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Metalworking (rec.crafts.metalworking) Discuss various aspects of working with metal, such as machining, welding, metal joining, screwing, casting, hardening/tempering, blacksmithing/forging, spinning and hammer work, sheet metal work. |
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Compressor Motor: HP v.s. Amps?
I have an older Sears compressor that was given to me because it had
pinholes in the tank. I would like to replace the tank with a larger unit (20 gal instead of the current 11 gal). I think I've located a suitiable portable tank. But, in the process, I wanted to learn a bit more about the actual compressor itself. The compressor currently has a 3/4 hp motor. At first glance I was kind of depressed thinking "Gee, just about every compressor I see these days has 3 + hp. Will this thing even work well?" In asking around I was told that amperage plays a big part in the actual torque of the motor. This is where I get confused... I thougth torque was the direct product of the motor's hp. How does the amperage come into play? Can you have a "strong" or "weak" 3/4 hp motor? What factors actually determine the torque? Or, am I looking at this equation in the wrong way? Specs of the motor I currently have (from the mfr plate on the cover): Doerr Insul Class: A Ser. Fact: 1.0 MC544 RPM: 3450 Duty: Cont Type: K Phase: 1 HP: 3/4 HZ: 60 FR: F56 Mtr Ref: 600702 H733 Thermally Prot: Manual V: 115 A: 14.4 Specs from the capacitor: STM A-2131-10 375MFD 110VAC 60 Cycle 1160-7317 Any advice would be greatly appreciated. Please post replys to the group. Thanks! Chuck |
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Compressor Motor: HP v.s. Amps?
On Fri, 03 Oct 2003 12:28:57 -0000, Chuck wrote:
I have an older Sears compressor that was given to me because it had pinholes in the tank. I would like to replace the tank with a larger unit (20 gal instead of the current 11 gal). I think I've located a suitiable portable tank. But, in the process, I wanted to learn a bit more about the actual compressor itself. The compressor currently has a 3/4 hp motor. At first glance I was kind of depressed thinking "Gee, just about every compressor I see these days has 3 + hp. Will this thing even work well?" In asking around I was told that amperage plays a big part in the actual torque of the motor. This is where I get confused... I thougth torque was the direct product of the motor's hp. How does the amperage come into play? Can you have a "strong" or "weak" 3/4 hp motor? What factors actually determine the torque? Or, am I looking at this equation in the wrong way? Specs of the motor I currently have (from the mfr plate on the cover): Doerr If its a Doerr, its a very good motor, and the data plate horsepower is exactly what it produces, not Sears HP. As its a 3450 rpm motor, thats where they are getting their rapid pumping from. A good unloader is a requirement, with a "high speed" motor. The torque is related to the size of the pully on the motor, and on the pump itself. Gunner Insul Class: A Ser. Fact: 1.0 MC544 RPM: 3450 Duty: Cont Type: K Phase: 1 HP: 3/4 HZ: 60 FR: F56 Mtr Ref: 600702 H733 Thermally Prot: Manual V: 115 A: 14.4 Specs from the capacitor: STM A-2131-10 375MFD 110VAC 60 Cycle 1160-7317 Any advice would be greatly appreciated. Please post replys to the group. Thanks! Chuck Cum catapultae proscriptae erunt tum soli proscript catapultas habebunt. |
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Compressor Motor: HP v.s. Amps?
Chuck sez:
"...I thougth torque was the direct product of the motor's hp. How does the amperage come into play? Can you have a "strong" or "weak" 3/4 hp motor? What factors actually determine the torque? Or, am I looking at this equation in the wrong way?" Torque is the capacity of an engine to do work whereas HP is the rate at which an engine does work. [Torque, in foot-pounds = (Horsepower x 5252) divided by RPM.] For instance, an engine doing 250 HP of work and turning at 1200 RPM has torque of 1094 ft. lbs. Torque is the force causing a shaft to turn, sometimes called "turning moment". Torque, discounting friction, is the same in each moving member of any transmission link - this is true because of the equation above. In a machine working at any given rate (HP), torque is the same at each link in the machine from the output shaft through the transmission and on to the wheels. RPM varies from link to link because of diameter differences but torque is the same everywhere. Consider the equation, above: Torque is directly related to HP and inversely related to RPM. Electrical power is defined as the product of voltage x current. Electrical power is measured in Watts and there are 746 Watts in 1 HP. For example, a 3/4 HP motor can develop [746 x 3/4 = 560 Watts] of power. A 3/4 HP motor running on 120 volts would have an input current of [560 divided by 120 = 4.7] amps. Because small single phase electric motors have an overall efficiency of around 50% it is customary, in rough calculations, to double the amount of calculated input current. That would mean an input current of 9.4 amps if the 3/4 HP motor was delivering its full output capability of 560 Watts (3/4 HP of work). Key to this is that output power is always related to input power. A motor has no inherent HP - HP always depends on motion. Delivered HP (Watts of work), discounting friction, depends on the amount of power (voltage x current) put into the motor. As seen above, the motor running fully loaded would "draw" about 9 amps of current. Unloaded and spinning freely, the current draw would be much less, probably less than 2 amps. Bob Swinney "Chuck" wrote in message . .. I have an older Sears compressor that was given to me because it had pinholes in the tank. I would like to replace the tank with a larger unit (20 gal instead of the current 11 gal). I think I've located a suitiable portable tank. But, in the process, I wanted to learn a bit more about the actual compressor itself. The compressor currently has a 3/4 hp motor. At first glance I was kind of depressed thinking "Gee, just about every compressor I see these days has 3 + hp. Will this thing even work well?" In asking around I was told that amperage plays a big part in the actual torque of the motor. This is where I get confused... Specs of the motor I currently have (from the mfr plate on the cover): Doerr Insul Class: A Ser. Fact: 1.0 MC544 RPM: 3450 Duty: Cont Type: K Phase: 1 HP: 3/4 HZ: 60 FR: F56 Mtr Ref: 600702 H733 Thermally Prot: Manual V: 115 A: 14.4 Specs from the capacitor: STM A-2131-10 375MFD 110VAC 60 Cycle 1160-7317 Any advice would be greatly appreciated. Please post replys to the group. Thanks! Chuck |
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Compressor Motor: HP v.s. Amps?
On Fri, 03 Oct 2003 12:28:57 -0000, someone who calls themselves Chuck
wrote: snip The compressor currently has a 3/4 hp motor. At first glance I was kind of depressed thinking "Gee, just about every compressor I see these days has 3 + hp. Will this thing even work well?" In asking around I was told that amperage plays a big part in the actual torque of the motor. This is where I get confused... I thougth torque was the direct product of the motor's hp. How does the amperage come into play? Can you have a "strong" or "weak" 3/4 hp motor? What factors actually determine the torque? Or, am I looking at this equation in the wrong way? Your old motor is rated in actual usable HP, while almost all small compressors (and many other consumer appliances where they sell by the Gee Whiz Factor) now are marked with "Peak HP" - basically, the highest horsepower output recorded right before the motor stalls. (And goes up in flames if you don't pull the plug fast.) Just like diagonal size inflation on TV screens... Note that on all the motors of these new compressors they don't have a motor manufacturer's HP rating on the sticker - Some I've seen leave a blank space there (so they don't contradict the sales literature), other motor nameplates have the HP block marked "Special". You have to go by current draw and voltage to get the real motor ratings, and by CFM @ PSI ratings to do a reasonable comparison between units. I'm not going to do the math, but your 3/4 HP motor would probably be sold as a "2 HP (Peak)" compressor today. 3 if they like to lie. -- Bruce -- -- Bruce L. Bergman, POB 394, Woodland Hills CA 91365, USA Electrician, Westend Electric (#726700) Agoura, CA WARNING: UCE Spam E-mail is not welcome here. I report violators. SpamBlock In Use - Remove the "Python" with a "net" to E-Mail. |
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Compressor Motor: HP v.s. Amps?
Dave sez: "...Horsepower is the same at any point in a machine, apart from
frictional losses. Torque varies inversely with rpm as altered by gearing. The whole point of a gearbox is to multiply torque...." Another way of saying the same thing. Torque varies inversely with RPM. Torque as well as HP is everywhere the same in a transmission link. And Dave further sez: "... RPM varies from link to link because of diameter differences but torque is the same everywhere. If that were true then horsepower would be being created from nowhere or dissipated to nowhere at different points in the machine, in violation of everything that physicists hold sacred." Guess you missed the math, Dave! Horsepower is passed through each segment of a transmission link - RPM varies, torque varies, but HP remains the same, discounting frictional losses. Bob Swinney "Dave Baker" wrote in message ... Subject: Compressor Motor: HP v.s. Amps? From: "Bob Swinney" Date: 03/10/03 15:10 GMT Daylight Time Message-id: t Chuck sez: "...I thougth torque was the direct product of the motor's hp. How does the amperage come into play? Can you have a "strong" or "weak" 3/4 hp motor? What factors actually determine the torque? Or, am I looking at this equation in the wrong way?" Torque is the capacity of an engine to do work whereas HP is the rate at which an engine does work. [Torque, in foot-pounds = (Horsepower x 5252) divided by RPM.] For instance, an engine doing 250 HP of work and turning at 1200 RPM has torque of 1094 ft. lbs. Torque is the force causing a shaft to turn, sometimes called "turning moment". Torque, discounting friction, is the same in each moving member of any transmission link - this is true because of the equation above. In a machine working at any given rate (H P), torque is the same at each link in the machine from the output shaft through the transmission and on to the wheels. Of course it isn't. If that were the case there would be no point in having gearboxes. Dave Baker - Puma Race Engines (www.pumaracing.co.uk) I'm not at all sure why women like men. We're argumentative, childish, unsociable and extremely unappealing naked. I'm quite grateful they do though. |
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Compressor Motor: HP v.s. Amps?
Chuck wrote: I have an older Sears compressor that was given to me because it had pinholes in the tank. I would like to replace the tank with a larger unit (20 gal instead of the current 11 gal). I think I've located a suitiable portable tank. But, in the process, I wanted to learn a bit more about the actual compressor itself. The compressor currently has a 3/4 hp motor. At first glance I was kind of depressed thinking "Gee, just about every compressor I see these days has 3 + hp. Will this thing even work well?" In asking around I was told that amperage plays a big part in the actual torque of the motor. This is where I get confused... That is intentional. Compressor ratings are largely a vast conspiracy of lies. You'll see lots of home shop type compressors at the local Home Depot with standard 15A 115 V plugs rated at 5, and now even * 6 * Hp! Well, there's no way to get 6 Hp out of a 15 A wall socket. You can barely get 2 Hp, and if you run so much as a 100 W bulb on the same breaker, it will trip after a while. Anyway, my rule of thumb is a decent single stage compressor will deliver about 3.2 CFM (at 90 - 100 PSI) per (real world) Horsepower. I also will throw out another rule of thumb, which is that 2 (real) Hp is about the lower limit you should try to use in a home shop. 3/4 Hp is just too small for serious air tool work. It would be fine for an air brush or tire filling, but almost any standard air tool, like a die grinder, air paint sprayer, (very small) sand blaster, air chisel, etc. will use at least 6 CFM, and some will use a lot more. Unless you want to wait 5 minutes out of every 6, you will soon be looking for a bigger compressor. Forget HP, as some compressors sold for industrial use DON'T lie about it, so it can't be used for comparisons. Just look at CFM at 90 PSI (don't be foold by ratings at 40 PSI, either.) The other bad news is that the oilless compressors tend to be EXTREMELY noisy, and will drive you (or your neighbors) nuts! Oil filled compressors generally turn much slower, and some good ones can be rather quiet. Jon |
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Compressor Motor: HP v.s. Amps?
Subject: Compressor Motor: HP v.s. Amps?
From: "Bob Swinney" Date: 03/10/03 20:34 GMT Daylight Time Message-id: t Bob's first statement "... RPM varies from link to link because of diameter differences but torque is the same everywhere. Bob's second statement Guess you missed the math, Dave! Horsepower is passed through each segment of a transmission link - RPM varies, torque varies, but HP remains the same, discounting frictional losses. That isn't what you first posted. Whether you meant to say "hp is the same everywhere" I have no idea but the first statement was categorically wrong. Dave Baker - Puma Race Engines (www.pumaracing.co.uk) I'm not at all sure why women like men. We're argumentative, childish, unsociable and extremely unappealing naked. I'm quite grateful they do though. |
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Compressor Motor: HP v.s. Amps?
This may be the original statement that Dave took exception to; I still
stand behind it: "...Torque, discounting friction, is the same in each moving member of any transmission link - this is true because of the equation above. In a machine working at any given rate (HP), torque is the same at each link in the machine from the output shaft through the transmission and on to the wheels. RPM varies from link to link because of diameter differences but torque is the same everywhere. Consider the equation, above: Torque is directly related to HP and inversely related to RPM...." Bob Swinney "Dave Baker" wrote in message ... Subject: Compressor Motor: HP v.s. Amps? From: "Bob Swinney" Date: 03/10/03 20:34 GMT Daylight Time Message-id: t Bob's first statement "... RPM varies from link to link because of diameter differences but torque is the same everywhere. Bob's second statement Guess you missed the math, Dave! Horsepower is passed through each segment of a transmission link - RPM varies, torque varies, but HP remains the same, discounting frictional losses. That isn't what you first posted. Whether you meant to say "hp is the same everywhere" I have no idea but the first statement was categorically wrong. Dave Baker - Puma Race Engines (www.pumaracing.co.uk) I'm not at all sure why women like men. We're argumentative, childish, unsociable and extremely unappealing naked. I'm quite grateful they do though. |
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Compressor Motor: HP v.s. Amps?
OOOOPPPS sorry Dave! My statement should have been that HP is constant from
link to link in a transmission network. It follows that torque by the equation: Torque = (HP x 5252)/RPM does in fact vary inversely with RPM. Bob Swinney "Dave Baker" wrote in message ... Subject: Compressor Motor: HP v.s. Amps? From: "Bob Swinney" Date: 03/10/03 20:34 GMT Daylight Time Message-id: t Bob's first statement "... RPM varies from link to link because of diameter differences but torque is the same everywhere. Bob's second statement Guess you missed the math, Dave! Horsepower is passed through each segment of a transmission link - RPM varies, torque varies, but HP remains the same, discounting frictional losses. That isn't what you first posted. Whether you meant to say "hp is the same everywhere" I have no idea but the first statement was categorically wrong. Dave Baker - Puma Race Engines (www.pumaracing.co.uk) I'm not at all sure why women like men. We're argumentative, childish, unsociable and extremely unappealing naked. I'm quite grateful they do though. |
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Compressor Motor: HP v.s. Amps?
"Bob Swinney" wrote in message . net... OOOOPPPS sorry Dave! My statement should have been that HP is constant from link to link in a transmission network. It follows that torque by the equation: Torque = (HP x 5252)/RPM does in fact vary inversely with RPM. Bob Swinney Erratum: Please see following correction notice sent to "Live Steam" magazine: Clover McKinley, Editor Live Steam Magazine One of the readers of the news group, rec.crafts.metalworking, has pointed out a misleading statement made in my article. Page 19, next to last par: "Wheel edge (pulling force) is everywhere the same in a transmission link." While fundamentally true, this statement could be misleading. It should, more accurately state: "Wheel edge power (horsepower) is everywhere the same in a transmission link". Sincerely, Bob Swinney |
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Compressor Motor: HP v.s. Amps?
Chuck wrote:
Can you have a "strong" or "weak" 3/4 hp motor? What factors actually determine the torque? Or, am I looking at this equation in the wrong way? All 3/4 HP motors at full speed will do the same work. At the same RPM doing the same amount of work they will output the same torque. Motors have different power curves, and plotting torque vs. RPM is a useful way of looking at the information. HP vs. RPM is usually graphed as well. To compare torque values for full speed, steady state running conditions with the same HP motors would be kind of pointless, unless I'm missing something. |
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Compressor Motor: HP v.s. Amps?
Chuck writes:
Any advice would be greatly appreciated. See my page, "Evaluating True Horsepower and CFM Ratings of Air Compressors" at: http://www.truetex.com/aircompressors.htm |
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Compressor Motor: HP v.s. Amps?
Bob Swinney writes:
Torque is the capacity of an engine to do work ... This, and many of your other comments here elided, are quite wrong. |
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Compressor Motor: HP v.s. Amps?
Bruce L. Bergman writes:
Just like diagonal size inflation on TV screens... Worse. TV diagonal inflation is at least limited to sqrt(2), and bears some meaningful proportion to the true size. "Peak HP" are many times true HP and have little significance. It is more like, "your TV screen would be X inches, if you put a giant magnifying glass in front of it." |
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Compressor Motor: HP v.s. Amps?
Jon Elson writes:
It would be fine for an air brush or tire filling, but almost any standard air tool, like a die grinder, air paint sprayer, (very small) sand blaster, air chisel, etc. will use at least 6 CFM, and some will use a lot more. Unless you want to wait 5 minutes out of every 6, you will soon be looking for a bigger compressor. Generally correct. But I found that an air chisel is so hard on the skeleton, that you don't want to apply it at anything close to 100 percent duty cycle. Now sand blasting, that is something else, you have an infinite appetite for air with that. |
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Compressor Motor: HP v.s. Amps?
Subject: Compressor Motor: HP v.s. Amps?
From: "Bob Swinney" Date: 03/10/03 20:34 GMT Daylight Time Message-id: t Guess you missed the math, Dave! If you have a look at my website you will find three articles on power, torque and their measurement which comprise one of the most comprehensive explanations of the maths and physics that underly this topic anywhere on the web. Dave Baker - Puma Race Engines (www.pumaracing.co.uk) I'm not at all sure why women like men. We're argumentative, childish, unsociable and extremely unappealing naked. I'm quite grateful they do though. |
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Compressor Motor: HP v.s. Amps?
So, Richard - we would like to hear your definition of torque. And could
you elucidate a bit on the many "elided" comments? Please, give us your "take" on the correct facts. Bob Swinney "Richard J Kinch" wrote in message . .. Bob Swinney writes: Torque is the capacity of an engine to do work ... This, and many of your other comments here elided, are quite wrong. |
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Compressor Motor: HP v.s. Amps?
Subject: Compressor Motor: HP v.s. Amps?
From: "Bob Swinney" Date: 04/10/03 02:58 GMT Daylight Time Message-id: vPpfb.489338$Oz4.334706@rwcrnsc54 "Richard J Kinch" wrote in message ... Bob Swinney writes: Torque is the capacity of an engine to do work ... This, and many of your other comments here elided, are quite wrong. So, Richard - we would like to hear your definition of torque. And could you elucidate a bit on the many "elided" comments? Please, give us your "take" on the correct facts. Torque bears no relation to any capacity to do work. Although the two quantities are expressed in the same units of force and distance, torque is a vector quantity and work is scalar one. Torque merely defines an instantaneous twisting force about an axis. It could be expressed as a capacity to overcome a given load applied to that axis but not to do a given amount of work. We need to also know speed to calculate that and thus horsepower is what defines capacity to do work. Inherent in the use of the word "capacity" is a time element. Any engine could theoretically do any amount of work if left running for long enough. The use of the term capacity without recognising the inherent time element makes the term meaningless. For example, the question "can an engine producing X amount of torque lift those bricks to the top of that building?" is meaningless. Appropriately geared any engine could do that but only the horsepower defines how fast it could do it. All torque therefore tells one is the shaft speed at which an engine produces a given amount of horsepower and the load the engine can overcome at that shaft speed without further gearing. Dave Baker - Puma Race Engines (www.pumaracing.co.uk) I'm not at all sure why women like men. We're argumentative, childish, unsociable and extremely unappealing naked. I'm quite grateful they do though. |
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Compressor Motor: HP v.s. Amps?
Dave Baker wrote:
Subject: Compressor Motor: HP v.s. Amps? From: "Bob Swinney" Date: 04/10/03 02:58 GMT Daylight Time Message-id: vPpfb.489338$Oz4.334706@rwcrnsc54 "Richard J Kinch" wrote in message . .. Bob Swinney writes: Torque is the capacity of an engine to do work ... This, and many of your other comments here elided, are quite wrong. So, Richard - we would like to hear your definition of torque. And could you elucidate a bit on the many "elided" comments? Please, give us your "take" on the correct facts. Torque bears no relation to any capacity to do work. Although the two quantities are expressed in the same units of force and distance, torque is a vector quantity and work is scalar one. Torque merely defines an instantaneous twisting force about an axis. It could be expressed as a capacity to overcome a given load applied to that axis but not to do a given amount of work. We need to also know speed to calculate that and thus horsepower is what defines capacity to do work. Yes, you could have torque applied, but no work being done at all. |
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Compressor Motor: HP v.s. Amps?
Subject: Compressor Motor: HP v.s. Amps?
From: "Bob Swinney" Date: 04/10/03 02:58 GMT Daylight Time Message-id: vPpfb.489338$Oz4.334706@rwcrnsc54 "Richard J Kinch" wrote in message 1... Bob Swinney writes: Torque is the capacity of an engine to do work ... This, and many of your other comments here elided, are quite wrong. So, Richard - we would like to hear your definition of torque. And could you elucidate a bit on the many "elided" comments? Please, give us your "take" on the correct facts. As to things elided.. Bob previously wrote "Torque is the capacity of an engine to do work whereas HP is the rate at which an engine does work." The two statements "capacity to do work" and "rate at which work is done" are actually the same. Capacity in this context is a rate by definition of the inherent time element. Two different measures, torque and horsepower, have therefore been used to define the same thing and clearly at least one of them must therefore be wrong. The one that is wrong is torque as explained in further detail previously. By the same token... ""Wheel edge (pulling force) is everywhere the same in a transmission link." While fundamentally true, this statement could be misleading. " This is not even fundamentally true, never mind just misleading, but strictly speaking it isn't even clearly enough defined to be meaningful in any way. If it is meant to mean the same sized wheel incorporated at different points in a transmission system then it is false. The edge force will be defined by the torque at that point and the wheel radius and the torque will differ at different points according to gearing. If it meant to mean any sized wheel at different points in a transmission system then it both false and misleading. It can only be correct if the wheel is sized to account for the torque at that point in the system and it then becomes just another part of the gearing system anyway. Dave Baker - Puma Race Engines (www.pumaracing.co.uk) I'm not at all sure why women like men. We're argumentative, childish, unsociable and extremely unappealing naked. I'm quite grateful they do though. |
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Compressor Motor: HP v.s. Amps?
Jon Elson wrote ...
... 3/4 Hp is just too small for serious air tool work... No argument in the context being discussed. However.... I've got three air conditioner compressors (one known good, two unknown). Couldn't tell you the sizes, but I'm thinking it doesn't matter much because I also have a 500 gallon propane tank that I'm thinking of marrying one of them to. Now I may have to let the sucker rung a day & a half to get up to pressure, but I'm thinking it would take a LOT of serious air tool use to see much of a pressure drop from a tank that size. Noise isn't an issue, the nearest neighbor is 1/2 mile & I can put the beast beyond the shop which is 100 yards from the house. Any thoughts other than to pressure test it from a good distance? It would be fine for an air brush or tire filling, but almost any standard air tool, like a die grinder, air paint sprayer, (very small) sand blaster, air chisel, etc. will use at least 6 CFM, and some will use a lot more. Unless you want to wait 5 minutes out of every 6, you will soon be looking for a bigger compressor. Forget HP, as some compressors sold for industrial use DON'T lie about it, so it can't be used for comparisons. Just look at CFM at 90 PSI (don't be foold by ratings at 40 PSI, either.) The other bad news is that the oilless compressors tend to be EXTREMELY noisy, and will drive you (or your neighbors) nuts! Oil filled compressors generally turn much slower, and some good ones can be rather quiet. Jon |
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Compressor Motor: HP v.s. Amps?
Dave sez, quoting facts originally set forth by myself:
""Wheel edge (pulling force) is everywhere the same in a transmission link." While fundamentally true, this statement could be misleading. " This is not even fundamentally true, never mind just misleading, but strictly speaking it isn't even clearly enough defined to be meaningful in any way. If it is meant to mean the same sized wheel incorporated at different points in a transmission system then it is false. The edge force will be defined by the torque at that point and the wheel radius and the torque will differ at different points according to gearing. If it meant to mean any sized wheel at different points in a transmission system then it both false and misleading. It can only be correct if the wheel is sized to account for the torque at that point in the system and it then becomes just another part of the gearing system anyway. Well, Dave, aside from all your pomposity and references to "your" website, I pretty well covered it in my earlier post which was an honest answer to Chucks question. Strangely, though, you gave no mathematical examples to lend clarity to your statements, and to gain position otherwise lost by all the posturing. I incorrectly challenged you on one point and I apologized to you for that. Kindly disregard that apology now, for the spirit in which it was given has been sullied by your boorish, pompous and pedantic attitude. The basic definitions I gave for HP, torque and RPM are all valid. Won't you please spare the other readers further "enlightenment" - the point has been beaten to death by now. If you wish to engage me in further discourse, kindly take notice of the mistletoe hanging from my shirttail. Bob Swinney |
#24
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Compressor Motor: HP v.s. Amps?
"Chuck" wrote in message
. .. The compressor currently has a 3/4 hp motor. At first glance I was kind of depressed thinking "Gee, just about every compressor I see these days has 3 + hp. Take a closer look at *every single display* that says this. They will *ALL* say "peak HP", which is completely and absolutely meaningless in this instance. Pure marketing drivel. Amps times volts equals watts, and for a motor, it'll take maybe 800 to 1000W for 1HP. Thus at 120V, it'll take at least 8A per HP. This you can likewise apply to other posters' numbers. Tim -- "That's for the courts to decide." - Homer Simpson Website @ http://webpages.charter.net/dawill/tmoranwms |
#25
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Compressor Motor: HP v.s. Amps?
Subject: Compressor Motor: HP v.s. Amps?
From: "Bob Swinney" Date: 04/10/03 04:47 GMT Daylight Time Message-id: zprfb.489686$Oz4.337254@rwcrnsc54 Well, Dave, aside from all your pomposity and references to "your" website, Are you trying to imply that it isn't my website? I pretty well covered it in my earlier post which was an honest answer to Chucks question. Strangely, though, you gave no mathematical examples to lend clarity to your statements, and to gain position otherwise lost by all the posturing. I'm not sure why you see it as posturing. You asked for comment on what torque really was and on the other statements that were not correct. If I took the liberty of replying on behalf of Richard Kinch then he can challenge my position or add to it as he sees fit. I could go into the maths ad infinitum but I see no point in repeating what is already explained in detail on my site. I incorrectly challenged you on one point and I apologized to you for that. Kindly disregard that apology now, for the spirit in which it was given has been sullied by your boorish, pompous and pedantic attitude. The basic definitions I gave for HP, torque and RPM are all valid. Although you have quoted the formulae quite correctly you apparently don't fully understand the underlying implications, or at least not to the point where you can explain them clearly to others. Torque and work are fundamentally unrelated. Dave Baker - Puma Race Engines (www.pumaracing.co.uk) I'm not at all sure why women like men. We're argumentative, childish, unsociable and extremely unappealing naked. I'm quite grateful they do though. |
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Compressor Motor: HP v.s. Amps?
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Compressor Motor: HP v.s. Amps?
Richard J Kinch wrote: Jon Elson writes: It would be fine for an air brush or tire filling, but almost any standard air tool, like a die grinder, air paint sprayer, (very small) sand blaster, air chisel, etc. will use at least 6 CFM, and some will use a lot more. Unless you want to wait 5 minutes out of every 6, you will soon be looking for a bigger compressor. Generally correct. But I found that an air chisel is so hard on the skeleton, that you don't want to apply it at anything close to 100 percent duty cycle. Now sand blasting, that is something else, you have an infinite appetite for air with that. It depends on the job. I haven't done much metalwork with an air chisel. But, I found a really odd way to use one. I have some of the hardest concrete ever found in the world. It is great for a tough foundation, until you want to drill a hole in it. I had to make a ~ 1.5" hole for a drain pipe from a "laundry tub" in my shop to the utility room where there is a floor drain. A Starrett carbide hole saw was instantly destroyed on this stuff, and hardly even made a mark on the concrete. So, I drilled a bit into it with a carbide masonry drill, and banged on things with a hammer a bit, and then the idea hit me to try the air chisel! I had a short pointed tool that came with it. It went through the concrete almost like butter. You just keep the point moving, and it shatters a little cement at a time. Eventually, the incredibly hard Jasper aggregate falls out, and there's new cement to attack. When I ran out of length on the provided tool, I made a 1 foot long version of it out of a McPherson strut rod that somebody gave me. I had to turn the air tool end down to match the tools that came with it. It was amazing! The added weight of the tool seemed to make it even more powerful. I made the entire hole through in one night, and then finished it to where a pipe would fit through it the next night. So, I ran the thing practically full blast for about 5 hours one night and 3 or so the next. I didn't find it particularly horrible to the bones and joints. Maybe it is worse in metal, with the rebound or something. It WAS a DIRTY job, I came up from the basement looking like a comics character, just 2 blinking eyes in a shapeless grey blob! Jon |
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Compressor Motor: HP v.s. Amps?
Bob Swinney writes:
The basic definitions I gave for HP, torque and RPM are all valid. No, you said, "Torque is the capacity of an engine to do work", which is just wrong. |
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Compressor Motor: HP v.s. Amps?
Dave Baker writes:
If I took the liberty of replying on behalf of Richard Kinch then he can challenge my position or add to it as he sees fit. You answered it fine, thank you. |
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Compressor Motor: HP v.s. Amps?
Daniel writes:
I also have a 500 gallon propane tank that I'm thinking of marrying one of them to.... Any thoughts other than to pressure test it from a good distance? Hold your nose. |
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Compressor Motor: HP v.s. Amps?
Jon Elson writes:
... the idea hit me to try the air chisel! I had a short pointed tool that came with it. It went through the concrete almost like butter. You just keep the point moving, and it shatters a little cement at a time. You have reinvented the star drill. So, I ran the thing practically full blast for about 5 hours one night and 3 or so the next. I didn't find it particularly horrible to the bones and joints. 20 minutes with an air chisel, and my hands are suffering vibration sickness. Half-paralyzed and tingly, like running a string trimmer for too long. Anti-vibe gloves help, but it still is too fatiguing for long sessions. This sort of thing can injure you seriously. |
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Compressor Motor: HP v.s. Amps?
Hi Tim,
Nothing personal, but as some aspects of this thread have become fairly pedantic, maybe we should continue in the same vein... Strictly speaking, volts times amps gives volt-amps (VA). If they are exactly in phase, then it's the same as watts. When the phase starts to shift, the line current increases *for the same true power delivered* (to an electric motor, for example). That is why the electric companies are always on about power-factor correction, because they need to keep their cable currents as low as possible - remember, resistive power losses in their cables is I-squared * R, which doesn't care about phase angles, power-factor, etc. Also, IIRC, your power meter on the wall measures true power, not VA, so you only get charged for the power you consume, not the VA that your equipment draws. So there's just a little more (useless?) trivia - like so many threads, we have drifted a long way from the original question... Roger Tim Williams wrote: "Chuck" wrote in message . .. The compressor currently has a 3/4 hp motor. At first glance I was kind of depressed thinking "Gee, just about every compressor I see these days has 3 + hp. Take a closer look at *every single display* that says this. They will *ALL* say "peak HP", which is completely and absolutely meaningless in this instance. Pure marketing drivel. Amps times volts equals watts, and for a motor, it'll take maybe 800 to 1000W for 1HP. Thus at 120V, it'll take at least 8A per HP. This you can likewise apply to other posters' numbers. Tim -- "That's for the courts to decide." - Homer Simpson Website @ http://webpages.charter.net/dawill/tmoranwms |
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Compressor Motor: HP v.s. Amps?
Richard J Kink sez:
"...No, you said, "Torque is the capacity of an engine to do work", which is just wrong..." Uh huh. And would you care to comment on exactly how that statement is wrong? Torque is a turning moment that defines the force applied to a shaft in order to do work. Without torque the shaft cannot turn, work cannot be done. Bob Swinney "Richard J Kinch" wrote in message . .. Bob Swinney writes: The basic definitions I gave for HP, torque and RPM are all valid. |
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Compressor Motor: HP v.s. Amps?
Bob Swinney wrote:
Richard J Kink sez: "...No, you said, "Torque is the capacity of an engine to do work", which is just wrong..." Uh huh. And would you care to comment on exactly how that statement is wrong? Torque is a turning moment that defines the force applied to a shaft in order to do work. Without torque the shaft cannot turn, work cannot be done. Bob Swinney These terms are all defined quite specifically. You can find them in any physics textbook. Look them up and compare them to your statements. You're just digging yourself in deeper. |
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Compressor Motor: HP v.s. Amps?
"Roger Head" wrote in message
... Strictly speaking, volts times amps gives volt-amps (VA). Ok, so step that up to 10 or 12A per HP due to reactive currents. Tim -- "That's for the courts to decide." - Homer Simpson Website @ http://webpages.charter.net/dawill/tmoranwms |
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Compressor Motor: HP v.s. Amps?
Subject: Compressor Motor: HP v.s. Amps?
From: "ATP" Date: 04/10/03 16:10 GMT Daylight Time Message-id: t Bob Swinney wrote: Richard J Kink sez: "...No, you said, "Torque is the capacity of an engine to do work", which is just wrong..." Uh huh. And would you care to comment on exactly how that statement is wrong? Torque is a turning moment that defines the force applied to a shaft in order to do work. Without torque the shaft cannot turn, work cannot be done. Bob Swinney These terms are all defined quite specifically. You can find them in any physics textbook. Look them up and compare them to your statements. You're just digging yourself in deeper. Just the top of a flat cap and a few stray locks of hair visible over the lip of the grave now. At regular intervals a shovel blade appears and another clod of earth flies over the edge and lands on the growing pile. As we get closer the sound of muttering and grumbling becomes audible from down below; it's a very warm day. Crickets chirp onomatopoeically in the long grass of the meadow behind the churchyard. An itinerant engine salesman wanders by and takes his ease on a tree stump. A clod of earth flies out and lands on his foot and he jumps up startled and lets out a small exclamation. The sound of digging ceases abruptly. A flat cap pops up above ground to reveal the red, sweaty, dust besmirched face supporting it. The face peers round and apprises the situation. "Sorry 'bout that guvnor. I didn't hear you come by." The salesman merely waves a languid hand by way of pardon and settles himself down again. He shakes the last grains of earth off his foot and takes in the labourer with a frank stare. "That's hard work for such a hot day my friend." he volunteers. "Too true guvnor. It's feckin hot work and no mistake." says Bob, for it is he. "Perhaps I can be of help then," says the salesman, "if an engine would ease your toil? I trade in such for my living." "Hmmmpf, engines." grumbles our worthy. "Tried one once and it b'aint no use." "How so?" queries the salesman. "Not enough torque. Weren't up to the job." The salesman raises an eyebrow and enquires further. "Torque?" "Aye guvnor, torque. For that's the capacity of an engine to do work and this one we tried didn't have enough. Oh it got there in the end but in hot weather like this it were a bit late if you take my drift." The salesman was apparently no expert at taking drifts and raised his eyebrow a fraction higher. Bob leaned forward confidentially. "The parson was doin' his nut, guvnor, and rightly so. By the time we was finished down 'ere they was starting to smell. It was alright in the winter like when you's got a day or two in hand but in the summer...well you can imagine what's it's like if we's late in this line of work." He grasps the end of his nose with two fingers by way of further explanation. By the expression of mild distaste on the salesman's face the drift has clearly now been well and truly taken. "I think I can supply you something that will meet your needs." he says. He reaches inside a battered valise and withdraws a well thumbed catalogue. He leaves through it briefly. "There are two engines I would recommend to you sir. One has a maximum torque of 50 pounds feet and the other has 75. Which of these would have the higher capacity to do work would you suggest?" Bob ponders this question but as he starts to reply our camera zooms out. The scene recedes into the distance until just the vague outline of a hump of earth and two people are visible. We can hear nothing further. So how did Bob reply? Dave Baker - Puma Race Engines (www.pumaracing.co.uk) I'm not at all sure why women like men. We're argumentative, childish, unsociable and extremely unappealing naked. I'm quite grateful they do though. |
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Compressor Motor: HP v.s. Amps?
In article rMAfb.683556$uu5.112144@sccrnsc04, Bob Swinney says...
Uh huh. And would you care to comment on exactly how that statement is wrong? Torque is a turning moment that defines the force applied to a shaft in order to do work. Without torque the shaft cannot turn, work cannot be done. Although to be a spoilsport, no work is done by a shaft that is providing a torque, but is not turning. A wrench on a stuck bolt, for example. Torque is still RXF but because the angular velocity is zero, work being done is zero. Jim ================================================== please reply to: JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com ================================================== |
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Compressor Motor: HP v.s. Amps?
In article , Richard J Kinch
says... No, you said, "Torque is the capacity of an engine to do work", which is just wrong. Possibly incomplete at worst. If there is no torque on a shaft, it cannot perform any work. That's close enough for me. Jim ================================================== please reply to: JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com ================================================== |
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Compressor Motor: HP v.s. Amps?
Aw Jeeze, Dave. I guess I was wrong about you. I had no further comment
until I read your little story, even if I was the butt of it. I do love a cockney story and who would have thought you were such a writer? Surely you have missed your true calling. Why, I'd even say your pomposity is exceeded only by your verbosity. Bob Swinney "Dave Baker" wrote in message ... Subject: Compressor Motor: HP v.s. Amps? From: "ATP" Date: 04/10/03 16:10 GMT Daylight Time Message-id: t Bob Swinney wrote: Richard J Kink sez: "...No, you said, "Torque is the capacity of an engine to do work", which is just wrong..." Uh huh. And would you care to comment on exactly how that statement is wrong? Torque is a turning moment that defines the force applied to a shaft in order to do work. Without torque the shaft cannot turn, work cannot be done. Bob Swinney These terms are all defined quite specifically. You can find them in any physics textbook. Look them up and compare them to your statements. You're just digging yourself in deeper. Just the top of a flat cap and a few stray locks of hair visible over the lip of the grave now. At regular intervals a shovel blade appears and another clod of earth flies over the edge and lands on the growing pile. As we get closer the sound of muttering and grumbling becomes audible from down below; it's a very warm day. Crickets chirp onomatopoeically in the long grass of the meadow behind the churchyard. An itinerant engine salesman wanders by and takes his ease on a tree stump. A clod of earth flies out and lands on his foot and he jumps up startled and lets out a small exclamation. The sound of digging ceases abruptly. A flat cap pops up above ground to reveal the red, sweaty, dust besmirched face supporting it. The face peers round and apprises the situation. "Sorry 'bout that guvnor. I didn't hear you come by." The salesman merely waves a languid hand by way of pardon and settles himself down again. He shakes the last grains of earth off his foot and takes in the labourer with a frank stare. "That's hard work for such a hot day my friend." he volunteers. "Too true guvnor. It's feckin hot work and no mistake." says Bob, for it is he. "Perhaps I can be of help then," says the salesman, "if an engine would ease your toil? I trade in such for my living." "Hmmmpf, engines." grumbles our worthy. "Tried one once and it b'aint no use." "How so?" queries the salesman. "Not enough torque. Weren't up to the job." The salesman raises an eyebrow and enquires further. "Torque?" "Aye guvnor, torque. For that's the capacity of an engine to do work and this one we tried didn't have enough. Oh it got there in the end but in hot weather like this it were a bit late if you take my drift." The salesman was apparently no expert at taking drifts and raised his eyebrow a fraction higher. Bob leaned forward confidentially. "The parson was doin' his nut, guvnor, and rightly so. By the time we was finished down 'ere they was starting to smell. It was alright in the winter like when you's got a day or two in hand but in the summer...well you can imagine what's it's like if we's late in this line of work." He grasps the end of his nose with two fingers by way of further explanation. By the expression of mild distaste on the salesman's face the drift has clearly now been well and truly taken. "I think I can supply you something that will meet your needs." he says. He reaches inside a battered valise and withdraws a well thumbed catalogue. He leaves through it briefly. "There are two engines I would recommend to you sir. One has a maximum torque of 50 pounds feet and the other has 75. Which of these would have the higher capacity to do work would you suggest?" Bob ponders this question but as he starts to reply our camera zooms out. The scene recedes into the distance until just the vague outline of a hump of earth and two people are visible. We can hear nothing further. So how did Bob reply? Dave Baker - Puma Race Engines (www.pumaracing.co.uk) I'm not at all sure why women like men. We're argumentative, childish, unsociable and extremely unappealing naked. I'm quite grateful they do though. |
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Compressor Motor: HP v.s. Amps?
Bob Swinney writes:
Torque is the capacity of an engine to do work And would you care to comment on exactly how that statement is wrong? No. Consult any post-medieval physics textbook on the topic of "rotational dynamics". Force, torque, work, power, etc., are all tidy concepts. |
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