digital display diference

[clifford210]

i notice when welding the other day that the volt reading went down about 0.5 v during weld i was using miller 252 went to see if the lincoln 350 machine do the same thing and the volts were increasing as much as 2.5v (both machines tip to work distance was shortend and lengthend) can anyone explain this to me i thought cv ment constant voltage

 

[shenion]

There is a bit of slope in a MIG welder. My Miller CP-250TS has an adjustable slope. I don't see it on newer machines.

Most transformer machines have a slope more due to the resistance of the transformer and reactor. On single-phase MIGs, the inductance introduces more slope. These have no feedback to automatically maintain a constant voltage. It it a CV source with practical limitations.

 

[clifford210]

digital display

sorry which is which most of what your saying is beyond me can you simplify for me please all machine are single phase

 

[shenion]

Slope is the drop in voltage with current:

The graph shows the voltage at the max and min voltage settings (leftmost points where lines converge.) Mine has 7 different settings on the slope or "Droop". 6 turns is normal. Even with no slope added, there is a drop in voltage with current.

 

[clifford210]

digital display

wow aparently i need to do some research on inductance and slope so i can understand better cause i'm kind of feeling stupid right now

 

[shenion]

weldreality had comments about the Miller CP-xxx seies being one of the best as the slope was programmable. He ranted about later machines having the wrong fixed slope.

Then again, the site is geared for heavy production welding and spray transfer. It is about the only reference to slope I have seen. Seems to be a non-issue these days.

As for inductance, for short-arc (dip transfer) you want high inductance. For spray-transfer you want a low inductance. I have noticed a considerable difference changing inductance (my Lincoln had a variable inductance and I have added a variable inductor to the Miller to support short arc.) For spray-transfer, a higher inductance did not effect the weld but it started with a few short-arc cycles and spattered. On low, it went quickly into spray transfer.

In short-arc, greater inductance increases the "wetting" of the weld pool. Many machines have two plugs for the return lead for high and low inductance.

Lincoln and Miller have references to short/spray/globular transfer in their MIG handbooks. They mention how the inductance works.

 

[clifford210]

digital display

thank for your help i'm going to look into it more