Subject: Re: Air Compressor

From: David Einhorn <[email-masked]>
Date: Wed, 5 Jun 1996 10:10:05 -0400

Shortly after I got married, I purchased a bunch of Sears power tools.
The self chucking drill would consistently drop bits, and died completely 
just after the 1 year warantee.  The circular saw shot sparks and died 
also after 1 year. The bench grinder's rests are as useful as thin sheet
metal rests can be.  The sabor saw lost a few parts, and now cuts pretty
much randomly.  And last but not least, when I went to build jigs for the
table saw, I found out that the slots were not parallel to each other.

My preference now is for commercial grade tools, and have sworn off of 
Sears power tools.

On Tue, 4 Jun 1996, Roger Gibbs wrote:

> The price/performance of the unit actually seemed pretty good.  I don't
> know how durable they will be. As of lately I have been avoiding Sears
> tools and "false advertising" wrt to hp ratings certainly does nothing
> to change my opinion.

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From: [email-masked] (David William Jenkins)
Date: Wed, 05 Jun 1996 21:13:13 GMT

In article <[email-masked]>, Jerry Fields ([email-masked]) writes:
>
>Sad to say, Sears is not alone on inflating HP ratings. The figures are 
>not measured, they are calculated using current and the electromagnetic 
>strength generated by the motor's windings. I have found the name-plate 
>figures much more honest about the motor's true HP...which is about 1/2 
>the advertised 'peak' hp. So, a 3hp (advertised) motor puts out about 
>1.5hp measured. If no plate is available, calculate the wattatge consumed 
>(amps times volts, say 10a @ 115v =1150 watts) and convert it to hp by 
>dividing by 746. (746 watts=1hp) In this example, the engine would be 
>rated at 1.54 hp.
>
>I suspect the 'peak' hp calculation also includes a capacitive discharge 
>from any starting or run capacitors the motor may have installed. 
>
>Check around and you will find that Sears is not the only retailer 
>playing games with hp ratings.
>
>-- 

And there's the other "con" - many moons ago in the UK, electric
motors used to be rated as _shaft_ power, i.e. what you actually
got at the pulley.  Now they're rated according to the calculation
shown above, using Watts consumed.  The actual power output varies
according to the build quality, rotor-to-field-winding gaps, etc.
On some cheap far-East motors I've seen, many Watts of input energy
goes into heating the windings and casing, so reducing output
power. 

My lathe motor is plated as 1/3HP, but doing the electrical
calculations gives a figure about 10 - 20% higher.  It was made
about 30 - 40 years ago when, perhaps, manufacturers played the
game fairly. 

David Jenkins              -- aka --             Lathyrus Computers Ltd
***********************************************************************
* All incorrect spelling and grammar is intentional.  Corrections are *
* superfluous and will be ignored.  So there.                         *

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From: [email-masked] (Greg Lewis)
Date: 5 Jun 1996 13:55:06 -0700

There was a long thread here about a year ago on compressors and I
recall one piece of advice: before you buy, go to an industrial
supplier and check for used commercial units. They don't play *Sears
math* and the units may be better built. Your Yellow Pages should list
local firms that deal in quality air equipment. As a general rule, I
have found that most tools and equipment sold in retail stores do not
equal the genuine pro stuff, but those suppliers may be harder to
find. In my area, these companies are usually listed (but no ads) in
the Yellow Pages but are found only on side streets in the industrial
parts of town. Prices may be high, but if quality is available, it is there.
___________________________________________________________________
[email-masked] 	 	 They don't Photojournalism
sequence 	 	 Call this place Department of Mass
Communication 	 An institution
     and Journalism 	      	   	     For nothing
CSU Fresno, Fresno, CA 93740-0010

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From: PPIERCE <[email-masked]>
Date: Wed, 05 Jun 1996 15:40:57 -0700

> >dividing by 746. (746 watts=1hp) In this example, the engine would be

presuming the subject  motor is operated on alternating current:

115 Volt X 10 Amps = 1150 volt-amperes (not watts)

assuming a power factor of .8, 
the input would be  1150 va X .8 = 920 watts

assuming an efficiency of .8,  
the output would be 920 (watts in) x .8 (eff) = 736 watts

The output hp would be 736/746 = .9+ hp

Of course breakdown torque, etc. may limit hp ratings.

At one time in the 1960s a given machine was marketed as a great 1/4hp, 
good 1/3hp, lousy (but passable) 1/2 hp.  Only the nameplate was changed 
(to protect the innocent?).  I believe the 1/2 hp under full load probably,
glowed in the dark

> >from any starting or run capacitors the motor may have installed.

Probably for a limited time also... Read the fine print on electric welders...

> goes into heating the windings and casing, so reducing output

Scratch out the "far East", above.  I recall oil burner motors that were about 60% 
efficient.  No one cared since PRICE was the golden calf...  The homeowner paid the 
price eventually in his electric bill.
> about 30 - 40 years ago when, perhaps, manufacturers played the

See above

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From: [email-masked] (Jens)
Date: Wed, 05 Jun 1996 21:34:15 -0700

As a matter of curiosity, I had a look at the name plate of the Baldor
motor on my lathe ... It is rated at 7.8 amps at 115 volts, it has a
claimed efficiency of 63% and a rated horsepower of 0.5.

The moral of the story - you get what you pay for .... it is probably
quite expensive for a 1/2 hp motor (I didn't buy it myself) but if you
compare it against a 2hp motor of dubious origin it's probably not so
bad.

Jens

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From: [email-masked] (Blake Malkamaki)
Date: Thu, 06 Jun 1996 00:21:43 -0400

In article <[email-masked]>,
David Einhorn <[email-masked]> wrote:

$ Shortly after I got married, I purchased a bunch of Sears power tools.
$ The self chucking drill would consistently drop bits, and died completely 
$ just after the 1 year warantee.  The circular saw shot sparks and died 
$ also after 1 year. The bench grinder's rests are as useful as thin sheet
$ metal rests can be.  The sabor saw lost a few parts, and now cuts pretty
$ much randomly.  And last but not least, when I went to build jigs for the
$ table saw, I found out that the slots were not parallel to each other.
$ 
$ My preference now is for commercial grade tools, and have sworn off of 
$ Sears power tools.

I believe the old Sears and Craftsman power tools (>20 years) were real
good.  Now I would not buy their power tools- Craftsman hand tools yes,
power tools no.

As far as compressors go-- if you want a good one that will last most of a
lifetime, get a Champion, a Curtis, or a Quincy, and be sure to verify
that it's 100% American.  Many compressors out there with American
sounding names have Chinese (or worse) pumps.  The tanks are almost all
made here as the other country's welding won't pass code.  Also seams the
slower the pump's rpms, the better and the quieter.

I just bought a 5 hp Champion two stage and I'm very happy with it.  It's
made in Illinois and has a 5 hp Baldor 1750 rpm motor and magnetic
starter.  Also an inter-cooler and 80 gallon tank.  It's great.

Blake
Blake Malkamaki, Little Mountain Ironworks, Concord, Ohio <[email-masked]>
>>Steam engines - Cletrac Crawler Tractors - Maple Syrup - Metal Signs<<
http://www.ncweb.com/users/blake

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From: [email-masked] (Peter Brooks)
Date: 6 Jun 1996 17:01:31 GMT

I'll pitch in my two cents, here.  I got a belt drive Craftsman a few
years ago, but back when a 3hp compressor actually had an honest 3hp
motor.  I run it off its own 220V circuit in my garage (what joy to have
a 100A service panel in a detached garage!) and it's been troublefree
>from  day 1.

Unless I'm running cutoff tools at 100psi, the compressor has little
trouble keeping up.  I just hung two 4 x 8 sheets of 1/2" ply in my 
garage, and since I couldn't find the 10d adapter for my Senco, I
put them in with 16 d nails.  After several bouts of tendinitis, many
caused by swinging a hammer, such a tool has a well-regarded place in
my shop.

I'm mildly embarrased to admit that I haven't checked the oil in the
compressor for quite a long time.  However, I drain the tank every time
I use the beast (it'll frequently go for weeks without being used--I don't
like air guns around my machine tools) to get the water out, and the thing
is working fine.

As far as general shop use goes, I'd recommmend the honest 3hp belt drive
system.  If you go with less power, you will eventually run out of cfm and
it's a royal pain to have to wait for the compressor to catch up.  If you
are debating between two power levels, I'd say to go with the bigger
compressor unless your current needs are *well* below the lesser machine.  I
got lucky; the Senco air nailer was one of the reasons I bought the
compressor, though I would not have regretted getting a 5hp.

(If all you want to do is air brush models, I'd skip the 5hp Ingersol Rand,
but I don't see any trouble with putting an airbrush downstream of an
oil filter on my Sears.)

Pete Brooks

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From: [email-masked] (Bob Fairbairn)
Date: Thu, 06 Jun 1996 10:13:29 -0600

In article <[email-masked]>, Jerry Fields
<[email-masked]> wrote:

> Roger Gibbs <[email-masked]> wrote:
> >[email-masked] (Jim Naylor) wrote:
> >
> >>>I certainly remember the 115v 4.5 HP shop-vac!
> 
> <snip>
> >
> Sad to say, Sears is not alone on inflating HP ratings.
> -- 
> Jerry Fields
> UW Whitewater, Whitewater, WI USA
> DoD #1697
> 
> "I'm a great believer in luck. The harder I work, 
>  the more I have of it." -- Thomas Jefferson
Snip...

I am seeing the inflated horsepower in shop vacs, Sears "stuff" and the
Cambell H???? stuff.  Where is Ralph Nader when you need him.  Take a look
a the name plate ratings on the motor, if it says "SP" or "Special"  you
will need to estimate the real HP.  Also it is interesting to see 16 AWG
wire on a  "5HP" motor; I know the wire is the fuse!

As as a side note household vacumm cleaners are now rated in amps.  Gee,
how big of a resistor can I put it there to draw 11amps!!!

Bob Fairbairn
Disbelieving Consumer
Sears Su??? Craftsman is a lie, Bob Villa sold out, and so did Norm!

-- 
"The meek shall inherit the Earth.  The rest of us                  will go to the stars." -- Heinlein?

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From: [email-masked] (Patrick Tufts)
Date: 7 Jun 1996 00:03:56 GMT

Roger Gibbs <[email-masked]> writes:
[...]
>I was in Sears last night to pick up something for my in-laws and
>decided to drop by the tools and looked at the air compressors.
>They had a "6 hp" compressor whose motor name plate rating was
>240 v - 14 amp.  By my rule of thumb (120v/10 amp, 240/5 amp = 1 hp)
>this would be about a 3 hp motor, by the above formula this would
>be about a 4.5 hp motor.  In any case, certainly not a 6 hp unit.
[...]

Sears does this with their vacuums, too.  A salesperson tried to sell
me a 4hp (120V, 15amp plug) vacuum.  

Incidentally, isn't it 120v * 6.2 amp ~= 746 watts = 1hp? 

--Pat "darn, where'd I put that 25 amp outlet?"

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From: PPIERCE <[email-masked]>
Date: Thu, 06 Jun 1996 19:25:50 -0700

> --Pat "darn, where'd I put that 25 amp outlet?"

for an ac motor
120v X 6.2a = 746 volt amperes input.
assuming a power factor of .8, that would be 595 watts input.
assuming an efficiency of .8 there would be 476 watts output.
that would be about .64 hp.

so much for a 4 hp vacuum.

They would like to rewrite the book.  Sad...

Paul in AJ AZ

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From: Roger Gibbs <[email-masked]>
Date: Fri, 7 Jun 1996 19:02:26 GMT

>claimed efficiency of 63% and a rated horsepower of 0.5.
snip
>Jens
I checked two motors I feel to be quality motors:
1. an older GE motor rated 1/2 hp, 8.4 amps, 115 v
2. a middle aged Leeson motor rated 1.5 hp, 17.4 amps, 115 v

As I recall, motors tend to draw as much (or as little) current as
required to maintain RPM.  So a 1/4 hp motor or a 1.5 hp motor which
is running against a light load will tend to draw the same current,
and these same motors driving a large load will attempt to draw the
same current also. (I dimmly recall that a large load results in a 
lower back emf which means that for a heavily loaded motor, the winding
resistance becomes the current limiting factor).

What this means of course is that a motor rated at 1/4 hp can draw
the necessary current to provide an output power of 3/4 hp or 1 hp
or more .... for a while. How long ? Well that depends on the wire
size used in the windings, the insulation qualities, air flow over
the windings, etc.  Eventually (or maybe vrey quickly) motors which
are used beyond their physical limitations will develop winding
shorts.

Buyer beware.

-Roger