spot welder

[Gregory]

To Obtain the required voltage I will have to reduce the Winding size .
What size would you recommend ?
I was under the understanding that it is the size of the wire that produces the current but After reading your reply I think there must be a balance between the 2.
Is that correct.

 

[colin55]

The way it works is this:

You have to fill the bobbin to get the maximum wattage.
We know the turns produce 2 voltage per turn so you really need the least number of turns possible. But since the turns are in short-circuit mode, you need at least 8 - 10 turns to produce the voltage to allow the current to flow. It looks like the transformer is approx 300-500VA. Make sure there is no air gap. I am just going by the fact that you said 3 turns did not work, even when the shunt was removed.

 

[Gregory]

Do I replace the iron shunt. What thickness should it be?

 

[marcbarker]

What are you spot welding by the way? Metal cans of transistors? Light bulb filament wires? Insides of thermionic valves(tubes)?

I have an ancient soldering gun, that has a 2-turn secondary. 100 W

 

[chemelec]

Here is one Transformer I made:
This operates on 110 VAC and still has the shunt on it.

The Secondary here is 1 1/2 Turns of 1/2 inch "Flattened Copper Water Pipe".
With Heavy Paper insulation Between Windings.
It produces 1 1/2 Volts out. (1 volt per turn)

And Spot Welding DIRECTLY on Top of these flattened ends, Works GOOD.

However, if you try to Extend these Leads, than the added Resistance, Reduces the Current Flow and it Won't work very good.

 

[RODALCO]

spotwelder

Excellent !! chemelec

That is exactly what you need for spotwelding.

High current 1 or 2 turns and rely on the hotspot created to fuse/spotweld the metals together.

Thanks for posting your photo

 

[Mr RB]

Commercial spot welders don't use 1.5 turns.

With such a low output voltage the full power can only be delivered when there is almost zero resistance from combined winding/cabling/tips/target steel. You are relying on almost every part of the secondary system being perfect.

If you bump the opencircuit voltage to 10 volts or so (as Colin and I suggested) the welding voltage at the target is maybe 4 to 5 volts after cable losses, joints from cable to the copper welding tips etc.

So you have a 600W transformer driven into an overload for short welding duty cycle (let's say 1kW) with about 60% 600W getting to the target so you can have as much as 4v @ 150 amps into the steel target, although more likely <1v @ >150 amps. Remember as the steel gets red hot its resistance rises a lot so the higher voltage supply will put a lot more watts into the target. Likewise the higher resistance of the oily steel exactly the 2 target pieces touch causes a hot spot (ie more watts heat there) to initiate welding. Experienced spot welders in industry control the welding tip pressure deliberately to keep the target joint resistance up a little.

Now compare a 1.5 turn secondary, the loaded secondary voltage (1v??) is too low to even deliver full power to the target given resistance of the cabling/joints/tips to target joints/ target resistance. Total resistances only have to add up to a few milliohm (and they will) and suddenly you're getting almost no power into the target. Then if it does start to weld the resistance jumps up even more!

I'm not saying you can't weld with a 1.5 turn secondary, but I really question the notion that its a "good" setup.

 

[RODALCO]

Commercial spotwelders are more in the 2½ to 5 kVA ranges or higher and have the extra power available.
They draw more primary current and can afford a higher output voltage 4 - 10 even 20 Volts open circuit.

Also a microwave TX (600 to 1200VA) is not designed for this type of work anyway although to great to experiment with.

Also the efficiency is less (more ironlosses) as the laminations are welded together at one end.

 

[Gregory]

I have Made changes to the transformer I have increased the Iron field to allow me to increase the windings as you can see in the photo.I will continue with the windings to fill up the transformer.but befor I do I need to know the answer to the questions below
Do I have to put the shunt between the windings or can I leave them out .
If I leave them out what is the damage that can be caused.
In the photo there is a gap on the side of the windings I have put in place.
I have room to place another winding around the outside and join the winding's together, will this help me with voltage and current.
If you do not understand what i have described I will try and make a sketch.
From what I have red on the forum and searched on the Internet I require 20V 20 amps to make a spot welder.
If this is not correct please say so. and then give me information.
Greg

 

[colin55]

The core has to be laminations of a metal called stalloy.
You cannot use solid material.
You are already getting 2 volts per turn so 8 turns will be sufficient.
Remove the iron shunt.
Make sure there is no air gap.
Keep the turns around the "core" of the transformer - the centre leg. If you can put more than 10 turns, it means the thickness of the wire is too small and you can increase the number of strands.
The faces must touch. This is called a "lap touch." Any air gap will kill the output. The faces should be lapped so they touch intimately.

 

[Mr RB]

Did you just weld big slabs of steel onto your transformer core???

 

[Gregory]

No I used another transformer from a microwave

 

[chemelec]

If you want a Bigger Core, You should use Two "E's", Instead of the "E & I" cores.
And DO NOT Weld them.

Also, Not sure What that Wire is, But the Rubber Insulation on it is taking away good useable space. Magnet Wire Would be BETTER.

 

[Gregory]

what is magnet wire

 

[chemelec]

what is magnet wire

Like Whats on your Primary. (Enamaled wire)

 

[tcmtech]

You guys are funny!

I checked out my commercial Miller 230 volt 2.5 KVA spot welder and it uses three full turns of braided copper wire about 3/8" by 1.5" thick. Its output is 4.4 VAC open circuit and its rated at 5200 amps with the short tongs on it. Actual weld voltage is around .5 Volts at the weld.

Personal design opinion.
The picture with the two turns of multi strand copper is closer to what you need. But I would use a matching pair of transformers stacked with the primary's at ends(E cores face to face) and a four or five turn setup of that multi strand stuff you had earlier in the middle.
The actual welding tongs or what ever you use will need to be very short and extremely thick.
Ideally just use the multi strand wire you made as the tongs. Or at least just make it long enough to get about a foot away from the transformer and forget about any connectors between them and Just run your heavy wire right to the welding electrodes you plan to use.

The tongs on my Miller are only about a foot long but made of 3/4" solid copper rod. It will spot weld two 1/8" steel plates together without any problem at all. After about ten good welds the copper tongs will fry spit easily!
But every single connection point has to be shiny clean and covered in electrical grease in order to prevent surface corrosion from forming at the connections or it wont weld worth crap.

Just some things to think about.

 

[Gregory]

Could yo place photo's of your welder setup Transformer and layout.

 

[tcmtech]

Its the older version of one of these. Miller 52 series portable spot welder. Mine has the bigger production rated tongs.

Theres not much to see. Just a long heavy transformer with massive wires and a switch.

 

[Gregory]

What is the advantage of having a primary winding top and bottom of the iron field's

 

[chemelec]

What is the advantage of having a primary winding top and bottom of the iron field's

None that I can think of!