# Air compressor problem



## grobljars (9 mo ago)

I recently upgraded my air compressor motor with a bigger pulley as the old one was way to small, so the RPM should now be correct, but now it doesnt work.
The problem is as soon as i disconnect the hose from the compressor head it works fine, but if its hooked to the check valve it wont work as the pressure is too high and the motor cant rotate anymore, i replaced the check valve with a new one and the problem is still the same, (inlet is 3/8" and out 1/2") is it possible that because of the 90degree angle and the small space inside the valve that it doesnt flow properly, could upgrading to a 1/2" in 1/2" out solve the problem or could it be something else?


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## motormonkey (Jul 10, 2016)

I have to guess that this compressor worked correctly until you "upgraded your air compressor motor with a bigger pulley, as the old one was way too small, so the RPM should now be correct."

How do you know the pulley was too small? How do you know that the "bigger pulley" is the correct size? How do you know that the RPM is now correct?


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## stevon (Mar 5, 2019)

grobljars,

A little research and calculations, first off the pump manufacturer will list what HP and recommended rpm at what HP. with this nifty calculator app there is no guessing.






Pulley Calculator. RPM, Belt Length, Speed, Animated Diagrams - Inch







www.blocklayer.com





So for example you find out that the pump has a maximum speed @ 5 hp to be 1000rpm. Pulley on pump = 12.0" diameter and the 5 hp motor RPM = 1725 rpm so what size diameter pulley is required for the motor drive pulley? you don't have to do any math to solve the equation just enter what you know into the calculator, hit "calculate" and answer is: 6.96 or 7 inches, then run nifty simulator, slide "rotate" for fun

Stephen


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## iowagold (Jan 22, 2020)

and the sheave change does affect the mechanical advantage.
and will affect start up.

the hp on the setup maybe too close...
they may have done a smaller motor dia to get back the advantage.

lots of math, and remember to have 10-20% more power than needed.
and watch the start up HP rating.

and yes you could have an issue on check valve, and all of the free wheel to start up parts.

pressure gauges in the right spots will show any issues.


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## stevon (Mar 5, 2019)

iowagold,

10-20 % extra margin, that's a good rule of thumb. Since compressor worked before and motor has been changed to *what motor*? what rpm? what type? service factor 1.0, 1.15, 1.25? type of motor farm duty? compressor duty? these are all open questions in this post. Question: was the rpm of motor changed from lets say from 1725 to 3500 rpm? need more info to solve this question, what is the specs of both motors?

Stephen


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## grobljars (9 mo ago)

So the air tank is 100l, the compressor head is FIAC AB360 - 350l at 10bar and 1500 RPM , recommended motor is 2.2KW 3HP, my motor is 2.2kw 2800 RPM before i had the pulley sized 8cm or around 3" and as i already used that calculator to find that i need a pulley sized 16cm or around 6" so i should have now around 14XX RPM, and that is all i changed, the motor pulley and the belt, so now the problem is it wont turn over, it does but really slow and the motor gets hot really quick.

It turns on when the air feed is disconnected, but when connected it doesnt, very small amount of air goes into the tank after a few seconds, i believe my motor actually has 2 speeds inside are 2 capacitors, maybe this is the problem ? and now the load is too big as the compressor spins twice as fast as before

My air feed is also kinda junk but it worked just fine before, from air compressor its 1/2" and i have it stepped down to a 1/2" barb connector and a double wall 8mm inner diameter rubber hose, on the other end is the same barb connector and then stepped down to 3/8" that fits the check valve. i did this just because i got the tank empty without the air line and i didnt find where i could get correct end fittings that are used to crimp/flare onto aluminum/copper tubes


Should i maybe try and add a pressure gauge just before the check valve if somehow i have more that 16bar of pressure now as most of the check valves that can be bought here are max 16bar?


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## grobljars (9 mo ago)

motormonkey said:


> I have to guess that this compressor worked correctly until you "upgraded your air compressor motor with a bigger pulley, as the old one was way too small, so the RPM should now be correct."
> 
> How do you know the pulley was too small? How do you know that the "bigger pulley" is the correct size? How do you know that the RPM is now correct?


i believe i answered your question up above, but as i said i measured both pulleys on the compressor and the motor, i know the motor has 2800 RPM and i calculated that i have around 800RPM on the compressor side, and the compressor itself needs around 1500 so with 6inch pulley on the motor i get around 14xx rpm, but that is all i changed, i added a new check valve with the same specs and its still the same not working


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## stevon (Mar 5, 2019)

grobljars,

Looks like you are definitely overloading your drive motor. Your problem may be that your specs are incorrect (wrong info) or that your motor is listed as overrated (a common marketing trick, it should show full load amps 12 to 14 amps) or that your power is the problem (too low voltage under load at the motor terminals, long run on thin wire, weak phase etc. 
With he 2.2 kw motor running at 1500rpm, that would be a 4 pole motor that has double the torque of the 2 pole 2800 rpm new motor. I looked up what the AB360 pump speed required by the manufacture with a 2.2 kw motor, shows as 1500 so derating by -10% it is 1350 rpm. (safe target speed) The FIAC AB360 pump pulley diameter I could find on the internet is 11" (measure yours to be sure). Now with a motor speed of 2800 rpm I get drive motor sheave or pulley size to be 5 5/16" in diameter, 1352.3 rpm at pump. For the 1500 rpm 4 pole motor sheave I get a 9 7/8" drive pulley, 1346.6 rpm at pump. The pump speed is the constant in your figures. Maybe there was some reason the OEM or the user had a slower pump speed (800) in the first place. At a target pump RPM of 800 rpm, the 2800 motor drive sheave comes out to 3.125 which is close to as small as you can go on a pulley driven by a 2.2kw motor. There are other tweaks you can perform, eg lower the top cutoff pressure, etc. but lets not get into that now. The basics, start with the basics

Stephen



grobljars said:


> So the air tank is 100l, the compressor head is FIAC AB360 - 350l at 10bar and 1500 RPM , recommended motor is 2.2KW 3HP, my motor is 2.2kw 2800 RPM before i had the pulley sized 8cm or around 3" and as i already used that calculator to find that i need a pulley sized 16cm or around 6" so i should have now around 14XX RPM, and that is all i changed, the motor pulley and the belt, so now the problem is it wont turn over, it does but really slow and the motor gets hot really quick.
> 
> It turns on when the air feed is disconnected, but when connected it doesnt, very small amount of air goes into the tank after a few seconds, i believe my motor actually has 2 speeds inside are 2 capacitors, maybe this is the problem ? and now the load is too big as the compressor spins twice as fast as before
> 
> ...


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## stevon (Mar 5, 2019)

grobljars,

Maybe the pump was too loud and ran too hot producing too much water. Slower pump rpm would help with these problems. An industrial, commercial pump almost never runs over 1000 rpm, 800 rpm or less is typical on commercial 5 HP and larger compressors

Stephen


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## grobljars (9 mo ago)

stevon said:


> grobljars,
> 
> Looks like you are definitely overloading your drive motor. Your problem may be that your specs are incorrect (wrong info) or that your motor is listed as overrated (a common marketing trick, it should show full load amps 12 to 14 amps) or that your power is the problem (too low voltage under load at the motor terminals, long run on thin wire, weak phase etc.
> With he 2.2 kw motor running at 1500rpm, that would be a 4 pole motor that has double the torque of the 2 pole 2800 rpm new motor. I looked up what the AB360 pump speed required by the manufacture with a 2.2 kw motor, shows as 1500 so derating by -10% it is 1350 rpm. (safe target speed) The FIAC AB360 pump pulley diameter I could find on the internet is 11" (measure yours to be sure). Now with a motor speed of 2800 rpm I get drive motor sheave or pulley size to be 5 5/16" in diameter, 1352.3 rpm at pump. For the 1500 rpm 4 pole motor sheave I get a 9 7/8" drive pulley, 1346.6 rpm at pump. The pump speed is the constant in your figures. Maybe there was some reason the OEM or the user had a slower pump speed (800) in the first place. At a target pump RPM of 800 rpm, the 2800 motor drive sheave comes out to 3.125 which is close to as small as you can go on a pulley driven by a 2.2kw motor. There are other tweaks you can perform, eg lower the top cutoff pressure, etc. but lets not get into that now. The basics, start with the basics
> ...


The motor is from an old bauer diving air compressor it could be that the specs are incorrect but the motor was rewinded newly as the old one melted it could be that it was rewinded incorrectly,
Should i be looking at a different motor then? and what specs 3kw and simmilar rpm

I have a rebuilt 4pole motor that was used before but rpm is around 1200 not sure exactly so that would be way to less 

The air compressor pulley is 30cm or around 11.8"

I could try and get a 14cm pulley for the motor so 2cm less than now maybe it would be enough to lower the load?


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## motormonkey (Jul 10, 2016)

Is there a data plate on that motor?


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## stevon (Mar 5, 2019)

grobljars, 

This would be a good place to start. also a cheap ammeter will tell you what's going on with HP produced and the load verses the specs on a nameplate.









6 Function Mini Clamp Meter


Amazing deals on this 6 Function Mini Digital Multimeter at Harbor Freight. Quality tools & low prices.




www.harborfreight.com





The full load or FL amps listed is the highest HP load that a motor can run at for a period of time. For a "compressor duty" type motor (50% on 50% off) that's about 10 minutes to one half hour at full load before it overheats and trips the thermal protection. If there is no thermal protection, it starts to burn up. In any case with a compressor the load increases as the pressure increases in the tank. You should start with less than the FL amps and finish filling tank at FL amps drawn (all the HP available). If you start at FL amps, you will never make it to a full tank and motor amps will go way beyond FL rating and possibly stall reaching LRA or Locked rotor amps (6 to 8 times FL rating)
Without the correct data either listed or figured out you're just randomly guessing

Stephen


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## stevon (Mar 5, 2019)

grobljars, 

The two capacitors are for starting the motor and possibly running the motor. if the start capacitor is bad or the start "clutch" switch is bad, you could see the issues that you are talking about. Maybe your motor has a problem, with an ammeter/volt meter this can be figured out



https://en.wikipedia.org/wiki/Motor_capacitor#:~:text=A%20start%20capacitor%20stays%20in,efficiently%20with%20a%20run%20capacitor


.

Stephen


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## grobljars (9 mo ago)

motormonkey said:


> Is there a data plate on that motor?


Not anymore but im 100% its 2.2kw singlephase 2800rpm


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## grobljars (9 mo ago)

I did some more digging, so yes my motor is 3HP and the pump calls for 2.2kw and 5HP motor, but all 2.2kw motors are 3HP, so to get 5HP i need 4kw three phase motor.

But the thing is if you look at the compressor, original fiac 100-360 its 100L with this pump that i have AB360 and that compressor has 2.2kw 3HP single phase motor listed in the details?

So could it really be that my motor has a problem? but both capacitors were replaced when it was rewind except the switch is still old that could be also junk.. ?


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## stevon (Mar 5, 2019)

grobljars, 

The AB360 pump is small , deigned for 1HP to 3HP motor use. If you use a 5HP motor, no harm is done but the load would be at max 3hp and only 3hp would be used of the 5hp available(less current drawn). The under load current draw tells the story even if the specs are incorrect or misunderstood. Your limitation is the maximum speed of the pump. That being said, 1500 rpm is very high IMO, it's the highest I've heard of in a reciprocating air pump design. At that speed heat, noise and stress is high and to be avoided. Most compressor companies are shy to run a pump that fast. The oil cooks and adds extra stress on components (shortens life). But that is the cheapest way to get more CFM out of a small pump design.
What are your current measurements? at no load (belt off) at start on an empty tank and at cutoff pressure? That will guide or trouble shoot your issue. 

Stephen


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## grobljars (9 mo ago)

stevon said:


> grobljars,
> 
> The AB360 pump is small , deigned for 1HP to 3HP motor use. If you use a 5HP motor, no harm is done but the load would be at max 3hp and only 3hp would be used of the 5hp available(less current drawn). The under load current draw tells the story even if the specs are incorrect or misunderstood. Your limitation is the maximum speed of the pump. That being said, 1500 rpm is very high IMO, it's the highest I've heard of in a reciprocating air pump design. At that speed heat, noise and stress is high and to be avoided. Most compressor companies are shy to run a pump that fast. The oil cooks and adds extra stress on components (shortens life). But that is the cheapest way to get more CFM out of a small pump design.
> What are your current measurements? at no load (belt off) at start on an empty tank and at cutoff pressure? That will guide or trouble shoot your issue.
> ...


I didnt do much measuring, i called up a guy locally that services and sells motors, im bringing my motor to him tomorrow so he will check it all with correct equipment, maybe some specs are incorrect, and he has a rebuilt motor with same specs that he will sell it to me and i will test the compressor with that one, if it still wont work i will exchange it for a three phase and hope that will work better.

As to me it makes no sense, the pressure switch is new, now the check valve is new, the pump is new, all that was changed was the pulley diameter on the motor and the motor it self was rewinded and has new capacitors but still on the old switch/clutch that is now prob 30years old so to me it looks like that is the only problem here, if the specs are correct and its the problem with the switch i wont need to buy another motor, but if i do buy it and it will work as it should that will be much better


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## stevon (Mar 5, 2019)

grobljars, 

1 phase or 3 phase has nothing to do with HP, HP is HP.
Three phase power is used in industrial applications because

A) it's readily available at industrial parks
B) cost less to run (lower power bill)
C) Motors are simple (no centrifugal starter required) 
D) Motors are less expensive and used motors available cheap

Cons: Usually not available in residential areas

Note: 1200 rpm motor is a 6 pole motor

Stephen



grobljars said:


> I did some more digging, so yes my motor is 3HP and the pump calls for 2.2kw and 5HP motor, but all 2.2kw motors are 3HP, so to get 5HP i need 4kw three phase motor.
> 
> But the thing is if you look at the compressor, original fiac 100-360 its 100L with this pump that i have AB360 and that compressor has 2.2kw 3HP single phase motor listed in the details?
> 
> So could it really be that my motor has a problem? but both capacitors were replaced when it was rewind except the switch is still old that could be also junk.. ?


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## stevon (Mar 5, 2019)

grobljars, 

Don't be intimidated about using an ammeter, just clamp on one of the power wires to the motor. This is a good skill for almost everybody working with electricity to have

This little training video will show you how to do it, remember to test only one of the wires at a time






Stephen


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## grobljars (9 mo ago)

stevon said:


> grobljars,
> 
> 1 phase or 3 phase has nothing to do with HP, HP is HP.
> Three phase power is used in industrial applications because
> ...


That i fully understand, but looking at the data for the pump as it calls for 5HP then i would need 4kw 3phase motor if that data would hold, but since the original compressor has the same 3HP motor then it should work fine for me as well, so something with my motor doesnt work as it should.

I have a multimeter at home and some basic knowledge of electrics, i could check with that, but since im already going to a specialist might as well have him check it up and if needed have it repaired.
After i would see how many amps it draws what would that tell me exactly?


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## motormonkey (Jul 10, 2016)

Just to be clear, when you had the small motor pulley on this compressor, you say the compressor worked fine. No motor overheating? Did the pressure tank reach full pressure? Did the pressure switch cut off and the motor stop when it did? Did you hear the hiss of air from the unloader valve when it did?

Your problem could be that the motor is defective, maybe a bad run capacitor, maybe a bad start capacitor or start cutout switch, maybe incorrectly wound, maybe incorrectly internally jumpered for the wrong voltage input.

Your problem could also be a defective unloader valve. It releases the pressure behind the check valve when the pressure switch reaches it high pressure cutout. Takes the load off of the motor when it restarts on low pressure cut on.


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## stevon (Mar 5, 2019)

grobljars, 

I like to say "what is your question specifically, then the answer will be apparent" 

My questions to be solved using an ammeter below. Make sure the motor guy has a load to test the motor, dynamometer or other load type

1) what is FLA listed for the motor?
2) what is the running current with no load? is the full rpm achieved?
3) what is the current under a light load? is the full rpm achieved?
4) what is the current under a heavy load? (ex: the pump is run up to 150 psi into the tank) is 95% of the full rpm achieved?

Once these questions are answered, the solution will follow. 
It seems that you have taken care of the possible mechanical issues so far.

Stephen


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## grobljars (9 mo ago)

motormonkey said:


> Just to be clear, when you had the small motor pulley on this compressor, you say the compressor worked fine. No motor overheating? Did the pressure tank reach full pressure? Did the pressure switch cut off and the motor stop when it did? Did you hear the hiss of air from the unloader valve when it did?
> 
> Your problem could be that the motor is defective, maybe a bad run capacitor, maybe a bad start capacitor or start cutout switch, maybe incorrectly wound, maybe incorrectly internally jumpered for the wrong voltage input.
> 
> Your problem could also be a defective unloader valve. It releases the pressure behind the check valve when the pressure switch reaches it high pressure cutout. Takes the load off of the motor when it restarts on low pressure cut on.




Sorry im a bit late, had some stuff to sort out.

So ive taken my motor to a specialist last time, and we measured the amps, he said its a bit low if it is really 2.2kw motor, by the size it looks right but the amp draw is too low, so our guess is it could be 1.5kw or it was rewinded incorrectly since id didnt have any plate on the motor it self. 

Both start and run capacitors were replaced at the same time, the start capacitor is 156-200uF 280V and the run cap is 40uf 450V.

The thing is i replaced the check valve again, this time for a bigger one 3/4inch out and 1/2inch in, at the shop where i bought it he said the one i had before was definitely too small since that size is usually used in 25/50l compressors.

AND this fixed half of the problem. The compressor now runs, BUT only when the tank is empty, when it has to restart its the same as before, turns really slowly and it the motor heats up fairly quick.

if i use the small pulley it works all the time, only when i use the bigger one it fails on the restart.

the unloader valve works fine, you can hear it when it stops, even if i take the tube off there is no pressure in between the valve and the compressor.

MY guess is that the motor is too weak, since the amperage showed a part of that, and i believe that when it restarts, it opens the valve but the pressure inside the tank is bigger than from the compressor and it leakes back and that breakes the whole setup.

So should i try and just go and buy a new 2.2kw motor single phase, it has only one cap, i believe its cap run type. Or could i "upgrade" my existing motor with bigger starting capacitor to get more torque?


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## grobljars (9 mo ago)

Here are the pictures of the wiring, if it could be incorrect,


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## grobljars (9 mo ago)

I forgot what the amperage draw with no load was when we bench tested it, but he said it was too low, now i wanted to measure it with my multimeter but it only reads DC amps so i could borrow one from a friend that reads ac amps, i tried using the wall plug that shows the watt draw, if it helps, using the small pulley it was around 10XX W after it was running for a minute and it was still going up, on startup it jumps to 18X0 W and its the same with the bigger pulley when the tank is empty


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## stevon (Mar 5, 2019)

grobljars, 

The motor guy gave you some information, but not of much use. The motor under *LOAD* tells you what HP the motor can produce. You know the load because the pump manufacture list the HP at speed so you don't have to use a dyno to create the information needed from scratch. The pump information provided gives you a fixed goal to meet. In the US, sales marketing BS sometimes HP is doubled or more verses the actual running HP under load. The actual amps drawn under load tells you how much real HP is actually being produced. Example: marketed vacuum cleaner states "develops peak 5HP" with a 15 amp cord and plug provided. In reality 5HP draws about 50 FLA amps on 110 vac, yeah develops 5HP just seconds before motor explodes and the cord starts flaming! With an ammeter we see the vacuum drawing 8 amps under load which is 1.04 HP actually being produced! So the marketing "HP" has no real value in the real world. I don't know how much time/money you have to play with this "unmarked mystery" AC motor. The amps under load would tell you if it could be used or not for your purposes. For $15 US I would buy a harbor freight ammeter and get something accomplished myself, though it is fun to play with used parts to save some money. A new or used motor with advertised specs on the name plate would be your quickest solution. I would still be using an ammeter to see what is going on with my load. Just my long winded 2 cents

Stephen


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## stevon (Mar 5, 2019)

grobljars,

1000 watts at 120 volt = 8.3 amps = 1.04 HP = 0.75 KW
1800 watts at 120 volt = 15 amps = 1.95 HP = 1.5 KW

Guessing the motor is a 1.5 KW or 2 HP basically. So if you run the motor on a 3HP (2.2 KW) load the motor will produce that but would quickly overheat and eventually trip thermal protection or just burn up. You see, it's possible to overload an electric motor to a degree but heat, stalling and LRA could be your result and we don't want that to happen!

Stephen



grobljars said:


> I forgot what the amperage draw with no load was when we bench tested it, but he said it was too low, now i wanted to measure it with my multimeter but it only reads DC amps so i could borrow one from a friend that reads ac amps, i tried using the wall plug that shows the watt draw, if it helps, using the small pulley it was around 10XX W after it was running for a minute and it was still going up, on startup it jumps to 18X0 W and its the same with the bigger pulley when the tank is empty


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## grobljars (9 mo ago)

stevon said:


> grobljars,
> 
> 1000 watts at 120 volt = 8.3 amps = 1.04 HP = 0.75 KW
> 1800 watts at 120 volt = 15 amps = 1.95 HP = 1.5 KW
> ...


Ill borrow the ampmeter from my friend then and ill test it when under load, im from eu so im looking at 230v then in your calculation, i have some time so ill play around with the motor tomorrow, but if its really not 2.2kw ill just buy another motor that should be correct


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## stevon (Mar 5, 2019)

grobljars, 

Sounds good, LRA is locked rotor amps which is about 6 times the listed full load amps so 10 FLA= 60 RLA. This is at startup under load at 0 rpm. As the rotor turns the amps go down to FLA or less. When you brutally overload a motor, it starts to stall and approach LRA amps. The windings and other wiring burns up hence the thermal protection (in most designs) The load is fixed at 2.2kw at X rpm so the question is if your motor can produce that. The only way to know is to mount the motor with the required pulley to turn the pump at listed rpm for that HP and measure the amps drawn on one leg of the circuit. The load will demand the required HP and the motor will produce it even if it is smaller but if it is not rated or designed for that load it will overheat, the more it is overloaded the faster it will overheat or stall. The only way to know if you are overloading the motor is to see the specifications stamped on the tag or plate of the motor. 

2.2KW, 3.0Hp, 1450 RPM, Single Phase, 230v, 50Hz 14 to 15 amps @ 93% efficiency. The current drawn under full 3 HP load should be approx 15 amps. That being said, the design has to meet your requirements. Meaning if you have a compressor turning on and off 50% of the time to cool in between filling of the tank cycles, then a "compressor duty" listed motor with thermal protection will work for you in that application. But if you run the compressor 70% on and 30% off you will be pushing the design limits of the "compressor duty" motor. I run my compressor duty or "light use" WEG motor to a 4 HP load, and can run over an hour straight without tripping the thermal over load protection. You can buy "severe duty" or "service factor 1.25 " motors but they cost near double the compressor duty motors. It all depends what your application demands.

Stephen



grobljars said:


> Ill borrow the ampmeter from my friend then and ill test it when under load, im from eu so im looking at 230v then in your calculation, i have some time so ill play around with the motor tomorrow, but if its really not 2.2kw ill just buy another motor that should be correct


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## stevon (Mar 5, 2019)

grobljars,

I purchased a 5 HP WEG (Brazilian made) 230 volt "light duty" compressor replacement motor for $150 (freight damaged) similar unit for sale:

WEG 5HP Electric Motor for Air Compressor 56 Frame 3440 RPM 5/8" Shaft 20.3 AMP | eBay 









retail price is $400, using it with my 2 stage compressor load, it runs at the top air pressure (fullest load) 17 amps of the 21 available which calculates to about 4 HP. It does run hot to touch but well within it's listed limits and has not yet tripped the thermal over load. The information on the number plate gives you what you need to determine a motor's use for a specific application. I'm happy to crunch the numbers for a successful outcome, fun engineering hobby.

Stephen



stevon said:


> grobljars,
> 
> Sounds good, LRA is locked rotor amps which is about 6 times the listed full load amps so 10 FLA= 60 RLA. This is at startup under load at 0 rpm. As the rotor turns the amps go down to FLA or less. When you brutally overload a motor, it starts to stall and approach LRA amps. The windings and other wiring burns up hence the thermal protection (in most designs) The load is fixed at 2.2kw at X rpm so the question is if your motor can produce that. The only way to know is to mount the motor with the required pulley to turn the pump at listed rpm for that HP and measure the amps drawn on one leg of the circuit. The load will demand the required HP and the motor will produce it even if it is smaller but if it is not rated or designed for that load it will overheat, the more it is overloaded the faster it will overheat or stall. The only way to know if you are overloading the motor is to see the specifications stamped on the tag or plate of the motor.
> 
> ...


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