Stick Welder Generator Sizing: Wattage, Amperage & Generator Types

A stick welder running 1/8" rods at 130 amps needs a minimum 7,000 watt generator. Running 5/32" rods at 200 amps requires 10,000-12,000 watts. The formula is simple: multiply welding amps by arc voltage (typically 25-35V for stick), then multiply by 1.5 to account for efficiency losses. That gives you the minimum continuous wattage rating you need.

Undersizing a generator causes voltage sag that makes the arc sputter, the rod stick, and the welder underperform. Oversizing by 20-30% gives you headroom for starting surges, running other tools simultaneously, and operating within the generator’s duty cycle without strain.

The Calculation

The power equation for stick welding:

Watts = Welding Amps x Arc Voltage x 1/Efficiency

Breaking this down:

Welding Amps: The actual amperage you set on the welder. Not the welder’s maximum rating, but the amperage you’ll typically run.

Arc Voltage: Stick welding arc voltage ranges from 20-35V depending on rod type, arc length, and amperage. A reasonable average for calculation is 25-30V.

Efficiency factor: Stick welders (especially transformer types) are 60-75% efficient. Using 1/efficiency, that’s a multiplier of 1.33 to 1.67. A multiplier of 1.5 is a safe middle ground.

Example Calculations

Surge Watts vs Continuous Watts

Generators are rated for both surge (starting) watts and continuous (running) watts. The surge rating is the peak power available for a few seconds during startup. The continuous rating is what the generator delivers steadily.

For welding, use the continuous rating. Stick welding draws sustained power for the duration of each rod burn (typically 30-90 seconds per rod). A generator rated at 8,000 surge / 6,500 continuous watts delivers only 6,500W during welding.

Generator Types for Stick Welding

Conventional (Open Frame) Generators

Standard portable generators with a gasoline or diesel engine driving an alternator. They produce 60 Hz AC power, which the welder converts to welding output.

Pros:

• Cheapest per watt
• Simple, serviceable design
• Available at every hardware store and rental shop
• Work fine with transformer-based stick welders

Cons:

• Heavier than inverter generators at the same wattage
• Louder (70-80 dB at rated load)
• Less stable frequency and voltage under load changes
• Some produce “dirty” power that inverter welders don’t like

Inverter Generators

Produce AC power, convert it to DC internally, then re-synthesize clean AC at precise frequency. The electronic regulation produces very stable voltage and frequency.

Pros:

• Clean, stable power output
• Lighter than conventional generators (typically 30-50% lighter)
• Quieter (50-65 dB)
• Better fuel efficiency at partial load
• Work well with both inverter and transformer welders

Cons:

• More expensive per watt (often 2-3x the cost)
• More complex electronics (harder to repair in the field)
• Maximum wattage typically tops out at 7,000-9,000W for portable units

Engine-Driven Welders

A generator and welder built as one unit. The engine drives a welding generator that produces welding output directly, plus auxiliary power outlets for tools and lights. Common brands include Lincoln Ranger, Miller Bobcat, and Hobart Champion.

Pros:

• Purpose-built for welding, no compatibility issues
• Welding output is clean DC or AC, independent of generator power quality
• Auxiliary power (120V/240V) for tools, lights, grinders
• Available in 200-400 amp welding output with 8,000-12,000W auxiliary power
• Standard equipment on construction sites and pipeline jobs

Cons:

• Expensive ($3,000-10,000+)
• Heavy (400-1000+ lbs)
• Requires dedicated trailer or truck bed mount
• Overkill for occasional home use

Choosing Between Types

Welder Types and Generator Compatibility

Transformer-Based Stick Welders

Older-style welders using a heavy copper/iron transformer. These are tolerant of generator power quality. They draw high inrush current at startup but run steadily once operating. Most conventional generators work fine with transformer welders.

Generator consideration: Allow for startup inrush of 2-3x the running wattage. A transformer welder drawing 5,000W while welding may briefly pull 10,000-15,000W at startup. The generator’s surge rating must cover this.

Inverter Stick Welders

Modern lightweight welders using electronic power conversion. More sensitive to power quality than transformers. They draw relatively low inrush current but may shut down or produce error codes if the generator voltage or frequency fluctuates too much.

Generator consideration: Inverter welders prefer clean, stable power. They work best with inverter generators or high-quality conventional generators with AVR (Automatic Voltage Regulation). Cheap generators without AVR can cause inverter welders to fault.

Some inverter welder manufacturers specify a minimum generator size in their manuals. Follow that recommendation. A common guideline is a generator rated at least 1.5x the welder’s maximum input wattage.

Specific Example

A typical 200-amp inverter stick welder has an input rating of about 5,500W at maximum output. Following the 1.5x guideline: 5,500 x 1.5 = 8,250W minimum generator. An 8,000-10,000W generator with AVR is the sweet spot for this welder.

Duty Cycle Impact on Generator Sizing

Duty cycle is the percentage of a 10-minute period that the welder can operate at a given amperage. Generators have their own duty cycle (continuous vs intermittent rating), and the welder’s duty cycle actually helps the generator.

How Stick Welding Duty Cycle Helps

Stick welding is inherently intermittent. You weld for 30-90 seconds (one rod), then stop for 15-30 seconds to chip slag, change rods, and reposition. In practice, the welder draws power about 50-60% of the time.

This intermittent loading means the generator gets rest periods between rods. A generator rated at 7,000W continuous can effectively support welding that peaks at 8,000-9,000W because the rest periods prevent thermal overload.

Don’t Count On It

While stick welding’s natural duty cycle helps, don’t intentionally undersize the generator based on this. If you’re running fill passes on heavy plate and burning rods back to back with minimal cleanup time, the duty cycle approaches 80-90%. Size the generator for the worst case, and let the natural rest periods provide extra margin.

Power for Additional Loads

On a field job, the generator runs more than just the welder. Grinders, lights, fans, and other tools draw from the same power source.

Add the tool wattage to the welder wattage to get the total generator requirement. Running a grinder while the welder is idle (between rods) works because the loads don’t overlap. Running a grinder while someone else welds requires a generator big enough for both simultaneously.

Generator Setup Best Practices

Placement

Position the generator downwind from the work area. Exhaust fumes and CO can accumulate around the welder, especially in low areas or partially enclosed spaces. CO poisoning from generators is a real and serious hazard.

Keep the generator at least 20 feet from the welding area. Use extension welding cables (not extension cords) to reach the work. Welding cables handle the high current without significant voltage drop.

Grounding

Ground the generator to an earth ground (grounding rod) for safety. The frame of the generator should be at earth potential. This prevents shock hazards from ground faults in the welder or connected tools.

Fuel

Run gasoline generators on fresh fuel. Ethanol-blended gasoline degrades after 30-60 days and can cause starting problems. Add fuel stabilizer if the generator sits between uses. Diesel generators are more tolerant of fuel age.

Keep spare fuel containers away from the welding area. Sparks and spatter can ignite gasoline vapors.

Maintenance

A generator used for field welding gets worked hard. Change oil at the manufacturer’s recommended interval (typically every 100-200 hours). Clean or replace the air filter frequently in dusty environments. Check voltage and frequency output periodically with a multimeter to verify the AVR is functioning correctly.

Troubleshooting Generator-Powered Welding

Arc is weak and rod sticks frequently: Generator undersized for the welding amperage. Reduce the welder’s amperage setting, switch to a smaller rod, or use a larger generator.

Generator bogs down when the arc strikes: The startup surge exceeds the generator’s capacity. The engine RPM drops, voltage sags, and the arc can’t establish. A larger generator or one with better surge capacity is needed. Turn off other loads before starting the arc.

Inverter welder displays fault code on generator power: The generator’s voltage or frequency is out of spec. Check voltage with a multimeter (should be 120V +/- 5% or 240V +/- 5%). Check frequency (should be 60 Hz +/- 3 Hz). If the generator lacks AVR, it may not hold these tolerances under welding load. Use an inverter generator or a conventional generator with AVR.

Generator runs fine but welder performance is poor: Check the welding cable length and gauge. Long runs of undersized cable cause voltage drop between the generator and welder. Use the shortest practical cable run and verify cable gauge matches the amperage. For 200-amp welding at 100 feet of cable, use at least #2 AWG welding cable.

Generator overheats on extended welding: You’re loading it near its continuous rating for too long. Allow cool-down periods, reduce welding amperage, or upsize the generator. Operating a generator consistently above 80% of its continuous rating shortens engine life and risks overheating.