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Advice on replacing an Ampzilla cooling fan? - Update
"Engineer" wrote in message ... (snip) Two points of information: 1. Shaded pole motors are not synchronous motors, they are induction machines that run below synchronous speed by an amount related to the torque load. This difference is called "slip" and it's the means by which current is induced into the rotor so that it can be pulled round by rotating the stator magnetic field. No slip = no torque, so it can't happen! A synchronous machine must run at synchronous speed. If it "pulls out" due to too much torque load, it stalls. In this case the rotor field is provided by a DC current source. Some synchronous machines are "induction start" - they accelerate as induction motors under no load, then "pull in". **Thanks for clarifying the differences. 2. A resistance in series with the motor stator field, in this case the shaded pole field coil, will slow it down but will reduce motor efficiency. A capacitance is more efficient (no I2R loss) but the motor loss due to high slip remains. This is never done in an industrial drive motor but will work on a small fan where efficiency is not the prime concern. I'll be the first to admit it's not elegant, but you can do it. **You sure can. Some of the results can be unpredictable, due to the inductance of the motor and the capacitance, when they form a resonant circuit. It does, indeed, work, however. -- Trevor Wilson www.rageaudio.com.au |
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