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Lincoln Electric SVM186-A service manual Figure E.7 SCR Operation

Models: SVM186-A

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E-7

THEORY OF OPERATION

E-7

 

 

SCR OPERATION

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A silicon controlled rectifier (SCR) is a three terminal device used to control rather large currents to a load. An SCR acts very much like a switch. When a gate signal is applied to the SCR it is turned ON and there is current flow from anode to cathode. In the ON state the SCR acts like a closed switch. When the SCR is turned OFF there is no current flow from anode to cathode thus the device acts like an open switch. As the name suggests, the SCR is a rectifier, so it pass- es current only during positive half cycles of the AC supply. The positive half cycle is the portion of the sine wave in which the anode of the SCR is more positive than the cathode.

When an AC supply voltage is applied to the SCR, the device spends a certain portion of the AC cycle time in the on state and the remainder of the time in the off state. The amount of time spent in the ON state is con- trolled by the Gate.

An SCR is fired by a short burst of current into the gate. This gate pulse must be more positive than the cath- ode voltage. Since there is a standard PN junction

between gate and cathode, the voltage between these terminals must be slightly greater than 0.6V. Once the SCR has fired it is not necessary to continue the flow of gate current. As long as current continues to flow from anode to cathode the SCR will remain on. When the anode to cathode current drops below a minimum value, called holding current, the SCR will shut off. This normally occurs as the AC supply voltage passes through zero into the negative portion of the sine wave. If the SCR is turned on early in the positive half cycle, the conduction time is longer resulting in greater SCR output. If the gate firing occurs later in the cycle the conduction time is less resulting in lower SCR output.

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ANODE

INPUT

CATHODE

OUTPUT

GATE

NOTE: AS THE GATE PULSE IS APPLIED LATER IN THE CYCLE THE SCR OUTPUT IS DECREASED.

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GATE

FIGURE E.7 SCR Operation

PRECISION TIG® 225

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Lincoln Electric SVM186-A service manual Figure E.7 SCR Operation
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SVM186-A specifications

The Lincoln Electric SVM186-A is a versatile and highly efficient welding machine that stands out in the competitive landscape of industrial welding equipment. Designed to meet the needs of both professionals and hobbyists, this machine combines advanced technology with robust construction, delivering outstanding performance in various welding applications.

One of the standout features of the SVM186-A is its multi-process capability. This welding machine can handle MIG, TIG, and Stick welding processes, making it suitable for a diverse range of projects, from light fabrication to heavy-duty work. This flexibility reduces the need for multiple machines, saving time and space for users who require versatility in their welding operations.

The SVM186-A is powered by a reliable and durable inverter technology, which ensures a stable arc and efficient operation across different materials, including stainless steel, aluminum, and mild steel. This inverter technology not only enhances performance but also reduces energy consumption, making it an environmentally friendly choice.

Another notable characteristic of the SVM186-A is its user-friendly interface. The digital display provides real-time information on voltage and wire feed speed, allowing welders to easily adjust settings for optimal results. This intuitive control panel design makes it accessible for both novice welders and seasoned professionals who value precision.

The machine is also built with safety features in mind. It comes equipped with overcurrent protection and thermal overload protection to prevent damage during operation. This ensures that users can work confidently, knowing that the equipment is designed to handle demanding tasks while prioritizing safety.

Portability is another advantage of the SVM186-A. Weighing in at a relatively light weight compared to other industrial welders, this machine is designed for ease of transport. Whether working on-site or in a workshop, welders can easily move the equipment as needed.

In summary, the Lincoln Electric SVM186-A is a sophisticated welding machine that merges technology and practicality. Its multi-process capability, inverter technology, user-friendly interface, safety features, and portability make it a top choice for those seeking dependable and efficient welding solutions. Whether for professional fabrication or personal projects, the SVM186-A is equipped to handle the demands of modern welding tasks with exceptional ease and effectiveness.