Portable Electric Air Compressors
PSI, Oiled vs Oil-Free, Pancake vs Hotdog etc. for Home Use
Apr 4, 2009
Homeowners can make good use of portable compressors:
- Inflating car tires, basketballs.
- Cleaning work benches, electronic equipment, air filters, coffee grinders.
- Driving nail guns, impact wrenches, engraving tools.
Unlike the smaller 12 volt air compressors, these compressors
- Run off mains electricity.
- Produce higher air pressure and air flow.
- Use 1 to 6 gallon storage tanks for smooth air flow.
Popular brands include Campbell Hausfeld, Ingersoll Rand, Husky and Porter Cable.
How Air Compressors Work
An electric motor drives an air pump that compresses air into a storage tank. When maximum air pressure is reached (cut-out pressure), the motor stops. Compressed air flows out of the tank through a flexible hose to run power tools.
The operator sets the output air pressure (always lower than the tank pressure) using the compressor's pressure regulator.
When the tank pressure drops below the minimum (cut-in pressure), the motor starts pumping again.
Air Compressor Pressure
Compressors are rated according to their maximum (cut-out) pressure. This can range from 100 to 200 PSI (Pounds per Square Inch).
More important is the minimum (cut-in) pressure. A 100 PSI compressor might have an 80 PSI cut-in pressure. Even if the regulator is set to 90, it cannot deliver 90 PSI all the time. The pressure has to drop to 80 PSI before the motor starts pumping.
Most power tools run from 50 to 90 PSI. A 125 PSI compressor will have a high enough cut-in pressure to run them. Nail guns can be run as high as 120 PSI. Anyone needing to drive 3.5 inch framing nails into hardwoods should look for a 150 PSI compressor.
Air Compressor SCFM Air Flow
Air flow is measured in units of SCFM (Standard Cubic Feet per Minute). Portable compressors can deliver 1 to 5 SCFM continuously (normally measured at 90 PSI).
For light occasional use, a small 1 SCFM compressor can be enough and 3 SCFM will cover many jobs. Portable compressors aren't suited for high flow tools such as grinders or paint spray guns.
Air Compressor Motors
Portable compressors range from roughly 1 to 2.5 input horsepower (6 to 15 amps at 120 volts), 25 to 75 pounds in weight.
Medium sized 2 horsepower (12 amps, 2-3 SCFM) 50 pound compressors are a good compromise size. Large 15 amp compressors can sometimes trip household circuit breakers, and are not easily carried.
Oil-lube compressors are quieter and last longer, but require occasional oil refills. Oil-free compressors require less maintenance.
Maximum duty cycle refers to how often the motor can be on. This can range from 50 to 100 percent. A 50% motor cannot run more than 50% of the time without overheating, limiting the SCFM.
Compressor noise can range from 70 to 90 dBA, with 80 dBA being average. Compressor size doesn't affect the noise level. Some large compressors are quieter than some small compressors.
Motors typically run at 1700 or 3400 RPM (Revolutions Per Minute), with the 1700 RPM motors being quieter and lasting longer.
Storage Tank Capacity
Storage tank capacity isn't critical. Motor power, duty cycle and SCFM determines how much air the compressor can deliver. Tank size determines how often the motor will switch on and off to replenish air pressure. The larger the tank, the fewer the on/off cycles, the longer the motor's lifespan.
The shape of the tank (pancake, hotdog) isn't important.
The Best Portable Electric Air Compressor
Which air compressor is best, depends on the intended use. For inflating tires, a small 6 amp compressor is light and convenient. Running power tools require larger compressors.
Resources
- Compressed Air vs Electric vs Cordless Nail Guns
- Explanation of noise levels, American Speech-Language-Hearing Association
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