Compressor causing breaker to trip at high pressure.
 

I picked up a 10 hp compressor, dual heads, 2 stage, 120 gallon tank.
The Pump has a centrifical unloader. The Motor is 3 phase 240 of which
I run on my 10hp rotary phase converter wired with 8-3 With Ground and
a 40 amp breaker.
The compressor starts fine but the breaker trips when the compressor is
near its top end around 160 psi. What are some causes for the breaker
to trip?
Thanks

When you get another breaker you might get with somebody who knows more
than usual about breaker selection. When getti nto larger sizes there
are sometimes other factors to consider.
Call the Square D rep and ask him. Perhaps their Web site will be of
some assistance.

"gtslabs" wrote in message
ups.com...
I picked up a 10 hp compressor, dual heads, 2 stage, 120 gallon tank.
The Pump has a centrifical unloader. The Motor is 3 phase 240 of which
I run on my 10hp rotary phase converter wired with 8-3 With Ground and
a 40 amp breaker.
The compressor starts fine but the breaker trips when the compressor is
near its top end around 160 psi. What are some causes for the breaker
to trip?
Thanks


I assume that you are you refering to a 40 amp single phase breaker on a
240 volt circuit that feeds the rotary converter.
The rotary converter isnt supplying perfect 3 phase.
Pumping at 160 PSI might be loading the compressor's motor to near its
max.
The 40 amp breaker is operating very close to the current where it is
designed to open.

If you want to experiment with this compressor current requirement, maybe
you can put a tachometer on the motor pulley. I suspect the motor is
turning at an RPM lower than its specified RPM at max power.

Jerry

40.96A isn't likely to make a typical properly functioning 40A breaker
trip soon enough to be of concern

If the breaker is functioning properly, and the breaker is tripping, you
have an overcurrent condition. Running a 10HP motor on a 10HP rotary
phase converter is pushing it. I would replace the breaker and see if
that resolves the problem. You may want to upsize the cable a few sizes
to minimize voltage drop and therefore current draw. Otherwise IMHO you
are looking at upgrading the circuit (breaker and wiring) to handle the
required current.

In article ,
footy wrote:
40.96A isn't likely to make a typical properly functioning 40A breaker
trip soon enough to be of concern

If the breaker is functioning properly, and the breaker is tripping, you
have an overcurrent condition. Running a 10HP motor on a 10HP rotary
phase converter is pushing it. I would replace the breaker and see if
that resolves the problem. You may want to upsize the cable a few sizes
to minimize voltage drop and therefore current draw. Otherwise IMHO you
are looking at upgrading the circuit (breaker and wiring) to handle the
required current.

You also might be able to reduce the current enough to avoid the
tripping if you take the time to tune your rotary converter. You will
need to add capacitance across the single phase input in increasing
values until you have the current when driving the load to a minimum.
(Too much capacitance will start the current to increasing again.) At a
guess, you probably want the capacitance value to minimize the
single-phase current ad about 75% of the way from an empty tank to a
full one.

Without tuning capacitors, the reactive current is significantly
larger than with a proper turning capacitor. (This will also probably
save you some electricity costs.)

I hope that this helps,
DoN.
--
Email: | Voice (all times): (703) 938-4564
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--- Black Holes are where God is dividing by zero ---

On Thu, 30 Jun 2005 03:01:12 GMT, Ignoramus4093
wrote:

On 29 Jun 2005 19:51:27 -0700, gtslabs wrote:
I picked up a 10 hp compressor, dual heads, 2 stage, 120 gallon tank.
The Pump has a centrifical unloader. The Motor is 3 phase 240 of which
I run on my 10hp rotary phase converter wired with 8-3 With Ground and
a 40 amp breaker.
The compressor starts fine but the breaker trips when the compressor is
near its top end around 160 psi. What are some causes for the breaker
to trip?

If the phase converter is rated 10 HP on the output, it takes more
power at input due to power losses. If, say, your converter's
efficiency is 83%, then it would take approximately 120% of output
energy.

120% * 10 HP = 1.2*7510 watts = 9012 watts.

At 220 volts, it is 9012/220 = 40.96 amps.

You need bigger breakers, and make sure that your wire capacity
matches the breaker.

i

And turn your max air pressure down to 120 psi. Your compressor will
love you and there simply is no need for any pressures higher than
that in most home shops.

Gunner

"Pax Americana is a philosophy. Hardly an empire.
Making sure other people play nice and dont kill each other (and us)
off in job lots is hardly empire building, particularly when you give
them self determination under "play nice" rules.

Think of it as having your older brother knock the **** out of you
for torturing the cat." Gunner

You might need all the air that this unit is capable of delivering, but if
not, I would probably consider removing the belt(s) from one head/pump.
That way you'll have emergency belts and a backup pump, should they become
neccessary.

The earlier recommendation to lower the maximum cut-off pressure setting is
valid. The motor is under the highest load at the highest pressure.
Generally, you can also reset the low cut-in pressure a little lower too.
Lowering the high point will most likely add longevity to the pumps.

WB
...................

"gtslabs" wrote in message
ups.com...
I picked up a 10 hp compressor, dual heads, 2 stage, 120 gallon tank.
The Pump has a centrifical unloader. The Motor is 3 phase 240 of which
I run on my 10hp rotary phase converter wired with 8-3 With Ground and
a 40 amp breaker.
The compressor starts fine but the breaker trips when the compressor is
near its top end around 160 psi. What are some causes for the breaker
to trip?
Thanks





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I would think that the obvious reason the breaker is tripping is that the motor
is drawing more than 40 amps. In the absence of any contrary indicator, I don't
see that anything is necessarily wrong. Ugley's says, in its table headed
"FULL-LOAD CURRENT AND OTHER DATA : THREE PHASE A.C. MOTORS":

10hp 230V 28amps 60A breaker #2 starter 32.2A heaters #10 wire 3/4 EMT

So from that I would conclude that even though the full load amp rating is only
28 amps it can draw a bit more so if I were you, everything else being met, I
would simply replace the 40A breaker with a 60A breaker.

Grant Erwin
Kirkland, Washington

"gtslabs" wrote in message
ups.com...

I picked up a 10 hp compressor, dual heads, 2 stage, 120 gallon tank.
The Pump has a centrifical unloader. The Motor is 3 phase 240 of which
I run on my 10hp rotary phase converter wired with 8-3 With Ground and
a 40 amp breaker.
The compressor starts fine but the breaker trips when the compressor is
near its top end around 160 psi. What are some causes for the breaker
to trip?

In article ,
lid says...
On Thu, 30 Jun 2005 08:32:26 GMT, Gunner wrote:
At 220 volts, it is 9012/220 = 40.96 amps.

You need bigger breakers, and make sure that your wire capacity
matches the breaker.

And turn your max air pressure down to 120 psi. Your compressor will
love you and there simply is no need for any pressures higher than
that in most home shops.


Mine starts at about 100 psi, and stops at about 140-145 PSI.


As Gunner says, unless you have a specific need for air at
the higher pressure, the compressor will be happier and run
more efficiently cycling between 90 and 120 psi. It's also
safer with regard to the receiver.

When I build a piece of equipment that's going into a
production environment I assume it'll have no more than 80
psi available. Line pressure in most large factories will
dip this low at times and most stuff keeps running just
fine.

Ned Simmons

I am rather receptive to this idea, but I am not sure how to adjust my
regulator, if it is at all adjustable. My compressor is a regular
looking 2 stage 3 HP 220V vertical 80 gallon compressor.


It isn't the regulator, it's the switch. Usually it's a little box, has a tube
going down into the tank.

GWE

On Thu, 30 Jun 2005 20:25:10 -0700, Grant Erwin
wrote:



I am rather receptive to this idea, but I am not sure how to adjust my
regulator, if it is at all adjustable. My compressor is a regular
looking 2 stage 3 HP 220V vertical 80 gallon compressor.


It isn't the regulator, it's the switch. Usually it's a little box, has a tube
going down into the tank.

GWE


There are typically two switches, or a lever system. a large spring
typically controls the high end, and loosening the spring lowers the
shutdown pressure.

Another spring loaded switch controls low end start pressure, often
adjusted by a screwdriver.

Loosen the big spring a fair bit, bleed down the tank a bit and as it
reaches the low end, adjust the screw driver adjustment until it turns
on the compressor at whatever low end pressure you want. Then increase
spring tension on the big spring until it stops at the high end
pressure you want.

YMMV of course, depending on odd switches etc.

Gunner

"Pax Americana is a philosophy. Hardly an empire.
Making sure other people play nice and dont kill each other (and us)
off in job lots is hardly empire building, particularly when you give
them self determination under "play nice" rules.

Think of it as having your older brother knock the **** out of you
for torturing the cat." Gunner

Grant Erwin writes:

It isn't the regulator, it's the switch. Usually it's a little box,
has a tube going down into the tank.

And do please *test the overpressure safety*. It's your last chance
against disaster, should one's tinkering with the regulator make it stick
on. (And a good routine in any shop.)

Thanks for all the good comments.
I have reduced the cut in/out level but am still having some problems.
It will load up and cut out at 120 but will not restart all the time.
about 50% of the time it will trip the breaker upon restarting at the
lower end (~80 psi). I removed the cover on the centrifical unloader
and it appears to operate freely. Plus there is an open line on top of
its housing that I belive helps bleed the air off so the heads dont
start under load.

Having one phantom leg of power from my Anderson phase converter I
wonder if 1 particular leg needs hooked directly to the motor and not
to the pressure switch. My switch has 4 poles, 2 lines and 2 going to
the motor, so my third leg goes directly to the motor. I measured the
current on each leg and was getting about 45+ amps on one leg and if I
remmeber corretly about 11 amps on the other 2 each. This was during
the running stage and not during the initial start-up. So I was
wondering why that one leg did not trip my 40 amp breaker every time.

I dont have a demand meter but am concerned about the power costs of
running this motor for my 40"x40" sandblast cabinet.

OK... If the motor does not want to re-start, we need to verify the
although the unloader is moving freely, ...... is it really
unloading?
Do you hear the air hissing after the motor stops, as the unloader
dumps the perssuer from the head?
Can you
turn off the power
then see how freely the compressor turns when the tank is full?
Pete

Thanks for all the good suggestions.
I replaced all the check and safety valves on the compressor. I also
added a second unloading port to the other head
where the recycled air line (the line with the cooling fins) is. I
teed these together and the heads appears to be unloading ok.
After the motor cuts out I can hear the hissing. I also unconnected
the lines to ensure no air was trapped in the heads. There was none.
However it still does not want to restart even at a tank pressure of 70
lbs. I can rotate the pump by hand at the end of the unloading so I am
pretty sure it is completely unloaded.

During its initial run from an empty tank I was reading about 37 amps
on one leg from my 10 hp phase converter near the high pressure end
~120 psi before shutting off. The motor is a continuous duty 230v 3
phase rated at 27 amps. So I am not sure why it is reading so high. I
believe these motors are suppose to run warm. Mine does, I wonder if it
is heating up too much.

So my next step is to find a bigger converter. I have a surplus 15 hp
motor but I can not start it even with my 10 hp converter and using a
pony motor to bring up the speed. I checked all 3 legs with a DC
battery and the shaft was resistive. I have read in these groups that
I should be able to start that unloaded motor with my phase converter.
This motor is a Vibration rated induction motor and is a beast - about
300 lbs.