When it comes to welding, using the right equipment is essential to get the job done properly. If you’re working in a location that doesn’t have access to electricity, a generator is one of those pieces of equipment.

Choosing the perfect generator for your welder can be daunting, considering all the available options on the market. Do you need a welder generator, a standard generator, a diesel-powered generator, an inverter generator?

There are a couple of things to consider, like portability, fuel efficiency, and power quality. But the most important thing is to make sure it has enough power for you to run your welder at max capacity.

So, let’s dive into how to pick the best generator for your welder. If you haven’t got a welder yet, check out our guide on choosing the best welder for you.

What Is a Generator?

A generator is a device which converts mechanical energy from another source into electrical energy for use in another circuit.

How Does a Generator Work?

A generator uses an outside fuel, in this case diesel, gas, or propane, to create mechanical energy, which is converted to electrical energy.

Mechanical energy is made when the external fuel is burned. Similar to how a car’s engine works, fuel combustion inside the generator creates an explosion, which moves the pistons and makes the crankshaft spin.

This movement creates kinetic (mechanical) energy, which is forced into an alternator, where a magnetic field converts it into an electrical current. The electric current is used to power a device plugged into the generator.

Why Do You Need to Use a Generator?

There are a few reasons you might need to run your welder off a generator:

• You need to repair a gate or fencing that’s nowhere near your house
• Your shed or garage isn’t wired with electricity 
• For one reason or another, there isn’t a nearby (suitable) power source

What it boils down to is that you don’t have access to the needed power, and your only other option is to use a generator.

Plugging your welder into a power circuit is much easier and cheaper, so if you don’t have to use a generator, don’t. On the other hand, don’t try to run your welder off a 50m extension cord because that will cause a whole other set of issues.

What Size Generator Do You Need to Run Your Welder?

When choosing a generator for your welder, the size will depend on how much input power your welder needs. How many watts does your machine need to run at its rated amperage output?

If you don’t want to work the math out for yourself, we’ve put together a list of recommended generator sizes for welder outputs.

Welder Amperage Output	Recommended Generator Size
Up to 140A	8kVA
140A – 180A	10kVA
180A – 200A	11kVA
200A – 250A	13kVA
350A+	20kVA

If the welder has built-in power factor correction (PFC), the recommended minimum generator size will be a lower kVA than if it didn’t have PFC.

We also include a minimum recommended generator size on all our machine data sheets, so if you’re unsure, you can find it in the specifications section.

The size of your generator will depend entirely on how many watts your welder uses. You’ll need a generator with slightly more watts than the welder you’re plugging into it.

How Many Watts Does Your Welder Use?

There are two different wattages that are relevant when picking a generator. The minimum number of watts required to run the welder and the ‘starting’/‘surge’/maximum watts.

The starting or surge wattage is generally around 30% more than the minimum the welder can run on.

When choosing a generator, you’ll need to make sure it has the same or more wattage than the surge watts. If not, you’re going to have issues with getting the welding arc ignited and running at max capacity.

Finding Your Welder’s Wattage

A welder’s output is listed as an amperage on its technical data plate. That means you’ll need to convert the listed amperage to watts before you can pick your generator.

Here’s one relatively simple formula to make the conversion:

volts x amps = watts

That means you’ll need the voltage the welder uses multiplied by the input amperage of the welder.

To find your volts, look for ‘Input Voltage’ or some variation of this title. UNIMIG welders specify ‘Primary Input Voltage’ on our data sheets or U1 on the data plate. If the input voltage lists a number and then a percentage, be sure to add the percentage before multiplying by the amps (e.g. 240V +15% = 276V).

To find the input amperage, look for the label ‘I_1max’ or a variation of this. UNIMIG’s online data sheets are labelled ‘Imax (A)’, while the data plates are labelled ‘I_1max’.

The label ‘I_1eff’, ‘Input Current/Amps’, ‘Ieff (A)’ or a variation of this label refers to the average amperage input over a 10-minute period. This measurement is used to determine the plug size of the machine.

You don’t want to use this number for your generator, as the average input is usually much smaller than the max, and you’ll end up with a generator that won’t start your machine.

This is what a typical data plate will look like:

Note

Not every online data sheet may include the input amperage, but it will always be available on the machine’s data plate (in Australia, it is legally required to be listed). You can find your machine’s data plate on the back or bottom of it.

Using the RAZOR TIG 200 AC/DC as an example, the formula will look like this:

240V x 25A = 6000W

Be careful when working out the wattage for your welder, as you also don’t want to use the output values, usually labelled with I2 or U2.

Converting Watts to kVA

Now that you’ve determined the welder’s wattage, it’s time to convert that into a usable kVA number. The good news is that working this number out is super easy.

Take your wattage, in this case, 6000, and divide by 1000. This will give you the kilowatts of the welder, which is the same number as the kilovolt-ampere, or kVA.

That means the RAZOR TIG 200 AC/DC has a running kVA of 6. Now, because the start or surge current needs to be considered, once you’ve worked out the welder’s base kVA, it’s a good idea to add another 30% to ensure the machine will start, which looks like this:

6kVA x 0.30 = 7.8kVA

We recommend an 8kVA generator for the RAZOR TIG 200 AC/DC, so the math checks out.

If you’re not sure what size generator to get, it’s always a good idea to size up just to be safe. You don’t want to break your welder or the generator trying to run something it can’t handle.  

Dirty vs Clean Power

As well as having the output capacity to run your welder, there are a few other things to consider when choosing a generator.

One of the more important factors is whether the generator is running on ‘dirty power’. When it comes to running sensitive electronics, like those in inverter welders (and computers), the cleaner the power, the safer (and better).

The standard household mains power that all your kitchen appliances run off is alternating current (AC). Because it’s AC, it forms the pattern of a sine wave. Perfectly clean power is a perfect sine wave and looks something like this:

The mains power that your house runs off is usually close to perfect and presents no issues. In comparison, dirty power is less safe and can cause problems, and is typical when using a portable generator to power your equipment.

Dirty power is electricity that has fluctuations, distortions, or irregularities in its waveform. These fluctuations in the power are called ‘harmonic distortion’ and lead to spikes or drops in voltage. The AC sine wave, with distortions in it, starts to look like this:

Harmonic distortion is measured in units of Total Harmonic Distortion (THD) as a percentage, for example, 6% THD.

Generator power can often be dirty because of several things, including:

• The quality of the generator
• Fluctuations caused by the start-up and shutdown of the engine
• Interruptions in the fuel supply, whether it runs out of fuel or there is a lull or pause in the supply
• Generator size in comparison to the load on it (how much power the plugged-in machines are trying to draw)
• The use of multiple machines and tools from the generator at once
• Poor maintenance of the generator

Regardless of the reason for the THD in the generator, it’s bad for your inverter welders. Inverter welders come with IGBT circuit boards installed, which work to provide better performance, efficiency and reliability from the power source. They are, however, also a sensitive electrical component and can be easily damaged by dirty power.

The maximum acceptable THD rating on a generator is generally considered to be 6%. Less is better, but any higher than that is unacceptable if you don’t want to damage your welder.

If you’re running a transformer welder from your generator, you won’t have any issues running on dirty power. They’re much more forgiving, and almost any modern generator can run a transformer welder.

Standard Generators vs Inverter Generators

There are a few different types of generators that you can get, including standard (conventional) generators and inverter generators. The one that best suits your needs will depend on the use case.

The main difference between these two welders is how they produce power. While they both create an AC sine wave, how they get the final AC output differs. 

Standard generators can run on petrol, diesel, or propane and use a mechanical alternator to produce AC power. The engine in a conventional generator runs at a constant speed to make this power.

Inverter generators use an alternator to produce AC power, but then they convert the AC into a direct current (DC) before a microprocessor inverts the DC back into cleaner, more stable AC power. The engine in an inverter generator can vary (or throttle) depending on the electrical demand.

The three step process that an inverter generator goes through means the AC is higher quality, more consistent, and more reliable – similar to your household mains power.

There are a few things to take into consideration when choosing between the two types of generators.

Power Quality

Inverter generators produce cleaner AC power, so if you’re using an inverter welder, they’re going to be the safer choice, providing a higher-quality power supply to the sensitive electrical components.

Standard generators, depending on the THD rating of the generator, might produce ‘dirty’ power. 

Amount of Power

Generally speaking, standard generators can produce more power and have larger kVAs (wattages) than inverter generators. They’re ideal for when high power and constant demand are needed.

Inverter generators are generally designed for lower outputs and have a smaller range of available kVA sizes.

Portability

Standard generators tend to be bulkier and heavier than inverter welders as a result of their larger engines and fuel tanks that allow them to produce more power for longer. While they can still be mobile, they’re more suited to stationary setups.

Inverter welders are usually very portable, as they’re often compact and lightweight (thanks to the inverter technology inside the generator).

Fuel Efficiency & Noise Levels

Standard generators consume more fuel because their engines run at a constant speed, which also makes them louder to run.

Inverter generators are more fuel-efficient because the engine speed adjusts to the power demand placed on the generator, so they run quieter in comparison.

Both types of generators have pros and cons, and which one you’ll need will depend on your use case.

Other Considerations When Buying a Generator

On top of deciding whether you want a standard or inverter generator, there are a couple of other things to consider when picking a generator in general.

Run Time

How long does the generator need to run continuously? Some generators will run at their max capacity for up to 10 hours on a full tank, while others might only last a handful of hours before needing a refuel.  

Extension Leads

Will the machine need to run off an extension cord to reach the workpiece from the generator? Where possible, you should avoid using an extension cord so that there’s no risk of voltage drop.

However, if an extension cord is needed, you’ll need one that’s heavy-duty enough to carry the necessary power over the distance.

See the table below as a guide based on the minimum necessary input power (in this case, 20A):

Cord Thickness/Cable Size (mm2)	Maximum Length of Cord (m)
2.5	30
4.0	50

Using an extension lead that is too small, or using it over a longer distance than recommended, will lead to voltage drops and cause problems with power supply.

Extra Accessories

You’ll need a bigger generator if you plan to run more tools than just your welder, like a grinder or drill. If you need an 8kVA generator just to run your welder, and then some of that power gets rerouted to run your other power tools, your welder isn’t going to run very well, if it runs at all.

The average starting wattage for power tools like drills, saws, sanders and grinders is around 2000. If you need 8000 watts for your welder, you’re looking at needing at least a 10kVA generator to run everything smoothly.

Altitude

If you’re planning to be welding off the grid at high altitudes, keep in mind that your generator may produce less power. Petrol, diesel, and propane engines will run less efficiently and make fewer watts due to the lower oxygen levels.

Can You Use a Small Generator for Your Welder?

One of the most common questions that people ask is, ‘Can I use a smaller generator?’ Will a 3kVA or a 5kVA generator work for a 180A welder? Technically, the welder might run, and that’s a very big might, but the reality is no, a smaller generator won’t work.

Using a generator with a lower power output than the necessary power draw for the welder you have connected is going to cause several issues.

The biggest problem is that it could cause damage to your generator or to your welding machine. The extra strain on the generator will increase the chances of power spikes, which in turn will damage the internal components of your welder or cause frequent shutdowns of the welder or generator.

If the welder does power up and run (which it likely won’t), the output from the welder will be severely reduced. For example, if you were trying to run a 180A on a 6kVA generator, you’d likely have the welder’s max amperage capped at closer to 100 amps. The generator won’t produce enough power for the welder to reach its full output.

If you plan to run more than just the welder off the same generator, you’ll face the same issues tenfold.

Picking the proper generator for your welder can significantly impact the quality of your work. Factors like the power output, generator type, portability and fuel efficiency will impact your choice.

While it may be expensive upfront, if you get something that’s too small, you won’t be able to run your welder at all.