Slide 4: Power Supply Types & Selection

Slide Visual

Overview

This slide compares power supply types used in modern plasma systems, their electrical characteristics, advantages and disadvantages, and selection criteria. Understanding power supply architecture is essential for equipment operation, troubleshooting, and safety.

Instruction Notes

Power Supply Fundamentals

A plasma cutting power supply must provide: 1. High voltage (100–400 V) for arc initiation and maintenance 2. High current (20–600 A depending on system rating) for energy delivery to the workpiece 3. Stable output to maintain arc continuity and cut quality 4. Rapid response to load changes (sudden cut thickness changes)

The power supply converts AC mains voltage (typically 208 V, 230 V, or 480 V three-phase) to a DC output suitable for plasma cutting. The conversion process involves transforming, rectifying, and filtering the AC signal.

DC Power Supply Types

Constant Voltage (CV) Supply A constant voltage supply maintains a fixed output voltage (typically 200–350 V DC) regardless of load conditions. As long as the load is below the rated capacity, the voltage remains relatively stable.

Advantages: - Simple design, more affordable than current-regulated supplies - Stable arc operation once established - Good for manual cutting (operator can vary amperage by changing torch distance)

Disadvantages: - No current limiting; if the arc is short (torch too close), current surges to dangerous levels - Requires careful operator control to avoid electrode damage - Poor arc initiation characteristics (requires very close electrode-to-workpiece distance to start the arc)

Constant voltage supplies are older designs and are rarely used for new plasma systems. However, some smaller shops may still operate CV supplies for oxy-fuel or light-duty cutting.

Constant Current (CC) Supply A constant current supply regulates the output current to a preset value, allowing the voltage to vary as needed. The output current remains relatively constant regardless of arc length changes.

Advantages: - Excellent arc stability over a wide range of arc lengths - Self-regulating: if the electrode moves closer, voltage drops but current remains constant - Better for mechanized/CNC cutting where precision is required - Safer: limiting current prevents dangerous surge currents if the electrode accidentally touches the workpiece

Disadvantages: - More complex and expensive than CV supplies - Requires proper regulation tuning for best results

Constant current supplies are the industry standard for modern plasma cutting systems. Most industrial systems use CC supplies with current regulation in the 20–600 A range.

Pulsed Power Supply A pulsed supply rapidly switches the output on and off at a high frequency (typically 5–20 kHz), creating a series of current pulses rather than continuous current. The duty cycle (fraction of time the output is on) determines the average current and power delivered.

Advantages: - Excellent arc stability, especially at low currents - Reduced electrode erosion (electrode cools slightly during off-cycle) - Reduced thermal stress on consumables - Better control over heat input (useful for thin materials or precision work) - Quieter operation (arc is pulsing rather than continuous)

Disadvantages: - Higher cost and complexity - Requires high-frequency filtering in the power supply (increases EMI—electromagnetic interference) - More sensitive to contamination and gas pressure variations

Pulsed supplies are becoming more common in newer systems, especially for precision cutting and automated applications.

Inverted/Resonant Supplies Modern high-end plasma systems use inverter-based power supplies that convert AC to DC using high-frequency (>10 kHz) switching circuits rather than traditional transformer/rectifier designs. These supplies are lightweight, compact, energy-efficient, and provide excellent regulation.

Advantages: - Very compact and lightweight (important for portable systems) - High efficiency (less wasted heat, lower operating cost) - Excellent arc stability and current regulation - Rapid response to load changes - Can be programmed with multiple voltage/current profiles for different materials

Disadvantages: - Higher upfront cost - More susceptible to electrical noise and interference (requires proper shielding and grounding) - Require trained technicians for repair (more complex circuitry)

Most new plasma systems (2010 onward) use inverter-based supplies. They are the future of the industry.

Mains Voltage & Three-Phase vs. Single-Phase

Mains Voltage Options: - 208 V single-phase: Common in North American shops; adequate for systems up to ~150 A - 230 V single-phase: Standard in many countries outside North America - 480 V three-phase: Preferred for larger systems (>200 A) and shops with industrial power; more efficient transmission of high power - 575 V three-phase: North American industrial standard for very large systems

Three-phase vs. Single-phase: Three-phase power is more efficient for delivering high power because it distributes the power across three separate phases, reducing losses. A 300-amp plasma system requires: - If single-phase 208 V: approximately 3,900 watts per phase (at unity power factor), easily overloading typical shop circuits - If three-phase 480 V: approximately 1,300 watts per phase, easily managed

Most shops with plasma systems use three-phase power. Single-phase is acceptable for hobby or light-duty systems but becomes impractical for production work.

Power Factor: Plasma power supplies have inductive loads, which introduces phase shift between voltage and current (power factor < 1.0). A power factor of 0.8 means that 20% of the apparent power is "reactive" power (not contributing to cutting work) but still flowing through the supply. This can cause problems with utilities (demand charges) and requires careful circuit design.

Thermal & Cooling Considerations

Plasma power supplies generate significant heat due to inefficiency in the conversion process. A 300-amp supply at 80% efficiency dissipates: - Input power (estimated): 300 A × 250 V ÷ 0.8 = 94 kW - Efficiency loss: 94 kW × (1 – 0.8) = 18.8 kW of heat

This heat must be dissipated by: 1. Forced-air cooling (most common): An internal fan circulates air over internal heatsinks 2. Liquid cooling (high-power systems): Circulating coolant (water or glycol mix) removes heat more efficiently 3. Heat exchanger: In some systems, coolant is cooled externally before returning to the supply

Cooling system maintenance is critical. If cooling vents are blocked by dust or the coolant level is low, the supply will overheat and shut down (thermal cutout). Many power supply failures are due to inadequate cooling maintenance.

Selection Criteria

When selecting a power supply for a given application: 1. Amperage Rating: Choose based on the thickest material and fastest cut speed required. Oversizing provides headroom for production increases. 2. Duty Cycle: Industrial cutting may require continuous operation (40 A continuously for hours). Hobby shops can accept intermittent duty (cut for 10 minutes, rest for 5 minutes). 3. Mains Power Available: Match the supply voltage to available shop power. A 480-V system requires a 480-V three-phase feeder. 4. Portability: Portable systems (for field work) must be lightweight; inverter-based supplies are preferred. 5. Cut Quality Requirements: Pulsed or inverter supplies provide better quality than basic constant-current supplies. 6. Material Mix: Different materials may benefit from different regulation strategies. Consult OEM documentation.

Learning Objectives

1. Explain the function and output of a plasma power supply
2. Compare constant voltage, constant current, pulsed, and inverter supplies
3. Understand the trade-offs between supply types
4. Relate mains voltage and three-phase power to equipment capability
5. Recognize cooling and thermal management requirements

Key Talking Points

• Constant current supplies are the industry standard
• Inverter-based supplies are the future (compact, efficient, excellent control)
• Three-phase power is more efficient than single-phase for high-amperage systems
• Cooling is critical; blocked vents lead to shutdown and equipment failure
• Always check the mains voltage and phase before connecting a new system

Standards and References

ANSI/AWS C4.1-2012, Section 1.3—Power Supply Requirements:

"The plasma cutting system shall be equipped with a power supply rated for the maximum cutting amperage and voltage required by the system. The supply shall have thermal cutoff protection and shall not exceed 60% efficiency loss under full-load conditions."

NFPA 70 (National Electrical Code), Article 630—Welding, Cutting, and Allied Processes:

"Welding and cutting equipment shall be connected to the supply through a disconnecting means and shall have adequate branch circuit protection."

OEM Reference (Lincoln Electric):

"Ensure that the power supply cooling vents are clear of dust and obstruction. Operating the supply above 75°C will trigger thermal cutout."

Session Details

• Duration: 35 minutes
• Delivery Method: Didactic + equipment inspection
• Equipment: Labels on your actual power supply showing input/output ratings, cooling vents, etc.
• Technology: Circuit diagrams showing rectifier and filter stages (optional)

Discussion Prompts

1. Why is constant current regulation better than constant voltage for plasma cutting?
2. If your shop has single-phase 208 V power, what is the limitation on plasma system size?
3. What are the advantages of inverter-based supplies, and why are they becoming standard?
4. If the power supply shuts down after 20 minutes of continuous cutting, what might be wrong?
5. Why is power factor important for the utility company?

Instructor Notes

• Identify your system: Point out your actual power supply and identify its type (CV, CC, pulsed, inverter)
• Check the nameplate: Read the input voltage, phase, frequency, and output rating from the equipment label
• Discuss your shop's power: If your shop has three-phase power, explain how it enables higher-amperage systems
• Thermal cutout: Mention that modern supplies have thermal protection; if the supply shuts down, let it cool and check cooling vents
• Efficiency: Emphasize that an 18 kW heat dissipation (from the example above) is equivalent to a space heater; cooling design is not optional

Adaptations for Different Learning Styles

Visual Learners

• Schematic diagram: rectifier and filter circuit with input/output voltage waveforms
• Comparison chart: CV vs. CC vs. pulsed vs. inverter (table with rows for efficiency, cost, control, etc.)
• Photos of different power supplies with input/output labels

Auditory Learners

• Explain the difference between constant voltage and constant current by analogy: "A constant voltage supply is like a faucet with a fixed pressure; the flow (current) changes if you adjust the nozzle size. A constant current supply is like a pump that maintains fixed flow no matter the resistance."
• Discussion: what would happen if you used a CV supply (meant for oxy-fuel cutting) for plasma?
• Peer explanations of power factor

Kinesthetic Learners

• Hands-on: Identify the nameplate on the actual power supply and read the ratings
• Trace the power cable from the wall socket to the supply
• (With power off) Feel the cooling vents and discuss why they must not be blocked

Reading/Writing Learners

• Detailed notes on supply types and characteristics
• Worksheet: match supply type to application (e.g., "light-duty hobby shop" → inverter, 40 A)
• Reference card: input voltage requirements and available supply ratings

Accommodations for Neurodiversity

ADHD

• Use a comparison table: supply type | constant voltage | constant current | pulsed | inverter
• Highlight the key advantage of each supply type
• Provide a checklist for power supply setup: (1) confirm mains voltage, (2) check cooling vents, (3) verify ground connection

Autism Spectrum

• Organize supply types by a single defining characteristic: constant voltage (fixed voltage) vs. constant current (fixed current)
• Provide explicit functional descriptions: "The power supply converts wall power to plasma-cutting power"
• Include a written procedure: "To verify your power supply type, read the output regulation label on the nameplate"

Dyslexia

• Provide circuit schematics and block diagrams rather than text descriptions of supply operation
• Audio narration of supply types

Anxiety

• Reassure students that the power supply is engineered for safety; it will shut down if it overheats (design feature, not a fault)
• Emphasize that modern supplies are "smart"—they monitor themselves

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Slide Version: 1.0 Created: 2026-03-15 Last Updated: 2026-03-18