Low volts and lots of amps make a good machine..I have a commercial spot welder Italian made, for sheet metal..

check this out...http://www.rcgroups.com/forums/showthread.php?t=741617


Have a look here too: philpem.me.uk :: electronics :: welder

You say you removed the 240 V pri.

Are you applying 240 AC to the original HV secondary?

Originally Posted by marcbarker

You say you removed the 240 V pri.

Are you applying 240 AC to the original HV secondary?

That would explain the poor performance.....

Originally Posted by Chippie

That would explain the poor performance.....

I suppose a possible workaround is obtain another microwave transformer and use its HV secondary* to feed into the present transformer's primary, which is really the secondary acting as a primary in reverse...er..I think.... I dunno now, I'm lost

* Suitable contestant entry into 2010 Darwin Awards

Originally Posted by Gregory

Have I removed the wrong winding.?

"Have I removed the wrong winding?" he says! What winding have you removed?

Looking at the picture...what's that 'thing' there in the middle?, sitting between the windings? it looks like it's made of iron...

And another thing... i get the gut feeling there's too many turns.

I Doubt he removed the Primary. In his Picture, it LOOKS like the primary is there.
That is too big of wire to be the Secondary.
And those Push Lugs are the 220 Line.

The Laminations Between the Primary and the Secondary is a "Current Shunt".
It Prevents the Primary from Overload, Even on a Shorted Output.

Removing those laminates Will allow for More current out, But Possibly a Blown Breaker Also, due to higher input current.

Just having a good look at you photo's and comparing it with one of my spare MOT's.
You have removed the correct winding (HT) and the 240 Volts winding is in place in your MOT.
You need to take the iron shunt out.
As most MOT's are about 800 to 1200 Watts, put a 2.4 kW electric heater in series to reduce (control) your current and perhaps reduce the secondary to 1 or 2 turns.

In arc welders the 'current shunt' is adjustable

Arc welders don't have resistance ballast, and I've never (yet) seen a welder with a heating element to regulate their power.

Originally Posted by Gregory

is the plates I have pointed to in the photo are they the Iron shunts.
Could you make a sketch of the heater that is mentioned and what should I do to increase the current
1 Increase the number of turns in the secondary.
2 Decrease the number of turns in the secondary and increase the wirer size.
3 Or increase the iron field size.
Can you give me help with this problem as I wish to make the welder do It's job.
Or am I better to dump this Idea and try a capacitor welder ?
Greg

My Microwave Transformer is 110 Volts on the Primary and I have 2 Turns on the Secondary.
I am using 1/2 Inch Flattened Copper Pipe as the Secondary Wire, And VERY SHORT Copper Pipe LEADS to the Welded Joint. It Works.
And I Didn't remove the Shunt Plates.

For Spot Welding, you need HIGH Current, But not much Voltage.

And as you Increase the Turns, You REDUCE Current.
But Since your on 220 Volts, the 4 Turns should be OK.

I Suggest Bigger Wire and Shorter Lengths to the Weld Spot.