Do it yourself hobby Spot Welder

[jonovid]

an old microwave oven becomes a 700W 500amp hobby spot welder
 

[BILLPOD]

Good Morning Jonovid,  VERY kewl.  can you show us a photo of the insides, especially the modifications made for the transformation?

[lokin4areason]

this is like an interesting build

what are the specs on it ?

does it still warm up food while you spot welding away ?

[jonovid]

the secondary winding wire is three  1.5 loops in parallel of 140 amp 100% copper automotive jumper cable.
with the 6 ends sweat soldered into two solid copper blocks top & bottom of the jaws
the two top & bottom electrodes are 8mm solid copper rod threaded into the copper blocks of the jaws.
the electrode tips are 45 degree taper with a 2mm face . I built this for maximum current capacity.
the jaw alignment is by 4 hex cap screws on the wooden fulcrum of the top jaw. timber is used for both jaws.
  aluminium shims are used for the sideways jaw alignment also.
the grounding of all metal- the transformer, the metal case has a metal tab on the side of the MBF timber base.
two foam rubber strips with adhesive backing are the feet of the MBF timber base of the spot welder unit.
input AC line filter is from the microwave oven as this has the 12A fuse on a PCB under the plastic fan housing.
a large magnet holds the jaws open as I had no space for a metal spring in-between the two primary input lugs of the transformer.
a 10amp AC momentary micro switch is currently used to activate the weld. the red plastic button on the top of the top jaw.
spot weld times are approximately 0.4sec for 0.7mm wire  0.8sec for 2mm wire or 1mm  steel sheet. 
a two part plastic housing was fabricated so the momentary push button AC micro switch and its 240v AC lugs was isolated on all sides.
the two plastic L profiles that make up the plastic housing came for a coffee machine tray-cup & the microwave oven door
as I do not own a 3d printer.
the white metal case cover is from the microwave oven. this was bent over and cut to size. with reliefs cut in-to the folded over rim of the metal work.
to help the new folding the metal sheet
the white metal case handle has two under-side support struts to prevent the top of the case bowing.
a cardboard from a Weet-Bix box was hot glued to one inside of the white metal case were a bundle of 240V AC wires are resting next to it..
the back of the case is made up of Masonite hardboard with a dual wall 10A AC light switch on it. and 10mm LED , diode & 100k resistor as a AC pilot light.
this is the main power switch or safety switch & fan switch.
I may need do more to prevent overheating as soldered solid copper blocks are a little too small to dissipate heat from extended use of the welder.
the fan at the back of the unit that took a lot of fabrication time is all but useless. as a fume extractor / fume dissipator for zinc galvanized metal winding.
I also may need to add a side clamp to help hold the work & a work light.
the solid copper 8mm threaded electrodes can be swapped out for two solid copper hex cap hex cap bolts, if extension cables are needed for parallel electrodes.
a plastic spacer is needed for safety as a electrode short circuit can dim the house lights & take huge chunks of copper out of the electrode tips!
so

a considered future upgrade would be to add a timing circuit
a choice between DIY circuit using a 555 & the 15amp 12v relay from the microwave PCB
or an aliex self contained NY-D01 spot welder controller that uses a 30amp or 100amp Triac BTA100-800B
complete with 4 x 7 segment displays & 2 potentiometers for time & current
I do not know how reliable this NY-D01 spot welder controllers are?