Wattage Needed for 3.5 HP Air Compressor – How Many Watts Does a Compressor Use?

A common question regarding air compressors is how much wattage they use? Users often find it difficult to work out. And so, this article will provide you with a way to calculate your air compressor wattage using your amperage and voltage values provided by the manufacturer, along with a worked example and reader questions and responses.

Table of Contents

• How Many Watts Does an Air Compressor Use?
• Calculating the Wattage of Your Air Compressor
• FAQs (Frequently Asked Questions)
• Reader Questions & Responses

How Many Watts Does an Air Compressor Use?

Your air compressor instructions (typically user’s manual) should specify the required starting and running wattages to run the compressor. If those details are not noted, you can use the guideline mentioned below.

In general, at least three to five times the amount of wattage is required to start a compressor as is needed to run it. Each type of compressor will be slightly different, so you must make sure that you note these individual differences.

Converting Air Compressor Metrics to Wattage

Because generators are typically characterized by wattage, you will need to determine these values for the air compressor to determine what size and power output you require.

Most electric air compressors will stay under 2 HP, which operates with 110-120V outlets commonly found in a home or garage. For larger compressors that run on over 2 HP, the outlet will need 220-234V outlets. This voltage impacts the size generator that will be required, with larger horsepower motors, therefore, requiring larger generators.

After determining the voltage of your air compressor, find the amperage. These details should be provided by the manufacturer and will be necessary for calculating the overall wattage. Air compressors will often detail both their running wattage and starting wattage for you, but if not, wattage can be easily calculated.

Calculating the Wattage of Your Air Compressor

To calculate the wattage of your air compressor, you will need to:

1. Find the voltage and amperages of the air compressor: You can find these individual values in the manual or detailed by the manufacturer.
   
2. Multiply voltage by amperages to calculate running wattage: Wattage is the product of amperage (how strong an electrical current is) and volts (electrical potential that sends a certain amount of force through the circuit). This combination results in your overall electrical power or wattage.
   
3. Take running wattage and multiple by 3 to determine starting wattage: Motors need a surge of power to start, and this is often 3x the amount of power that it will need while on and running but sometimes it may be more.
   
4. Use a generator that provides wattage greater than starting wattage: Make sure the generator can handle the starting wattage of the compressor so it can successfully start.

Calculating Wattage of Air Compressor Worked Example

Let’s take a look at an example:

A 1 horsepower air compressor with a motor that draws 10 amps at 120 volts.

10 amps x 120 volts = 1200 watts (running wattage)

1200 watts x 3 = 3600 watts (starting wattage)

Therefore, a 3600-watt generator would be required to start and then run this air compressor.

FAQs (Frequently Asked Questions)

Reader Questions & Responses

What’s the Wattage for a 3 1/2 HP Air Compressor?

Question

I have a 3 1/2 horsepower 10-gallon tank and was wondering what size generator ill need to have it run properly

Response

Darrell, according to www.google.com/intl/en/help/features.html#calculator, 1 horsepower = 745.699872 watts

I am not an electrician nor a motor mechanic so my advice is suspect. Yet, is it logical to think then that you will need at least 2500 running watts? Inrush will require more.

Any electrical gurus out there can help Darrell?

Cheers,

Bill

Response

I’m not an engineer…but here goes:

P=EI for the power formula in watts

Therefore, 120 x amps of the motor = number of watts that your generator will need to deliver when running the compressor.

However, a compressor is an inductive load device, and the same as a fridge when it first comes on, lights dim and there’s a power inrush until the motor comes up to designed speed. So while it comes up to speed it sucks more current than at normal running speed.

And this lower run current (start-up inrush) must be factored into the generator’s size.

Honda.ca shows this in their generator chart.

So you will wind up selecting a generator bigger than the compressor’s running watts to cover the start up load, and then maybe go to the next size bigger for winter compressor use when both the generator oil and the compressor oil is thicker – it could use the next size up to handling the load, help like having a big V8 under the hood, even though a 6 cylinder might do the job.

If you’re interested in changing compressor motor voltages visit our guide here!

If you have any questions regarding how much wattage an air compressor uses, please leave a comment below, with a photo if applicable, so that someone can help you!

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