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Locked rotor, no burnout
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#217432 - 07/30/16 06:37 PM Locked rotor, no burnout
poorboy Offline
Member

Registered: 06/02/05
Posts: 127
Loc: Central Maine
A small fractional HP pump stopped working in a customers little garden pond (she creates a 12 inch waterfall with it). The braided line from a duck decoy had been sucked into the intake(no filter)and wrapped around the impeller shaft and stopped the submerged motor cold for a couple days.

I took the cover off, removed the string, and reassembled it and it works fine.

What prevents this motor from overheating and shorting the windings?


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#217433 - 07/31/16 12:44 AM Re: Locked rotor, no burnout [Re: poorboy]
gfretwell Offline

Member

Registered: 07/20/04
Posts: 9012
Loc: Estero,Fl,usa
My guess is liquid cooling and a fairly modest current draw in the first place. Is it "shaded pole"? They are pretty resilient in LR but you pay for it with virtually no starting torque.
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#217586 - 09/07/16 02:26 AM Re: Locked rotor, no burnout [Re: poorboy]
Entropy Offline
New Member

Registered: 09/05/16
Posts: 1
Loc: Washington
Definitely a problem with the liquid cooling.

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#217648 - 09/29/16 01:18 PM Re: Locked rotor, no burnout [Re: poorboy]
jraef Offline
Member

Registered: 07/21/04
Posts: 89
Loc: San francisco, CA, USA
99% of those little pond pumps are cheap little shaded pole motors. They are "impedance limited" in terms of protection, meaning they don't need a fuse or breaker because they are inherently current limiting at their own rated current. So stopping the rotor is, to the motor, no different than running at full load, other than the fact that instead of moving water, it just heats it.
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#217654 - Yesterday at 04:48 AM Re: Locked rotor, no burnout [Re: poorboy]
andey Offline
Member

Registered: 08/05/08
Posts: 30
Loc: germany
It is not fully impossible for a shaded pole Motor to overheat, it depends on the size and design. See link.
Maybe, because the water pump manufacturer did a little thinking, they designed their motor expecting it to get stuck by obstacles once in a while.

http://www.electrical-forensics.com/BathroomFans/BathroomFans.html

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