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  1. #1
    Join Date
    Aug 2009
    Posts
    140

    Question TIG torch amp rating when using pulse

    As an example, a WP9 family torch is rated at 125 amps DC (per the Weldcraft web site). If this torch is used on a pulse TIG power supply with the following settings:

    Pulse frequency 100 Hz
    Max amperage 200 amps
    Peak time 50%
    Background current 50 amps

    the AVERAGE current through the torch would be 125 amps. Would it be correct to conclude that these parameters are within the capability of the torch?

    TIA,

    Ken

  2. #2
    Join Date
    Oct 2004
    Location
    Edmonton, Alberta
    Posts
    7,683

    Default

    Well, I'm guessing the question is can you run 200 amps through a torch rated at 125 amps, Hmmmm, yes for a short while till the internal conduit has a melt down.

    Not sure, try it and tell us how long your torch lasts.

  3. #3
    Join Date
    Sep 2010
    Location
    Sorong, Indonesia
    Posts
    62

    Default

    @Taylor: I think its close. Like Cruizer said, try it and then let us know.

  4. #4
    Join Date
    Jul 2010
    Location
    Salem, NJ
    Posts
    271

    Default

    Lets say that 1 amp = 1 degree in heat

    So if you were pulsing at 200/50 then your cord is running 200/50 degrees.

    The problem with your theory is that you assume that the internal wiring of the tig torch cools down to 0 degrees between pulses. If your torch is running at 200 degrees for .01 second, then 50 degrees for .01 second, then back to 200... The laws of heat dissipation say that the torch would run around 180-185 degrees and would burn up because if the torch is rated for 125 amps / 125 degrees during the span of the duty cycle.

    Now with that said, I ran a WP17 on my 200 DX with 50/50 helium at 200 full amps for about 5 hours. Yes the torch did end up dying at the end but I had to get the job done and the torch was put in the bill.

    So yes its possible for a short time, yes you will damage the torch over the span of a half hour, yes you can just buy the head since that is what went on my line.

  5. #5
    Join Date
    Aug 2009
    Posts
    140

    Default

    Well I had some coffee this AM and thought through my question a little more. The issue is dissipation of heat by the torch. The heat generated by the flow of current through the torch may be represented as:

    P=I^2 * R

    Where P is the power or heat, I is the current and R is the resistance of the torch. If we assume that the resistance of the torch is constant and simply solve for the pulse max current which is equivalent to 125 amps constant current and using my original example:

    I = max pulse current
    I/4 = background current
    1/2 = fraction of time at max or background current

    125^2 = (I^2)/2 + ((I/4)^2)/2

    multiplying both sides by 2 gives

    31,250 = I^2 + (I/4)^2 = I^2 + .0625 * I^2

    solving for I

    I^2 = 31,250/1.0625

    I = SQRT(31,250/1.0625) = SQRT(29,412) = 171.5 amps

    How does that sound? I may send a question to Weldcraft and see what their answer is. And I need to ping Miller to see if they have duty cycle charts for the Dynasty 200 when used in pulse mode

    Ken

  6. #6
    Join Date
    Feb 2011
    Posts
    20

    Default

    Why don't you just upgrade the torch, and be done with it?

  7. #7
    Join Date
    Oct 2004
    Location
    Edmonton, Alberta
    Posts
    7,683

    Default

    Pulse mode DOES NOT decrease the heat the the torch nor the head, It simply provides you with a spacing to add filler.

    Get a larger torch and be done with it. ie, your making a mountain out of a mole hill.

  8. #8
    Join Date
    Dec 2008
    Location
    Arizona
    Posts
    812

    Default

    Quote Originally Posted by taylorkh View Post
    Well I had some coffee this AM and thought through my question a little more. The issue is dissipation of heat by the torch. The heat generated by the flow of current through the torch may be represented as:

    P=I^2 * R

    Where P is the power or heat, I is the current and R is the resistance of the torch. If we assume that the resistance of the torch is constant and simply solve for the pulse max current which is equivalent to 125 amps constant current and using my original example:

    I = max pulse current
    I/4 = background current
    1/2 = fraction of time at max or background current

    125^2 = (I^2)/2 + ((I/4)^2)/2

    multiplying both sides by 2 gives

    31,250 = I^2 + (I/4)^2 = I^2 + .0625 * I^2

    solving for I

    I^2 = 31,250/1.0625

    I = SQRT(31,250/1.0625) = SQRT(29,412) = 171.5 amps

    How does that sound? I may send a question to Weldcraft and see what their answer is. And I need to ping Miller to see if they have duty cycle charts for the Dynasty 200 when used in pulse mode

    Ken
    Too much math for my pea brain...
    Miller Syncrowave 200
    Homemade Water Cooler
    130XP MIG
    Spectrum 375
    60 year old Logan Lathe
    Select Machine and Tool Mill
    More stuff than I can keep track of..

  9. #9
    Join Date
    Aug 2009
    Posts
    140

    Default

    The question was not "should I get a larger torch?" I have a WP17 and a CK FlexLoc both rated at 150 amps DC. I could have used one of them as the example. I recently purchased a Dynasty 200 DX and I am exploring the ramifications of the pulse feature.

    Miller has a video describing the advantages of pulse and sums it up in one word "control". My limited experience with the machine so far bears that out. Pulse allows for a less fluid puddle but still with sufficient penetration. Pulse does decrease the heat input to the weld so it would make sense that it reduce the heat input to the torch and the heat generated in the power source when comparing the peak amperage in pulse vs. the constant amperage in non-pulse mode. Miller tech support, in response to my inquiry, told me
    Use the average current to figure duty cycle.
    Ken

    p.s. At 1 pulse per second or so, yes you can dab filler between the pulses. At 100 Hz your filler hand would have to be faster than a cold wire feeder

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