The "Slider" Myth

We have recently been "set upon" by hordes of welders with new Lincoln Classic II, III, and 300D machines who have asked us to design them an electronic "Slider" so that they could modify their machines to weld better on uphill or vertical passes.

We even considered using our Ampmate series electronic rheostat to replace the big 350 watt resistor that was being installed by a lot of repair shops as the "SLIDER." We could not bring ourselves to cheat the welding public in furthering the myth of the "Slider" by taking financial advantage of them for a product that really produced nothing!

One of the most basic electronic formulas is I = E/R. I is current, E is voltage and R is resistance. Why the formula? To show how resistance causes changes in your machine's welding amperage.

As you turn your machine's fine current control up and down you are varying the resistance (R) of the circuit. This in turn increases the amperage passing through the machine's shunt fields, thereby increasing the magnetism induced into the armature of the welding machine causing an increase or decrease of output welding amperage.

With the welding machine running at weld speed the voltage (E) of the exciter stator remains constant and does not change with the rheostat movement. The only change in the circuit is caused by movement of the fine current control (R) which affects the series circuit current (I) in the entire circuit.

When the machine was designed and manufactured, the engineers determined the ratio of resistance to the machine's shunt coil's inductive reactance at exactly 60 HZ to accurately design a dial-plate to indicate welding amperages on the fine current control panel. This is why the machine's fine control rheostat has a specific resistive value and if replaced-----it must be identical. If not, the dial plate becomes misleading and in error.

One wire going to your machine's rheostat (fine current control) is cut and the resistor is inserted in series (in between) the cut wires to your rheostat. That's all. Of course you have all of the costs of the parts and labor to install this resistor and consequent testing.

By placing resistance in series with the machine's rheostat it lowers the machine's Open Circuit Voltage (OCV) by placing more resistance in series with the main shunt fields. In layman's terms this means that the OCV is lowered and the welding arc must be held closer to the work to maintain the arc. Consequently welding uphill or vertical seems to be improved over the original factory settings.

First and foremost--------you are fooling yourself! With the "Slider" in the circuit your machine's fine current control is in ERROR! The dial settings are much lower than indicated due to the increased series resistance and the machine is totally out of calibration. Worse yet, you cannot turn your machine up to 100% and have maximum output. The resistance added by the "Slider" prevents that!

You can do the same thing as the "Slider" simply by lowering your fine current control. All that you are doing is increasing the circuit resistance and reducing your OCV and consequent welding amperage. At least you will know that the panel setting is correct.

The "Slider" is simply a "sugar pill" such as 250 or 300 amp brushes in SA-200 machines to increase amperage or to better stabilize the arc. It's a "gimmick" and nothing more.

We will not become part of this "medicine show" and do not intend to manufacture any product that claims to improve the welding characteristics beyond the original design of the manufacturer.

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