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Burned out motor.........Why?

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Old 09-17-2010, 06:10 AM
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KNowAceHere
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Default Burned out motor.........Why?

I have a Great Planes Ultimate Bipe 3D EP ARF that I put a Turnigy 35-30c 1250 kv brushless outrunner moter on using a HobbyKing 40amp ESC and a Turnigy 3S 2200mAh 25c battery It was swinging a 11x7 prop when it went down after 1 min on it's 3rd flight. The motor was very hot and smelled burnt. It would only chatter after that. My questions is why did the motor burn out? The motor should be able to handle the 11x7 prop with no problem, the ESC is a non issue. Everything is fine with it. The battery I'm not so sure about. I am new to electric flight and this is my first power system I put together myself. From what I have learned on here the bigger the prop the more amps the motor will pull, but the 11x7 prop should not be that big for the motor. If I figure right my 22000 mAh 25c battery should have about 55amps in it at full charge. Is this to much of a battery? I thought the battery was fuel for the motor, drawing on it's amps as it needs them. Does the battery push amps too? Was it pushing 55 amps into my motor because it is rated that high? I thought you are suppost to use a battery with more amps then the motor needs so you wont tax the battery to much. Maybe I'm wrong about this but I am still new and learning. Maybe the motor is just a bad one, it has several reallly good reviews. Thanks for any help with this in advance. AND yes I now have a watt meter on order so I can check this in the future.
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Old 09-17-2010, 11:34 AM
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NeveSSL
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Default RE: Burned out motor.........Why?

Sounds like to me you just had a motor failure. It happens.

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Old 09-17-2010, 04:17 PM
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Default RE: Burned out motor.........Why?

Be sure to check your ESC. I had a motor "chatter" with a bad ESC (which smelled burned.)
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Old 09-18-2010, 02:14 PM
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Default RE: Burned out motor.........Why?

You need to understand that at any particular voltage the size of the prop determines what the motor will try to draw... the battery is just supplying what the motor wants... I reckon that 11x7 was causing that 1250Kv motor to draw a LOT more than it is designed for!

I have not tested your particular motor but a Turnigy C3530-1100 (~1075Kv) drew over 21A with an 11x7 and got very hot very fast. A higher Kv motor like yours will draw even more. A Turnigy SK 3530 (~1275Kv) I tested was drawing over 20A with just a 9x5... I'd say an 11x7 might have caused it to draw 30A+. Despite their optimistic specs those Turnigy 3530-size motors are probably no good for more than 225-250W.

Can you give me a link to your motor... I can't find a 3530-1250 anywhere (1100, 1400, 1700 yes... but not 1250Kv).
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