From: gary_preckshot@lccmail.ocf.llnl.gov (gary preckshot)
Newsgroups: rec.woodworking
Subject: Re: developed vs rated hp
Date: 30 Sep 92 20:46:34 GMT
Distribution: na
Organization: LLNL

In article <1992Sep29.154830.7703@porthos.cc.bellcore.com>, patter@dasher.uucp (24224-guthrie) writes:
> 

> The exagerated claims made in this manner by
> some companies (notably Sears) may or may not be indicative of the
> relative quality of the product, but they are certainly indicative of a
> low standard of morality, as far as I'm concerned. I don't buy from such
> firms.
> 

Actually, it's interesting that the only flaky motor ratings I've seen
have been from US mass retailers such as the one George mentions.  I've
got a number of imported tools from Taiwan and China and every one has
an accurate, continuous-duty horsepower rating on the motor nameplates.

> Basically, though, you should ignore horsepower. Look at two items. If it
> says "motorized", don't buy it. These items have universal motors, which
> have more moving parts, produce less power, and are louder than induction
> motors. While they're fine for things like jig saws, you don't want them
> in something like a table saw or band saw.

I'll pass on George's comments on universal motors, since in their place
(like in routers) they work fine.  However, you should not ignore horsepower.
It really means something and it's meaning is precise in accurately rated
industrial motors.  If you could get the torque VS rpm curve, as published
in an example by another poster on this thread, that would be better.  But
those curves are rarely supplied by tool manufacturers.

> 
> Then, when comparing induction motors, look at the amperage draw and
> voltage. If the product of the amperage and the voltage of unit A is
> higher than that of unit B, unit A produces more power. Again, you must
> "compare apples and apples", as the saying goes. You should either ignore
> "peak" or "starting" amperage and compare the basic unloaded amperage
> draws (which are required by law to be on the data plate of the unit),
> compare the peak amperages of the two units.
> 
> I have found that the published amperage figures in advertisements and
> catalogues are directly comparable from manufacturer to manufacturer.
> 

George is right about checking the current rating, although he errs when he
calls it "the basic unloaded amperage draws...".  The actual current on the
nameplate is supposed to be the current when the motor is loaded to normal
usage (or rated) horsepower.  This is required for a UL rating for fire
protection purposes.  However, what you should do is check whether the
current rating is reasonable for the horsepower rating.  If it isn't, you
are being lied to.

There are two other things you should check.  These are "duty", and "service
factor".  If duty is "cont", this means the motor should deliver rated horse
power continuously.  If it is "spec" or "farm", or "compressor", watch out!
This means the manufacturer has rated the motor for some off-the-wall
operational scenario, like pumping up your compressor air tank once an hour.
Our friends at S***rs are prone to this.  The service factor is the number
you can multiply the horsepower rating by and still get continuous duty
service.  In other words, the motor is purposely under-rated.  I thought that
this was to allow for undervoltage operation, but another poster in another
thread opined that it allowed for duty with many start/stop cycles, which
would tend to overheat the motor due to being on the starting windings a
lot.  Either or both may be true.  The usual ratings for both parameters
on conservatively rated industrial motors are "cont" and "1.15".

G.