You really can't really "control" the speed of a the commonly available home-use 120 VAC fans.
The problem is that most of the motors on the "regular" fans are synchronous motors, and they want to sync with the line by virtue of frequency. Fans with different speeds have different windings in them that are specifically set up for the different speeds. A switch allows the different windings to be selected. Simply reducing the line voltage will only reduce the torque the motor will supply, but will not directly affect its speed. The lower torques will cause the motor to slow down, and that's true, but this is not necessarily a good thing as the fan was not designed to run like this.
Sophisticated electronic variable frequency drives (VFDs) are designed to provide AC power but at a frequency you can control. Your ability to control the frequency gives you the ability to control the speed of the fan directly. But these units cost. For the smaller non-commercial units, it is smarter (and cheaper) to just get another fan with multiple speeds than to try to fool around and control the speed by some "gizmo" or something else.
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I beg to differ. Most home fans are inexpensive single phase AC motors, either with a capacitor (PSC) or shaded pole. These are not synchronous motors. A simple light switch dimmer (aka phase controller or triac controller) can be used to control the fan. Caution: be careful to avoid fan stalling when setting at low speeds. The dimmer controls the speed by reducing the effective voltage to the fan. At low voltages (and resulting speeds) the fan torque is also reduced. Thus the likelihood of stalling is higher. If the fan stalls with the power on, the motor will overheat and possibly catch on fire.
VFDs are definitely not the right choice for a simple fan. These require motors (almost always 3 phase) designed for use with VFDs (aka, inverters) or a special output filter for the controller. Otherwise the bearings will pit within months to a year. Besides, VFDs with a single phase output is very rare.
With DC motors you use a DC motor drive which will adjust the out put voltage to adjust the speed of the motor. AC motors you would use an AC motor drive or VFD (Variable frequency Drive) and the most common ones will adjust the output voltage and frequency to keep the volts/ hertz ratio the same. There are many different types of AC motor drives and they are usually selected depending on the load (ie. constant torque, variable torque, constant power).
Speed control of AC motor:
First let us know the basic equation for speed.
N=120f/p
N= speed in rpm;
f= supply frequency;
p= number of magnetic poles;
1. Number of poles was decided during the design of motor so we cannot change this factor to controll the speed.
2. By inceasing or decreasing the supply voltage frequency motor speed can be changed accordingly.
3. Another method is by varying the supply voltage but this may affect the torque produced by the motor.
4. Combined variable voltage and frequency method(v/f method)
I assume you mean when driving and then using the gear box to help slow the car.
This is because when changing gears the speed will slow of the rotation of the motor and the flywheel. Then subsequent changes will slow a little bit more, also ever try to do 100 in first gear, most cars cant, each gear has a limit that it can reach for speed.
Use an auto transformer.
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For AC system speed of generator will be decreased and then frequency decrease, if there is no trip the motor load will be automaticaly reduced as Load Power = torque x speed and speed of motor vary acc to frequency. Finally the motor will be run at new lower speed that load = power generation. The other effect is voltage in the system will be decreased and result of lower load consumption
AC voltage controllers are used for controlling the speed of universal motor or induction motor by changing the firing angle :) -vinodh gav
On an AC motor you basically vary the frequency on a DC you can vary the voltage.
An induction motor connected to an existing ac supply normally runs at less than the synchronous speed by an amount described as the 'slip' which is proportional to the torque demanded at the shaft. If the same motor is instead coupled to an engine and driven at a speed higher than the synchronous speed, with negative slip, power then travels back into the ac supply and the motor has become a generator. The amount of power produced depends on the speed. However a normal induction motor will not behave as a stand-alone ac generator. For ac power generation synchronous generators are invariably used because it is necessary to set and maintain the frequency of the supply accurately.
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well, you either have to program the operating frequency crystal to a better remote control, (if you are using a remote control,get remote control which can control the speed) or, try using a more powerful or less powerful battery to increase or decrease the speed.
It is done to control the speed of the motor.
the speed of ac motor can be controlled by controlling the synchronous speed (Ns=120f/p). and synchronous speed can be varried or controlled by changing frequency or by changing poles. but practicaly pole can not be changed. but we can change the frequency. the frequency can be VFD (Variable frequency Drives). so the speed of ac motor can be chaged or controlled by VFD.
yes, by stepping it up or down with a transformer.
The motor is slowing down due to the load. DC Speed controllers can only slow down motors, not increase the speed/power. 3 phase AC motors are slightly different, in that the speed is controlled by a VFD (Variable Frequency Drive), which can increase or decrease the speed of a motor, provided the motor is large enough to handle the load initially. If the motor is slowing down after a load is applied, and does not regain running speed after the load has "spun up", a more powerful motor is required. Read motor data sheet for running speed. If the motor is hot while running a load, it is more than likely overloaded or at the load limit. Motors with at least 10% to 25% extra power over bare minimum should be used to make up for loss of efficiency, bearing issues, etc. over time.
The higher the frequency the higher the RPM the motor will turn
A dc series motor with speed control can be connected on ac supply because dc machines are totally reversible.
Answer #1 It varies the frequency fed to a synchronous AC motor. As the frequency changes, so does the motor speed. Answer #2 The formula for calculating speed is: (120 X motor supply frequency) / number of poles 120 is a fixed number, so is the number of poles for a given motor, hence the only variable is the motor supply frequency. AC drives vary the motor supply frequency in turn achieving speed control.
A variable speed module in a motor can work with ac or dc source
The Synchronous motors will operate at a constant speed from noload to fullload. Even it is classified as an AC motor, we have to fed the motor both AC and DC supplies. That we have to supply DC to the Field (Normally Rotor) and AC to the Armature (Normally Stator).
An AC Drive used for a speed control of a motor by using vary frequency.