Air compressor question...

jimmysgarage · Jun 2, 2011

Hello all,

I am having an issue with my air compressor. 5HP, 80 gallon, 2 stage, 175PSI Speedaire 1 phase 220v unit.. My question is when it gets to 175psi and shuts down, it trips the breaker. I have it running on a 30amp breaker, as the motors amp draw is 23. Does the amps spike at the time of shut-off, thus tripping the breaker? Should I just up the breaker to a 40amp?

Any and all comments welcome!
Thanks! JG

Ohio_Ford_Farm · Jun 2, 2011

I think breakers trip around 80% of ratting. so a 30 amp would trip around 24 amps. Sounds like you pushing the limit of the breaker. My 5 hp single stage the motor is rated for 21 amps at 230 Vac. It ran and filled on a 30 however it would trip when It called for more air and had to start filling at 80 psi. Upped to a 40 amp and #4 wire, its been fine for the last couple years.

mikeknell · Jun 2, 2011

Unless you put an amp gauge on the circuit, you will not know how many amps the compressor is drawing.

In my experiences, compressor manufactures will overload the motor to some extent, to get better cfm ratings. For example, I have a 5 hp compressor which is suppose to draw 23 amps at 5 hp. When I put an amp meter on the motor, it was drawing about 28 amps at 175 psi.

Because my compressor runs 100% when bead blasting, I changed to a smaller motor pulley to get the amperage down to a level that I felt was safe for the motor.

Bob C · Jun 2, 2011

I had a similar problem and it was a bad capacitor making it pull to many amps.

tailstock · Jun 2, 2011

I agree with all of the above and have also run in to weak breakers that have worked well for a long time but seem to trip more as they age. Could be a tad high on amps and a weak breaker

MichaelP · Jun 2, 2011

I just wonder how to explain the fact that the breaker is tripped at the shutdown (vs. motor startup when all the inrush current is taking place).

Ohio_Ford_Farm · Jun 3, 2011

MichaelP said:
I just wonder how to explain the fact that the breaker is tripped at the shutdown (vs. motor startup when all the inrush current is taking place).

There is a amp spike at the end as the contacts of the starter pull apart. Not a larger spike but there is one there. Sounds as its enough to trip the breaker with the running load right on the edge of the amp limit.

AIR-O-LATOR · Jun 3, 2011

The motors are not overloaded by the compressor mfg. Motor tags state normal running amps. for example 25 amps at 230volt. However the amps may be higher than that due to volt fluctuations, wire size etc. However it will not overload for it isnt the true max amps. Max amps includes the motor servive factor which is included on the i.d. tag under sf1.15. So 25 amps x 1.15 = 28.75 which is the true max amps.

adama · Jun 3, 2011

Depending on the breaker but the long hard run upto pressure may well be heating it up to near tripping point, with out knowing the class of the breaker or its method of function its hard to be more precise.

rons · Jun 3, 2011

jimmysgarage said:
Hello all,

I am having an issue with my air compressor. 5HP, 80 gallon, 2 stage, 175PSI Speedaire 1 phase 220v unit.. My question is when it gets to 175psi and shuts down, it trips the breaker. I have it running on a 30amp breaker, as the motors amp draw is 23. Does the amps spike at the time of shut-off, thus tripping the breaker? Should I just up the breaker to a 40amp?

Any and all comments welcome!
Thanks! JG

Going from 150 to 175 psi on your tank is wasting electricity. And you don't get much for
the higher tank pressure. Adjust down to 125-130(on) - 150(off).

SND · Jun 3, 2011

Mine kicks in at 90psi and stops at 140psi.

Is the breaker warm/hot at shut down? what about the wire? what awg?

thruthefence · Jun 3, 2011

I've been told (by a REAL electrician) that a breaker actually has a limited # of rated circuit opening cycles in it. It will start popping at a lower draw eventually. You can manually switch 'em off & on with no effect on longevity, but the repeated heat & trip takes a toll.

Maybe this is something they tell you to sell more circuit breakers?

440roadrunner · Jun 4, 2011

adama said:
Depending on the breaker but the long hard run upto pressure may well be heating it up to near tripping point, with out knowing the class of the breaker or its method of function its hard to be more precise.

It may just be that either the breaker is "weak" or the terminals on either end are loose enough to generate heat over the course of a cycle.

(Don't discount a bad conection at the buss end.

One of the first things I did when checking "nuisance" tripping in HVAC/R work, after checking amps draw on the unit was check/ tighten breaker connections and maybe just replace the breaker(s)

jimmysgarage · Jun 4, 2011

Thanks to all...

Well, after checking the amp draw and all else, I replaced the breaker with a new 30 amp. I am no longer having the troubles as before. It appears my eyes are needing a check-up, as the previous breaker was a 20amp :rolleyes5:

!!!

Thanks once again,
JG

MichaelP · Jun 4, 2011

That was an easy fix!

Make sure the wiring is rated for 30 Amp.

MichaelP · Jun 5, 2011

Ohio_Ford_Farm said:
There is a amp spike at the end as the contacts of the starter pull apart. Not a larger spike but there is one there.

Sorry, I missed your answer.

How do explain current increase in this situation? I understand why it'll be arcing between opening contacts, but I don't see what will cause current to increase.

Thank you.

Ohio_Ford_Farm · Jun 5, 2011

MichaelP said:
Sorry, I missed your answer.

How do explain current increase in this situation? I understand why it'll be arcing between opening contacts, but I don't see what will cause current to increase.

Thank you.

The ark and resistance increase as the contacts pull apart. Higher resistance = higher amperage. It's a very short and small spike.

MichaelP · Jun 5, 2011

Ohio_Ford_Farm said:
The ark and resistance increase as the contacts pull apart. Higher resistance = higher amperage. It's a very short and small spike.

Higher resistance= lower amperage (if voltage remains the same).

In inductive circuits, current tends to stay the same at the moment and shortly after contacts opening (there is a law describing the transient processes in relayed circuits, AFAIK). The resistance increases, but since the current remains the same, by Ohm's Law, we see voltage increase causing arcing.

matt_isserstedt · Jun 5, 2011

rons said:
Going from 150 to 175 psi on your tank is wasting electricity. And you don't get much for
the higher tank pressure. Adjust down to 125-130(on) - 150(off).

+1 for this, I run my compressor at 120psi tank although it is more than capable of hitting 175psi.

Unless there's a specific need for that pressure, typically its regulated down to the ~100psi range anyway.

Ohio_Ford_Farm · Jun 5, 2011

MichaelP said:
Higher resistance= lower amperage (if voltage remains the same).

In inductive circuits, current tends to stay the same at the moment and shortly after contacts opening (there is a law describing the transient processes in relayed circuits, AFAIK). The resistance increases, but since the current remains the same, by Ohm's Law, we see voltage increase causing arcing.

The spikes are there. With a 5 hp I am sure there pretty small. Back in my days of steel coil processing I have seen the spike on large motors when the starter would drop. We seen it a lot on the over head cranes. have a 50 or 80 Hp lift motor running close to full load, then the starter drop out and the contacts pull apart there would be a amp spike at the end.

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