Help me to choose spot welder

[sairfan1]

I'm looking for spot welder to mostly weld batteries like 18650, AA or AAA size. here are the options that I short listed.

https://www.aliexpress.com/item/1005004046376531.html

https://www.aliexpress.com/item/1005005368401641.html

I also want to know what type of strip is more suitable for this kind of application (specially low power projects)

[barshatriplee]

Cannot enter the links. Maybe the aliexpress website is down.

[jpanhalt]

My homemade welder used handheld electrodes.  It works, but I would prefer something with machine-fixed electrodes as that might allow more accurate placement of welds and connector strips.  Other than that, it is impossible to assess which is "better" on Aliexpress.

I use nickel strips (not nickel plated steel) and have never has a problem with a weld or the strip.  I believe using nickel is pretty common.

[BradC]

I use one of the super cheap-o "board of MOSFETS and a timer".
Something like this : https://www.aliexpress.com/item/4001150764513.html

Takes some fine tuning and practice, but I've only managed to set fire to one cell so far.

[Jwillis]

I have the Sunkko 737DH and it's awesome. I can weld 18650 batteries for Dewalt 20VV packs in very little time. No waiting for charge and no heating up. I also use the SUNKKO 73B Welding Pen. Makes the job really easy.

[beatman]

i use sunko 737U till now only few welding jobs done and was successfully very good construction of the unit

[Doctorandus_P]

You would first have to decide whether you want "cheap", or "quality and reliability".

My preference would verly likely be for the mains voltage powered big box. I assume it's got a mains voltage powered transformer in it and a triac to control it.

The other smaller box has a small wallwart in it, which means it is probably built around a few Li-ion cells and MOSFets, and pulling such high current peaks from Li-Ion is far beyond the recommended operating conditions of those things, but lot's of people do it and apparently it does work. A lot of welders of this type do have a serious flaw. During the high welding current, the battery voltage sags, and sometimes also the gate voltage of the FET's. When this happens, the FET's can get partially closed, which can increase the dissipation in the FET to instant destruction. If you have a welder of this type, then always do a check of the Ugs voltage during welding. Adding a small diode and capactor can buffer the voltage for feeding the electronics during the welding pulse. But I assume that the better versions have a step-up regulator to make an Ugs of 12 to 15V. (This usually halves Rdson compared to an Ugs when the FET's are just opened).

[BradC]

A lot of welders of this type do have a serious flaw. During the high welding current, the battery voltage sags, and sometimes also the gate voltage of the FET's. When this happens, the FET's can get partially closed, which can increase the dissipation in the FET to instant destruction. If you have a welder of this type, then always do a check of the Ugs voltage during welding.

The easiest way to make that work is a couple of big lead acids in parallel. Personally I use 4 x 55ah SLAs with a relatively high CCA rating. I already had the batteries, so using a $34 "spot welder" did the job quite neatly and reliably.

If you don't have sufficient grunt to back it up, then "bad stuff" might happen. Of course if you can afford "quality and reliability" then go for it.