Compressor humming for a few seconds, then tripping breaker - SOLVED!

[Northland]

In regards to the motor stalling and tripping the breaker..I don't believe these three facts has been discussed yet.

Cheaper compressors don't usually come with a proper motor starter contactor, they use the air pressure switch to make and break the motor current. The air pressure switch contacts get pitted and burned over time and can easily cause a significant voltage drop across the bad contacts. A 10% voltage drop can cause a 20% drop in starting torque.

If the unloading valve on the goes bad, the compressor pump will have to overcome the tank pressure to get up and spinning...most won't compressor motors won't be able to overcome that head pressure.

There is an internal switch,in the motor, that operates the start capacitor. These switches can fail over time.

Hopefully the replacement cap will be the solution....but there are several more possibilities.

 

[sqslabs]

As an update, the compressor started acting up again on Wednesday and I finally got a tech out to the shop.  In addition to the other things already discussed, he brought up some of the things that Northland mentioned above, and is leaning toward the internal switch failing, at which time we'd have to either track down a replacement switch or replace the motor altogether.  In addition, we are seeing a voltage drop at the unit, which he said was due to the length of the wire run from our panel, and the wire gauge being too small.  He also replaced our 30A breaker with a 60A, and fixed an air leak that was causing the unit to run more than necessary. Otherwise, it ran fine while he was there and he gave us the A-OK.

For the most part, it seemed to run fine all day Thursday.  After speaking with a couple forum members and the tech, I'll likely be purchasing a secondary industrial piston unit for now, which will act as our main compressor.  I'll use the current compressor's tank for additional air capacity, and also as a backup unit in case we run into any issues with the main one.  I have a newer 3ph panel (that we installed when we got our new press/dryer) within 10 feet of where our compressor is, and will move the wire run to that box to ensure there is no voltage drop.

This experience has really helped me to understand the importance of redundancy, and how two smaller units can be better than one of the biggest and best. Fortunately we were still able to meet all our deadlines, but I really don't want to end up in this position again and will be doing whatever is necessary to ensure we don't. 

Thanks again to everyone who took the time to post here or contact me privately.

[sqslabs]

Made the upgrade today with a nice Craigslist find.  Barely used Ingersoll-Rand 10HP w/ 120 gal tank, and a brand new Hankison chiller.  Coincidentally, it turned out to be another screen printing shop in the area that was using them as a backup system.  Got a great deal, and made a new friend in the industry.  Our current compressor will be used for additional air capacity (for a total of 200g) as well as a backup unit. 

[numbercruncher]

Just wanted to say that the willingness to share a wealth of information on compressors/chillers was impressive. Kudos to all of you !