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#11
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Air Compressor Horsepower/Wattage/Amperage
Thanks, Don. As you say, it is "interesting" but it doesn't speak to the
point. So far I haven't had an on-point reply. This link is technically good as it tries to relate the impossibility of some advertized horsepowers pumping out SCFM, but SCFM relates to electrical power not. Forget I said compressor except for the calculation of wattage/amperage required in a partially full compressor tank. All I need to do is to rationally or experimentally match a generator with a motor that HAPPENS to be connected to a compressor. To hell with inflated horsepower claims, airplane engines, and the like. Simple question. One horse compressor motor. How much peak amperage/wattage to start it zero PSI in the tank, how much to keep it running to max PSI of (say) 100 psi, and how much to REstart it when the pressure drops to 80 psi. Jim -- "Dream as if you'll live forever. Live as if you'll die today." --James Dean "Don Tuite" wrote in message ... Jim, this is interesting: http://www.truetex.com/aircompressors.htm (Sorry if it's a repost.) Don |
#12
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Air Compressor Horsepower/Wattage/Amperage
RST Engineering wrote: To hell with inflated horsepower claims, airplane engines, and the like. Simple question. One horse compressor motor. How much peak amperage/wattage to start it zero PSI in the tank, how much to keep it running to max PSI of (say) 100 psi, and how much to REstart it when the pressure drops to 80 psi. Jim: I'll check at first light and give you actual model numbers for my old oilless. I used to run it off a 4500watt/5000 watt surge genset until one of the brushes in genset let go and the compressor motor burned up while on a trip. The compressor would start under any load condition in the tank on the genset with one exception, and that was with over 100 psig in the tank and ambient air temp over 110 degrees F. and having been used nearly continously for over an hour. At that point, I would have to bleed the tank pressure to under 100 psig toi get it to start. Craig C. |
#13
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Air Compressor Horsepower/Wattage/Amperage
Jim: Here are the nameplate specs for the compressor that I have.
It's listed as a 4HP Model 919.152921 125 psi max 120/240 V 1 phase 15/7.5 amps Calif. Code 462 (L)(2) / Max RPM 3450 Hope this helps a little at least. Craig C. |
#14
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Air Compressor Horsepower/Wattage/Amperage
On Jun 19, 10:09 pm, "RST Engineering"
wrote: Forget I said compressor except for the calculation of wattage/amperage required in a partially full compressor tank. All I need to do is to rationally or experimentally match a generator with a motor that HAPPENS to be connected to a compressor. To hell with inflated horsepower claims, airplane engines, and the like. Simple question. One horse compressor motor. How much peak amperage/wattage to start it zero PSI in the tank, how much to keep it running to max PSI of (say) 100 psi, and how much to REstart it when the pressure drops to 80 psi. A belt-driven compressor relies on its flywheel to drive it through a compression stroke. The electric motor produces an amount of torque that probably won't be enough to run a compressor without a flywheel, or a compressor that has been stopped and has to start against pressure. For that reason, most compressors have an unloading system that exhaust the discharge line to let the compressor spool up before it has to work against pressure. I've tried to measure peak amps on a starting motor, and it isn't easy. The mass it is driving affects it a lot, and even with no load a squirrel-cage motor draws a bunch, maybe double its running current, but it's so brief that the circuit breaker puts up with it. Running off a generator means either a limited current supply that causes massive voltage drop on start, so that the motor won't come up to speed. And if you are starting against 80 psi with a non-unloaded compressor you will need both a BIG motor and a BIG generator. Sorry I can't give you numbers. Most of us won't be able to. There are too many variables and I don't have even the basic info. Even the motor type affects it: capacitor or non-cap start, compressor size and mass, on and on. What is the motor rated to start? A low load like a jet pump or table saw, or a heavy load like a big fan? I built my own compressor years ago using an old truck compressor, and drove it with a 1-horse 3450 RPM jet-pump motor. This motor has next to no starting torque, so the compressor is set up to run continuously and the original unloaders in it are engaged when tank pressure is reached. I have to manually unload it to start it, and shut it off when I'm done. Truck compressors have a device that hold the intake valves open when the tank is full so that it can't compress anymore. The crankshaft keeps turning. Dan |
#15
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Air Compressor Horsepower/Wattage/Amperage
wrote in message oups.com... I built my own compressor years ago using an old truck compressor, and drove it with a 1-horse 3450 RPM jet-pump motor. Dan How did you supply oil pressure to lube the crankshaft? or did this compressor have its own closed sump and pump or splash lube system? TIA |
#16
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Air Compressor Horsepower/Wattage/Amperage
On Jun 20, 12:31 pm, "Private" wrote:
wrote in message oups.com... I built my own compressor years ago using an old truck compressor, and drove it with a 1-horse 3450 RPM jet-pump motor. Dan How did you supply oil pressure to lube the crankshaft? or did this compressor have its own closed sump and pump or splash lube system? TIA It was a base-mounted belt-driven compressor that was supplied oil from the engine's oil system. I made a steel base plate to close it off, drilled the side of the case and tapped it for a 1/2" 90° pipe elbow for a filler/level check plug, and drilled and tapped the con rod caps for 1/8" pipe street ells that acted as scoops to grab the oil from the sump and jam it into the bearings. The main bearings were ball bearings and get plenty of splash to keep them happy. The thing has run happily for probably 100 hours over the last 20 years and shows no sign of distress. Dan |
#17
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Air Compressor Horsepower/Wattage/Amperage
wrote in message ps.com... On Jun 20, 12:31 pm, "Private" wrote: wrote in message oups.com... I built my own compressor years ago using an old truck compressor, and drove it with a 1-horse 3450 RPM jet-pump motor. Dan How did you supply oil pressure to lube the crankshaft? or did this compressor have its own closed sump and pump or splash lube system? TIA It was a base-mounted belt-driven compressor that was supplied oil from the engine's oil system. I made a steel base plate to close it off, drilled the side of the case and tapped it for a 1/2" 90° pipe elbow for a filler/level check plug, and drilled and tapped the con rod caps for 1/8" pipe street ells that acted as scoops to grab the oil from the sump and jam it into the bearings. The main bearings were ball bearings and get plenty of splash to keep them happy. The thing has run happily for probably 100 hours over the last 20 years and shows no sign of distress. Dan I have had good luck and extensive service from these compressors, but always by mounting them on engines where I was able to connect them to the engine's pressure oil and coolant systems. I used an electric clutch pulley so they did not need to run continuously, IMHO they are very good compressors. The current high cost of fuel makes it an expensive way to obtain pressure air in any quantity unless the engine will be operated anyway. Happy landings. |
#18
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Air Compressor Horsepower/Wattage/Amperage
On Jun 21, 10:40 am, "Private" wrote:
wrote in message ps.com... On Jun 20, 12:31 pm, "Private" wrote: wrote in message roups.com... I built my own compressor years ago using an old truck compressor, and drove it with a 1-horse 3450 RPM jet-pump motor. Dan How did you supply oil pressure to lube the crankshaft? or did this compressor have its own closed sump and pump or splash lube system? TIA It was a base-mounted belt-driven compressor that was supplied oil from the engine's oil system. I made a steel base plate to close it off, drilled the side of the case and tapped it for a 1/2" 90° pipe elbow for a filler/level check plug, and drilled and tapped the con rod caps for 1/8" pipe street ells that acted as scoops to grab the oil from the sump and jam it into the bearings. The main bearings were ball bearings and get plenty of splash to keep them happy. The thing has run happily for probably 100 hours over the last 20 years and shows no sign of distress. Dan I have had good luck and extensive service from these compressors, but always by mounting them on engines where I was able to connect them to the engine's pressure oil and coolant systems. I used an electric clutch pulley so they did not need to run continuously, IMHO they are very good compressors. The current high cost of fuel makes it an expensive way to obtain pressure air in any quantity unless the engine will be operated anyway. Happy landings. This was an old aircooled unit, circa 1950, that showed up in some returned cores. Instead of the usual unloader pistons that lifted the intakes, it has intake ports in the cylinder wall that the piston uncovered near the bottom of the stroke. The unloaders are separate small valves in the head similar to small-engine valves, opened by a lever operated by metal diaphragm that received the air signal from the governor. The whole design of these old compressors resembled an outboard motor powerhead, and in researching the origins of Bendix- Westinghouse compressors I discovered that the first units were converted Evinrudes. So much for the similarities. By the way: of the thousands of compressors we rebuilt, I would say that at least half of the cores had nothing wrong with them except for worn unloader piston O-rings, damage caused by a worn-out $20 governor. New O-rings were a few cents. A shot governor doesn't apply the unloading pressure suddenly, as it should, and the intakes bang the lifting pins and work the pistons up and down rapidly and wear the o-rings out. Leaky o-rings cause a pressure drop in the governor when it cuts the compressor out, it thinks the tank pressure has dropped, and it cuts in again so that the compressor is on/off/on/ off rapidly and the driver or mechanic thinks it's shot. About a fifth of cores were those off Detroit Diesels and had the phenolic drove coupling that would shear internally off its steel hub but remain attached to the hub and look perfectly normal. It couldn't drive the compressor, a compressor that had nothing wrong with it. And the rest had been allowed to eat dust through old/missing/ cheap air filters, and dust destroys a compressor faster than it will an engine. It sticks to the thin film of oil on the cylinder wall instead of being vaporized and blown out, and the cylinder and rings eat each other. Maybe you guys aren't interested in all this, but the point is that most of our troubles with machinery are our own fault, either through ignorance or just being plain cheap. Dan |
#19
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Air Compressor Horsepower/Wattage/Amperage
Dan : Which models of truck compressors would work good for a homemade, engine driven unit? I need to have the capability of developing about 25-30 cfm at 70+ psig for s shop project. Tankage is a 650 gallon propane tank and I don't mind ganging two compressors together and having split cut-in/cut-out pressures. Craig |
#20
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Air Compressor Horsepower/Wattage/Amperage
wrote in message ps.com... Dan : Which models of truck compressors would work good for a homemade, engine driven unit? I need to have the capability of developing about 25-30 cfm at 70+ psig for s shop project. Tankage is a 650 gallon propane tank and I don't mind ganging two compressors together and having split cut-in/cut-out pressures. I don't know what it would cost to buy and fit a truck compressor, but have you seen this? http://www.wttool.com/product-exec/p...ompressor_Pump I built a 2 hp from a Mopar A/C compressor that I used for several years. But I think if I had to do it all over, I might just buy a pump from China. When my 5 hp Saylor Beal failed a few months ago, I bought a complete 10 hp that I believe uses this same compressor. It makes a lot of air even at 175 psi. Almost 35 CFM I think. |
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