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Old 04-30-2012, 07:04 PM   #831
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Quote:
Originally Posted by Jason M
An ac motor shouldn't run backwards by accident. It should run backward only if u change the polarity
Jason,.. A bee isn't suppose to be able to fly either but,......? Lol .... All I know is that it DID happen and apparently, it's happened to others too.
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Old 04-30-2012, 07:22 PM   #832
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It does happen with those power heads but what was said was that ac motors somtimes run in reverse. Which they don't. The powerheads running in reverse maybe because of extremely cheap crappy built motors and that is a rarity for any motor to run backwards by itsself. If ac motors in general did do that a lot of lives would be lost in the process. I don't know how the power heads are designed but I have seen at as well. They would be the only one ac motors I've ever heard of that do that. That is if it is the motor causing it. I don't know if there are anypther components in play for the powerheads that may cause that issue
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Old 04-30-2012, 07:29 PM   #833
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U got me thinking now about it and my stand is that the motor Jang running backwards but another componet is causing the reversal. It is just simply impossible for a magnent to change its polarity without u changing the legs on the power supply. Oh and i thought its said that a bumble bee is not suppose to be able to fly. Not all bees I think
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Old 04-30-2012, 07:29 PM   #834
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I ment to say the motor can't be running backwards sorry
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Old 04-30-2012, 07:41 PM   #835
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Check out how a AC induction motor works before making statements. Quite different from a DC motor where polarity controls the direction of rotation. The impossibility of the motor running backwards is pretty apparent in Darys case as well as many others documented by Korallia, it happens. That is why a physical rubber stop was used. There are many safety measures in modern induction motors to insure they start in the right direction, I guess these fans have simpler motors in them.

There are no "other" components. The motor connects directly to the prop.
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Old 04-30-2012, 08:15 PM   #836
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Reversing the polarity of the start winding in relationship to the run winding reverses the direction of rotation of all single-phase and three+phase ac motors. There are only two types: induction and asyncronous. The difference is that induction motors run a bit slower than the frequency they are fed. A asyncronous will run at the same speed as the frequency. U do know what that means right?. Induction, asyncronous, dc doesn't matter they all use magnets to create force moving a shaft or what ever else u put in there. Unless that coil inside the motor where to magically re wire itself of the poles connected to the 1 and 2 stamped in the connection point. It isn't changing. I read online that there are pieces between the shaft and motor. I couldn't find a technical drawing showing the design though. To be honest I dont care. It's just when I see a statement such as ac motors run backwards accidently sometimes I can't help but argue.
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Old 04-30-2012, 08:31 PM   #837
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From what I've found out about that stop u talk of is that it stops the impeller from reversing while the polarity of the coils adjusts itself for the first 60 cycles. It's 60 because here in America we run with a frequency of 60 Hz. That's means there are 60 cycles per second of electricity reversal in an ac circuit for those that don't know. And if that stop at the end of the impelled isn't there the impeller can't right itself and stays in the wrong direction
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Old 04-30-2012, 08:39 PM   #838
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Name a few of those safety measure will u Greg because I can only think of one and it doesn't have anything to do with "making sure the motor starts on the right direction"
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Old 04-30-2012, 10:28 PM   #839
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i dont know much about electricity, but im sure i am not imagining this. i can probably post a vid if it would help.
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Old 04-30-2012, 10:35 PM   #840
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Don't worry, I got this.

HYDOR componenti per acquari
At the bottom.
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