Mike asked:
> I am in the process of finally getting rid of my Sears 6.5HP Airless
> compressor for a real compressor.
(I'm jealous. My 1.5 hp unit is truely an "airless" unit...)
>
> So what does a magnetic starter do ? why do I need one ?
I saw the discussions about the compressor, but didn't see an
answer to this part.
My only reference point was the "magnetic switch" which is often
part of higher end tools like table saws. Here, the function
is so that if power goes off while the tool is running it doesn't
restart when power comes back on (takes another push of the start
button). It's basically a relay, with the external switch to
trigger closing the contacts. But that isn't the issue for
a compressor...
But I wasn't sure about the reference as a "magnetic starter".
After a bit of searching, I wound up reading:
http://www.cs.uu.nl/wais/html/na-dir/woodworking/motors.html
(it's part of the rec.woodworking faq -- this version
created in 1994! Probably a newer one posted somewhere...)
In addition to lots of other info, it says in part:
>>Motor starters are big relays mounted in expensive metal
>>boxes with heater overloads matched to the motor they start.
>>They serve two purposes: 1) The relay contacts are heavy duty
>>and are rated for the motor starting current. Delicate contacts,
>>such as those on a pressure switch, will fail if used directly
>>to start a large motor. Delicate contacts are therefore
>>wired to operate the motor starter relay rather than the
>>motor. [2 says it protects the building wiring and the
>>motor on overload.]
I think case 1 is exactly why a magnetic starter is good on
a compressor. 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.
Does that make sense? Do others agree or disagree?
Joe
flake@a3115jmf.atl.hp.com
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