Ok, then you really shouould upgrade your wire and and breaker sizes. As mentioned, a 20 amp breaker shouldn't be loaded at more then 80% capacity for any time more than a few minutes. Doing so will tend to weaken it and cause it to eventually trip too soon. Also, although you are within the #12 wires rating of 20 amps, if you increase the breaker size, then the #12 wire is too small. A heavier wire will result in lower operating costs due to lower voltage drop over time.
Electric Motor Starters
- Thread starter Toolguy
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gizmo
Silver Member
From what you said, it sounds like you think you have the motor wired for 240VAC (2 legs?). 3HP and 240VAC equals about 11 amps and 120VAC would be 23 amps full load. So, either you are wired for 120VAC or you are overloaded. In either case, something needs to change. Either increase the wire and breaker size for 120VAC, or wire for 240VAC.
If in fact you are wired for 240VAC and still drawing 18amps steady state you have a problem:
the motor is failing either electrically or mechanically
the motor is undersized for the application
the compressor is failing
your meter is reading incorrectly
FYI, balancing the load through the meter has no effect on your power bill. You are charged for the energy you consume regardless of the configuration. Some will argue about line loss at higher current, but it is negligable in a home setting.
If in fact you are wired for 240VAC and still drawing 18amps steady state you have a problem:
the motor is failing either electrically or mechanically
the motor is undersized for the application
the compressor is failing
your meter is reading incorrectly
FYI, balancing the load through the meter has no effect on your power bill. You are charged for the energy you consume regardless of the configuration. Some will argue about line loss at higher current, but it is negligable in a home setting.
BobRip
Elite Member
gizmo said:
Gizmo, I did the math and my numbers come out close to yours. On the other hand I have a 1.25 horsepower well pump which is rated at 9 amps at 240 volts. So I think we are not accouting for inefficiences and power factor enough. He should look at the name plate for the ratings not use our calculations.
caver
Veteran Member
- Joined
- Dec 20, 2006
- Messages
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- Southeast Missouri
- Tractor
- Fisher Price, toddlers first tractor.
My pocket book, that I often use in the field if a motor nameplate is ineligible or missing, says 17FLA/230V/3hp.
mudcat
Platinum Member
kmdigital said:
Here are some pictures of the compressor and the motor plate. The quart of oil in the picture is just there to give it some size comparison.
Today, I changed the 20amp double breaker to a 30amp. The 20amp breaker kept tripping when I tried to start it this morning. No problem tonight with the 30. As soon as I get time I am going to change the 12ga wire from the breaker box to the compressor to 10ga. This compressor will not be used on a regular basis. Unless I have problems after that I am going to leave it alone. So far, it is doing what I want it to do. Thanks for all of the good advice.
Today, I changed the 20amp double breaker to a 30amp. The 20amp breaker kept tripping when I tried to start it this morning. No problem tonight with the 30. As soon as I get time I am going to change the 12ga wire from the breaker box to the compressor to 10ga. This compressor will not be used on a regular basis. Unless I have problems after that I am going to leave it alone. So far, it is doing what I want it to do. Thanks for all of the good advice.
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dqdave1
Veteran Member
You need to change wire size to at least 10 guage.
Steve_Miller
Veteran Member
Couple of questions if your still looking for answers, if you can take the belt off and just run the motor unloaded, what does it draw for current? With the belt on and starting from no air pressure in the tank, what does it draw say up to 20-30psi? Same thing except starting from 120psi, what is the draw? Are there capacitors in the motor junction box? If so, what are the values on them? If the starting cap is weak, you'll get less starting torque, if the run cap is weak you'll have less power and higher current. Just my two cents.
Steve
Steve
Actually, If I would not have checked the amps when I first installed it, you would never suspect that anything is unusual. When it kicks on at 120psi it only takes about 1 second, or less, to get up to full speed. The only thing noticeable is that the lights flicker. With my old, smaller compressor the lights never changed when it started. The flickering lights are what got my attention so I got out my digital, clamp-on amp meter. It is possible that the meter is wrong, though. When I get the chance I'll borrow a different one and compare. I am going to change the wire to 10ga and call it good for now. Thanks again.
