Welding a MOT

[Alberto]

Hi everyone. I´m making a spot welder so I have removed the secondary of a MOT and put 2 turns of 13mm wire.

To do that I removed the "lid" and weld it again, but I have realised that during the weld in one side  is slighly displaced. The "crack" starts in A and goes to B, with the shape of a wedge, so the plates don´t face with the rest of the plates



Does affect this to the performance of the transformer?

Thank you

[Da_Stier]

As far as I'm aware it shouldn't really matter, it would work the same even if you had two completely different cores.
The only thing is that it might rattle a bit if one piece is loose.
In that case some glue should fix that.

Greetings,
Michael

[davekni]

Does affect this to the performance of the transformer?

Agree, that little separation of laminations is not any issue.

To do that I removed the "lid" and weld it again

Not sure what you mean by "lid".  Can you show an image of the weld?  The possible issue would be weld shorting between laminations, defeating the purpose of having a laminated core.

[Alberto]

Thanks for your answers





I cut the original weld with the angle grinder and later weld it again with TIG (using steel rod) 

I was careful with no overheat and at the end I checked that there was no contact beteewn the coils and the armature

[davekni]

cut the original weld with the angle grinder and later weld it again with TIG (using steel rod)

Looks fine, as the new weld isn't making a conductive loop around most of the magnetic path.  Probably will heat somewhat at the new weld, as it is likely deeper than the original.

Thank you for the pictures.  Now I understand what you did.

[Alberto]

cut the original weld with the angle grinder and later weld it again with TIG (using steel rod)

Looks fine, as the new weld isn't making a conductive loop around most of the magnetic path.  Probably will heat somewhat at the new weld, as it is likely deeper than the original.

Thank you for the pictures.  Now I understand what you did.

Thanks to you for all your help!

[Mads Barnkob]

Just for future references, core parts are normally called I, E or C cores, as the letters represent their form when viewed from the side

[Alberto]

Ahh ok ok. Thank you for the explanation.

And one more question. I want to weld a pair of parts to attach the arms of the welder. Does that affect to the performance of the transformer? I mean 2 parts like m8 screws

[Mads Barnkob]

Ahh ok ok. Thank you for the explanation.

And one more question. I want to weld a pair of parts to attach the arms of the welder. Does that affect to the performance of the transformer? I mean 2 parts like m8 screws

The feet or mounting plate of a transformer is often just spot welded onto the cores.

You do not have to worry that much about a spot welder transformer. It is very short on-times, not continues use. There is plenty of time for it to cool down between welds

[Alberto]

Ahh ok ok. Thank you for the explanation.

And one more question. I want to weld a pair of parts to attach the arms of the welder. Does that affect to the performance of the transformer? I mean 2 parts like m8 screws

The feet or mounting plate of a transformer is often just spot welded onto the cores.

You do not have to worry that much about a spot welder transformer. It is very short on-times, not continues use. There is plenty of time for it to cool down between welds

Thanbks for your answer. no no, I didn´t mean about the temperature of the welds. I mean since I´m attaching steel parts to the armature, they could change the flux of the magnetic field

[Mads Barnkob]

I meant the welds of the transformer being used for spot welding, not welds of attaching the M8 bolts.

Because spot welding is very short term load, the transformer might be unbalanced, but if that results in higher losses, its not a problem when spot welding is not a continues load.

[Alberto]

I meant the welds of the transformer being used for spot welding, not welds of attaching the M8 bolts.

Because spot welding is very short term load, the transformer might be unbalanced, but if that results in higher losses, its not a problem when spot welding is not a continues load.

Ahh ok ok thank you!

[klugesmith]

I agree with Mads and Dave: you can weld stuff to outside of MOT core block without much effect on its use in a spot welding machine.

>>The feet or mounting plate of a transformer is often just spot welded onto the cores.

Technically, the mounting plate connections in that stock picture and this one here are plug welds, not spot welds. Made by arc welding process similar to that which joins the E and I core blocks.  No welding tool pressure or intentional large current passing through the joint.

[Alberto]

Thank you

I always learn a lot in this forum. But I don´t have too much idea and I can only ask instead to contribute

[Alberto]

Done!!



Thank you again for all your advice.

And I know what are you thinking, I bought it because it looks like brand new but I really made it 

[davekni]

And I know what are you thinking, I bought it because it looks like brand new but I really made it   

It does look like a successful project.  Is it working well?  Are you using commercial spot welding electrodes at the tips?

[Alberto]

Thank you!

I only tried once to weld 0,75 mm steel and did it fine.

The electrodes are 10mm the thick ones and 6mm the thin ones. They are regular copper bar

[breezetix]

Hi everyone. I´m making a spot welder so I have removed the secondary of a MOT and put 2 turns of 13mm wire.

To do that I removed the "lid" and weld it again, but I have realised that during the weld in one side  is slighly displaced. The "crack" starts in A and goes to B, with the shape of a wedge, so the plates don´t face with the rest of the plates



Does affect this to the performance of the transformer?

Thank you

It's fine. Doesn't affect performance. Probably a VERY tiny amount.