Barn fan often blows 15 amp breaker


  #1  
Old 05-13-19, 09:18 PM
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Barn fan often blows 15 amp breaker

So this is not exactly the kind of fan that gets discussed in this forum but I have no doubt that many of you can explain it to me

I have a 4ft by 4 ft box fan that spins a 3 ft 3 bladed blade. It was 220v but my greenhouse only has 110v so I swapped the motor for one I had laying around. Motor is 1/3 HP NIB old stock and it works good.

It spins up pretty quick and produces a hell of a breeze but it blows breakers. Sometimes it happens almost immediately upon reaching full speed, other times it runs for some time.

I believe it spins at around 1750rpm but I'm sitting on my couch and didn't know I'd be asking. Am I missing something obvious.

Thanks
 
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Old 05-13-19, 09:37 PM
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If you have or can borrow a clamp on amp meter you should check the amps. Does the motor have a capacitor?
 
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Old 05-14-19, 06:56 AM
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What else is on the circuit?
 
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Old 05-14-19, 11:11 AM
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Is there a direct drive from the motor to fan or is there a belt reduction? If it's direct drive then you may be overloading the motor with a blade that was meant for a lower speed. Does the old motor state its RPM?
 
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Old 05-16-19, 01:15 PM
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I suspect that the 1/3 HP motor has just enough power to drive the fan, BUT when you get a gust of wind, the RPMs drop, the fan stalls or slows, the current surges, and you trip the breaker.

I would see if you can find a set of exhaust louvers to prevent gusts of wind from trying to force the fan to turn backward.

Now, a 48" box fan would usually get a motor up around 1 HP motor. Might try a 1/2 HP motor and see if that has enough power to keep the fan from stalling in a gust of wind.
 

Last edited by Hal_S; 05-16-19 at 01:32 PM.
 

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