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:

<p>I am really impressed by this project. I only wish he had put all the instructions here rather than linking out to another page.</p>
<p>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?</p>
<p>Can I use an arduino with a relay?</p>
No, thyristors, see the article<br>http://www.avdweb.nl/arduino/hardware-interfacing/spot-welder-controller.html
<p>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.</p>
<p>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. </p>
<p>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.</p>
<p>how did you measurement current? I want how to do that</p>
<p>Measure the<br>voltage between 2 points, with a distance of about 20cm, of at the weld cable,<br>I=U/R</p>
<p>WAY TOO MUCH trouble for my lazy butt it is very cool..</p>
<p>Please put a step by step pictures on how to build this awesome thing! And the list of parts needed to build one. thanks</p>
I am really impressed by this project. I only wish he had put all the instructions here rather than linking out to another page.

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