[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

[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

p.s. Sorry Jody if this is too PhD like I guess I will have to buy another tig finger in penance