Ac motor speed control

AC motors are constant speed devices but their speed can vary if you change the input voltage or frequency or the windings that make the motor rotate. The most common and efficient way of changing the speed is to vary the frequency by using an inverter as the power supply.

This method has become popular with the development and decrease in cost of power electronics. Methods involving reducing the voltage to the motor windings with resistors, transformers or motor winding taps are still in use and are the low cost and preferred methods for certain clearly defined applications. Use an inverter to power the AC motor. Select an inverter that can supply the motor voltage and current including the starting current.

Use the range of speed variation required to select the range of frequency that the inverter must be able to supply. The inverter controls will vary the frequency supplied to the motor and the motor speed will vary accordingly. Add a variable resistance in the motor circuit to reduce the voltage across the main winding if an inverter is too costly and accurate speed control is not required. The motor "slip," normally close to zero, will increase as reduced power is supplied to the motor, and the motor poles don't receive enough power to produce the force necessary to keep up their normal speed.

The motor must be designed for high slip, and the resistance and circuit design is specific to the particular application. Use a variable voltage transformer to change the voltage supplied to the main winding if you desire a high slip, reduced voltage speed control, which is more efficient.

The variable voltage transformer has low losses compared with the variable resistor. The transformer may have a series of taps that yolu can change manually to control the motor speed or it may have a motorized tap changer. In either case, the motor speed changes in discrete increments and the detailed design is again specific to the installation where it is used.

Use an AC motor with tapped windings to change the speed if available. Such a motor has a certain number of taps on its main winding, which allow it to run with different voltages applied to its magnetic field. The number of taps and the number of speeds available for a particular motor is usually not more than four.

This method is common in fans that have low, medium and high speeds with a switch selector. The exact speed in these devices is not important, and the speed control method is low cost. This article was written by the It Still Works team, copy edited and fact checked through a multi-point auditing system, in efforts to ensure our readers only receive the best information. To submit your questions or ideas, or to simply learn more about It Still Works, contact us.

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Items you will need Variable frequency inverter Variable resistor Variable transformer Motor with winding taps. About the Author This article was written by the It Still Works team, copy edited and fact checked through a multi-point auditing system, in efforts to ensure our readers only receive the best information. Photo Credits motor image by Petr Efremov from Fotolia.Length: in.

Mass: ozm lbm g kg ozm lbm g kg. Weight: oz. Oriental Motor offers a wide range of motion control products to meet a wide range of applications, select the appropriate application type below. Speed Control Stepper Motors. Rack and Pinion Linear Actuators. Free Shipping for Online Orders. Terms and conditions apply. Oriental Motor Co. Our speed control motor packages include the motor, the driver controllerand a potentiometer which allows for easy speed control adjustment.

There are three speed control motor product groups. The "AC speed control motor unit" that uses the most popular single-phase capacitor-run induction motor, the small and highly efficient "Brushless DC motor unit", and the "Inverter unit" that combines a three-phase induction motor with a small inverter. This article explains the structure, principle of speed control and the features of each product group, and our standard products are introduced.

A large number of motors are being used for general purposes in our surroundings from house-hold equipment to machine tools in industrial facilities. The electric motor is now a necessary and indispensable source of power in many industries.

The function and the performance required for these motors are wide-ranging. This article explains the structure, the speed control principle, and the features of the following three product groups that can control the speed relatively easily by using an analog input.

The output control method of a speed control circuit can be divided roughly into two groups: phase control and inverter control, which make up the product groups shown in Fig. When the speed of this motor is to be controlled, a tacho-generator is used to detect the speed and is attached to the motor as shown in Fig. The tacho-generator is made of a magnet connected directly to the motor shaft and a stator coil that detects the magnetic poles, and generates an AC voltage at 12 cycles per revolution.

Since this voltage and frequency increase with a rise of the rotational speed, the rotational speed of the motor is controlled based on this signal. Principle of Speed Control Rotational speed N of an induction motor can be shown by the expression 1. In the case of an induction motor as shown in Fig. To make it possible to operate reliably even in the above-mentioned unstable range, it is necessary to detect the rotational speed of the motor and use a voltage control mechanism closed-loop control that reduces the speed error when compared to a set value.

Available voltage control methods include control by a transformer or by phase control. This method is not so easy to do with an AC speed control motor. Speed control is obtained by the phase control method by controlling the r. This AC speed control method can provide steady speed control by closed-loop phase control even in the unstable range.

When this timing is slow, the voltage applied to the motor becomes low and the rotational speed of the motor decreases. The lowered rotational speed is fed back again and the control is repeated so that the difference between the speed detected value and the speed set value may always be constant.One of the very popular of them is by applying chopped AC waveform — means changing phase angle of applied AC waveform.

This method is used in many different devices like. The firing angle of a thyristor like TRIAC - that gives supply to motor, is delayed to decrease the motor speed or it is fired earlier to increase motor speed. As firing angle is changed, the part of AC waveform applied to motor is chopped more or less.

Speed control methods of induction motor

So the average AC voltage applied to motor changes — that changes speed of motor. There are different techniques to control speed of AC motor. In domestic fan regulator to vary speed of fan. In electric drill machine to rotate shaft at different speed. In modern electric hand blander machines. To vary the speed of blowers or fans used in industries for different application.

The firing angle of a thyristor like TRIAC — that gives supply to motor, is delayed to decrease the motor speed or it is fired earlier to increase motor speed. Here the given circuit uses same principle to vary AC motor speed. Let us first understand the block diagram of the circuit. It is followed by circuit description and its detailed working and operation. Block diagram description:. Let us understand functions of different blocks to understand how the circuit works.

Bridge rectifier — it generates rectified output from applied AC input. ZCD — it generates short duration positive and negative pulses when AC waveform crosses zero mark. It is used as reference to chop AC waveform applied to motor. Circuit Description:. Q1 and Q2 both are connected in switch configuration as shown. It is configured in monostable mode.An induction motor is practically a constant speed motor, that means, for the entire loading range, change in speed of the motor is quite small.

Speed of a DC shunt motor can be varied very easily with good efficiency, but in case of Induction motors, speed reduction is accompanied by a corresponding loss of efficiency and poor power factor. As induction motors are widely being used, their speed control may be required in many applications. Different speed control methods of induction motor are explained below. Induction motor speed control from stator side 1. Hence, for providing the same load torque, the slip increases with decrease in voltage, and consequently, the speed decreases.

This method is the easiest and cheapest, still rarely used, because large change in supply voltage is required for relatively small change in speed.

Hence, the synchronous speed changes with change in supply frequency. However, this method is not widely used. It may be used where, the induction motor is supplied by a dedicated generator so that frequency can be easily varied by changing the speed of prime mover.

Also, at lower frequency, the motor current may become too high due to decreased reactance. And if the frequency is increased beyond the rated value, the maximum torque developed falls while the speed rises. As in above method, if the supply frequency is reduced keeping the rated supply voltage, the air gap flux will tend to saturate.

ac motor speed control

This will cause excessive stator current and distortion of the stator flux wave. Therefore, the stator voltage should also be reduced in proportional to the frequency so as to maintain the air-gap flux constant. Hence, if the ratio of voltage to frequency is kept constant, the flux remains constant. This method gives higher run-time efficiency. Along with wide range of speed control, this method also offers 'soft start' capability.

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Changing the number of stator poles From the above equation of synchronous speed, it can be seen that synchronous speed and hence, running speed can be changed by changing the number of stator poles. This method is generally used for squirrel cage induction motorsas squirrel cage rotor adapts itself for any number of stator poles.I wanted some way to control the speed of a Jigsaw and decided to use a light dimmer.

You could also use this to control the speed of a drill or any electric tool that has a motor. It actually works really well so if you do need some way to control speed, then this is a simple and dirty way to go about it. There is a clip of it in action but you will need to skip to the 1 minute mark to see it in action. Lastly, this uses AC mains so if you are unsure of how to correctly wire AC or are worried about the polarities, then I would probably get someone in to help you.

You can easily get all of these parts from any hardware or electrical store. Light Dimmer Controller — eBay. Extension Cord — eBay. The premise of this speed controller is to add the male and female ends of an extension cord to a variable controller light dimmer. All you are really doing is splicing in the controller between the extension cord.

If you really wanted to, you could just add the dimmer to the live wire on the extension cord and that would be that. However, I wanted to be able to turn it off as well so got a dimmer with a switch. The dimmer that you buy should come with instructions on how to wire up the power.

There are all different types of dimmers out there so make sure that you ready the instructions and understand which wires go where. First connect the neutral wires together from the extension cord and add these to the dimmer where indicated.

AC Motor Speed Controller - Motor Speed Control - Motor

Next you will need to add the hot wires to the dimmer. In my one, a wire from the dimmer and the extension cord was connected and then secured together in the dimmer.

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The other hot wire was secured by itself and so was the wire from the dimmer. So there was a total of 4 connectors in the dimmer for the wiring. I have also included a basic, generic schematic so you can understand better how this needs to be wired up.

Once you have wired everything up, screw on the dimmer to the junction box, grab a drill and test to make sure it works. Gday lonesolesurfer.

AC Motor speed control using ZCD-IC555-DIAC-TRIAC

Good instructable. Concise and easy to follow. Just about your dimmer and its rating.Speed, torque, power and voltage are all important considerations when choosing a motor. AC motors are unique because they are built to run at specific speeds regardless of their design or manufacturer. Common AC motor units are constructed with either two or four poles. A magnetic field is created in the stator poles that induces resulting magnetic fields in the rotor which follow the frequency of the changing magnetic field in the stator.

Two pole AC motors operating at 60 Hz will always run at approximately rpm, and four pole AC motors will have speeds around rpm.

Keep in mind that the speed of an AC motor will not run at these exact numbers—and will be slightly lower—because there is a certain amount of slip that must be present for the motor to produce torque. The rotor will always rotate slower than the magnetic field of the stator and is playing a constant game of catch up.

Noun phrase

This produces the torque to get an AC motor running. The difference between the synchronous speeds of the stator and rpm and the actual operating speed is called slip.

ac motor speed control

A control can be used to alter the speed of a three phase AC motor by increasing or decreasing the frequency that is sent to the motor, causing it to speed up or slow down.

These motors are plugged directly into a standard wall outlet and operate using the set frequency available. An exception to this rule of thumb would be a ceiling fan that runs using single phase AC motor, but has three different speed settings. The number of wire turns in an armature, the operating voltage of the motor, and the strength of the magnets all affect motor speed. If a DC motor is running on a 12 V battery, that is the maximum voltage available to the unit and the motor will only be able to perform at a speed rated for 12 V.

If the battery is low and supplying less voltage, the speed will decrease accordingly. DC controls adjust speed by varying the voltage sent to the motor this differs from AC motor controls which adjust the line frequency to the motor. Typical no load or synchronous speeds for an AC fractional horsepower motor are or rpm, and rpm for DC fractional hp motors.

Narrow your search by selecting motor type, gearbox, voltage, and phase options for your desired motor. Select a dominant variable: choose one of the three parameters to narrow your search. The selected variable determines which slider bar you will be able to manually move. Use the slider corresponding to your dominant variable to further narrow your motor selection. The other sliders will automatically move to show available ranges based on the range of your selected variable.

Results will upload as your search criteria changes. If you have any questions regarding your results or how to use the search tool, you can chat with us using the green tab on the left-hand side of your screen. Note: Groschopp Universal motors are custom built to fit your application so no additional options are available to narrow the search. Selecting the Universal motor type will prompt a message taking you to the Universal product page.

One of our team members would be happy to help. Contact us at or by email at sales groschopp. You can also chat with us using the green tab on the left side of your screen. Groschopp Universal motors are custom built to fit your application so no additional options are available to narrow the search.

Standard frame sizes and motor features can be found on the Universal page. Selected Products. How did you hear about us? AC Induction Motor Speeds AC motors are unique because they are built to run at specific speeds regardless of their design or manufacturer.

How to use the Motor Search Tool Narrow your search by selecting motor type, gearbox, voltage, and phase options for your desired motor. Yellow represents selected option. Dark gray represents available options.The speed the motor turns is determined by the voltage it gets from the power source; reduce the voltage and the speed of your single-phase motor decreases.

Increase the voltage and the speed of your motor increases. Never increase the voltage above the input voltage labeled on the motor; that will burn out the motor windings. Install a variable rheostat and you can control your motor's speed. Disconnect the single-phase motor from the power source. Use a knife and cut the wire that connects the motor to the power source.

Make the cut about 12 to 18 inches away from the motor. Cut off about 2 inches of outer plastic from the two cut ends of wire using wire strippers. This reveals the inner wires. Loosen and then remove the screws on the rheostat cover using a screwdriver. Lift off the cover from the rheostat base.

ac motor speed control

Locate the two plastic terminal blocks attached to the base of the rheostat. Replace the cover on the rheostat. Put the screws in the holes and tighten the screws using a screwdriver.

Connect the wire to the power supply. Turn on your single-phase motor. Control the speed by turning the dial or moving the lever on the rheostat. James Stevens has been writing articles for market research companies in the U.

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He has written various country profiles for inclusion in comprehensive market reports including Vision One Research and Investzoom Market Research. By: James Stevens Updated April 12, Share It. Things You'll Need.

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