This paper explains some of the design benefits of the Workhorse line of welders, and adds some commentary of comparisons to different designs.

Every design team faces the dilemma of choosing between several possible solutions to design challenges over the course of a project. Each choice will have advantages and drawbacks when compared to other choices and solutions. The choices made must eventually relate back to the main objectives of the product being developed. A design team for an off-road truck will optimize differently than the design team for a sports car
.
All Workhorse power sources are designed with three main characteristics in mind:

• Great welding characteristics

• Reliability

• Ruggedness

At first this may sound like objectives that all welding machine designers should have, but subordinating the design to these objectives often lead to trade-offs. These trade-offs may make the product unsuitable or less optimized for certain applications.

We at ARCON Welding target customers operating in rough or harsh environments such as:

• Shipyards

• Mines

• Offshore oil rigs

• Construction sites

• Paper Mills

• Power Plants

• Fertilizer Plants

Below is a list of some of the advantages and trade-offs from incorporating ARCON Welding's three design objectives.

SMOOTH WELDING CHARACTERISTICS AND SIMPLE OPERATION

1. Constant Power

Advantage:
The power (measured in Watts) heats up the weld puddle. When using Constant Power, the heating is less dependent on the arc length. This enables a good weld to be accomplished, even by an inexperienced welder with an unsteady hand.

When welding with Constant Current machines, an increase in the length of the arc also increases arc voltage or welding power, which makes the puddle hotter. This increases the chance of burn-through.

Trade-off:
When observing the actual current displayed on the digital readout during welding, the current measurement will vary to compensate for varying arc length (=arc voltage).

2. Command Arc

Advantage:
The Workhorse 300S has a unique GMAW Transfer Mode that we call Command Arc. Unlike machines which initiate or accomplish metal transfer by the wire short-circuiting to the workpiece, Command Arc is sensing the arc voltage, and when the arc length reaches 12 volts, a pulse of current and voltage is released on Command that expels the molten tip of the wire across the arc onto the work. Because there is no short-circuit, spatter is minimized, and fusion, even at low current and voltage is maximized.

This is due to there being no short-circuit. In “short-arc”, the arc is extinguished for relatively long periods of time, allowing lack of fusion to occur. Metal transfer occurs only during short-circuit. Because it is NOT “short-arc”, Command Arc may be used in many Code Welding applications without qualification. The Transfer Mode most closely resembles Globular Transfer, as defined by the American Welding Society, but at lower current and voltage, and it is possible to use Command Arc in all positions.

Trade-off:
None that we can think of.

RUGGEDNESS:

1. Fiberglass case as compared to aluminum, sheet metal or polycarbonate.
An alternative to fiberglass was to use Polycarbonate, which is a modern and very strong material. We chose not to use this material because a hot electrode could penetrate this type of case. Should this occur, the operator could be subjected to the high voltages inside the machine.

Advantage:
Our fiberglass reinforced case is capable of withstanding greater abuse in a tough environment. For example, in Jacksonville, FL a Workhorse Stick/TIG welder fell 25 feet from the side of a ship down onto the dock and continued working. Later, it was discovered that the back panel was pushed in and prevented the fan from turning causing the welder to turn off at high welding currents. A railway car was set on top of a Workhorse in a mine in Alabama. The machine was used until the replacement case was installed weeks later.

Trade-off:
Our reinforced fiberglass case is heavier than less sturdy alternatives.

2. "Membrane" chassis

Advantage:
The chassis onto which all components are mounted is a membrane between the top and bottom halves of the machine. This design allows the chassis to flex, dampening the "g-factor" of the components if dropped.

Trade-off:
None

RELIABILITY

1. SCRs (Thyristor) Inverter components

Advantage:
SCR components are slower than IGBTs and MOSFETs which allows time to protect components from spikes and over-voltages using an internal circuit breaker. Higher frequency components have properties which prevent use of internal circuit breakers or fuses to protect them.

The “energy for fusing” (=destructive energy), for one of today’s commonly used high frequency components (IGBT), used in a 400A welder drawing 50 A at 240V is 1500 Amp sq seconds. The most sensitive Semiconductor fuse from the leading fuse manufacturer is also 1500 Amp sq seconds which makes it a poor protector of the IGBT. Consequently, these inverter components are not always well protected.

The energy for fusing the SCR in a 400 Amp welder is 250,000 Amp sq seconds! A fuse can therefore easily protect the SCR, or even better, the SCR can be protected by a fast circuit breaker.

The ideal thermal construction incorporating double-sided cooling surfaces is a "hockey puck" assembly of both SCRs and diodes. This design is used in high power/high voltage DC power transmission lines where SCRs and diodes operate in the megawatt range. Alternative higher frequency welding designs use IGBTs and MOSFETs semiconductors cooled only on one side. These components have been developed from components for low power applications.

Trade-off:
Lower inverter frequency results in heavier magnetics. The size of a transformer is roughly proportionate to the frequency, which is the reason why an inverter welder is so much lighter than a transformer/rectifier welder. The Workhorse operates at about 5,000Hz, as compared to 60Hz for a transformer/rectifier welder. For instance, at 20,000 Hz, the magnetic components become even lighter, but with the drawback of increasing electrical losses elsewhere, including the switching elements and snubber circuits.

SCRs have been around for a long time, and may seem to be old technology. However, flashy and glamorous components are in opposition to our design criteria which incorporate Ruggedness and Reliability, the reason being that we are manufacturing a Workhorse, not a Racehorse.


2. 5-Zone Thermal Protection

Advantage:
The welder is thermally protected from virtually all abnormal conditions. For instance, if one phase "disappears" the capacitors can become hot enough to self-destruct. We have placed thermal sensors inside the capacitors to shut down the machine before any damage can occur. With our 5-zone protection, it will just shut itself off. In effect, we have made it hard to accidentally destroy the welder.

Trade-off:
Higher component costs

3. Extensive MOV protection coupled with a simple, straightforward Circuit Breaker.

Advantage:
The welding machine is better able to survive in an environment with "dirty power" such as power plants, shipyards, construction sites and where motor generators are used. The MOVs will protect the circuitry for short spikes, and if the condition extends too long the circuit breaker will trip and the machine shuts off.

Trade-off:
Higher component costs

4. No Automatic Voltage-Switching circuitry

Advantage:
Less circuitry that can fail making the machine more reliable.
No chance of "confusing" the welding machine at startup and destroying the circuitry. This disaster can occur with a generator when the welder's voltage-sensing circuitry locks in at 240V and does not continue to adjust when the motor-generator's output voltage increases to 480V on startup.

Trade-off:
Our simple design is not as versatile, but only if multiple input voltages are actually needed by the user. We offer dual voltage models (240/480V) of our Stick/ TIG and MIG/Stick machines that can easily be switched between these voltages. Our circuitry makes switching "idiot proof". If a welder was set for 240V but connected to 480V, the circuit breaker will trip without damage to the welder.