On Mon, 9 Mar 2009 08:12:29 -0400, "Stormin Mormon"
When you find that mythical motor that puts out 1HP per 800w the world
will beat a path to your door.
About all you will ever get from a 120v@15a rated motor is ~1HP.
Campbell Hausfeld et al got sued over those 5HP stickers they put on
their 1HP compressors and the whole "class" got a free power tool.
On Mar 9, 8:05 am, email@example.com wrote:
748 watts happens to be 1 hp of electrical power.....of course motors
are not 100% efficient at turning lectrical energy into mechanical
But even standard efficiency motors are in the 80%+ range with the new
premeum units having higher than 90%
so 15amps @ 120v = 1800 watts ( 2.4 hp electrical)
factoring in 85% efficiency gives you ~2 hp
a 20amp circuit would give you 2.7 hp (at 85%) and nearly 3 hp at 91%
so those mythical motors (1 hp at 800 watts......93.5%) may not exist
but some are pretty close
On Mar 10, 8:02 pm, firstname.lastname@example.org wrote:
the 12-13a range on the nameplate. <<<<
I'm not disputing what you see but I'm pretty sure my calcs & info
are correct; based on the definition of a hp(E) and typical motor
Maybe the motors have really bad efficiencies or the mfr's have them
tagged "conservatively" ?
The current draw for even an "old school" / giant motor 1hp should
be ~7.5 or so...
I remember my dad having a GIANT 1hp rated motor from the 60's & the
nameplate read 7.2 / 3.6
....12 to 13 amps seems way too high. JMHO
You're leaving out the other factor besides the efficiency (as well as
assuming new motors of only 1 hp are really built to such high
efficiency numbers) which is the power factor.
Spec's for a fairly typical Baldor (not inexpensive) general-purpose 1hp
Catalog Number: VL3509
Specification Number: 35C013X964
Full Load Amps: 11.8/5.9
Usable at 208 Volts: 6.1
Frame Size: 56C
Service Factor: 1.25
Full Load Efficiency: 68
Power Factor: 82
hp = 115*11.8*0.68*0.82/748 --> 1.0
This is a list price motor of $400.
At least a couple in the same general classification were 0.65/0.65
efficience/power factor (at roughly $300 price point).
One of their (very few at this low a hp) premium efficiency 1hp motors is
Catalog Number: EL3510
Specification Number: 35J385S758G1
Full Load Amps: 8.5/4.25
Usable at 208 Volts: N/A
Full Load Efficiency: 82.5
Power Factor: 91
hp = 115*8.5*0.82.5*0.91/748 --> 0.98
That comes at a price, however -- $643 catalog list
At a high-enough usage and for long enough, eventually one would make up
the initial cost difference, but for intermittent use it would take
quite a long time.
Thanks for the detailed response. Good comment about super high
efficiency motors being expensive / rare in the 1 hp range.
Your analysis explains why the other post "I see a lot of 1HP
motors in my travels and they usually have a FLA in
the 12-13a range on the nameplate" is, in fact, correct.
I had no idea that typical 1hp motors have efficiencies & PF's that
I guess that's why SoCal Edison gives such good rebates on the
purchase of high efficiency pool pump motors.
Teflon tape is fine. Be sure when you buy fittings that you get the right type.
There are more than one type in the stores, and they don't intermingle.
Bigger hose for bigger runs or higher volume uses. Mine is all 3/8". Better to
use a larger long hose than an extension cord to reach distances.
How do you know it was never drained? How much water came out?
FWIW, I acquired an old compressor tank. I talked to the county "tank and
boiler" inspector about getting it tested, and he volunteered to come by, and
tested several spots on the tank with an untrasound thickness guage, and assured
me the tank was fine.
Unless you know it was done recently, replace the compressor oil soon with oil
specified in the manual.
In addition to the other replies, I think the only good use for the coiled
hoses is over a workbench in an air-plumbed shop and over a tire changer in
a garage. It'll hang retracted and out of the way overhead until needed.
I know it was never drained as I asked the previous owner, when he last
drained the tank, and he looked at me and said he never did.
The compressor is oiless so there is no need to replace oil?
Here is the online reference for the unit.
I've been using Marvel Mystery oil. How would you compare that to the above?
Make sure you use a heavy duty cord if you do that. Too small of a cord can fry
the motor. I do fine with a large home-built powered reel with 150 feet of hose,
and an occasional additional 50 feet (all 3/8"). But my compressor is a heavy 2
stage, and not movable and probably supplies significantly more pressure than
Can't really say. ATF and air tool oil are compounded to work with
rubber O-rings, seals and such. MMO may well be as compatible since as
an upper cylinder lube it shouldn't attack intake manifold seals.
You got me there, Bob. I should have considered that some young 'uns
may not remember the laws of diminishing voltage with increasing
length. Good point.
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