What Size Generator Do I Need for Mobile Welding / Fabrication Shop?
Power a mobile welding and fabrication operation with a welder, grinder, and lighting. Welding requires a large generator due to the high power draw of welding equipment. This scenario represents the minimum electrical load for field welding and repair operations.
Appliance Breakdown for Mobile Welding / Fabrication Shop
The table below lists every appliance included in this scenario with its running and starting wattage. The running watts represent continuous power draw during normal operation. The starting watts represent the brief surge when a motor-driven appliance first turns on. The generator size recommendation accounts for the largest single starting surge occurring while all other appliances are already running.
| Appliance | Category | Running Watts | Starting Watts | Surge Gap |
|---|---|---|---|---|
| MIG/Stick Welder | Power Tools | 7,500 W | 10,000 W | 2,500 W |
| Angle Grinder | Power Tools | 1,200 W | 1,800 W | 600 W |
| Fluorescent Shop Lights (4 fixtures) | Lighting | 320 W | 480 W | 160 W |
| Total Running Watts | 9,020 W | |||
Recommended Generator Type: Whole-House Standby Generator
A whole-house standby generator in the 14,000 to 20,000 watt range is the recommended solution. At this capacity, a permanently installed standby generator with an automatic transfer switch provides the most reliable and convenient power delivery. The Generac Guardian 16kW, Briggs & Stratton 20kW, and Kohler 14RCAL are popular choices in this range.
When shopping for a generator, look for the continuous (rated) wattage specification, not just the peak (starting) wattage. The rated wattage is the power the generator can sustain continuously, which must meet or exceed your running load with the safety margin. The peak wattage specification indicates the brief surge the generator can handle for starting motors, which should be at least as high as your peak starting watts of 11,520 W.
When to Use the Mobile Welding / Fabrication Shop Generator Setup
Mobile welding and fabrication operations require substantial generator power due to the high energy demands of welding equipment. A MIG or stick welder rated at 180 to 220 amps draws approximately 7,500 watts during welding and can surge to 10,000 watts when the arc is initiated. Combined with an angle grinder for weld preparation and cleanup, plus shop lights for visibility, this scenario demands a large generator. Many welders purchase a generator-welder combination unit that integrates a welder and a generator in a single machine, providing both welding current and auxiliary AC power from one engine. These combo units are purpose-built for this application and are often more cost-effective than buying a separate generator and welder. If using a standalone generator, ensure it has adequate peak surge capacity and that the power output is clean enough for consistent arc quality.
How the Calculation Works
The generator size for this scenario is calculated in four steps. First, we sum the running watts of all 3 appliances to get 9,020 W of total continuous load. Second, we identify the appliance with the largest starting surge gap (the difference between starting watts and running watts). Third, we add that largest gap to the total running watts to get the peak demand of 11,520 W. This represents the worst-case moment when the highest-surge appliance starts while everything else is running. Fourth, we multiply the peak demand by 1.25 (25% safety margin) to get 14,400 W, which we round up to 15 kW.
The safety margin ensures your generator is not running at maximum capacity continuously, which extends its lifespan, reduces fuel consumption, accounts for manufacturer specification tolerances, and provides headroom for any additional appliances you might need to add later. A generator running at 75-80% of its rated capacity operates in its most efficient and durable zone.
Frequently Asked Questions
What size generator do I need for mobile welding / fabrication shop?
Based on the appliances in this scenario, you need a generator rated for at least 14,400 W (15 kW) to handle all loads simultaneously with a 25% safety margin. The total running wattage is 9,020 W and the peak starting wattage is 11,520 W. The recommended size of 15 kW accounts for the worst-case scenario where the highest-surge appliance starts while all other appliances are running.
Can I use a smaller generator for mobile welding / fabrication shop?
You may be able to use a slightly smaller generator if you practice careful load management. By staggering the startup of motor-driven appliances and avoiding running all appliances simultaneously, you can reduce the peak demand. However, this requires constant attention and the risk of overloading the generator increases. We recommend sizing to at least 15 kW for reliable, hands-off operation.
Should I get a portable or standby generator for this scenario?
At 15 kW, a standby generator with an automatic transfer switch is the recommended solution for this load level. While large portable generators exist in this range, the convenience of automatic operation, the reduced noise of liquid-cooled standby engines, and the ability to run on natural gas or propane make standby generators the superior choice for loads above 7-8 kW. The investment in professional installation pays for itself in convenience and reliability.