Diy Spot Welder

Hello, this is my first post here at Instructables. I will get straight to the point. I plan to build a diy spot welder. However, in most of the diy spot welder projects I have looked at, including Hack a Day and Instructables, a MOT (Microwave Oven Transformer) is used. The secondary is rewound with thicker wire, and the transformer is used to step down voltage and step up current. I have heard that these transformers can supply as much as a kiloamp at very low voltages. However, I do not own a MOT, they are too costly to buy, and I do not want to retrieve one from a microwave because-
A) Nobody happens to be throwing away a microwave in my area.
B)The guys who own the scrap metal and thrown away appliances will only give me a microwave oven at a hefty price.
C)I would prefer to live a very long life, and do not want to gt myself electrocuted poking around the innards of a microwave.
SO, I did a thorough search, and found that some people made a welder from a stereo amp transformer. Again, I did not own one, but what I did own was an ultrasound generator that was supposed to drive away rats. After making  bloody inroads into it`s innards, I found a transformer quite a bit larger than the regular step downs. It is 5 cm long, 4 cm wide and 1.7 cm tall.  Input voltage is 220 volt AC from the mains, at 60 hertz. Output is 12 volt AC at a maximum of 300 MA. Speaking from experience would anybody please tell me whether this is suitable for a spot welder? Please ask me for additional information, including pictures, if required.
Thank you.

sort by: active | newest | oldest
TheLightningConductor (author) 1 year ago
TheLightningConductor (author) 1 year ago

I also found this-

TheLightningConductor (author) 1 year ago

Hello, could I use a current transformer like this one-

According to wikipedia, these transformers consist of a single ring as a core, and wire wrapped around it is the secondary. A copper bar is the primary. Could I try powering such a transformer backwards? From what I can see, the core appears to be quite large, and can sustain a large magnetic field.

Please forgive my obvious naivete. Thank you.

TheLightningConductor (author) 1 year ago

Firstly, I would like to thank you all for commenting.

bravoechonovember1- 180 dollars is 11970 rupees. Which is way beyond my budget. Besides, I believe I will learn a lot building one.

Downunder35m- For me, waiting for the transformer to cool down is really not an issue. I don`t want to weld anything fancy, just very thin sheet metal. However, if even a MOT won`t work, I will look up isolation transformers. I suppose mine would just overheat too quickly to do anything useful.

Yonatan24-Thanks for the link! The transformers on there are definitely cheaper than what I have seen. I will attempt to select one from there.

I have done some work with a single mot and if the chokes are removed and one finds thick wire that is both well insulated and able to bend around these tight turns.....
For a simple spot welder the only way to go would be to integrate the mot into the actual clamps for the welding.
Otherwise the cables are too long, too much resistance too much loss.
If I am not mistaken I even saw in Instructable for those once but there are plenty on the web and Youtube.

You can also try asking around for faulty or unused transformers!
Keep in mind the main thing is a big core, you can always make a new primary and secondary coil ;)

Thank you again, downunder35m. Your comments have been very helpful. There are some stores in my area which contain old and unused appliances, metal, etc. I will check there. As for the cable, I believe I already have some that might work. I will have to, of course, confirm that based on the core I manage to obtain.

I think the best option would be to just buy one. Google says the go for around $180

If you check the size of real transformer used in a welder you will realise why even a MOT is not really suitable.
For me only two mots in series worked for more than a few minutes without overheating.
Sometimes size does matter...
The core not only needs to provide room for the wire but also do the task without too much saturation.
A spot welder might get away with these problem if it is not too small as you only use it for a few seconds and then it is off till you do the next spot - but working a nice line of spots for a panel can end up to be quite time consuming.

Another option that is often overlooked is to salvage transformers that served a totally different purpose.
One example are isolation transformers for machines.
Another as said above is to use multiple transformers in series but is not a good solution!
Best option for you is to really use a big size transformer that in original condition is rated for at least 10A on the input side.

Yonatan241 year ago

I don't think so. Sounds too small to me.

I know you don't want to use one, but a microwave transformer would probably be the best. I found these on eBay: