Air Compressor and Garage Wiring Question

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threeputtpar

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I have an older air compressor that I like to use in the garage for various maintenance projects. It is rated at 15 amps, but I don't know if that is just at the time the motor is started or if it draws 15 amps at all times.

All of the wiring in the garage is run back to 1 or 2 15 amp circuit breakers, which are at the other end of the house in the basement.

The compressor works just fine when I first start it up and it is empty, but when it needs to cycle again and refill from 90 psi the motor starts very slow and the breaker trips.

When it is full and has to fight 90 psi to start, does the motor draw more than 15 amps and thus trip the circuit? If I knew that there was nothing else on the circuit that I was using could I up the breaker to 20 amps so it won't trip? If I did go to a 20 amp circuit, being that the wire is likely 14 ga would running it at its maximum of 15 amps for short bursts to refill have the potential of overheating? The house was built in 1995, so that was the code it is up to.

The only outdoor dedicated 20 amp circuits I have are on the opposite end of the house, and I would need a 100' extension to get to the garage. I don't think that would be a good idea, and the cord would be around $100.

The plug on the compressor is a normal 3 prong grounded one, not the one with the sideways prong that only fits in 20 amp rated outlets.

Anybody have any ideas for me? Thanks.
 
If you run it at 220 volts instead of 110 you can probably get a longer run out of it, but I wouldn't run a compressor on a 100' extension cable unless it was 6 or maybe 8 awg wire.

It's probably tripping because you're trying to run too much current through what I'm assuming is something like 14 awg romex. But either way I'd run a bigger line to wherever it's going to be plugged.

You shouldn't run a compressor through 100' of 14 awg wire.
 
K. The compressor pulls 15 amp at start up but less once turning. Leave the compressor plugged in as close as possible to the power source. Buy more hose to get where you gotta go.
I use the small electric compressors for trim. If you run them off cord it shortens the motor life,flips breakers,melts extension cords,melts the switches.
Buy more hose and eliminate the problem. Plug it in as close to the panel as possible and you will never have another issue.
Leave the breaker alone. It's a safety issue. If you are going to install a bigger breaker go 20 tops. Otherwise it will pull too much power at start up and possibly melt the switch
 
Many compressors have a "dump valve" that unloads the compressor when the pressure switch shuts off the power. This insures that at the next starting cycle, the compressor is starting with no pressure in the compressor itself. If the "dump valve" is not working, you will have the problem that you have described. Check it out. FWIW--Oldtommy
 
Originally Posted By: 2oldtommy
Many compressors have a "dump valve" that unloads the compressor when the pressure switch shuts off the power. This insures that at the next starting cycle, the compressor is starting with no pressure in the compressor itself. If the "dump valve" is not working, you will have the problem that you have described. Check it out. FWIW--Oldtommy

Correct. Every direct drive compressor I've seen has that valve. It lessens the amperage required at start up. I've not seen a belt drive with one though. they have a metal switch type thing that you stand up,which stops them from pumping air into the tanks,so there is no resistance when you pull start them,then flip it down to have them go full throttle
Our gas driven belt drives pump air non stop but I played with the "thingy" that controls when the pump starts pumping air into the tanks.
They ship them to me with them set at 90 pounds they start pumping into the tanks and stop once the tank pressure hits 140. I adjust them so they start pumping air into the tanks at 110 tank pressure and stop at 150 in the tanks.
Then I regulate the guns to 110 pounds. My adjustment means even when rapid firing staples into sheathing the regulated pressure almost never going under 100,therefore they never have to let the compressor catch up.
I can run a sheathing stapler so fast I can cycle it 5 times per second. Sounds like a machine gun.
Cha'ching
 
Originally Posted By: 2oldtommy
Many compressors have a "dump valve" that unloads the compressor when the pressure switch shuts off the power. This insures that at the next starting cycle, the compressor is starting with no pressure in the compressor itself. If the "dump valve" is not working, you will have the problem that you have described. Check it out. FWIW--Oldtommy


You will hear it when the machine shuts off. But smaller machines do not have one.

I would run another circuit using #12 wire and a 20 amp breaker.
 
Thanks for this suggestion. I will check my parts diagram to see if it does have a dump valve.

It sounds similar to the easy start function on a snowblower engine to make pull starting less of an effort.
 
Originally Posted By: Donald
Originally Posted By: 2oldtommy
Many compressors have a "dump valve" that unloads the compressor when the pressure switch shuts off the power. This insures that at the next starting cycle, the compressor is starting with no pressure in the compressor itself. If the "dump valve" is not working, you will have the problem that you have described. Check it out. FWIW--Oldtommy


You will hear it when the machine shuts off. But smaller machines do not have one.

I would run another circuit using #12 wire and a 20 amp breaker.

My 1.5hp prime brand electrics have a dump valve. And my 2hp CH ones do too.
The small oil-less porter cables don't though. In fact none of the oil-less ones we have have a dump valve,just the oiled pumps.
I never noticed that before.
 
Originally Posted By: threeputtpar
Thanks for this suggestion. I will check my parts diagram to see if it does have a dump valve.

It sounds similar to the easy start function on a snowblower engine to make pull starting less of an effort.

Just follow the copper pipe that goes from the pump head to the tank. It should be inline of that,close to the switch housing.
 
Originally Posted By: Clevy
Originally Posted By: threeputtpar
Thanks for this suggestion. I will check my parts diagram to see if it does have a dump valve.

It sounds similar to the easy start function on a snowblower engine to make pull starting less of an effort.

Just follow the copper pipe that goes from the pump head to the tank. It should be inline of that,close to the switch housing.


I did just that, and in that line is a valve that I had diagnosed as being bad when the tank wouldn't hold more than 90 psi. It would just continuously run. Ordered one yesterday on Amazon and will replace when it arrives. Hope this cures all the problems.
 
There's usually a capacitor on compressors to prevent huge surges when the motor turns on. If you don't suspect wiring (as I would, in this case) it's possible the capacitor is dead.
 
It'll draw far more than 15A at start-up, but not for very long. 15A is the draw while running, depending on the load.

What other loads are on and tied to the garage ckt? 15A breaker sounds like 14ga wire. If I remember right, a 20A breaker is max for 12ga wire.

IF you have 220VAC in the garage, is it possible to run the motor on it? Many induction motors are capable of running on either 110 or 220V. The later will result in faster rotation on start and lower current draw.

Finally if it's an old compressor and uses capacitor start & or run, the caps may have dropped enough in value to warrant replacement.
 
Originally Posted By: sleddriver
It'll draw far more than 15A at start-up, but not for very long. 15A is the draw while running, depending on the load.

If this was the case, wouldn't it have trouble starting up every time? It only has trouble after the tank is up to 90 psi.

Quote:
What other loads are on and tied to the garage ckt? 15A breaker sounds like 14ga wire. If I remember right, a 20A breaker is max for 12ga wire.

I even made sure everthing was off and still had the same problem.

Quote:
IF you have 220VAC in the garage, is it possible to run the motor on it? Many induction motors are capable of running on either 110 or 220V. The later will result in faster rotation on start and lower current draw.

Sorry, no 220 in the garage.

Quote:
Finally if it's an old compressor and uses capacitor start & or run, the caps may have dropped enough in value to warrant replacement.

I think it was built in the late 80s, so I have no idea about a capacitor. All I know is that when I test ran it on a 20A circuit, it had no problems. I will check to see what gauge wire the 3 foot cord has.
 
I would also consider the voltage drop over the length of the 14 gauge wire from the breaker to outlet. 75 feet of 14g romex @ 15 amp load is almost a 6% drop, 5% is generally considered the maximum. Even if you break code and install a 20 amp breaker, the compressor might seem fine but it's a strain on the motor.

A dedicated 20 amp line with 12g would be my answer. Make sure that dump valve is working as well. A 240v 23 amp compressor can draw over 200 amps during that split second startup just to get a perspective on things.
 
Originally Posted By: tom slick
You have some type of unloader valve issue. Some unloader valves are built into the pressure switch.
http://www.about-air-compressors.com/unloadervalve.html
http://www.about-air-compressors.com/pressureswitch.html

It's not a start capacitor problem or the motor wouldn't rotate.


I think this is the root issue. When I receive the new check valve and install it, hopefully it will solve the problem. The compressor will run continuously and not built over 110psi (cutoff is at 120psi), and I can hear air escaping somewhere. It must be coming back out through the check valve and escaping through the unloader.

Thanks, everyone for the help. I'll try to update if this in fact fixes the issue.
 
Quote:
If this was the case, wouldn't it have trouble starting up every time? It only has trouble after the tank is up to 90 psi.
Without getting into too much technical detail, it's called in-rush current and it can be up around 80A or so, but it quickly decreases as the motor starts, within 50ms or so.

If the later is true, then you do have a problem with the valve mentioned in other posts.

Quote:
I think it was built in the late 80s, so I have no idea about a capacitor. All I know is that when I test ran it on a 20A circuit, it had no problems. I will check to see what gauge wire the 3 foot cord has.


The round motor housing will have one or two 'bumps' sticking out usually. That's where the capacitors are. As they age and drop in value, they cause the motor to pull more current, eventually shortening the life. If you lose the start winding, you'll need a new motor.

I recently checked all the capacitors on my AC fan motors, indoors & out, and compressor. They were 22 yrs old and they were out of spec as the uF rating had dropped by 35%. So I replaced them.
 
Yes, there are two "bumps" on the side of the motor housing. I guess it does have capacitors.

I replaced the valve over the weekend, and it now fires up from empty on the 15A circuit and holds pressure at 120psi without leaking. I unplugged it when it was full and came back 5 minutes later and plugged it back in and it fired up just fine when still full. I also had to replace the plug because of some minor damage.

I think the problem is solved, at least enough so that I can use it for the few things I need it for in the garage.
 
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