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Air compressors

Chris Cramer

Chris Cramer

Super User
Vendor
Premium Member
My Air compressor keeps tripping the breaker when ever it tries to start pumping more air into the tank with any pressure above 10 psi. When I use my plasma cutter and the compressor looses too much pressure, I need to empty the remaining air pressure for it to start and keep running without tripping the breaker. It can keep running all the way to 120 psi from 0, most likely by the strength/energy of the momentum from the higher speed of the motor at a lower level of resistance.
I already tried replacing the oil, and emptying the water, now I'm wondering if it would work if I purchased a new and maybe higher powered motor for replacement.
 
Typically in the pressure switch

But you have never mentioned what compressor it is you have....there are many....
 
Might be low voltage from too long a line run from the breaker panel. How big is the compressor and is it 220v or 110?

Chris
 
If your not hearing the 'pshhht' when the compressor finishes, I would highly suspect the unloader, it is what allows the compressor to start without having to overcome the pressure in the tank
 
Follow that tube, it's most likely built into the pressure switch

Is it blowing the breaker on both 120 and 240?

Drain it down, let it pump up until it stops, listen for the telltale "psssssshht" of the unloader valve after the pump stops
Screenshot_20230127-214704935~2.png
 
I do hear it release air once it finishes, and the machine came with a 120v plug which is what I use. Would it only be the small valve ontop of the switch?
16748815642591962079417515255437.jpg
 
The manual states the draw on 120 is 15a, it's possible the unloader isn't unloading enough, but it's also possible your just drawing to much for that circuit, especially if you have literally anything else on that circuit

Have you tried it on 220?
 
Sorry I missed you said you have only used it on 120

Before you spend any real money, wire it on 220 and try again, you may just have a weak breaker that pops easily, a 15a appliance on a 15a breaker is on thin ice

Just follow the tube, the unloader is often integrated into the pressure switch/on off

The pressure relief Craig is referring to is the brass thing just above the pressure switch in your photo
 
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I tested the unloader valve by adjusting the pressure limit screw to a lower pressure. It successfully released air, and after plugging it back in, I increased the pressure screw which successfully activated the pump but struggled to run and tripped the breaker again. I'll try using 220v to run the machine.
 
Since you hear the unloader, I'd bet you are just marginal on your breaker. Anything drawing 15 amps should be on its own dedicated circuit with nothing else on it. Sometimes the operators manual will even specify a 20 amp (12 gauge) circuit.

But l'll bet you have other things on that circuit like lights or Plugs that are adding a bit more current. Sometimes the breakers get weak too.

Switching to 220 will clobber that problem.
 
Compressors are notoriously hard on breakers. When they are rated for 15 amps they likely run 13-15amps and in-rush is up to 20-25amps.

So a couple of simple fixes:

1. Replace our you breaker under high load usage they get tired and start to trip earlier. Will give you a new lease on good operation for a while.

2. Put in a dedicated 20amp with wiring and breaker upgrade. My shop is set up this way as for all my 110/120vac outlets. As any tool rated for 15amps will eventually cause this issues but compressors are the worst because of the repetitive start cycle. This long term is the best and only solution.
 
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There should be some sort of check valve between the compressor and tank maybe in the unloader valve assembly. Check to see if working and holding pressure. If not the compressor will be trying to start under load, resulting in high current draw.
I have a Gardner Denver 2 stage with a 5HP motor on 220V and 20 amp breaker.
I found the compressor in the scrap but it had no unloader ,so I installed a N/O Asco 120V solenoid valve on the discharge to the tank. with a check valve. Added a timer so the valve would be exhausting to atmosphere for about 5 seconds till the compressor built up speed. When the tank reached max pressure, motor would shut down, the solenoid valve would deenergize and relieve pressure between the head and and tank check valve. Never tripped a breaker yet in 30+ years
 
Degen said:
This long term is the best and only solution.
Click to expand...

I agree with most of your comments. But I don't agree that a 20 amp circuit is the best or the only solution. Yes, it's a good solution and I already recommended it. But 220 is a better solution if the compressor motor supports it.
 
I was curious if the motor was capable of 220V by simply switching motor wires, which would be a big plus. Or if they mean 'model comes in 110 or 220V flavors'. I think its the former? Some excerpts below which may still be other issues.

IMO if you are going to play in the panel, I'd make a 220V circuit. Motor will draw lower amps for the same power & be happy. 220V is useful for many other machines down the line, likely the only option for many machines in that HP class or larger. Hopefully the panel is in the vicinity & you can run a short length external line. Example pic @Dabbler recommended this panel tie-in & external cable mode to run a 40A line to other side of shop because my walls & ceiling are drywalled. The drywall cut was confined to just above the panel & I just put a façade board to cover the hole. What I learned on my mill is that RA (running amps) & FLA (full load amps) are 2 different things. We need to pay attention to FLA because motors typically pull more current initially. So if it says give me 18 & your breaker says 15, the breaker wins & you never get to RA. We have lots of electrical experts online (and I ain't one of them LOL)

from the manual
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1674929480433.webp


1674930222172.webp
 
Susquatch said:
I agree with most of your comments. But I don't agree that a 20 amp circuit is the best or the only solution. Yes, it's a good solution and I already recommended it. But 220 is a better solution if the compressor motor supports it.
Click to expand...
I agree in that regard, but it does limit on how and where the compressor can be used. It looks like a heavier duty portable unit that may be used elsewhere.
 
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