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Compressor-related motor question

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Subject: Compressor-related motor question
From: "Karl Vacek" <>
Date: Thu, 15 Jul 2004 11:05:27 -0500
Thanks, Randall, for your (seems like anyway) annual refresher course in how
Sears, C&H, etc. flat lie to people on motor horsepower.  The big HP numbers
these guys throw around -- even HP numbers for 110 volt, under-15-amp
handheld power tools -- pure baloney !!

Now for a related question --

Decades ago, when I moved and needed to convert my big compressor from
3-phase to single-phase, I noticed that HP for HP, 3450-RPM motors were
significantly cheaper than 1725 RPM motors.  Seemed a simple choice - just
change pulleys and save some cash.  However, my old electrician pal warned
me off  -- he said the 3450 RPM motor had fewer poles and thus less start-up
torque even when "geared" back to the same RPM by a pulley change.  He told
me that even unloaded, I might have or would at least eventually develop
starting problems in compressor service.  And he got me a deal on a new 1725
RPM motor, so problem solved.

Eddie's long gone, but I've always carried that bit of lore with me, always
suspecting that it wasn't really quite that simple.  So is it true or not?


Karl Vacek

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