4S pack.

4S battery pack for Kweld spot welder

Finished product is in 3D prited housing recommended by Keenlab.

Kweld spot welder and 4S Battery pack

Finally, here are STEP and STL files for the battery pack.

First testing showed super quality welds.

Kweld first tests with 4S battery pack

Internal connections from the battery pack are connected to DB9 connector on the housing. All battery power connections are made of 16mm2 welding (fine braided) wire.

Cells interconnections are made of dual copper bars, attached with seld retaining M6 nuts

Spot welds are repeatable and consistent.

Excellent quality spot welds

The battery pack during the welding pulse drops as shown in oscillogram below. The pulse was set to 40J (40Ws). The pulse time was 22ms and the battery voltage during the pulse droped to 6V, which is 300A drain from the battery:
40Ws / 0.022s = 1.8kW
1.8kW/6V = 300A

I would like to recommend the Kweld to anyone who wants excelent tool for spot welding without selling the kidney for professional spot welder. At the end the total cost was:

  • 145€ Kweld kit
  • 140€ battery cells
  • 15€ small parts, screws, nuts, cable shoes, …
  • 5€ filament (250g)

Leave a Reply