Air Compressor motor

[St3v3]

Hey everyone, I have a question about what to look for in a compressor motor. I need a 2 hp motor with 3450 rpm. I'm looking at one that says the duty cycle is continuous, that's good right? And it says service factor 1.0???? Not sure on that. Here are the specs:
Is this a good one

 

[PoorUB]

Anytime the tag HP has SPL listed instead of a number I am suspect of the HP. Also it states 15 amps at 120 volts, looks like it is really about 1-1/2 HP to me.

A "real" 2 HP motor will not run on a standard 120 volt outlet as it will draw around 20 AMPS.

What motor are you replacing?

 

[Citation]

If you are replacing a motor on a typical belt drive, 120v compressor then yes, this should be fine. If you are replacing something other than that more information is needed.

 

[joe_padavano]

"SPL" on the tag means "Danger Will Robinson".

Here's a real 2HP Marathon motor. It draws 17A at 115V.

https://www.tractorsupply.com/tsc/product/marathon-electric-air-compressor-motor-2-hp

 

[Walkers]

SPL means we don’t want you to know the true horsepower of this motor and since we have been sued we can longer lie about it.

 

[JRC3]

What's it going on? Plenty of rotten tanks out there with good motors to be found on CL and the like.

 

[St3v3]

It is going to go on a 12 gallon compressor with a 2 HP pump. And I'd like to run it on 120.

 

[PoorUB]

That TSC motor should do it.

 

[St3v3]

So that TSC motor is a true 2hp for $350 and all the motors I see going for $150-$199 are probably SPL hp. Even the one above of the pic I posted was advertised for $119.99 I thought that was to good. But you get what you pay for most of the time. Thank you fellas I appreciate your input and hope you all had a good New Years.

 

[Citation]

Was the original motor really a true 2hp? I know that some older belt drive compressors really did come with 2hp motors that required a 20A circuit and included a 20A plug (the one with the horizontal prong). I can't think of any one I've seen recently that wasn't a 15A or less motor (my CH included). A compressor rated motor is likely fine, especially if it's $120 vs $350.

 

[St3v3]

Was the original motor really a true 2hp? I know that some older belt drive compressors really did come with 2hp motors that required a 20A circuit and included a 20A plug (the one with the horizontal prong). I can't think of any one I've seen recently that wasn't a 15A or less motor (my CH included). A compressor rated motor is likely fine, especially if it's $120 vs $350.

No It's an old Sears compressor 1 hp the specs say it can run on a 15 amp circuit by itself. Says at max pressure it pulls 15.5 amps. But I had to replace the pump, and the new one says its a 2 hp. The old motor was working but then it started tripping the breaker like 15 seconds after starting. It has a new run capacitor, but still trips the breaker. So I figure I need to just look for a 2 hp motor to match the new pump.

 

[CallumRD1]

If you're tripping the breaker while running then your motor is demanding more current than the breaker can supply. Unless you get a high efficiency motor like a Baldor Super-E then trying to switch out to a more powerful motor won't solve your problem, it will just demand even more current. A true 2 hp motor running with a 2 hp load will pull a solid 20 amps. A general rule of thumb for motors is that they draw 10 amps per horsepower.

 

[Citation]

If I understand the new pump is a higher power unit vs the original. Was the pulley ratio changed to account for this?
Are you referring to the breaker for the household wiring or the breaker in the compressor motor (I think all small induction motor compressors have one)

Is the 15 seconds dependent on tank pressure? Does it trip if you leave the tank drain valve open?

It's quite possible the only issue is your motor is too small for the pump. You can probably fix this with a change in pulley size (assuming you can get a smaller motor or larger pump pulley).

If you are looking at $200+ to deal with this can you just get a new compressor? Walmart is unloading some 8 gallon, low flow rate quiet compressors for under $100. Of course that may not be sufficient for your needs.

 

[St3v3]

If I understand the new pump is a higher power unit vs the original. Was the pulley ratio changed to account for this?
Are you referring to the breaker for the household wiring or the breaker in the compressor motor (I think all small induction motor compressors have one)

Is the 15 seconds dependent on tank pressure? Does it trip if you leave the tank drain valve open?

It's quite possible the only issue is your motor is too small for the pump. You can probably fix this with a change in pulley size (assuming you can get a smaller motor or larger pump pulley).

If you are looking at $200+ to deal with this can you just get a new compressor? Walmart is unloading some 8 gallon, low flow rate quiet compressors for under $100. Of course that may not be sufficient for your needs.

Yes the new pump claims to be a 2hp unit, even though the SCFM specs are the same as the original 1hp pump (5.3@90psi & 6.2@40psi)

Yes in the 15 seconds it's tripping the breaker with the tank drain open.

And yes I did change the motor pully. But its still a little smaller than what is needed. I ordered a 3.5" that it calls for, currently I have a 2.5" its the only one I had at the moment. Not sure if just an inch would cause the tripping.

 

[Citation]

A 2.5 vs 3.5 could make a big difference. That's trying to speed the pump up by 40%. Very big difference and very likely why the breaker would trip.

Definitely try the correct size pulley. Incidentally, how did you decide pulley size? Did you calculate the correct pulley size for the pump's stated operating RPM?

 

[St3v3]

A 2.5 vs 3.5 could make a big difference. That's trying to speed the pump up by 40%. Very big difference and very likely why the breaker would trip.

Definitely try the correct size pulley. Incidentally, how did you decide pulley size? Did you calculate the correct pulley size for the pump's stated operating RPM?

I used a calculator at blocklayer.com
I'll post the out come when I get the pulley. I didn't even think about it that way, I was just figuring that the pump would be turning with way less rpm. Forgot it would work the motor more. Well until the right pully gets here.

 

[seber]

No. 2 1/2" drive pulley will turn the pump slower not faster than 3 1/2". But it is true that a 110 circuit will never run a true two horse motor even with no load at all.

 

[Citation]

No. 2 1/2" drive pulley will turn the pump slower not faster than 3 1/2". But it is true that a 110 circuit will never run a true two horse motor even with no load at all.

Yeah, I had that backwards. If the correct pulley was 2.5" and you are using 3.5" then yes, it is getting over driven. If you are using a smaller pulley then it shouldn't be getting over driven.

It sounds like both motors are 15A motors regardless of their HP ratings.

OP, if you pull the belt entirely does it still trip the breaker? If 3.5" is the correct pulley size and you are using a 2.5" then yeah, you are way under driving the pump and I wouldn't expect the motor to have any issues. Perhaps the starter cap or centrifugal switch is bad.

 

[St3v3]

Well everyone thankyou for your input. Well I am waiting on a new motor to get shipped to me, its a 2hp and should work well. As for my old 1 hp that came with the original unit, I got the correct pully for it and it did spin faster but same thing. So I also out of curiosity re-wired the motor from 120 to 230v. And it seemed to do better at first but now instead of tripping the circuit breaker it trips the thermal switch (I think its called) that's built in to the motor?
So when I ran the motor at 120v it would trip my circuit breaker at the box, which means it's pulling a lot of amperage I guess. And running it 230v it's getting to hot right away so it shuts off with the motors, built in thermal switch. I guess it might be the centrifugal switch plate thing, since I replaced both capacitors run & start. But I'll save that for another time. Hopefully the new motor will get me going now with a working compressor. Thanks again..