Spot Welder - Cell Connections

Owned by Micah Black
Last updated: Nov 23, 2020

Spot Welder Choice

The spot welder used last year for MSXII was a SUNKKO 787, a very underpowered cheap Chinese unit that produces lots of sparks while spot welding. We also acquired a SUNKKO 709A spot welder, capable of 500A for the welds, which is good for up to 0.2mm pure nickel strips.

K-Weld   ~$250

https://www.keenlab.de/index.php/product-category/kspot-welder-kit/

Joule-metering approach, will dump a constant amount of energy into each weld, making consistent welds no matter the resistance between probes and cells - buildup on probes and different pressure on probes when spot welding will not make a difference to the welds. Provides audio feedback for good or bad spot welds. Also has a automatic and manual mode. Sold as a complete kit, cables, probes, etc also available as extras. We might want some extra probes, as they are the most likely component to wear out. Power comes from an external battery (3S 500mAh 130C LiPo recommended) to power the controller and deliver the power required to weld the battery. Capable of achieving welding currents of up to 2000A, depends on the battery chosen. With the recommended battery, about 1300A are delivered to the welds. Being battery powered, we do not have to worry about any regulations on AC powered devices.

https://www.youtube.com/watch?v=rQnODV4VQjU

https://www.youtube.com/watch?v=4WfwNfpFOrQ


Arduino Battery Spot Welder    ~$160

https://malectrics.eu/product/diy-arduino-battery-spot-welder-kit-v3-2-2-full_bundle_car_battery/

Timed pulse approach will create different welds based on amount pressure of probes on cells, buildup on probes, no feedback. Powered by an external LiPo battery or car battery. Apparently a few other solar car teams are using this spot welder as well. Current delivered to the welds is dependant on which battery is used.


Sunstone Spot Welder    upwards of $4500

https://sunstonewelders.com/product/standard-battery-welding-system/

Professional spot welding system, uses the joule-metering approach as well in order to dump a specific amount of energy into each cell, and includes a unit to ensure even pressure on the cells. Due to the price tag on this model, it is out of scope for this project, but it is useful to know what technologies commercial systems use.


The K-Weld is essentially a commercial spot welder with a hobbyist spot welder price. It has been extensively tested, and is able to produce consistent, solid welds on up to 0.3mm pure nickels strips. Being able to use thicker nickel strips will mean less resistance and thus less heat loss. The Arduino Battery Spot Welder is a reasonable option as well, but for not much of a price jump, the K-Weld provides much better technology to produce consistent welds.



Edit:

I have become aware of a few other spot welders since creating this page, and wanted to link them here for future consideration if we ever need a new spot welder.


BOSS Welder    ~ $120

https://endless-sphere.com/forums/viewtopic.php?t=89076

This welder by Aulakaria is super small, though seems to require an external fan and heatsink for the FETs. Powered with XT90 connectors from a 3S LiPo similar to the kWeld. Only does time controlled welding as far as I know. Claims to be able to weld 0.1 and 0.2mm copper with multiple pulses. Apparently someone also used the design to make a super tiny spot welder. Also has an output to power a soldering iron. Great info on the thread as well about spot welding in general and electroplating copper. Because this still uses a LiPo and common FETs, the current would still be roughly what the kWeld delivers.


Ian Hooper Welder     ~ $100-300?

https://www.zeva.com.au/Projects/SpotWelderV2/

A spot welder project for personal use that I found recently. Some good discussion on the design in the build log and the comments. Gerber files are available on the site, and parts are not crazy expensive. Per some quick math in the comments, this seems to be capable of around 2000A.


Edit 2:
There's a lot more welders that have popped up recently. One that I am more familiar with is Julien Lemay's spot welder pen. Still the same timed pulse method, but putting it here for completeness.
Its also not too hard to design your own, so that's an option in the future as well (at least for an experienced electrical engineer).


There was another one I saw that used 72 N-Channel TO-220 FETs connected to a 2S3P stack of LiPos that I believe came from a car pack.