Making a battery spot welder

Discussion in 'The Projects Forum' started by Jon Sam, May 9, 2017.

  1. Jon Sam

    Thread Starter Member

    Apr 6, 2016
    42
    1
    Hello everyone,

    I would like to build a small spot welder for lithium batteries (cylindrical of course).

    I don't want to use a microwave transformer because it is not practical, it is heavy and it does not serve any purpose just to weld plates on lithium batteries.

    Here, someone uses a capacitor of 2.7V 500farad:


    I need a mosfet for the duration of the welding with an arduino (or other)?


    How can I charge this capacitor correctly?


    thank you in advance


    Cdt
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Sounds like a capacitive discharge stud welder.
    Usually a SCR is used to dump the charge.
    Max.
     
  3. BR-549

    AAC Fanatic!

    Sep 22, 2013
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    That looks cold to me. What's the resulting resistance?
     
  4. KeepItSimpleStupid

    AAC Fanatic!

    Mar 4, 2014
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  5. Jon Sam

    Thread Starter Member

    Apr 6, 2016
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  6. BR-549

    AAC Fanatic!

    Sep 22, 2013
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    I meant the joint looked cold. Have you heard the term...a cold weld? A cold joint? A cold solder joint?

    It was just an observation with an old set of eyes. A cold joint can have variable resistance and break with vibration or strain.

    I would want a little more heat for that task. But I can't keep up with all the new stuff.

    That link from KISS was quite a project.
     
  7. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    Voltage is the easy way to increase the power to the weld.

    A 10 fold increase in voltage will get you a 100 fold increase in power delivery.

    A simple 10,000 uf at 10 volts will have the same power as a 1 F super cap @ 1 volt.
     
  8. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Looks like very poor control, the capacitor gets dumped as soon as contact is made, I suspect in a factory set up it is a proper stud weld method of spot welding, for this you apply the necessary pressure and then dump the charge with a SCR.
    Also helps if a indentation is made with a centre punch first to cause a raised bump on the weld side for optimum weld area.
    IOW, could use some refining.
    Max..
     
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  9. Jon Sam

    Thread Starter Member

    Apr 6, 2016
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    so 10 x 1000uf 25v caps will be enough to make one spot welding ?

    Regards
     
  10. MaxHeadRoom

    Expert

    Jul 18, 2013
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    You can find out empirically what is needed,but not very reliable without creating some predictable material/weld conditions.
    Max.
     
  11. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    The metal type. Probably pure nickel strips in this case.
    It's thickness, plus that of the metal below it, plus thermal heat sink losses, plus the mass and pressure of the electrodes affect it. Lots more than two thin pieces metal to take into account.

    Experiment has always been quicker. I think anyway. :)
    10-20 volts on 1F should make a nice red momentary weld joint on a standard battery tab plus single nickel strip. (Proper electrodes assumed)

    Again, I suggest you lean towards higher voltage for power. Not HIGH voltage. But more than 24.

    Wire size and joint resistance and component mounting and capacitor charging is smaller or more efficient or cheaper. If you use it for more than one project don't cheap out on quality caps from a good 1st hand source. I'm looking at you ebay brains out there.
     
  12. FrankLee11

    New Member

    Jul 25, 2017
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    Charge capacitors is an effectively thought. The more skill mechanical spot welders (still up to several kA) utilize a major transformer and a major triac to give the mains a chance to direct at a brief little time.
     
  13. bassbindevil

    Member

    Jan 23, 2014
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    Has anyone tried a soldering gun as a mini spotwelder? (The kind that has a transformer inside and a trigger switch for nearly instant heat.) Swap the soldering loop tip for a couple of pieces of solid copper wire. I don't have access to one myself to try this.
     
  14. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    That is basically how my Miller sheet metal spot welder works. Though with those you need access two both side of the metal, it melts the interface of the two sheets. But it also make way more amps than a soldering gun.
     
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