From: clewis@ferret.ocunix.on.ca (Chris Lewis)
Newsgroups: rec.woodworking
Subject: Re: developed vs rated hp
Date: 30 Sep 92 21:23:39 GMT
Distribution: na
Organization: Elegant Communications Inc., Ottawa, Canada

In article <1992Sep29.154830.7703@porthos.cc.bellcore.com> patter@dasher.uucp (24224-guthrie) writes:
>In article <5824@dove.nist.gov> wack@ariel.ncsl.nist.gov (John Wack) writes:

>>Forgive me if this has already been discussed to death or is in the FAQ,
>>of which I don't have a current copy.  My questions are: what is the
>>real meaning behind "developed HP" and, if the meaning is what I think
>>it is, should the use of "developed" as opposed to "rated" on a power
>>tool's description incline one to be, for lack of a better word, 
>>suspicious, like suspicious of its quality?

>You are correct. I believe that Bennett Leeds can provide as much detail
>on this as you could possibly want (he was very informative in advising
>me on my router purchase). 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.

That must mean that you don't have a router...  ;-) *All* routers are rated
in DHP.  Certainly anyone advertising a 3HP router is.  (Except possibly
the Freud, (I think it was the Freud) which has a 220V plug)

>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.

"Motorized" doesn't necessarily mean "universal".  It seems more to
be just a jargon term for a particular "grade" of tool.  Many benchtop
saws are labelled "motorized", but a lot of these simply have (standard
formfactor) induction motors on a mounting bracket.

[Much like "contractors saw" is also used as a term to refer to
belt-drive table saws, that often have motors mounted externally.]

Furthermore, universal motors *do* produce more "real" horsepower per
pound than induction motors usually do.  Certainly you wouldn't want
to have portable power tools with induction motors - they'd weigh a ton.

Yes, they're usually louder (compare a router to a high-end table saw),
but not always objectionably so.  I have a 15A universal motor in
my table saw, and it's not that much louder than many induction motor
saws.  It's more a function of RPMs.  And universals are often way up
in the 10's of thousands, whereas induction motors are some factor
of 3600.  I think my saw's motor is actually around 3600 RPM - it's
geared *up* for its rated 5500 RPM.

>While they're fine for things like jig saws, you don't want them
>in something like a table saw or band saw.

They're not merely "fine", they're essential for portable power tools.
Induction motors are "commodity" items, better suited for high power,
continuous duty, standard formfactor, don't care how much they weigh,
applications.  Ie: stationary power tools.

I agree, however, you generally want induction motors on stationary
tools.  Unless the unit you're thinking of has a good track record.
(My saw is just great, thank you)

>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.

Agreed, all things being equal (efficiencies, motor type), the
plate rating on motors for amperage is the best comparison.
Here, induction motors also have to have their continuous [*]
HP rating stamped on them.  This is also trustworthy.

"Peak" or "startup" currents are frequently a trifle misleading.
They can both be well beyond the continuous rating of the unit.
"under rated load" is better.  And this is what is stamped on motors.
(though, sometimes you get other numbers too).

Induction motors tend to have constant current drain (when used
within their power curve) - it's the phase of the current relative
to voltage that determines the power produced.  It's only when the
motor is about to stall (or during startup) that the current goes up.

Universal motors tend to have extremely variable current draw.
From virtually zero with no load, to high levels under
high load.

[*] continous in terms of the motor rating.  Induction motors
are generally placed in several different categories.  From
intermittent duty thru 24-hour/day continuous.  "continuous" here means
"used in a manner approved for this motor".
-- 
Chris Lewis; clewis@ferret.ocunix.on.ca; Phone: Canada 613 832-0541
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