I had a gentleman tell me that setting the pressor on the tank to high will not overload a motor. I would think that it would, cause of the head pressor of the compressor is adding extra load. The tank is set to its maxium 160 psi. I watched the current of the motor go over the FLA once it went over 140 psi. Is this because of head pressor.
Air compressor
- Thread starter JdoubleU
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- Licensed Electrician
More pressure equals more load, true. May not be a problem if the service factor on the motor is high enough and the voltage is correct.
It sounds like he is creating life expectancy problems on many levels here.
In a previous career I worked on industrial air compressors.
What is the ASME rating of the tank? (liability)
What type of pump is he using, single stage, rotary screw or 2 stage? If it is the first 2 he is severely shortening the life expextancy of the pumps.
As you know he will probably let the smoke out of the motor soon too, but hopefully you will get to sell and install the new one.
In a previous career I worked on industrial air compressors.
What is the ASME rating of the tank? (liability)
What type of pump is he using, single stage, rotary screw or 2 stage? If it is the first 2 he is severely shortening the life expextancy of the pumps.
As you know he will probably let the smoke out of the motor soon too, but hopefully you will get to sell and install the new one.
weressl
Esteemed Member
Compressors that are designed to load/unload are routinely run over their 'nameplate' FLA rating. This happens close to the high pressure cutoff point. This is done by design. The cyclical operation of the compressor starts them with the low pressure switch way below their FLA and the amperes will rise as the pressure rises. After they reach the cutoff pressure, they are shut down and wait until the low pressure calls for operation again. Druing the rest period the motor is cooling down. This cyclical loading results in the net I^2*t to keep the motor winding thermal profile just below the damage curve that a motor is designed for continuous operation. Remember that a motor is allowed to 'experience' higher than nameplate current for momentary - starting - or short periods of overloads - like above - without it adversely effecting its design service life. Overload protection is designed to accomodate these conditions, see Class 10, 20, 30 or even higher overload designs as an example, or installed RTD protection that allow overcurrent to occur if it does not result in adverse temeprature rise because of lower than design ambient temperature, etc.
Having said that I would be hesitant to raise the HP cutoff above the manufacturers recommendation, but if the overload is properly sized the motor would still be protected, you may just experience nuissance trips.
kwired
Electron manager
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- NE Nebraska
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- EC
You also have to figure the air demand. If high enough there is not much cool down time per cycle, the compressor itself could have a duty cycle also.
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Plenty of compressors use a by-pass instead of a pressure switch and motor runs till the workday ends.
kwired
Electron manager
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- NE Nebraska
- Occupation
- EC
Well when people want to start tampering with designs, who knows what else may be original and what may have changed. The problem starts with wanting a higher pressure setting than it was designed for, next may come motor overloading problems, then they put a larger motor on this compressor(after the first one burns out) and solve motor load problems, but the compressor is still the same as it was before, and is likely overloaded.
weressl
Esteemed Member
In that case the compressor is also operated outside of its nameplate CFM rating. Compressor rating - and sizing - has two main components, air pressure and volume to be delievered over a time period.
weressl
Esteemed Member
dupl
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