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Re: Air Compressors

To: "'Shop Talk'" <>
Subject: Re: Air Compressors
From: Randall Young <>
Date: Mon, 12 Feb 2001 08:25:12 -0800
Joe Flake wrote:
> The pressure switch can be a much more delicate
> item, than if it had to be big enough to directly switch a
> high hp motor.  One site I read, specifically suggested
> the magnetic starter option on their larger 5 and 10 hp motors.

Makes sense to me. 
Also, compressors that use induction motors usually have an 'unload'
feature so the motor doesn't have to start under full load.  I would
_guess_ the magnetic starter also provides an interlock so the motor
doesn't try (and fail) to start under load after a power failure.

I do know that on some 3-phase applications, the magnetic starter
contains an interlock to prevent trying to start the motor if one of the
phases is missing (which may damage the motor).

Interesting observation while wandering the local Sears store the other
day : they apparently do carry some 'honest' air compressors.  I saw a
unit rated 5.5hp that put out over twice the air of a 5hp unit right
across the aisle.  But, a little motor plate examination showed it also
drew over twice as much power.

2.5 hp airless perpetual motion machine

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