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Tool Talk Discussion Forum

Compressor can't get up to speed

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Mark

08-14-2003 14:28:30




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I just bought an old Wards heavy duty 20 gal. compressor. It is being used at a 9000' elevation. I put a brand new Harbor Freight 3hp motor on it. It also has a new pressure-unloader switch on it. I also was using a long cord with it. I'm sure that was a mistake. Any time you try to start it, it does not get up to speed, before the breaker cuts out. I'm suspect of the long cord and the adjustment of the unloader in the switch box. ? how do you set the unloader valve ?
Any help would be appreciated.

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John Humphrey Morocco IN.

08-15-2003 12:39:41




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 Re: Compressor can't get up to speed in reply to Mark, 08-14-2003 14:28:30  
#1 Size the breaker according to the locked rotor amperage,,ie,,40 amps LRA = 40 amp breaker.
#2 Size the wire according to above rating. Good to 50', after 50' go up one wire size for avery 50'. This is assuming that the motor is strong enough to pull the load.



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Richard Fazio

08-15-2003 04:53:28




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 Re: Compressor can't get up to speed in reply to Mark, 08-14-2003 14:28:30  
When you say long cord, how long do you mean? Length is a big thing with motorized equipment. If you have even 50' of extension cord that could be your whole problem.



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buickanddeere

08-14-2003 23:13:17




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 Re: Compressor can't get up to speed in reply to Mark, 08-14-2003 14:28:30  
Measure the motor terminal voltage while starting. Anything less than 160vac won't even bring a fan up to speed. Compressors and other reciprocating loads need within 10%, 226vac to start thier full rated load. If the 3HP motor is undersized and putting out 4 or 5 HP as max pressure is being reached. Or if it isn't a capacitor start with a high resistance rotor, it just won't start the load.

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markct

08-14-2003 16:32:49




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 Re: Compressor can't get up to speed in reply to Mark, 08-14-2003 14:28:30  
is your motor a capacitor start motor, if it isnt it will do just what you state it it doing



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Bus Driver

08-14-2003 15:44:39




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 Re: Compressor can't get up to speed in reply to Mark, 08-14-2003 14:28:30  
Including the cord on the compressor motor, plug the compressor directly into a 20 amp receptacle using no more than 10' of cord total. The long cord causes lots of voltage drop. Use of the compressor will involve lots of air hose and a very short cord.



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JohnnyB

08-14-2003 14:50:20




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 Re: Compressor can't get up to speed in reply to Mark, 08-14-2003 14:28:30  
Take a look at your check valve if it is stuck open then your compressor will be working against the tank pressure.



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