What Size Generator Do I Need for a Welder?

Should I Get a Welder Generator, or Use a Welder with a Stand-Alone Generator?

A combo welder generator is just a generator and a welder built into the same case. There isn’t anything unique about the generator side of the system. The welder is sized to use most of the power the generator can produce. when the welder is off, you can use the full capacity of the generator to power tools. For example, you can keep a light on over your work area while you weld. When you’re done welding, you can use the generator to power an angle grinder for finishing.

It’s easy to find stand-alone generators that support AC, DC positive and DC negative welding. However, all but the largest welder generators support only AC or only DC. While stand-alone AC welders are usually cheaper than DC welders, both AC and DC combo welder/generators are about the same price. TIG and MIG welder generators are available, and some machines will do both with some add-ons.

Which Type of Welder Do You Need?

Here’s a quick rundown of the differences.

AC Welding Pros

AC Welding Cons

DC Welding Pros

DC Welding Cons

The biggest disadvantage of these combo systems is weight. A 10,000 watt generator usually weighs around 250 lbs, while a combo welder and generator with that much power can tip the scales at over 600 lbs. Likewise, a 4,000 watt generator weighs between 100 and 140 lbs, while a generator welder weighs around 250 lbs. While these machines take up less space, you may find that it’s a lot easier to move your setup if you keep the generator and welder separate.

Do I Need an Inverter Generator or an Inverter Welder?

Inverter generators and inverter welders use inverters and rectifiers to modify power in different ways.

All generators have an engine that spins an alternator. This alternator makes alternating current. In a regular generator, this current goes directly to the sockets. Electrical interference and engine speed fluctuations affect the switch between negative and positive polarity. This “dirty” power can burn out electronics.

Inverter generators add a rectifier and an inverter between the alternator and the sockets. The rectifier turns the alternator’s power into direct current. The inverter turns this DC power back into AC. This separation removes polarity fluctuations, creating “clean” power that is almost identical to what you get from the grid.

Old welders send AC power directly to a transformer, which converts it into whatever electricity is needed for the weld. AC power mode is limited to 60 Hz, which is inefficient for converting power into low voltage, high amperage power needed for welding. To compensate, these machines require large, heavy transformers.

An inverter generator has a rectifier that turns AC power into high voltage DC power. In AC welding modes, an inverter turns that DC power into high frequency power, typically between 10,000 to 30,000 Hz. From there, a transformer turns that power into the high amp, low voltage power needed for welding.

High frequency power is easier to convert, so the transformer can be a lot smaller. The end result is a more efficient machine that’s a fraction of the size and weight of a transformer welder. It also allows for fine control that you can’t get from a transformer welder, resulting in better welds.

Inverter welders make heavy use of electronics, and not just for their digital displays. They also use capacitors for the inverter and rectifier. These parts are highly susceptible to damage from dirty power. If you want to use an inverter welder, you also need an inverter generator.

Can I Run a 240 Volt Welder Using a Generator?

Most 240 volt welders require three-phase power. This combines three alternating current power sources that have staggered switches in polarity, so power never drops to zero. The only generators that make three-phase power are large stationary and trailer-based units. There are portable generators that provide 240 volt power, but this is single phase. This power is intended for use with large RV air conditioners, not three-phase welders and motors.

That said, there are now transformer generators on the market designed for 240 volt single phase power specifically for use with generators. This is handy for large welders, because it means they’re compatible with 15-50R sockets. With a large enough generator, you can draw over 6,000 watts from this connection, compared to 2,500 watts from a 5-20R socket.

How Do I Get the Most Power from My Welder?

If you’re using a small welder, you may be able to upgrade the connection. Most 120 volt welders support 15 and 20 amp power sources. The difference comes from the plug and socket. The 5-20R receptacles on a generator have one socket that is “T” shaped, so it supports both 15 and 20 amp plugs.

You can usually get the full 20 amps by swapping the power cable on your welder for one with a NEMA 5-20 plug. This plug has one tine blade sideways to fit the T-shaped hole in the socket. Keep in mind that these generator sockets are wired in duplex, so pairs of plugs share the same electrical circuit. If you have something else plugged into the other socket, your welder won’t be able to draw full power.

How Much Power Do I Need for My Welder?

It takes more power to start an arc than it does to maintain it, causing a load spike when you start the weld. Electric motors also require more power to start than they need to run. If you have a wire feed welder, it needs a little extra power when you first push the trigger. This demand drops while you’re welding. Generators offer “surge power” for these starts, temporarily delivering more electricity than usual.

Here’s how much power you need for most welders:

How Much Power Does a Generator Actually Produce?

If you have a 100 amp generator, you can just pick up a generator that makes 4,500 watts of surge power and 3,000 watts of surge power, right? The truth is actual output won’t be quite that high, and you don’t want to push your generator to the limit, both for its sake and yours.

There are three things you must consider when you decide on your generator’s desired power output:

There are two other factors to consider: fuel consumption and noise. Both are usually quoted at 25 or 50 percent load. Fuel consumption may average out, since you’ll need to stop to change position or move the work piece as you weld. However, you can’t run a long extension cable between the welder and the generator, which means it’s going to be close by.

Noise ratings are taken anywhere from 10 to 30 feet away, so you’re going to be exposed to more noise than the quoted dB rating when you weld. At best, this will be annoying. At worst, you’ll need hearing protection while you work, along with all of your welding gear. It might be worth the extra money to pick up an enclosed generator or a larger generator that can run at lower engine speeds to keep sound to a minimum.

Gas Welding or Electric Welding?

Oxy-acetyline welding burns gas to heat up metal and create a welding pool. This is different from gas arc welding, which uses an inert gas to shield the weld and prevent oxidation. Gas welding seem like a great alternative to electric welding, since you don’t need a generator for welding on the go. However, this process comes with some major disadvantages:

An oxy-acetyline setup is cheaper than an electric welder. However, the added time for welds and the practice required rarely makes gas a viable alternative to arc welding.