> > I have the Campbell-Hausfield 2.5HP 20 gallon tank version, and I have
> > it running on a 15 amp circuit without too much trouble. If it switches
> There are a number of 120V compressors on the market these days which
> are rated between 2 and 3 hp (Sears sell several). 120V X 15A = 1.8 Kw
> and 120 X 20A = 2.4Kw, so one has to wonder about these ratings. I
> don't recall the conversion factor off hand but I believe it's something
> like .75 X Kw = hp. I've been told that these ratings refer to "peak"
> power or something like that, which implies to me that these hp ratings
> are a bit bogus for sustained output.
I don't think the rating relates to "output of compressed air" - I think it's
more along the lines of "power output of the electric motor". From that point
of view, 2.5hp comes out to 15.6 amps, which I would guess is just the
motor starting current - except for the hair-trigger circuit breakers,
most breakers can take that much over-current for a short period. When the
motor fires up, the lights in the house dim for about 1/4 second, which is
within the tolerance for most breakers. Oh, and my computer UPS clicks into
"Battery" mode for a moment. The MIG welder, on the other hand, can put
the UPS into battery mode and make the audio alarm sound. Glad the computer's
not plugged straight into the wall...
> Maybe someone can clarify what these ratings really mean and if there's
> any advantage to buying one of these "higher" hp rated compressor.
The key rating on a compressor is the CFM rating at the operating pressure
you want to use. There is a relationship between CFM@psi and horsepower,
but it's a bit non-linear due to efficiency & thermodynamic considerations
and of course there's a different curve for each compressor design and
even for each unit... so what you wind up doing is: get the CFM supply
requirements of the tools you want to run, take the highest, and add that
of any other tool that you might want to run at the same time, add about a 10%
margin, and that's the CFM you want the compressor to push. Mine turns out
to be just a bit too slow for the orbital sander at top speed, and the bar
stock cutter, but it's hard to set things up so well that you need to run
top speed for an extended period. I find that I get a lot less tired if
I use the tool for about 20 to 30 seconds at a time, then stand up and
rest a bit, then use the tool... and the compressor keeps up with that
just fine. No such difficulty with the air ratchet or impact tools...
> Roland "still dry and odor free" Dudley
I take it that you are refering to the fuel tank on your snake,
and not your secret underarm deodorant formula...
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John R. Lupien
lupienj@wal.hp.com
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