Tell me about electrical motors

[verbotenwhisky]

I think, from my experience everyone is sorta right at the same time. First understand this is a 'from scratch build', I got a deal on a new tank and then started sourcing parts to build it into a compressor. I bought a compressor pump, actually a Harbor Freight. That pump is rated at around 900 rpm. The motor, whichever one I end up with, will have a correctly sized pulley added to it so that the compressor does in fact turn at or just below 900rpm. If the motor is a 1750rpm it will get a larger pulley than a motor turning 3450. I would like a lower rpm motor because it does have more torque, and like a low rpm compressor it 'should' last longer than a higher rpm unit. Since I'm building from scratch, I made sure the unloader will remove pressure from the head and about 18" of piping each time the compressor stops. When the pump starts up there should be no pressure to overcome.

I think you have it covered. Which of those heads did you buy? My brother and I have been looking at those for his shop, please let us know how it turns out.

 

[Investigator]

I think you have it covered. Which of those heads did you buy? My brother and I have been looking at those for his shop, please let us know how it turns out.

I did a lot of research, reading and youtubing....I got the Harbor Freight

5 HP 145 PSI Twin Cylinder Air Compressor Pump

Amazing deals on this 145Psi Twin Cylinder 5Hp Air Compressor Pump at Harbor Freight. Quality tools & low prices.

www.harborfreight.com

Now that I look it up online it says that pump is on clearance. I wonder, they are adding a McGraw brand in the smaller pumps, I wonder if they are going to have a new larger size as well. I also see it is a 1050rpm pump, so I'll make the numbers work with the right pulleys.

I hope to get this together and running in the next couple weeks.

I'll do a thread on the compressor build when I get it done. But basically I had a 5hp baldor motor that I got local for $20. Yes, twenty. Unfortunately it was shorted. I have a friend who has his own motor shop and he said he would rewind it for me. I've been waiting for over a year for it to get done, and was at the point I was just going to buy one and here we are. BUT, then last night I saw my buddy and mentioned to him I was going to buy one (basically so he didn't have to work on it) and he told me he had it about half done and I should have it in a week or so.

I'm looking forward to seeing how the compressor pump works and how well it lasts. I made a couple modifications as I was building.

 

[Beckerkumm]

Thanks for the clarification. I've done the build thing too but with old Quincy QR pumps. They are by far my favorite to work on and the sound is not annoying in comparison to most. Watch CL and Facebook Mktplace for motors. I've found many used motors for cheap and they are probably as good as the pump in longevity. Dave

 

[Investigator]

Thanks for the clarification. I've done the build thing too but with old Quincy QR pumps. They are by far my favorite to work on and the sound is not annoying in comparison to most. Watch CL and Facebook Mktplace for motors. I've found many used motors for cheap and they are probably as good as the pump in longevity. Dave

Yeah, it started with the thought and plan that I was going to build an awesome large tank and relatively high CFM compressor for dirt cheap. All in all I will still be far below what it should cost but the time it has taken has been a killer. Looking back now and mainly considering how long it has taken to get to this point, I should have just gone to one of the big box stores and bought as large as I could afford and been done.

 

[Eddyde]

Eddyde,

If the pump comes with the pulley as most do and has a tag which says to use a 3600RPM motor then that is what it is designed for. They are designed to run for x length of time then shut down; so, if you use a 1750RPM motor, you are not doing yourself any favors, . PSI is pressure per square inch meaning for every square inch of piston surface area you are dealing with that much force. If the compressor drops to 80 PSI before kicking on and your piston has 2.5 square inches to before it ever turns over it first has to overcome 200 pounds of force and that force will build as the pressure builds until it shuts off. The big heavy pulley is also a flywheel which once moving provides inertia through rotating mass to help over come that force, rotating that mass at a slower than design RPM actually creates additional load and heat. As I said in a previous post, I am not against either the 1750 nor the 3600 RPM motor, I am advocating to use the motor specification the compressor head is designed for.

Yes I agree, compressor pumps are designed to run at different speeds. My point is the slower speed compressors are usually better made and last longer. Hence they are usually more expensive.

"Heat will be an issue either way, the longer it runs the more heat will build up slowly" Not necessarily, the rate of heat dissipation must be considered. Example, With a slower compressor the heat may be dissipated at the same rate it is generated. If the same compressor is run faster it may not be able to dissipate the heat fast enough, causing it build up and possibly cause damage.
Yes, If one has a compressor designed to give x CFM at x speed and runs it slower it will give less CFM and take longer to reach the target pressure. However IMOH, it will run cooler, quieter and probably last longer, Albeit with some sacrifice in delivered air volume. Again, it depends what fits ones needs.