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Converting stick welder to tack welder.

Discussion in 'Electronic Basics' started by Tim Zimmerman, Feb 22, 2005.

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  1. I need a tack welder for joining thin plates and electronic
    components. Like the tack weld you see in your NiCad battery packs.
    I have no practical use for my 120v, 80-Amp stick welder so now I'll
    convert it into a tack welder.

    I like to get some ideas on how to make a setup that will be safe and
    precise enough to do small electronic welds like the welds found on
    some relays. Does this sound possible, if not can you point me to a
    place to get a spot welding setup?

    Thanks
     
  2. Clandestine

    Clandestine Guest

    Those "tack welds" are created by resistance heating between the
    parts. There is no arc involved. It takes considerably more power
    (watts) to weld by resistance than by arc. They are also done faster
    than most arc welds. To put this in perspective those electrical
    components required about 1,000 Amps in ½ second. Usually the current
    is turned on/off by an SCR (or similar switch). I have never heard of
    converting an arc welding power supply into a resistance welding power
    supply. Keep in mind these critical factors during this type of
    welding

    FORCE - you must "pinch" pieces together (approximately 500 lbs)
    POWER - you need a high, controlled amount of electricity
    TIME - You need to regulate the power flow within 1 cycle (1/60
    second).

    Unitek-Miyachi makes small resistance welders. www.unitekmiyachi.com
     
  3. Clandestine

    Clandestine Guest

  4. I can vouch for the Unitek-Miyachi system, they work well and the price
    is usually decent. They're step-pulsed, capacitive-discharge systems,
    and are as far removed from arc welding as swimming is from bob-sledding...

    I worked for 4 years at a battery "wholesaler" my main job was to crack
    dead packs open and "re-cell" them, and then glue them back together.
    generally cheaper for the customer than buying a new pack, and 9 times
    out of 10 they had more capacity. If you're looking into this kind of
    stuff, let me know and I'll give you my former boss's contact info and
    he'll be able to point you to our connection on the west coast where we
    got our welder from.
     
  5. Jamie

    Jamie Guest

    find your self dead microwave oven ( high power line), use the
    heater tap on the transformer.
     
  6. Si Ballenger

    Si Ballenger Guest

    Check the rec.crafts.metalworking news group. Lot of info there
    on things like this (and a lot of other DIY stuff).
     
  7. Likely a capacitive discharge to deliver the high current.

    Or like said a RC that drives an SCR as a switch of a storage Cap.

    Martin
     
  8. Barry Lennox

    Barry Lennox Guest


    I believe you are following the wrong path here. You need little
    voltage, but a LOT of current.

    I made a very good spot welder for batteries and similar tasks from an
    ex microwave oven transformer, the biggest I could find. Hack off the
    HV secondary, thousands of turns of very fine wire, then I rewound it
    with just 3 turns of wire, but I packed in as much 8g and 12g wire as
    would fit, and paralleled all the turns.

    The secondary is controlled by a SSR (Croydom CSD2410) pulsed by a
    simple 555 timer circuit. It can vary from about 75-300 mSec I can
    also switch in one of 3 wirewound resistors in the secondary to give
    me fine control.

    The electrodes must be made to suit your exact application, and some
    trial and error can be expected. I first used copper and brass, but
    now get much better results from a proper spot welding electrode
    machined to suit my application. It was not cheap, about $11 for a
    3/8" rod about 3 inches long, but it gives very good results. It had a
    trade name like "Elkalloy" IIRC.

    For optimum results, it is also important to control the electrode
    pressure, but I find I can achieve satisfactory results by hand.

    Barry Lennox
     
  9. Eric R Snow

    Eric R Snow Guest

    Tim,
    The reason your stick welder is not good for spot (what you call tack)
    welding is because the voltage is too high and the current too low. I
    experimented with a microwave oven transformer and was able to get 400
    amps at 3 volts. This is done by removing the high voltage secondary
    windings and replacing them with a few windings of heavy wire or even
    copper bars. See other replies for links etc. for building your own.
    ERS
     
  10. mike

    mike Guest

    How well did this work when YOU tried it? How did YOU keep from killing
    yourself on the high voltage winding?
    mike
    http://nm7u.tripod.com/homepage/welder.html

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  11. Steve Taylor

    Steve Taylor Guest

    When I did it, I drilled the HT winding out. Brutal, but fast. To be
    honest, the idea didn't work for me at all, and I built a miniature
    capacitor discharge welder that DID do the job - a modest bank of old PC
    power supplies yielded enough capacitors to hold "useful" amounts of
    energy.

    Steve
     
  12. mike

    mike Guest

    Post some details on voltage, capacitance, how'd you switch it?
    electrode construction?
    mike

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  13. Guest

    Hi. Oddly enough, you can do spot welding with an arc welder. I tried
    it, and all I got was the typical mess that you would guess. Burned up
    spots with no strength.

    But, just because I cannot do it does not mean that it can't be done.
    There are plans on Ebay:

    385664469
    This auction is for a set of completely illustrated plans to build a
    spot weldi
    ng/cutting gun that works with your arc welder for less than $50.00.

    I have not tried this out, so please buy the plans and report back to
    the group.

    Or, you could try Eastwood's version, which is very similar, but uses
    carbon electrodes. Also, please report back to the group after trying.

    http://www.eastwoodco.com/jump.jsp?itemID=795&itemType=CATEGORY&iMainCat=688&iSubCat=795

    Recently, I tried to do a blind spot weld with 1/8" steel. It worked
    just great. So, the problem may be power, control, and excessive heat,
    which the above solutions allude to. Note that this is arc welding,
    not resistance welding with a low voltage rewound microwave oven
    transformer.
     
  14. With only 3 volts, the resistance of the metal and any 'dirt' best be doing zero ohms...
    Not much punch through voltage.

    Martin
     
  15. Nick Huckaby

    Nick Huckaby Guest

    How about 12V? Would two car batteries work?
     
  16. mike

    mike Guest

    Repeatability is a BIG issue with this. A CD system tries to deliver
    fixed energy. That's less dependent in path resistance.

    Sure, if you had some way to turn them on/off quickly.
    Be sure to use a heavy metal box to contain the battery explosion
    if something goes wrong.



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  17. mike

    mike Guest

    FYI
    Here's the voltage waveform for a Unitek 125 intoa .001 Ohm load .
    http://nm7u.tripod.com/homepage/uniwvfm.jpg
    mike

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  18. Steve Taylor

    Steve Taylor Guest

    mike wrote:

    Hi Mike,

    We needed to weld some exotic metals, that required CD welding. Our
    welder was built in a glove box, The electrode construction was similar
    to your, we modified a toggle clamp to do the job with 1/16" diameter tips.

    The cap- bank was around 2200uF (10 x 220uF 400V reservoir caps) Energy
    supply was a large variable O/P PSU, large because thats what we have
    around. Drive was 0-400V. Welding occured at around 40V.

    Discharge was effected by a very large old automobile relay , with
    contacts bigger than US pennies (around 1" - like the old UK pennies)

    Job was pinched in the jaws of the spotter, then the hands had to
    operate two buttons simultaneously to activate the spot.

    Yes, I'd have preferred to use a huge ignitron, or a hockey-puck
    thyristor, but we didn't have time - this was a two day
    oh-god-we-have-to-do-this-yesterday kind of thing.

    We just about managed to weld molybdenum foil ~0.2mm thick, with it.

    Steve
     
  19. I'd be nervous calling it a 0.001 ohm load - but ok.

    I think the connectors are exceeding that - two clamped down with bolts and the two
    on spring loaded clamps.

    I'd measure the Tr fro 10 to 90% point :)

    Thanks for the waveform and idea.

    Martin
     
  20. mike

    mike Guest

    You're being too picky.
    The manufacturer publishes a specified waveform for their device
    under controlled conditions.
    Gives you some idea of what you're up against welding battery tabs.
    mike

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