DIY Battery Tab Resistance Fine-spot Welder




Introduction: DIY Battery Tab Resistance Fine-spot Welder

A fine-spot welder is one of the few equipment where building yourself is cheaper than buying. There are already published a lot of DIY spot welders, this one has some unique features:

It can be used in 2 welding applications: opposed and series configuration.
The construction is kept very simple.
Accurate electrode force adjustment.
It has a solid electrode holder, made of a radiator earthing clamp.
An Arduino microcontroller is used to set the weld time accurately.
Creates a double pulse which improves clamping.
The current can be reduced for welding sensitive parts.

See more here:



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21 Discussions


i ordered your pcb almost two years ago to the day (4/22/16) and never got around to building the spot welder. well, it seems that you have been busy since then, and now have an updated version that you sell pre-assembled. question: can the time for pre-weld, pause, and weld be set via push-buttons using the spot welder based on the "original" pbc, or should i just order the updated one from you? let me (us) know, and thanks for sharing.


2 replies

thanks for the reminder re: the push-buttons. i am currently populating the pcb with components.

i realized that your .xls mouser shopping list shows (1) as the quantity for mouser part # 538-08-50-0185. i think it should be (2) as wire housing part # 538-10-11-2023 is 2-position.

i ordered the following tft from amazon, same price as ebay:

and this foot pedal as well:

The old version has the same menu control as the new smd pcb version.

What size and type wire is used to make the new secondary on the microwave oven transformer? How thick is the insulation? Can motor rewind wire be used? It is square or round copper wire with a varnish on it. Other articles I have read about modifying microwave oven transformers give a general rule of thumb of about 1 volt per turn on the new secondary.

1 reply

Hi! Just got the controller board from you. Building the welder now. Can you please tell me what were the settings you used to weld tinned copper wire to the 18650 battery tab?

1 reply

I never used tinned copper, copper is hard to weld because it has too low resistance to get heated by the weld current.

Very good work on this project! Although I am not convinced yet, I have only seen one pic of a weld done with the machine and it showed some discoloration. If the maker or either anyone who have done this could provide one example I would be very grateful.

Thank you!

What would cause the transformer to burn up as soon as unit plugged in?
In US- so using 110v. Also, my transformer is- AVB 2,0/2/9
I check all my other components against your pictures and everything else looks exactly the same. I did not cut the 2 inside terminals on this transformer because I didn't think it was necessary. Could that be why it happened? Once again, as soon as I plugged it in- poof. I didn't touch any switches at all. The LED lit for a second and then transformer went.
Also, is there a way to test before I waste another transformer?
I have spent a lot of time on this. Please help me when you get time.
All I wanna do is weld these 4000 batteries I have. Please!!!???

1 reply

I think te transformer is mounted reversed, so primairy windings to mains. Please sent a picture of the board.

I have built this eventually, the problem I am having is, on the timmer settings 1 to 3 the spots look good but they haven't welded, on 4 an above its too powerful and has burn marks on the tabs. the transformwer says 700e on it, is this transformer too small?

No, thyristors, see the article

Well, I used a relay anyways and it works. Its a simple relay module for the arduino and it costs $1. You can modulate it to control the current too.

A word of advise. Order his ATmega328 with his software already loaded on it. I just spent almost two day's getting a blank, $3 ATmega328-PU loaded with the required software. If you a fairly competent with Arduino, you might bet a blank chip setup. If you are not good with Arduino, you definitely want to order his unless you are planning on using the Arduino UNO and just build the power supply section. Even then, just getting all the software required loaded into the Arduino board is a royal pain. Definitely not worth the few dollars you might save. Understand also, some of those cheap, fake boards out of China don't have the bootloader in them and may cause you problems.


2 years ago

Does current flow through the u-shaped welding arms or are the wire and electrodes isolated/insulated from them? I was thinking of using wood for the welding arms.

how did you measurement current? I want how to do that

1 reply

Measure the
voltage between 2 points, with a distance of about 20cm, of at the weld cable,

WAY TOO MUCH trouble for my lazy butt it is very cool..

Please put a step by step pictures on how to build this awesome thing! And the list of parts needed to build one. thanks