What Size Generator Do You Need To Run A 140 Amp Welder?

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Whether you want to build a greenhouse in your garden or help a friend whose truck has broken down on the trail, you’ll need a welder. You’ll also need a portable generator to run it because there aren’t any power sockets out in the fields. 

But what size watt generator should you get and what do you need to know about getting the right one? We’re answering all this and more. 

In short, a 3600 to 4800 watts generator maximum output will get the job done. However, there is a lot more to getting the correct portable generator. Read on for this information. 

Why Size Matters

If the generator is too small, you’ll kill your welder. But if it is too big, it will cost too much to run, require significant effort to move, and unnecessarily take up a lot of space. Therefore, it is super important to find the perfect size for you. 

Here’s How To Figure Out What Size Generator You Need

Now, math can be a little scary but this simple formula will make your life so much easier. With just a few clicks on a calculator, you can figure out exactly what generator you need. 

Volts x Amp = Watts

Volts or Voltage is defined as the difference in electrical potential between 2 points. It’s a bit like pressure. Think of volts as the nudge that is responsible for the flow of electricity. 

Amp or Ampere is the unit for electric current. It is the rate of flow of electricity. 

The last part of the formula is watts. This is the part that will tell you what generator you need. 

So all you need to find out the ‘watts’ is the voltage of the welder you’re using and its input amps. Both are available in your tool’s information manual. The volts or voltage are often referred to as power or input voltage. Each means the same thing in this context. 

If the manual lists a range, add the upper limit for your calculations to stay on the safe side. This will look something like ‘± 15%’ or ‘±15 volts.’ Manufacturers may refer to this range as ‘specified tolerance.’

Once you’ve got the amperes, plug in the values to the formula and get an answer. The number you get is referred to as the ‘running watts.’

Generator makers recommend adding up to 30% to this figure. This is because power tools need a lot of watts to start. While the ‘running watts’ will be enough to keep it working, it will not be enough to get it started. 

The only exception to this rule is if you’re using a value labeled ‘I1max’ The ‘1max’ notation means main input power and includes starting watts. You don’t need to add an extra 30% here. 

Volts x Amp = Watts

Inverters Vs. Transformers

Once you’ve figured out what generator specifications work best for your situation, you have to decide whether you want a transformer or an inverter

The latter is often described as ‘dirty.’ It has repeating and small fluctuations in power level while the engine is running. This means that it has the potential to damage any number of sensitive electronic components inside your welding machine. 

The technical name for these fluctuations is ‘harmonic distortion.’

Smaller generators are more likely to have this issue. Unfortunately, these are the kind of machines you’ll be using for your 140 amp welder. 

Even so, there isn’t a guarantee of harm. There is a good chance you’ll get the job done without any complications. However, you should know that there is an albeit small but credible risk. 

Transformer-powered generators are way better in this regard. They don’t have as much harmonic distortion and pose less risk to your welder. 

Other Factors To Consider When Purchasing A Generator

For a 140 amp welder, you’ll need a generator with around 3600 to 4800 watts powered by a transformer. But in addition to getting the right size and type of generator, you also need to consider environmental suitability. 

Not all generators can work on every terrain. You need to choose yours carefully. Just because you’re meeting the first two metrics doesn’t mean you will have a good time with your machine. Consider the following factors. 


We all know there is less oxygen at high altitudes. But did you know that diesel, gasoline, and propane engines don’t work effectively there? Your welding generator will produce fewer watts at higher altitudes than it would at sea level. 

Therefore, if you’re working at a height, expect the required power to go up. Add about 3.5% for every 1000 feet increase. You can also invest in a high-altitude kit. Almost all the big generator manufacturers offer them. 

Run Time 

Run time refers to the time period the generator can run at full capacity. This is important because you need to be sure your tool can last as long as you need it to. It can be quite annoying if you want to work for 5 or 6 six hours at a stretch and the generator dies after 3. You must always check that you have enough fuel to keep it running

Some of the better machines on the market run for as long as 8 to 10 hours. This is especially important if you are buying a generator for emergency use.


Generators tend to make a lot of noise when they’re working. However, some are so loud that they can affect your hearing. It is important to avoid those kinds. 

Check the information manual. Anything over 90dB is bad for you. dB ratings over 120 are as loud as hunting rifles are drag racers. 

Extra Tools

Each extra tool puts a burden on your generator. You need to figure out which ones you’ll want before you buy a machine so you can adjust the size. 

If you’re running your 140 amp welder alongside a cell phone charger, you’ll only need 10 running watts. However, if you’re using a regular 10 inch table saw, you’ll need 1800 running watts and 4500 starting watts. 

Frequently Asked Questions

How many watts does a 140 welder use?

If your welder output is 140 amps, and your welding voltage is roughly 20 volts, then you can use the formula: 140 x 20 = 2800 watts.

Will a 5000 watt generator run a welder?

The answer depends, but you can see our additional post to see if a 5000-watt generator runs a welder.

How many watts does a Lincoln 140 use?

To find this out, you will need to multiply the amps by voltage. In this case, a Lincoln 140 will use 35 x 120 = 4900 watts.

When is the best time of year to buy a generator?

Generators aren’t cheap so you need to ensure that you find one within your budget. Just ensure that you choose the best time to buy a generator as some seasons become more expensive.

Wrap Up 

You can very easily figure out how many watts you need for a welder. However, that isn’t the only thing you have to think about. Also take other factors like altitude, run time, noise, and other paraphernalia into consideration.

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