transformer questions

[kdog]

Hi all
ive been playing with a 1200w microwave transformer to build a spot welder. learning as i go... in aus so on 240AC
i have a few questions that someone hopefully can answer ( ill have a crack- let me know if im even close )
-The shunts (a bunch of lams) sandwiched between the primary and secondary coils. do i need to keep them? i read somewhere that they keep the power going through the primary coil down. is that the case? i figure that they shunt flux back to over the primary coil sort of like back EMF- is this correct?
if i took them out would it over power the primary when quiescent? or only when secondary is loaded?
itd be difficult to do so not real keeen...but if i get more power it might be worth it.
- does copper fill (like a motor winding) apply to the winding i put in? ( to generate as much current as possible in the secondary coil)- i figured it is exactly the same priciple so it should matter.
- why are the main lams seam welded together. i though the were sposed to be electrically insulated from each other. is this just cheap and nasty construction or is there something more to it.
im getting some welds happening so ill be doing a timer circuit next to help stop blowing holes in things!
anyway thanks for your input-
kdog

 

[DrKraut]

I can tell you how it worked for me:

1. remove the secondary and replace it with 4 turns of big welding cable. i also removed the shunt.
2. put some copper electrodes on the welding cables
3. put a light switch in series with the primary and fix it to a "foot pedal". with this you can "adjust" the welding time by pressing short/long with your feet on the light switch
4. get some old 18650 some 0,1mm nickel strips and start your first welding experience.

Have fun

 

[kdog]

Thanks DK
I did a bit a research and understand flux flow through a transformer better now. I'm going to leave shunts in for moment cause I have plenty of power. Got excited about a putting in a variable shunt (same as an old school welder) but I'll work on my welding technique first.
The welded core lams seems to be a cheap way to hold core together and when loss is not important, cost trumps efficiency

It's working well- cost aprox $50, sweet

 

[DrKraut]

Yes the transformers are really really cheap made.
As i took mine apart, i sawed the top off and removed the primary. I saw the primary wasn´t even copper, they used aluminium. Same with the laminations, thick as hell
But i got it for free, so i can`t complain.