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#1
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Air Compressor Horsepower/Wattage/Amperage
I thought I had this compressor power thing down to a pretty good science
until they started screwing around with "rated watts" and "peak power" and all that crap that makes their compressor look really good until you go to use it. Back when we were using "real" horsepower I used a figure of 750 (to make it easy to calculate, I believe 746 is the actual number) watts per horsepower and an efficiency factor of 85% so that a one horse motor would take 860 watts to do the actual work. But then you multiplied that times two for "starting" wattage for a couple of seconds to give 1725 watts under start and then times three for starting under some volume of air left in the compressor reservoir or about 2600 watts. That presses my 2200 watt continuous duty (2800 watts peak) fairly close to the load limit, but certainly gives a margin for error that seems reasonable. Before I tell elebendy bazillion Kitplanes readers that the Harbor Freight Subaru 2200 watt generator will drive the Sears 1 horse compressor (and even worse, buy the Sears compressor only to not have it work), will somebody please do a reality check on me for horsepower/watts for this lashup. (Note ... convert watts to amperes by dividing watts by 120 volts). 860w=7a 1725w=14a 2600w=21a Sears and Harbor Freight are damned near clueless about this sort of stuff. If anybody has a source I can reference for running/starting/starting under load for air compressors it would be well received. I'd LIKE to buy a 3/4 horse compressor but they go from the kiddie's 1/4 horse toy straight to one horse with darned little in between. Jim -- "Dream as if you'll live forever. Live as if you'll die today." --James Dean |
#2
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Air Compressor Horsepower/Wattage/Amperage
On Jun 18, 2:49 pm, "RST Engineering" wrote:
I thought I had this compressor power thing down to a pretty good science until they started screwing around with "rated watts" and "peak power" and all that crap that makes their compressor look really good until you go to use it. Back when we were using "real" horsepower I used a figure of 750 (to make it easy to calculate, I believe 746 is the actual number) watts per horsepower and an efficiency factor of 85% so that a one horse motor would take 860 watts to do the actual work. But then you multiplied that times two for "starting" wattage for a couple of seconds to give 1725 watts under start and then times three for starting under some volume of air left in the compressor reservoir or about 2600 watts. That presses my 2200 watt continuous duty (2800 watts peak) fairly close to the load limit, but certainly gives a margin for error that seems reasonable. Before I tell elebendy bazillion Kitplanes readers that the Harbor Freight Subaru 2200 watt generator will drive the Sears 1 horse compressor (and even worse, buy the Sears compressor only to not have it work), will somebody please do a reality check on me for horsepower/watts for this lashup. (Note ... convert watts to amperes by dividing watts by 120 volts). 860w=7a 1725w=14a 2600w=21a Sears and Harbor Freight are damned near clueless about this sort of stuff. If anybody has a source I can reference for running/starting/starting under load for air compressors it would be well received. I'd LIKE to buy a 3/4 horse compressor but they go from the kiddie's 1/4 horse toy straight to one horse with darned little in between. Jim -- "Dream as if you'll live forever. Live as if you'll die today." --James Dean Have you ever noticed that in the horsepower place on the motor dataplate it says something like "SPL"? The motor mfg doesn't want to be complicit on the out right lying done by the compressor mfgs, who never heard that 750 watts = 1 hp. Charletons. BH |
#3
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Air Compressor Horsepower/Wattage/Amperage
On Mon, 18 Jun 2007 14:53:30 -0700, "
wrote: Have you ever noticed that in the horsepower place on the motor dataplate it says something like "SPL"? The motor mfg doesn't want to be complicit on the out right lying done by the compressor mfgs, who never heard that 750 watts = 1 hp. NOTHING beats Shop-Vac HP ratings. 6HP from a 15 amp 120v outlet! Awesome! G |
#4
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Air Compressor Horsepower/Wattage/Amperage
B A R R Y wrote:
On Mon, 18 Jun 2007 14:53:30 -0700, " wrote: Have you ever noticed that in the horsepower place on the motor dataplate it says something like "SPL"? The motor mfg doesn't want to be complicit on the out right lying done by the compressor mfgs, who never heard that 750 watts = 1 hp. NOTHING beats Shop-Vac HP ratings. 6HP from a 15 amp 120v outlet! Awesome! G Good golly, I hadn't noticed that before! 15 amps at 120 V is 1800 watts Roughly 746 (100% efficiency) watts per HP 750 x 6 = 4476 watts Less than 1/2 the claimed power! I wonder if I could take it back and exchange it for a REAL 6 hp vac??? |
#5
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Air Compressor Horsepower/Wattage/Amperage
"B A R R Y" wrote in message
news On Mon, 18 Jun 2007 14:53:30 -0700, " wrote: Have you ever noticed that in the horsepower place on the motor dataplate it says something like "SPL"? The motor mfg doesn't want to be complicit on the out right lying done by the compressor mfgs, who never heard that 750 watts = 1 hp. NOTHING beats Shop-Vac HP ratings. 6HP from a 15 amp 120v outlet! Awesome! G 240% efficiency is very impressive--for a single phase motor! The last time that I wandered through the tool department at Sears, I saw what appeared to be the same compressor that I used to own. Mine could manage about 2CFM at 40PSI, and claimed to be 2HP on the aforementioned 120V circuit--IIRC with a continued draw of about 10A. The new ones were claiming either 4 or 6 CFM, and I believe that the pressure may have been higher as well, on the same electrical power. So the problem is not new, but it is getting much worse. Peter (In the future, tools will be rated like sound systems.) |
#6
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Air Compressor Horsepower/Wattage/Amperage
Peter Dohm wrote:
(In the future, tools will be rated like sound systems.) Let's hope the tradition doesn't extend to airplane power plants. G |
#7
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Air Compressor Horsepower/Wattage/Amperage
B A R R Y wrote:
Let's hope the tradition doesn't extend to airplane power plants. G Oh don't worry, it will. |
#8
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Air Compressor Horsepower/Wattage/Amperage
kontiki wrote:
B A R R Y wrote: Let's hope the tradition doesn't extend to airplane power plants. G Oh don't worry, it will. Well, there was the 150 horse Franklin... |
#9
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Air Compressor Horsepower/Wattage/Amperage
B A R R Y wrote:
Peter Dohm wrote: (In the future, tools will be rated like sound systems.) Let's hope the tradition doesn't extend to airplane power plants. G Well, there was the 150 horse Franklin. And the 60 horse VW. |
#10
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Air Compressor Horsepower/Wattage/Amperage
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