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Generator For Welding Machine | What Size Generator For Welding?

Welding is a powerful metal joining process and it requires a high voltage and current supply to perform the task. Therefore, a lot of welding jobs have to be performed indoors, in a workshop, or in a garage with a stable electric power supply. It allows the welder to perform the task without worrying about running out of power or underperformance of the weld caused by a disturbance in the power supply.

But, it also becomes problematic if the welding is needed to be performed at a certain site, or outdoors. Here, finding a reliable electric wall outlet can be problematic. And on top of that, you will need to find one that matches the requirement of your welding setup. So, you cannot rely on the portability of a welding machine. Which is unless you are traveling with a generator for welding.

There are a lot of electrical generators on the market that can be ideal for welding jobs since they offer high voltage output and offer decent fuel efficiency. But, it is important to choose the right generator for your welding setup if you want the best results. Failing that might cause damage to some critical components of your welding setup. To be on the safe side, you need to pay attention to all important qualities of the generator such as size, output ports, output capacity, compatible fuel, etc.

Suitable Generator Size For a Welder

There are a lot of reasons why a welder would need to have access to a portable generator to allow remote welding jobs. However, choosing the right one according to the welding setup is crucial. If the generator power rating is too low, it can cause defects in the expensive welding setup, or even permanently damage some of the electrical components. On the other hand, an overly powerful generator would be a hassle to move around and will have a very high running cost, sometimes exceeding that of the welder itself.

To tackle these problems, you will have to choose the right size generator for the job. Here, the aspect of size refers to the output capacity of the generator. To find out the perfect size of the generator suitable for your job, you will have to consider factors like the amperage requirements, wattage rating, the fuel efficiency of the generator, etc. ‘

The problem appears when you are trying to compare your welder and its power requirements to what is offered by the generator. Since all manufacturers use different standards to show specifications, the rated output levels can vary from product to product. So, it is better to not consider the amperage output rating while you are considering a generator for welding. The only important factor here is the wattage requirement of the welder and whether the generator can provide that or not.

Here’s how you can compare the input requirements of the welder with the output offered by the generator.

Welding Wattage Requirement

There is a basic formula that allows you to relate voltage, amperage, and wattage with ease. We all know that Watts = Volts x Amps. So, you can find the wattage rating by simply multiplying the voltage with the amperage rating. But, let us try to understand what each of these factors means since it can help you to carry out the calculation more precisely.

Voltage: Voltage is technically the difference between potential energy between 2 points in an electrical circuit. So, the voltage level basically indicates the potential energy present at any point in the circuit. You can also think of it as the potential energy present in the water when it is stored at a high point.

Amperage: An ampere is a unit that represents the flow of electrical current in the circuit. So, a high amperage rating represents faster current travel and a lower rating represents slower. Amperage rating will simply give you the amount of electrical current flowing through the system of the maximum amount of currency accepted by the circuit within its safety standards.

Wattage: Unlike other parameters, wattage simply measures heat energy in an electrical system. Therefore, this is the most important parameter when it comes to welding jobs. By carrying out the calculation based on the wattage requirement of the welder, you can easily check if a generator is compatible with the setup or not.

How To Calculate Welding Input Requirement?

Now that you have understood the basic parameters that affect the compatibility of the generator with the welder, let’s see how you can actually calculate the ratings and compare them to see if they are compatible.

Calculating The Welding Power Requirement

First of all, you will have to check the power and current levels needed by your welder to operate. The best way to check that is the operator’s manual which comes with all standard welding machines. Here you can find both, the voltage as well as the amperage rating of the welder. The voltage rating usually has a tolerance of a certain percentage, so make sure you also consider that while calculating the wattage.

For example, if the voltage rating says 220 Volts with 15% tolerance, you will have to consider 253 Volts in the calculation. The added tolerance will ensure that the generator you are choosing can handle the welder at its peak power requirement.

After that, you will need an Amperage rating to put into the equation. The standard highest input current for 110 Volts is approximately 46.3 Amps. So, the approximate wattage requirement for a 110 Volts welder would be about 5856 Watts. But, keep in mind that this is just a preliminary rating and you need to add a safety margin which is about 30% more.

So, the 30% addition to 5856 Watts adds up to 7612 Watts. But, it is always better to round up the calculation to a higher point to increase the factor of safety. Therefore, for a 110 Volts welder, you will need a generator that can offer an output of around 6000 Watts. And for the added 30% which is needed for starting the machine and increasing power spikes, it should be around 2000 Watts higher. So, the peak wattage capacity of the generator should be around 8000 Watts.

If you carry out the same calculations for a 220 Volts welder, you will find the most suitable option for a generator is the one that offers about 8500 Watts wattage rating and about 11000 Watts peak wattage capacity. Even if you can’t find the information in the operator’s manual, you can easily find the power and current input requirements stated on the welder itself.

What Are The Differences Between Inverter and Transformer Welder?

Another thing that you need to keep in mind before buying a generator for your welder is the type of welder you are currently using. Your welder can either be a transformer welder or an inverter welder. While it may not affect the output results of the welder at all, it can definitely create problems in terms of input and generator compatibility. The main reason to consider this factor is the fluctuations caused in the power levels which should be supported by the generator.

For almost all types of welding jobs, there are bound to be continuous fluctuations in the power levels. These distortions are also calculated in a percentage tolerance which is approximately 5% in most cases. If you are working with a transformer welder, you don’t have to worry about harmonic distortions. Almost all modern generators are compatible with transformer welders without any problems.

The issue arises if you have an inverter welder, which is also quite common in the industry.   The control circuits of an inverter welder are susceptible to damage caused by harmonic distortions. To counter that, the design of an inverter welder includes capacitors to minimize the distortions. And to compensate for that, the generator must have inverter filters so that they can be paired with inverter welders.

Factors That Affect The Choice Of Generator For Welding

Apart from that, there are a handful of external factors that also affect your choice of generator for welding. Factors like installation position, necessary tools, noise levels, etc should not be undermined since you probably will be using the same generator for the next decade or so. Therefore, make sure you keep an eye on the factors mentioned below to make the right choice for a generator for your outdoor welding jobs.

1. Installation Position

The installation position of the generator can actually impact its performance and compatibility with the welding job. Due to the absence of Oxygen at higher altitudes, fuel generators such as gasoline, propane, or diesel generators offer reduced performance efficiency. And with that, the wattage rating also drops with an increase in altitude. You can consider around a 3.5% percent drop in efficiency of the generator with every 1000 feet increase in installation height.

2. Added Tools and Accessories

You may want your generator to power some other tools and kits apart from the welder, which is not surprising since welders usually need a lot of other tools too such as a portable grinder, cooling fan, lights, and some other necessary equipment such as a laptop, smartphone, LED display, etc, As the power requirement increases, you will have to increase the output capacity of the generator as well before you make the choice. For operating heavy-duty tools like saws, drill machines, or grinders, you will need about 2000 Watts extra power on top of the previously calculated running wattage and peak wattage rating. You can also go for a secondary, smaller generator for other smaller applications and keep the primary one exclusive for welding to possibly reduce the initial investment.

3. Overall Run Time of The Generator

As you may already know, electrical generators run on fuel like gasoline, propane, or diesel. Therefore, each generator has a fuel tank. So, you can basically get an approximate run time of the generator to know how long you can use the unit before its tank requires a refill. If you are going with an efficiency option, you can get up to 10 hours of run time on a generator before it needs to be refueled. This is perfect for outdoor applications, especially in places where other sources of power are not available. As the output capacity of the generators increases, their overall run time goes down. So, larger generators might only offer up to a couple of hours of runtime. Thus, they are considerably more expensive in terms of running costs.

4. Noise Levels

Generators work in a similar fashion as a fuel engine, except the brake power is used to create electricity instead of pushing the vehicle forward. So, generators also have a combustion chamber where a mixture of fuel and air is compressed and then combusted to generate power. As a result, generators can get pretty loud. Apart from that, you also need to consider the exhaust gasses coming out of the generator which is pretty close to what you see in the exhaust of vehicles. Therefore, you need to choose a generator that you can install at a considerable distance from where you are working. As for the noise levels, make sure that the generators are not above 80 to 90 dB noise levels since it can get quite harsh paired with other sounds in the workshop.

5. Compatible Extension Cords

Another factor that affects the choice of generator for welding jobs is their compatibility with power extension cords. As we saw earlier, it is better to keep the generator away from the place of work to avoid exhaust gasses and noise. So, an extension cord becomes necessary for outdoor jobs. We have a reference chart for compatible extension cords based on the wattage rating of generators provided by the National Electrical Manufacturers Association. So, if it’s not possible to plug the welder directly into the generator, you should get an extension cord by following the gauge rating provided here.

Wattage Rating Suitable Length For 10 Gauge Cord Suitable Length For 12 Gauge Cord Suitable Length For 14 Gauge Cord Suitable Length For 16 Gauge Cord
2400 Watts Up to 250 feet Up to 150 feet Up to 100 feet Up to 75 feet
4800 Watts Up to 125 feet Up to 75 feet Up to 50 feet Up to 25 feet
7200 Watts Up to 60 feet Up to 35 feet Up to 25 feet Up to 10 feet
9600 Watts Up to 30 feet Up to 15 feet Up to 10 feet Not Suitable

Which Welding Generators Are Suitable For Your Job?

Now, you must be familiar with the process of how you can find the right generator based on the specifications of your welder as well as the output capacity of the generator itself. But, instead of going through complex calculations, you can simply refer to the comparison table that we have created for you. Here, we will compare the approximate generator wattage directly with the welder’s amperage rating. So, you can follow the wattage rating provided here before buying the generator.

Approximate Welder Amperage Minimum Required generator Wattage Recommended Generator Wattage
Less than 100 Amps 3000 Watts Up to 4500 Watts
120 to 160 Amps 4500 Watts Up to 6500 Watts
180 to 200 Amps 6500 Watts Up to 8000 Watts
210 to 250 Amps 10000 Watts Up to 13000 Watts


If you are looking for an ideal pick for a generator for outdoor welding jobs, you have arrived at the right place. In this guide, we have covered the basics of a generator, their compatibility with welders, and steps to how you can find out the perfect option for your welder. Therefore, you can easily pick up the best size generator for your welder once you go through our guide. We also have a reference chart in case you want a quicker approach for standard welder specifications. However, make sure that the generator you are choosing has at least 30 to 50% more power output rating than what is required by the welder. While it may increase your running costs, it is certainly a good call for long-term use and future upgrades.

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