TIG torch amp rating when using pulse

[taylorkh]

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

[cruizer]

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.

[steph]

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

[Country Metals]

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.

[taylorkh]

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

[wkdivr]

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

[cruizer]

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.

[nocheepgas]

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...

[taylorkh]

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