In an normal elec. motor w/ a capacitor, the capa. kickstarts the motor. Well, if the capa. is on when the rotor comes by, then when the affect of the stator is too small, shut off the electromagnet stator to charge the capacitor for the next round. The effect is a continual kickstart motor that conserves energy expenditure (less net loss per rotation than conventional motor with few poles). It may even increase torque (one main reason that electric motors are usually not used in transportation applications)-- empty89, Jan 07 2004 What?-- phoenix, Jan 07 2004 What [phoenix] said.-- Letsbuildafort, Jan 07 2004 If you shut off the stator, but then begin charging the capacitor, you will still be drawing current somewhere at all times. I don't understand how this conserves energy.
From what I've gathered, the product in the link from humanbean works by limiting the conduction portion of each cycle to produce only the required torque to maintain a speed setpoint. The inertia of the rotor maintains rotation through the non-conduction portion of the cycle. The device supplies only the required current for a particular load, thus saving energy. That being said, I am not privy to that company's design secrets, and I may be completely, horribly wrong.-- xrayTed, Jan 08 2004 IIRC, a typical electric motor never has times "when the affect of the stator is too small". It achieves this by having many poles, and using only those poles that lie within a small range of angles. (I'm talking about real-world reasonably-sized motors; small units may have a very low pole count).
Capacitors are there to smooth out the spiky load presented to the power supply (or similarly to bring the presented power factor closer to 1), or to aid starting in the case of some single-phase AC designs (which otherwise wouldn't know which way to spin).
Feel free to correct me or explain the idea further.-- benjamin, Jan 08 2004 Benjamin is correct. The starting load for even a smallish,3-5 HP electric motor can easily be 3 or 4 times the maximum load when running. The capacitor stops you from blowing your circuit breaker every time you start. I am not an expert on electric motors, but I am not sure that you would experience any noticable gain by using the capacitor in the motor starter anytime after the motor is started, its sort of like attempting to use the starter motor in your car for some extra boost, that is not what its designed for.-- austere_apathy, Jan 10 2004 In this case, the starter capacitor is used to shift the voltage of one of the (normally balanced) phases toward one of the other phases during motor starting. This causes an unbalance of forces which in turn causes the rotor to begin rotating. This is a different application of a capacitor than power factor correction, or harmonic (noise) filtering.
This idea may actually work to increase torque, (in some clever arrangement) but probably not to conserve energy.-- xrayTed, Jan 10 2004 I'm sorry, but this is too hard for me to explain while getting the point across. But I'll try my best:
Armature alligned (cap. is on and boosts electromagnet propulsion)
Armature moves from allignment (no use [unless poles switch] for single poled electromagnet)
As the electromagnet is not in use, cap. charges
As armature realligns, cap. boosts again ________________ Really, it would help it I could draw it. Hey! I have a new idea for a post! The bakesperson (site coordinator, Julia?,) should introduce a paint/draw section for our ideas!-- empty89, Feb 18 2004 And I though that capacitors were for playing practical jokes on friends !-- finflazo, May 06 2004 I'm not sure about starting the engine, but todays hybrid and electric vehicles use large capacitor banks to even out the battery's load and/or to temporarily store the energy absorbed from braking or going down-hill.-- Ouroborus, Jun 01 2006 //one main reason that electric motors are usually not used in transportation applications//
Nonsense.
In fact, an eletric motor of the same size and weight as an internal combustion engine produces *more* torque.
The reason electric motors aren't used is because batteries have low energy density.
//less net loss per rotation than conventional motor with few poles//
If the purpose is to smoothen out the torque, why not just use a three-phase motor, which produces constant torque by design?-- kinemojo, Jun 01 2006 One major advantage of the DC motor is its ability to produce maximum torque from standstill.-- david_scothern, Jun 01 2006 random, halfbakery