What Size Generator Do I Need To Run An Inverter Welder?

Did you know the wrong generator size could kill your very expensive welder?

The size of the generator used to power a welder has a significant impact. Unlike the main energy supply, the generator’s supply power might cause harm to the inverter welder’s internal electro-sensitive components

The question that should be answered is, what size generator do you need for the welder?

Consumers, aware of the influence of generator size on the welder, select the most appropriate size compatible with their welders. 

Below we’ll discuss all crucial aspects of choosing the most suited generator. 

Why Use A Generator For Welding?

Before we get into which generators to use with particular equipment, you should understand why people use generators to power their welders. One of the most prevalent reasons is a work need

This implies that some welding tasks cannot be performed indoors or even near a reliable power supply; this is where portable generators come into play.

Typically, generators run on fuel rather than electricity, so you won’t have to rely on an energy source to power your welder.

Welder Types – Who Needs What?

Generators are often divided into conventional and welder generators, which are mainly intended to operate with welders.

The latter can likewise be used for the majority of the jobs that a regular generator can, except that a standard generator generates an inconsistent sine wave.

The Welder Talk: Inverter Vs. Transformer Based

Inverter welders use smaller transformers and less power, which means any generator can often power them. First, however, you should check whether the inverter has a built-in voltage protection mechanism

Because of the ‘dirty power,’ older inverter welders couldn’t be used with generators.

Typically, the extreme voltage and frequency fluctuations may blow up the internal electronics, but inverter welders and generators can now be used together without issue.

On the other hand, a transformer welder may not function on a regular generator due to a lack of a stable sine wave or sufficient amps; in this instance, a welder generator may be required. 

Transformer welders are not affected by unclean electricity. Therefore they may function effectively with generators. 

To be sure, consult your user manual or a reseller of the equipment you’re using. Manufacturers’ suggestions may differ based on the model of your equipment.

Why It Is Absolutely Necessary!

Most welders, whether experts or beginners focus on determining the suitable wattage when selecting a generator for a welder, completely ignoring the other aspects that complement the proper generator size.

The guarantee that the welder performs its best is dependent on the generator’s smooth function.

This Is How It’s Done!

Generators, like welders, come in lots of different sizes. So there are a lot of features and options available. And you’ll need to decide if you want 120-volt output, 240 volts, or both.

The trickiest thing to watch out for is that generators are rated in total power output, but welders are rated for output amperage.

That means you need to figure out how many watts a welder needs to produce its rated amps.

Confusing? Let us rescue you!

Watts: How Many Does Your Welder Need?

There’s a fundamental math equation to move back and forth between volts, amps, and watts:

Volts x Amps = Watts

Volts: The technical definition is “a measurement of the difference in electrical potential between two points.” Think of volts in the same way you think of water pressure. It’s the available “push” that gets the electricity going.

Amps: Amperes are a way to measure the flow of electrical current. Keeping with our water supply analogy, think of amps as the flow rate in the pipes, fast or slow.

Watts: A watt measures the amount of energy needed by any device to work. As electrons flow through the circuit, friction makes heat, measured in watts.

So what you need is the voltage the welder uses, multiplied by the input amps of the welder.

Step 1: A Dive Into The Manual

First, you need to know what power and current levels your welder need to run. A commonplace to find this info is in the manual.

Here’s an example from the manual for the PrimeWeld Stick 160.

Example of how to find the power and current levels of your welder

Look at “Power voltage(V).”  That’s your input voltage.

It’s essential to go with the “plus 15 percent” for calculations to be certain your portable generator is large enough to fit your needs.

110 volts + 15% = 126.5 volts

220 volts + 15% = 253 volts

Step 2: Onto A Little Math

Second, you want the “Input current (A)”.

The highest input current on the 110-volt side is 46.3 amps.

Now you can do your math:

126.5 volts x 46.3 amps = 5,856.95 watts, a “running watts” number. But you still need to add a good safety margin for “starting watts.” An extra 30 percent is recommended.

Let’s check the 220-volt numbers.

Input current on the 220 sides is 32.9 amps.

253 volts x 32.9 amps = 8323.7 watts for your operating load on the 220 sides. As always, add a 30 percent safety margin to provide enough starting power for your machine. 

Let’s talk more about this 30 percent in a minute.

The Generator Pageant – Which Will You Choose?

Now we’ll get to the essential part of the process: selecting the correct generator for your welder. The welder’s flexibility determines the input voltage and output amp.

In most circumstances, a welder that supports TIG, MIG, Stick Welding, and Grinding will need more power to create the output required to complete all tasks.

On the other hand, a simple stick welder will require less input voltage to control the single purpose.

The needed wattage for each welding equipment is determined by the input voltage and the output amp. Therefore, various extra parameters must be considered when defining the proper wattage for inverter welders.

The Battle Of The Sizes

The size of a generator to run a welder depends on the required power of the welder. For this, you need to calculate the total wattage of the welder by the following formula:

Power Voltage (V) × Input Current (A) = Power (watts)

You will find the power voltage and the input current on the label of the welder. Use this value for finding the appropriate generator.

1. 3000-Watt Generator

If the wattage of the welder is less than 3000 watts, then the welder can be run by a 3000-watt generator. Most of the small 120-volt welders with a maximum output of fewer than 120 amps can be run using the generator with 3000 running watts.

2. 4000-Watt Generator

If the wattage of the welder is less than 4000 watts, then the welder can be run by a 4000-watt generator. A 4kW generator can sustain most small 120-volt welders with a maximum output of fewer than 120 amps.

3. 5000-Watt Generator

If the wattage of the welder is less than 5000 watts, then the welder can be run by a 5000-watt generator. 

For example, the generator with 5000 peak watts can run a 120-volts welder with maximum output under 160 amps.

4. What Does The 140 Amp Welder need?

If the power voltage of the 140 amp welder is 120-volt, then the input current will be less than 30 amps. However, the welder needs input current close to 40 amps in some cases. Therefore, a generator with running watts between 3600 and 4800 can run a 140 amp welder.

5. What Does The 220v Welder Need?

Knowing only the power voltage, in this case, 220v, is not enough to answer this question. The required power depends on both power voltage and inputs current.

For example, if the input current for this welder is 45 amps, the generator must be at least 9900 running watts.

Can You Run A Stick Welder On A Generator?

The short answer is yes as long as the generator has the output wattage to match the needs of your arc welder.

More About The Generators

Compact and reliable, a modern portable generator will power your welder and other tools at any job site and keep your lights and refrigerator on at home during power outages. Let’s look at two general categories below.

Conventional Generators for Welders:

Traditional general-purpose generators, essentially motor-driven AC alternators, produce electricity in a single step. At 3600 RPM, the alternator generates 120 volts at a frequency of 60 Hz.

Any change in this speed generates a fluctuation in voltage and frequency, resulting in harmonic distortion. Sure, the governor will strive to keep the RPM constant, but any considerable shift in load will result in a transient spike up or down.

Traditional transformer-based welders function well with standard generators, but the electricity does not satisfy clean requirements. You should not use this type of generator to power inverter-based welders that need 5% or less THD (Total harmonic distortion).

Inverter Generators for Welders:

It turns out that the same inverter technology that provides steady output to welders also assists generators in producing clean electricity in three steps:

  • Using an engine-driven alternator, generate high-frequency alternating current
  • Convert alternating current to direct current
  • Invert direct current into a lower and more stable alternating current supply.

AC starts with a high energy source, giving the inverter greater control over the end output. The result is a steady sine wave with minimal THD (less than 5%), ideal for inverters, traditional welders, and other sensitive devices.

Other Factors To Consider 

After solving the crucial parts of this puzzle, you need to fill in the gap with extra yet important components. These several factors affect your choice of getting yourself the right generator.

Higher The Altitude, Fewer The Watts

There is less oxygen at high elevations. As a result, engines powered by gasoline, diesel, or propane operate less efficiently and provide less power. At high elevations, your welding generator will produce fewer watts than it would at sea level. 

Generator manufacturers recommend allowing for a 3.5 percent power loss for every 1,000 feet of elevation.

It may be scarcely visible or significantly less forceful depending on the elevation. High-altitude kits are available from generator manufacturers.

Is The Run Time Enough?

Some can run as long as 8-10 hours, while some big generators might only last a couple of hours between refills if they’re working hard.

You need to consider the workload and its frequency before purchasing the generator. Constant refills will be frustrating and unpleasant. 

Noise – Your Ears Might Bleed!

Although not quite as loud as other tools and automobiles, generators are noisy. The noise is a real bummer in a populated society and can upset the neighbors big time!

To determine how loud it is, look at its dB rating. Anything above 90 dB is harmful to one’s hearing. Drag racers, artillery, jet aircraft, and hunting rifles with decibel ratings of 120 or above are practically deafening.

You Almost Forgot…!

Do not forget to consider the additional power needs of any fans, lights, and compressors you may use when welding.

You’ll need power generators that can supply double your welder’s maximum watts in a team arrangement, so you’re not out of luck once you start grinding and cutting with machines that demand over 1800 watts each.

Making It Simpler For You!

Here’s a quick reference table we’ve put together to give you an idea of what size generator you should be aiming for, depending on your welder’s current level.

Welder Current LevelMinimum Generator SizingRecommended Generator Size
Up to 160A7kva 0r 7000 watts8000+ watts
180–200A8kva or 8000 watts10,000+ watts
210-250A13kva  or 13,000 watts15,000+ watts
*These values are merely an estimate; they may vary for your devices

Free Yourself And Weld Outside

Some of you are looking into what size generator to use with an existing welder, while others already have a generator and want to know what size welder it can handle.

In any case, you can now make an educated selection based on the minimum watts necessary to run a welder at maximum capacity. So before you go out and get yourself a generator, do your research on the power requirements you have. 

Remember that acquiring something with greater power-producing potential is preferable to acquiring something with less. It is better to be safe than sorry!

These generators allow you to increase your abilities to repair and construct in ways that would otherwise be impossible.

It’s time to bring your welder out of the shop and into the fresh air! 

What Are You Waiting For?

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