This is a great toy for about the price of dinner and a movie. Get a short
heavy duty extension cord, the type with the "zip cord look" so you can
separate out the leads and split one out for the clamp. You can then get a good
eye opener about exactly what your tools really draw.
When I first got mine I went around debunking things like the "1800 watt" hair
dryer and "6 HP" compressors. I don't know how they come up with these numbers.
Sorry but you are wrong with respect to current/horsepower going DOWN at
high pressure. most air compressors are positive displacement
(piston/diaphragm type) machines for which power goes up as discharge
pressure goes up. There is rule of thumb in the Hydraulic Institute
Standard that give the formula. Vacuum cleaners are on the other hand are
centrifugal compressors where at free flow (open suction and discharge fully
open) power consumption is the highest.
"Greg" < email@example.com> wrote in message
I only know what the meter says. There may be some kind of unloader in there
but I really think it is just that it can't take in any more air.
This is the C/H diaphram oilless compressor with a 6.25 sticker and a 1HP
motor. In the middle of the range it actually draws more than the labelled FLA,
then tapers off. That was the day I bought it.
If you have the January archives of this NG, I posted the actual curve
If it is a 'dim' scenario, you didn't budget enough for lighting! <grin>
Note, I was expressly talking about 'worst case' situations -- any rational
engineering *does* _design_ to the worst-case scenario specifications. Yes,
you can 'get away' with 'less' in many situations, but, eventually, it *WILL*
'bite' you, probably "at the worst possible time, in the worst possible way".
There is a reason, borne of painful experience, that O'Brien's Law ("Murphy
was an optimist!") exists.
The _last_ thing you want is the *feeder* to a building with sharp, rapidly
spinning metal thingies to shut down. You lose all the lights -- and thus
can't see _where_ those sharp thingies are -- *and* they're still spinning,
at least until they coast to a stop. This is a significant argument in favor
of a _separately_ protected, separate feeder for the lighting circuits. And
for splitting the lighting across (at least) two circuits, as well. ("Yes,
I _do_ have far more experience in dealing with Messrs Murphy and O'Brien
than I really care to; why do you ask?" :)
As for the rest, lighting is a 'static' load; an air-conditioner draws quite
close to 'rated' amps while the compressor is running; the air-compressor --
kicking in to 'top off' the tank -- is going to draw around 80% of rated load;
a dust collector runs 'normally' at close to rated load, as well.
Re: your comment about a 2hp motor, and a 5hp one drawing similar current under
similar loading; that claim _is_ true, but only as far as it goes -- static
load, under static conditions. The 5hp motor will draw *considerably* more at
start-up; also at other times when the motor undergoes a significant increase
in load, over the short term.
One final comment: For power feeder/distribution, the 'cost' associated with
"over-engineering" the implementation to 'worst case' specifications is minor.
Materials cost is usually swamped by labor expense. Also, the 'down side
risk' of finding out _after_the_fact_ that the newly done work is 'inadequate'
and requires replacement, puts the minor additional cost of the 'do it right
the first time' approach in the realm of "*really* cheap insurance".
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