On Thu, 10 Dec 2009 19:52:54 -0500, wrote:

On Thu, 10 Dec 2009 15:59:27 -0800 (PST), Joe wrote:

On Dec 10, 4:56*pm, "Roger Shoaf" wrote:
"Stormin Mormon" wrote in message

...





Can't remember if it was this list. The question was raised,
does compressor amperage decrease as pressure increases. I
set up an informal test, using equipment on hand. Plugged in
a Kill A Watt meter, and set it to read watts consumption.
Plug in my 3 HP Harbor Freight pancake compressor.

I turned on the compressor, and noted the reading as the
pressure went from 0 PSI to 100 PSI. The readings are as
follows:

PSI -WATTS
10 - 198
20 - 199
30 - 211
40 - 220
50 - 229
60 - 233
70 - 237
80 - 240
90 - 255
95 - 248 (wasn't sure the compressor would make it to 100)
100 - 250

Hope the information is of some use to someone. If nothing
else, it used a few minutes of my afternoon.

You forgot one factor. *Time.

I bet if you noted the time that it took to attain the increase in pressure
when you saw the apparent dip in watts consumed between 90 and 100 psig you
would find that the total load (power consumption)increases.

I suspect if you were also to apply the gas laws to the equation where the
temperature of the air in the tank was held constant, you will find that the
cost in power would increase for the volume/pressure of air in the tank.
--
Roger Shoaf
If you are not part of the solution, you are not dissolved in the solvent.

Spot on, Roger. Power is not measured in watts, it is measured in watt-
hours. That's what that nice meter on the side of your building
records.

Joe

No power is watts. Also known as power dissipation, Power
CONSUMPTION is watt hours.
Horsepower is also a power rating, and is an INSTANTANEOUS
measurement. - A snapshot in time.

This obviously explains why my Yamaha 9.9 hp outboard motor has a spec
for its output power measured in kilowatts. :-)

..7457 Kilowatts=1 BHP