Fried my compressor motor and need advice on new motor. - Hot Rod Forum : Hotrodders Bulletin Board
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Old 05-23-2007, 09:55 AM
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Fried my compressor motor and need advice on new motor.

My compressor motor burnt out. The motor I had was 3.5 hp motor @ 3450 rpms. I have another new motor with the same 7/8 shaft and 2.25 shaft length but it is 5 hp and 3600 rpms. My compressor pulley is 18" and my motor pulley is 5". Both motors are 220 volt. My old motor pulled 17.3 amps and the new motor pulls 22.5 amps. Will the increased amps bother my pressure shut off switch? Will the increased rpm of the new motor hurt my compressor? All mounting patterns are the same.

Bob

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Old 05-23-2007, 10:05 PM
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Probably the extra RPM will not hurt the pump since it is such a small increase and with the extra power available it will just result in better performance. You need to check the switch rating to make sure it will handle the AMPs because overloaded switches have a tendency to stick and fail to shut off which can result in excess tank pressure. What kind of pump do you have? Was the other motor/pump combo a factory set-up?
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Old 05-24-2007, 08:24 AM
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Fried Compressor

The other pump/motor combo was original. The pump is a 17 cfm @90 Dayton pump. Bought a 4.75" motor pulley yesterday to replace the 5" original pulley. Buttoned it all up and it seems to work good. I think I will get a 30 amp switch just in case, they can't be that expensive.

Bob
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Old 05-24-2007, 09:36 AM
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You did not say why your motor burned out. You might need to check the check valve thats between the pump and the tank......when they go bad or stick...they will cause the motor to burn out. This is the number one cause for motor burn out.
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Old 05-24-2007, 09:50 AM
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Fried Compressor

I will check the valve "that I did not know existed" to make sure its good. I believe the reason my motor burnt out is the green ground wire in the pressure regulator was not tight from the factory. It wasn't just loose, the screw holding it in place was only in two turns. Unfortunately the incoming feed ground wire was connected to the same ground. I should have check it before I plugged it in.

Bob
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Old 05-24-2007, 10:40 AM
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Henry is right about that valve if it leaks then the pump will have pressure on it when the motor kicks on requiring far too much torque for a proper start which will overload the motor (thanks Henry you caught me sleeping on that one ). Something else does not seem right here since the CFM rating of 17@90 PSI is way too high for 3 1/2 HP But no matter as long as the motor draw does not exceed the AMP rating all should be fine. As long as the new motor is up to the task then that extra RPM should not hurt the pump at all and if you use the original pulley then you could take advantage of the extra power available from the larger motor. In any case since there are some questions here I would recommend checking the AMP draw with a meter before running this thing and make sure it does not exceed the start-up AMPs (at normal tank pressure not an empty tank) and does not exceed running AMPs at cut-off pressure. If the tank check valve is good the start-up will make little difference with the tank empty or full however if it is bad then the start AMPs will probably be exceeded by quite a bit if there is normal cut-in pressure on the tank. Also the tank check valve can be good but the unloader to the pump may not be working which will cause the same problem so if start-up AMPs are exceeded then you will need to determine if there is pressure on the pump before start up and if there is why.
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