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Welding Problem: SPOT WELDERS (AMPS, WATTS, VOLTS)

Discussion in 'Power Electronics' started by powerspy1010, Oct 31, 2020.

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  1. powerspy1010

    powerspy1010

    1
    0
    Oct 31, 2020
    Hello,
    I have been wandering for the past two days on Ebay trying to figure out what would be fit for my hobby in matters of welding. I only need to weld tiny spots, like on jewellery or batteries. But there are a few Chinese-made machines that drew up my attention:
    1. 1,3KW / 3,2KW / 4,3KW machines that sell at around 100-300USD, some of which come with welding pen attached to the base unit. Their power is ranked in terms of KW, although it is stated that they can only weld up to 0.3mm nickel sheets.
    (https://www.ebay.com/itm/4-3KW-Spot...023926?hash=item5b7fda1a36:g:TB8AAOSwwqBfkA20)
    2. 200W / 400W/ ....4000+W machines that sell at relatively higher prices. They are updated with argon channels and are usually more expensive than the previous category. No problem until now, but the description states that they can weld from 0.3mm up. How can they weld a higher width material than the previous category, if the WATTS are lower???o_O
    (https://www.ebay.com/itm/Pulse-Argo...774108&hash=item2f155ce333:g:EQQAAOSwj1hae-Ai)
    3. 30 A / 50A / 100A / 150A machines that seem to be the most expensive, but which are attached with seemingly lower WATTS power, yet they are advertised to achieve the most satisfactory results... for example 100W:
    (https://www.hajettool.com/Pulse-Spot-Welders/150a-argon-arc-spot-welder.html)
    4. Finally, there are machines listed with their voltage power, but this is not so important for me right now, since they are scarce and I imagine it is some sort of advertising scheme.

    Can someone please help me elucidate this mistery: Which machine is the best to acquire for jewellery welding of tiny spots? Which is the link between AMPS, WATTS and VOLTS (and I mean the deeper meaning, because I have already understood the hydraulic analogy...). The reason why I am asking these stupid questions resides in the fact that the machines with power rated from 1.3 to 4.3KW achieved low results up to 0.3mm metal sheet, while the machines rated with 200-400W could acquire more powerful crafts....:(
     
  2. davenn

    davenn Moderator

    13,671
    1,892
    Sep 5, 2009
    That would probably destroy your fine objects like jewellery and batteries
     
  3. Technomaniac

    Technomaniac

    33
    3
    Oct 31, 2020
    Hi, powerspy1010.
    I use a little unit that I bought from the shop attached to the local rubbish dump. I don't use it very often, but have used it for spotwelding tabs of nicads together, and repairing battery contacts in vintage electronics, remote controls etc. after battery leakage cleanup.
    It is 110v powered but I have transformers around the shop. It dumps the charge in a big electrolytic capacitor across the welding contacts. It can take as long as it likes to charge the capacitor so the unit has a low wattage rating, because it can charge the big cap over a little while, with a low current. I have had it for years, and did a little research when I got it home, I think it was intended for welding dental things, like braces for misaligned teeth. I can't remember what voltage it uses for the weld, maybe just whatever you get when you rectify 110, but I recall that a colleague came in with a job once and we had a little trouble getting a good joint straight away, several attempts were needed, so perhaps a welder with a higher voltage might work a little better in such circumstances, where there is tarnishing etc. Photo below. Spotwelder.png
     
    hevans1944 likes this.
  4. WHONOES

    WHONOES

    952
    249
    May 20, 2017
    Sounds like the unit you are describing in post #2 is a stud welder. Stud's / Bolt's are difficult things to weld to panels. These welders use studs with a slightly conical tip that has been copper plated and are made for purpose. The capacitor bank is charged up. Then the panel is connected to one end of the cap' bank whilst the stud is connected to the other. The stud is quickly presented to the panel whereupon all the energy stored in the cap's is discharged through the stud which welds the two together.
     
    hevans1944 likes this.
  5. hevans1944

    hevans1944 Hop - AC8NS

    4,543
    2,116
    Jun 21, 2012
    Hello, @powerspy1010. Welding is not a skill that you can learn by reading about it, or even by viewing any number of videos. It requires a LOT of hand-eye coordination and a LOT of hands-on practice doing actual welding to become proficient. Unless you are a robot. Robots excel at repetitive tasks like spot welding.

    If you have taken the steps required to learn how to manually weld properly, then you will have been exposed to both the equipment and the instructors best suited to your learning purposes. I would suggest you visit local jewelry shops that offer repair services (not all of them do, as much of the work is "sent out" instead of performed "in house") to see what equipment is used and, most important, how it is used. If you express an interest in the craft, perhaps someone will offer to take you on as an apprentice.

    AFAIK, most jewelry is made or repaired by brazing NOT welding, and the heat for brazing is provided by a gas torch, not an electric welder. However, you did say this is a hobby and you needed to weld only "tiny spots, like on jewellery or batteries," so perhaps what you really need is a capacitance-discharge spot welder. These are simpler than a TiG (Tungsten inert Gas) welder and usually much less expensive. They also do not require much experience before you learn to make a good weld. And, if you are so inclined, you can build your own!

    Most of the Asian welders you linked to are tungsten inert gas (TiG) pulse welders used to spot weld nickel strips of electrical conductors to create battery packs. These welders use argon shielding gas, provided from a bottle of argon gas through gas pressure-regulators, to prevent the weld puddle from oxidizing while it cools and solidifies. Argon is bottled at pressures up to 2000 psig and must be reduced to a few psi with a controlled flow rate for shielded gas welding. Although argon gas is not extremely expensive (it is distilled as a cryogenic liquid from air), the gas regulators, gauges, hoses, and bottle rental all add cost to your initial investment. Make sure you have your argon gas supply and the accessories needed to use it before you purchase a welder that requires it.
     
  6. Minder

    Minder

    3,015
    640
    Apr 24, 2015
    I agree with whonoes, a stud welder is relatively easy to make, just a DC supply, a large capacitor and a SCR.
    One thing to ensure pressure on the electrode when the SCR is triggered.
    M.
     
  7. hevans1944

    hevans1944 Hop - AC8NS

    4,543
    2,116
    Jun 21, 2012
    It is also important that the "welding" electrode be made of pure, OFHC (oxygen-free, high-conductivity) copper that conducts electricity readily and absorbs heat. You do not want the welding electrode to become part of the weld!

    And, as @Minder stated, adequate pressure must be maintained during the spot welding process.
     
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