Making AC tig welder

  1. hobby_machinist Member

    Messages:
    56
    Location:
    Croatia
    I was bored and found used high voltage transformer that has 7.5kv output for cheap, i have old ac stick welder that serves me no use.
    My idea is: add a simple on/off switch to primary of hv transformer and use that a on/off switch for welding, maybe add a capacitor if needed.
    Next connect the two secondary vires that carry hv one to ground clamp and another to valve torch so the voltage never drops to zero and arc never cuts out and I can mantain long enough arc for tig welding.
    Will i need spark gap?

    I know this is fire hazard and pointless but Im bored and have a fire extinguisher :laughing:

    Hope this inst :offtopic: or :rules:
     
  2. voipio Member

    Messages:
    1,001
    Cambridge, UK
    A defibrillator, and someone on hand that knows how to use it, might be preferable to a fire extinguisher!!

    The available current from a 7.5kV (presumably a neon sign transformer?) is potentially lethal. The human body will present effectively a short circuit to the HT and the short circuit current will be quite a bit higher than the design current. The other gubbins connected to the torch will short out the 7.5kV, so it will never develop a high tension spark, in the way that HF start does on a TIG welder. Tig welder HF start is acheived by having relatively few turns of heavy gauge wire as the secondary of the HT transformer, connecting that in series with the main welding current supply, and then using high dV/dT (change in voltage over time) as a means of getting those few turns to generate high voltage.
     
  3. Rrobson

    Rrobson Member

    Messages:
    248
    Location:
    West Yorkshire
    I think there’s an appropriate smiley for this...

    :welder::flame:

    :D:D

    good luck, unfortunately I can’t offer any advice but interested to see the outcome...
     
    Memmeddu likes this.
  4. barking mat

    barking mat Barking at Pigeons

    Messages:
    4,622
    Location:
    Brittany, The Arz Valley.
    I think you might have more luck with an alternator.

    Rings a bell somewhere.
     
    Memmeddu likes this.
  5. Morrisman

    Morrisman Forum Supporter

    Messages:
    2,712
    Location:
    Staffordshire, England
    I didn't understand a word, but it sure sounds impressive. :D Anybody who masters the black art of electricity is worthy, in my book.
     
  6. WorkshopChris

    WorkshopChris Forum Supporter

    Messages:
    5,050
    Location:
    South East Essex
    For a start, medical insurance may be good.

    It's doable as I almost sort of got it working once while rebuilding a big old tig set.
    But you need to do more research. the output of the 2 transformers are never directly connected, it's done via induced voltage with a coil you will also need a spark gap.
    Have you considered keeping an eye out for a hf add on box, they used to be used on-site with gensets before small inverter sets became available.
     
    Mr Roo and Memmeddu like this.
  7. Memmeddu

    Memmeddu Member

    Messages:
    2,951
    Location:
    Italia Sardegna
    I've seen on internet something built by using
    IGBT or MOSFETs ,a spark plug coil,a couple of spark plugs,hall current transformer both bought or homemade and some heavy wire
     
  8. Wedg1e

    Wedg1e They call me Mr. Bodge-angles

    Messages:
    6,611
    Location:
    Teesside, England
    7.5kV? Pah, kiddy voltages. I have some ex-xray equipment transformers here running 80kV secondaries... and some diode/capacitor doubler stages to get it up to 160kV if you really want to wake yourself up :D
     
    minimutly, Mr Roo and Seadog like this.
  9. slim_boy_fat

    slim_boy_fat Forum Supporter

    What would you use those for? [serious question :ashamed:]
     
  10. Gazello Member

    Messages:
    109
    Location:
    Bavaria
    Puh .. powder coat gun runs 100kv
     
    Memmeddu likes this.
  11. Wedg1e

    Wedg1e They call me Mr. Bodge-angles

    Messages:
    6,611
    Location:
    Teesside, England
    They generate the high tension needed to accelerate the electron stream in an x-ray tube. In industrial x-ray a 'small' or low-power system would be rated at 100kV; 160-200kV is 'medium' power. The big boys play with 320 and 450kV systems, but then the hairy-chested meatheads get their Linacs (linear accelerators) out and the big boys become small boys :D
    I've designd and built a series of irradiation cabinets used in cancer research; they blast mice with a 320kV set running flat-out from 18" away which kills the mouse's immune system in a couple of minutes. It needs a 50mm thick solid lead housing to permit an operator to stand adjacent to it while it does the business.
    That same 320kV would punch through 50mm of steel and then get to work on you...

    If you fancy building an x-ray set (or for a description of the workings) in your shed see here:

    http://physicsopenlab.org/2017/10/24/x-ray-generator/

    but if and when the HSE and Environment Agency knock on your door, don't say I didn't warn you, they take a dim view :whistle:
     
  12. Wedg1e

    Wedg1e They call me Mr. Bodge-angles

    Messages:
    6,611
    Location:
    Teesside, England
    Sounds hairy, I have a DIY powdercoat system that runs at 5kV and I wouldn't be sticking my hand anywhere near it. 100kV can jump one hell of an air gap.
     
  13. Chris Snow Member

    Messages:
    75
    Location:
    Nottingham
    I do a bit of work in 132KV substations, bare busbars probably 3M off the ground and you can walk below, rules are simple, don't put your hands above your head... tape measures are also not allowed!
     
  14. Gazello Member

    Messages:
    109
    Location:
    Bavaria
    Its the power p = volt * amps that kills you , 100kv at 0A just a little ozon smell
     
  15. mtt.tr

    mtt.tr Member

    Messages:
    4,071
    Essex England
    but you would conisider strapping that to your arc welder
     
  16. Wedg1e

    Wedg1e They call me Mr. Bodge-angles

    Messages:
    6,611
    Location:
    Teesside, England
    Not me, I have HF start already :D
     
  17. Wedg1e

    Wedg1e They call me Mr. Bodge-angles

    Messages:
    6,611
    Location:
    Teesside, England
    :confused: Obviously no current flow = no hazard, but when it finds a conductive path I don't want to be part of it!
     
    slim_boy_fat and WorkshopChris like this.
  18. Seadog

    Seadog Forum Supporter

    Messages:
    6,974
    Location:
    NE London - UK
    Has anyone else stood in a station by the track, in the rain, with an umbrella? You can hear a discharge from the overhead lines if you point the sharp end at them.
     
  19. mtt.tr

    mtt.tr Member

    Messages:
    4,071
    Essex England
    Problem with hv most things are conductive
     
  20. Exuptoy

    Exuptoy Member

    Messages:
    2,524
    Location:
    Maesteg, South Wales
    A place where I sometimes work has 2 X Electron Beam machines made by ESI in the States which changes the properties of the plastic which they make there. The terminal (gun) in the machine runs at 406kv in a vacuum generally around 1x10-7 Torr and the HV then changes the structure of the plastic as it passes by a titanium window outside the vacuum!
    It's well over my head but a weekly test is to take a Caesium 137 source to verify the calibration of a Geiger counter before scanning the machine for radiation leakage. It scares the feck outta me but the operators just wander around within meters of the oven and pay it no mind!
    I certainly wouldn't be messing around with HV. I've done my switching course and seen plenty of nasty videos to keep me right!
     
    slim_boy_fat likes this.
Advertisements