Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

How to measure amperes with a constant current welder?

  1. May 10, 2015 #1
    Hi guys and gals.
    I have a constant current welder. 150 Amps DC/ 230 Amps AC output.
    There is no provision for measuring output current when the machine is welding.
    I'm thinking of adding a shunt to either the work lead or the return lead.
    I don't know what size and rating I need.
    The input voltage is 220-250 volt.
    I'm often hooked up to a 230 volt 60 HZ source.

    I'm often welding DC work negative.
    Would there be any difference in measuring the AC and DC?
    Are they different shunts????
    Thanks a ton.
     
  2. jcsd
  3. May 10, 2015 #2

    berkeman

    User Avatar

    Staff: Mentor

    I'd recommend using a Hall Effect clamp-on current meter (it can measure either AC or DC). Are the individual wires available (so you can clamp onto one or the other, and not around both at the same time)?

    Something like this (in the appropriate current range):

    http://www.toolsource.com/prod_images/103545.jpg [Broken]
    http://www.toolsource.com/prod_images/103545.jpg [Broken]
     
    Last edited by a moderator: May 7, 2017
  4. May 10, 2015 #3
    The wires are individually insulated.
    #0 gauge.
    Those clamp on deals look pricey. I'll see if I can bum one off of someone and report back.
    Thanks.
     
  5. May 10, 2015 #4

    berkeman

    User Avatar

    Staff: Mentor

    Maybe a little pricey, but safe, accurate and reliable. :smile:

    BTW, if you just want to know the current occasionally, you could maybe have someone watch your electric power meter (at the power entry to your home/shop) to see how much faster it spins when you have your welder going. You can calculate the difference in power, and from that work back to the change in current demand when the welder is welding...
     
  6. May 10, 2015 #5

    Averagesupernova

    User Avatar
    Science Advisor
    Gold Member

    Buy a cheap starter current indicator and lay it on the ground cable in the same manner they are meant to be laid on the battery cable. Of course this limits you to DC.
     
  7. May 10, 2015 #6

    jim hardy

    User Avatar
    Science Advisor
    Gold Member
    2016 Award

    Yes there are different shunts. They make standard voltages for their range, like 50 millivolts or 100 millivolts or 200 millivolts.

    Ten feet of #0 is almost exactly one milliohm... that'd make a shunt, but i dont see a clean way to tap into your return lead.


    The right way would be to put one of these around the return lead inside the welder, where it's still AC (between transformer and rectifier) and mount the meter on your welder face.

    http://www.ebay.com/itm/AC-0-200A-R...468?pt=LH_DefaultDomain_0&hash=item2a38a4428c


    ignore buttons is back



    .
     
  8. May 11, 2015 #7

    jim hardy

    User Avatar
    Science Advisor
    Gold Member
    2016 Award

    wow i owe you an apology, i mis-read your question as being about shunt current ranges not AC vs DC shunts.
    Thought you said "are there different shunts"...(as in for 150 vs 230 amps)

    The same shunt will measure AC and DC,
    trouble is it takes different meters to read them out.
    A multimeter with scales for 200 millivolts DC and 200 millivolts AC would work with a 200 millivolt shunt.


    However - i prefer a current transformer and panel meter over a shunt and DMM,
    because it isolates the measuring circuit from the welder output,
    lessening the likelihood of a shower of sparks where you don't want one.

    hope i didnt cause you any trouble.

    I see somebody bought one of those EBAY meters last night - was that you ?
    I'm contemplating one myself...have an old Lincoln cathedral welder , and a huge diode bridge to add DC capability.....
    Meter would be a nice finishing touch.

    old jim
     
  9. May 25, 2015 #8
    Lincoln Cathedral?
    You mean the big red "tombstone" or "buzzbox" as they are colloquially known?
    The specs on that are comparable to the thunderbolt.
    Both sound like they contain a mechanical particle accelerator of some sort :)
    The Miller is infinitely adjustable and the Lincoln is tapped at different parts on the coil.
    The Miller allows for high-frequency "TIG stabilizer modules" with standard foot pedal control while the Lincoln does not. The modules are somewhat archaic and difficult to find for a reasonable price. They also lower the output efficiency by 10-20%. On a machine that is barely pushing out 230 amps with no TIG controls, it's probably not worth it. I do a lot of 1/4 structural aluminum with MIG, but I would like to TIG it instead. MIG is just butchery...

    No, I did not buy that Ebay meter. It would look nifty on the nameplate. I just don't want to modify the sheet metal given that I am probably retiring this machine and buying a full size miller dynasty in the 300+ amp range, IF I can get the utility to run 3 phase power to the workshop.
     
    Last edited: May 25, 2015
  10. May 26, 2015 #9

    jim hardy

    User Avatar
    Science Advisor
    Gold Member
    2016 Award

    That's the one. Entry level hobbyist machine. Around here they're considered "Handyman's Secret Weapon" , everybody has one.
    I remember when they were $79 new.
     
  11. May 26, 2015 #10

    dlgoff

    User Avatar
    Science Advisor
    Gold Member

    When I saw the meter it looked like a good one for my collection and thought about buying one. Until I saw "Country of Manufacture: China". :oldgrumpy:
     
  12. May 26, 2015 #11
    Since this thread is still alive - I am thinking a Hall effect sensor, 10V meter, power supply -- could build a 300A meter for about $100 in parts...the problem wiht the shunt is then the circuitry is all exposed to the electrical noise of the welder - more easily filtered out at 10V than when directly connected. __ If nneded the Sensot can be mounted on the weld cable connection and the display on the welder -- or even remote... actually would be a pretty cool RF or Bluetooth - so the sensor is staitonary but the display can be located at the workpiece --- ok %$$# I have another project...
     
  13. May 26, 2015 #12

    jim hardy

    User Avatar
    Science Advisor
    Gold Member
    2016 Award

    Indeed, a good Simpson panel meter costs upward of $75.

    Worth it for industrial use, i put them in the test equipment we made for our shop (in my avatar).

    But hard to justify for a $75 secondhand home use welder.
    I look for them .in equipment at metal salvage yard - thirty to forty cents per pound.
     
  14. May 26, 2015 #13

    jim hardy

    User Avatar
    Science Advisor
    Gold Member
    2016 Award

    Ahhh youth. You guys are not constrained by the past like i am. RF Telemetry on a home project? I've not yet mastered RS232....
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: How to measure amperes with a constant current welder?
Loading...