I have a couple of questions for some of you who are likely far more knowledgeable about air compressors...I have a Kellogg American 321 2 stage compressor pump that I bought several years ago, still new on it's original shipping pallet. I since obtained a good 80 gallon tank and am in the process of trying to finally set it up. I have a Baldor 3 HP motor that I am intending to use - It's a REAL one, weighs in at 78 lbs...In the place I have to set this up, I only have access to 120V power. According to the wiring diagram on the motor, it can be wired for either 110 or 220. Was looking for a pressure switch to use with it and simply cannot find one that says it's rated for 3 HP on 120 volts. I'm relatively ignorant about the finer points of electrical assembly but have no trouble with things like wiring this motor according to the diagram and other things of the sort. First question is about the pressure switch. I like the Condor brand of switches and have had good luck with them before and would like to use on of theirs on this set up. The closest thing I can find is one on Ebay - a model MDR3, which is a pressure switch and magnetic starter all in one. That sounds really good but the specs say it is for single phase 220V. Some others can be found that will work with 110 volts but with 2HP motors or less. Also, I can't figure out why the HP of the motor is critical in relation to the pump. As long as the RPM for the motor and pump match, what difference does it make if it's a 1 1/2HP or a 3HP? If you pull up the specs on a 321 pump, it shows 2HP as the max HP for this pump. This pump has a double sheave pulley, as does the motor I have. I've checked the diameter of the pump pulley and the motor pulley and it gives exactly the RPM needed for this pump. Can anybody out there shed some light on the particulars of all of this? I pics are needed, I can possibly figure out how to attach a few...I don't want to set something up to fail and don't want to waste a bunch of money on the wrong things...Any enlightenment would be much appreciated!
Kellogg American 321
- Thread starter drsamm
- Start date
A photo of the motor nameplate would be very helpful for providing assistance with selecting a pressure switch and/or motor starter. Otherwise if you could provide the P/N of the motor, that nameplate info could likely be source online.
I looked up the Condor MDR3 on their website. [url]https://www.condor-usa.com/air-compressor-switches-mdr3-usa [/URL]
It looks like this unit is only rated for 2HP with 120V single phase power. I've attached a screenshot of the section of their website that provides this info.
As for the HP requirements of your pump... Since you said that you've already ensured that the pump will spin the correct speed based on motor RPM and motor pulley to pump pulley ratios, then as long as your motor is rated for more than or equal to the HP requirement of your pump (which you say it is), than you'll be fine. As you've already figured out the pump requires a max of 2HP, that number would have been calculated by the manufacture, based on the max pressure that the pump is rated to. As you build more pressure with the pump, it puts more of a load on the motor, thereby drawing more power through the motor, therefore your working pressure and the motor HP required will have a direct correlation. If you were to try using a smaller motor than recommended, than you could run into a situation where at high pressures, the motor would be put under more load than it is rated, thereby drawing more power (current/amps) than the motor is rated, resulting in tripped breakers or letting the magic smoke out of the motor. So it's actually a benefit that your motor is over-sized, it will run at lower load, therefore generating less heat, which should result in a longer motor lifespan.
I looked up the Condor MDR3 on their website. [url]https://www.condor-usa.com/air-compressor-switches-mdr3-usa [/URL]
It looks like this unit is only rated for 2HP with 120V single phase power. I've attached a screenshot of the section of their website that provides this info.
As for the HP requirements of your pump... Since you said that you've already ensured that the pump will spin the correct speed based on motor RPM and motor pulley to pump pulley ratios, then as long as your motor is rated for more than or equal to the HP requirement of your pump (which you say it is), than you'll be fine. As you've already figured out the pump requires a max of 2HP, that number would have been calculated by the manufacture, based on the max pressure that the pump is rated to. As you build more pressure with the pump, it puts more of a load on the motor, thereby drawing more power through the motor, therefore your working pressure and the motor HP required will have a direct correlation. If you were to try using a smaller motor than recommended, than you could run into a situation where at high pressures, the motor would be put under more load than it is rated, thereby drawing more power (current/amps) than the motor is rated, resulting in tripped breakers or letting the magic smoke out of the motor. So it's actually a benefit that your motor is over-sized, it will run at lower load, therefore generating less heat, which should result in a longer motor lifespan.
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Firebrick43
Well-known member
It a specific number of hp to turn a pump a specific rpm pumping up to a specific pressure/cfm. If that number is 3hp you can NOT turn that load with 1-1/2 hp period.
You could however turn the pump slower with different set of pulleys(sheaves are the correct terminology, pulleys are flat belts) but it’s a compromise. Turning slower will lower the cfm rating of the pump. Setting the pressure lower will typically lower the horse power somewhat as well.
Now you can only turn a splash lubricated pump so slow or lubrication will fail.
https://www.equipupstore.com/uploads/K321-Manual.compressed.pdf
Page 12 of this manual has a chart of hp requirements in the lower right hand corner based on rpm and pressure setting.
Note running at 400 rpm will be significantly quieter than 750-800 rpm. My personal compressor is actually a nominal 7.5 hp pump turning 425 rpm with a 5hp motor and you can talk on the cell phone right next to it and the person on the other end can’t hear it.
As far as 120v vs 220 v it is strictly a manner of amps. Even if you could actually wire the motor the wiring and breakers for 3 hp FLA is 34 amps!!! By going to 220 you only pull 17 amps. I imagine you could find one but I have never seen a single pole (110v)breaker rated over 30amps. I don’t think there is any 110v plugs rated over 30 amps either. You would need 8 gauge Wire.
On the other hand 2 pole (220v) 20amp breakers are common as dirt and there are several styles of plugs/receptacles rated for 20 amps. You would use 12 gauge wire.
You could however turn the pump slower with different set of pulleys(sheaves are the correct terminology, pulleys are flat belts) but it’s a compromise. Turning slower will lower the cfm rating of the pump. Setting the pressure lower will typically lower the horse power somewhat as well.
Now you can only turn a splash lubricated pump so slow or lubrication will fail.
https://www.equipupstore.com/uploads/K321-Manual.compressed.pdf
Page 12 of this manual has a chart of hp requirements in the lower right hand corner based on rpm and pressure setting.
Note running at 400 rpm will be significantly quieter than 750-800 rpm. My personal compressor is actually a nominal 7.5 hp pump turning 425 rpm with a 5hp motor and you can talk on the cell phone right next to it and the person on the other end can’t hear it.
As far as 120v vs 220 v it is strictly a manner of amps. Even if you could actually wire the motor the wiring and breakers for 3 hp FLA is 34 amps!!! By going to 220 you only pull 17 amps. I imagine you could find one but I have never seen a single pole (110v)breaker rated over 30amps. I don’t think there is any 110v plugs rated over 30 amps either. You would need 8 gauge Wire.
On the other hand 2 pole (220v) 20amp breakers are common as dirt and there are several styles of plugs/receptacles rated for 20 amps. You would use 12 gauge wire.
Thank you for the quick responses...Will try to attach pics of the motor plate so we can get to the bottom of what will actually work and what will not. I would 100% rather just run on 220 but the upper garage of my home has no provision for it and the breaker box is in the basement garage. The way the house is built, I can see no possibility of running a line that far and thru the obstacles that exist. I was really hoping to make the 110 work, but as I said, I am by no means an expert on the finer points of correctly doing something like this. Hopefully I can get a pic attached. Sometimes is a bit vexing to do this on the various forums...Light was a bit reflective, so have attached 3 that look the same but maybe one is better over the others...
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American Locomotive
Well-known member
I mean, as it sits right now that motor will need a dedicated 40A (minimum) circuit to run on 120v. It's really unlikely you have a 40A 120v service going to your garage.
No matter what I think you'd have to run a new power feed to your garage.
No matter what I think you'd have to run a new power feed to your garage.
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Yes, that's what I was afraid of. And of course you are right, certainly no 40 amp 120V circuits anywhere. I have a couple of 220 plugs in the basement garage for my welders, plasma cutter and a very large 2 stage Devilbiss compressor, but none elsewhere. Although I suspected that it didn't look quite right, I guess wishful thinking got the better of me. So now I'm left to some little Craftsman or Home Depot special to use upstairs and certainly nothing 2 stage. Thanks to all who responded. I knew I could come here and get clear and correct information.
American Locomotive
Well-known member
Why not just run an external conduit or air line along the outside wall?
One word...(And potentially the most deadly of all) - wife. Might could possibly work on her for a while and figure a way to run it in a really unobtrusive way. Looks like my only option, if I want to set this thing up. If I did that, of course, I'd simply run 220 up there. So on another note - do you think, if I was able to run the 220 up there, that this set up would be better off with a magnetic starter too? Some of the Condor pressure switches actually have them built in and it looks like a pretty good set up...what's your opinion?
marinusdees
Well-known member
If the pressure switch is rated to handle the nameplate ampere rating of the motor, then you don't need a mag starter. Typically, the pressure switch will have an ampere rating but also a HP rating and you need a HP rating equal or greater than the motor HP. It will obviously work with a mag starter, and depending on the coil voltage of the starter, allow a remote switch to energize the coil.
American Locomotive
Well-known member
There are some 5HP compressors running directly off a pressure switch, and do okay. If you get a 5HP pressure switch, it will likely live a very long time with a 3HP motor. You could get a mag starter if you want, but I don't really think it's necessary for a 3HP motor.
An external conduit painted the same color as the house would be really unobtrusive, IMO. Really wouldn't be any different than the electrical feed providing power to your house...
An external conduit painted the same color as the house would be really unobtrusive, IMO. Really wouldn't be any different than the electrical feed providing power to your house...
Yes, you may have a good idea with the painted conduit, especially if I could run it along the bottom edge of the siding on the kitchen side of the house. It is only exposed to a small garden area, so nobody would have any idea what it was and it's also where the power meter and internet box are located. I might can sell that...also, in regard to the magnetic starter...don't they provide a sort of soft start for the motor instead of just a bam you're on sort of thing? I would think, although maybe not entirely necessary, that it might not be a bad idea with a motor pulling so much amperage. But again, I am NOT an electrical guy, so I'm just thinking out loud. Thanks for the quick responses and good advice! Please feel free to add to any of it at any time...
American Locomotive
Well-known member
Mag starters don't provide a soft start. They just have larger contacts and a more powerful mechanism to ensure the contacts make/break correctly compared to a pressure switch.
OK, I thought they were to sort of ease the load of big amps being introduced to a line as opposed to just an on/off like a light switch. I much appreciate the correcting information. I guess this is the danger of a relative novice trying to figure out something like this without proper guidance!
American Locomotive
Well-known member
Mag starters do two things:
The allow for the controller (whatever is deciding to turn the motor on/off) to be much smaller, and they usually have "overload heaters" which cause the mag starter to turn off if the motor draws too much power for too long.
Your motor has built in protection (the THERMALLY PROTECTED on the dataplate), so you don't need the overlord protection provided by most mag starters.
There are devices to "soft start" a motor - literally called soft-starters - but they are in no way related to mag starters.
The allow for the controller (whatever is deciding to turn the motor on/off) to be much smaller, and they usually have "overload heaters" which cause the mag starter to turn off if the motor draws too much power for too long.
Your motor has built in protection (the THERMALLY PROTECTED on the dataplate), so you don't need the overlord protection provided by most mag starters.
There are devices to "soft start" a motor - literally called soft-starters - but they are in no way related to mag starters.