Introduction: DIY Battery Tab Resistance Fine-spot Welder

Picture of 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:


asvybre (author)2017-10-27

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!

Burgrc8b (author)2017-09-30

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!!!???

avandalen (author)Burgrc8b2017-10-02

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

Southerner (author)2017-06-08

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.

Happymacer made it! (author)2017-05-27

Hi all, I have built the electronics based on this design, thanks Avandalen! I designed my own PCB (and got the thyristors backwards (D'OH)!) nevertheless it works wonderfully now.

I'm using a cheap Chinese Arduino micropro as the controller, and I dropped out some of the transient protection devices as I felt they are unlikely to be needed...I'm gambling on that! Programming the Micropro is easy and cost me very little. I did have some problems with it though as the through holes vias are not that well made and I could not get it to trigger reliably. Soldering the wire both sides fixed that. By then I had added shottky diodes already so I left them in place.

Ive yet to build the electrode holders, but I bought some 6mm spot welding electrodes from AliExpress, but they are a 5mm shaft cut with a M6 thread, and that has caused me lots of grief.

Anyhow, I did a recording of the output using a Powermonic PM35 power quality monitor with 3000A CT's, output shorted. Results attached. You can see the 50ms and 400ms pulses clearly at about 1100A RMS, and the impact on the supply voltage when operating as I was also measuring the 240VAC source voltage at the load. I could not record shorter pulses as the rise time is too slow for the PM35 to trigger a transient recording (the snubber works!).

A test weld on a battery with 400ms pulse burned a hole, but I suspect thats my poor test electrode holder and I did not apply enough pressure.

I like this design - it works well and teh control is easy to modify if needed. Kudos to the original author.

AndreasP25 (author)2016-11-04

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?

SamM70 (author)2016-09-14

Can I use an arduino with a relay?

avandalen (author)SamM702016-09-14

No, thyristors, see the article

SamM70 (author)avandalen2016-10-09

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.

BenKeith (author)2016-10-07

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.

TimB14 (author)2016-04-22

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.

家豪劉 (author)2016-04-21

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

avandalen (author)家豪劉2016-04-22

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

billbillt (author)2015-12-15

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

rush_elixir (author)2015-07-02

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

quantumquark (author)2014-01-01

I am really impressed by this project. I only wish he had put all the instructions here rather than linking out to another page.

About This Instructable




More by avandalen:Non-blocking Virtual Delay Library for the ArduinoSAM 15x15 Arduino compatible development board 15x15mm with SAMD21G18 DIY simple solder paste micro-dot dispenser
Add instructable to: