Introduction: KP Point Welder

This a story is about how I made a point welding transformer.

I found an old E-form, 220/24V transformer which had as secondary winding a wire 3mm in diameter. The idea was to replace that with a different winding.

Disassembling was easy. First, I tried to get a smaller number of windings on secondary and test if I can get greater amp output and lower voltage. I read somewhere that voltage in this form of welding should be from 1.5V up to 6V and amps as much as possible.

Step 1: Rewiring the Old Transformer

I made a wooden mold to help hold the old primary winding. Using the old secondary copper wire (3mm dia) I wound a double parallel winding over existing primary coil. This gave me about 6V on secondary side and test showed that it was not enough power to melt 1 mm steel wire. Additionally the transformer became very hot very fast.

Step 2: Triple Parallel Winding

I tried the same trick but used 3 wires parallel which is equivalent to 21 square mm. Voltage measured 3,84 V on secondary side. I started to assemble all the parts on a board and I started to make end copper connections. I was sure that I got what I wanted from the beginning - Dear Murphy!

Still It was not enough amps.

Step 3: Test Board Misc.

I made a simple construction (test board) to find out how this work. Micro switch was inserted on the top level in a small walnut wooden box (lacquer comes later). Lower electrode was mounted on a aluminium square rod.

Step 4: A/mm2

Finally, I bought a length of 60 mm2 copper wire, removed the insulation and got a smaller diameter. I wrapped this wire with common thin scotch tape. The goal was to put 4 windings in transformer. Insulation was ok because between each loop is max 0.7V. In the end I got 2,54 V at the terminals and hopefully plenty of amps. I finished the new copper terminals for the secondary winding as well.

All this was finished after I went back to read, study and learn from the beginning (see step 7).

Repetitio mater studiorum est!

Step 5: Succes!

I got enough power. About 2.5 V and almost 70 Ampers! 1mm steel wire burned out in seconds. But switching it on and of manually is not accurate. I constantly burn out thinner material.

Sometimes the weld was perfect, but Murphy does not sleep!

Step 6: Intermezzo

In the meantime I needed to weld a small chimney for my tent stove.

I used my welder as is and successfully, hand pressing switch, I made from tin cans 12 cm diameter a smaller 6 cm diameter tubes.

I used an aluminium tube 3 cm in diameter as lower electrode, wrapped this with a tape for isolation, and on one end mounted a screw head as a welding point. The other electrode was freely pressed by hand from above.

Step 7: Triacs an So On

I found an article about how to regulate transformer action on primary side. This was using a triacs similarly as is in a light bulb dimmer or in vacuum cleaners. Lowering power splitting sinusoidal wave. According Fig 11. I collected the necessary components, assembled the circuit, put it in a aluminium box and connected it to the transformer.

Perhaps because of insufficient knowledge, it didn't work as I wanted it to. I could not regulate amps and time duration. I burned out constantly my thin sheets.


Murphy still does not sleep.

Step 8: Conclusion

Let's get serious.

First, learn what the world already tested and wrote. I started with math from the books/web and in a spreadsheet form made a calculator with all the formulas (Proračun transformatora -Transformer calculation) and calculated the dimensions of transformer based on my core. This gave me a figure what my core is capable of. Rewinding the primary and secondary was then necessary.

My frend Mirko Jukl, drew me a simple 555 circuit schematic (Odgoda vremena i trajanje impulsa - Time delay and impulse time) to control time-duration of welding impulse on secondary side. I can choose delay from a few seconds and duration in miliseconds. Small movies show tests with 220V bulb, transformer an when everything was assembled and finished.

And it works!

Because this project was a back and forth process that lasted almost half a year this instructable is a bit inconsistent. Here is the final data of transformer:

Transormer core (E shape) - total square 28 cm2 ... cca 784W.
Primary windings 370 ... for 3,41A ... 1,5 mm dia
Secundar windings 5 ... for 261 A ... 11,54 mm dia

I hope that this DIY project helps somebody to get better results and extend knowledge.

Sincerely...

Comments

author
acheide (author)2016-07-17

Very nice. Thanks.

author
bell an (author)2014-07-13

good job

author
altomic (author)2014-03-01

excellent work. thanks for publishing/

author
padbravo (author)2014-02-27

Great!
tks for the technical data, and the circuits...

author
amclaussen (author)2014-02-26

Good work. I guess a larger core transformer, say from a discarded Microwave oven (used backwards, feeding 120 VAC on the secondary to get a much larger current on the thicker wire winding) could be better... but Murphy is always lurking!

By the way, I have a multimeter very similar to yours, I bought it from Radio-shack in 1996, but I guess it was made for them by METEX. Very good inexpensive, powerful and versatile one. Has served me very well for its price (US$130 in 1996). Nowadays, Radio-Shack is selling only chinese, terribly cheap multimeters, but the METEX is much better. Amclaussen, Mexico City.

author

Thanks. Transferred power incl. losses, is determined almost only by the cross surface of inner core.. More cm2 - more power. Microwave transformer is also determined by the above rules. Density A/mm2 is also determined in optimum of 2-4A/mm2 ,respectively, because of overheating. And so on...METEX have a perfect instruments - agree..

author
rimar2000 (author)2014-02-25

Very good work, congratulations.

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