Undocumented: ways to reduce fan speeds
We have already repeatedly in the pages of “Komputerra” magazine and Ferra site.We used to touch on computer noise in general and fan and cooler noise reduction in particular (see., e.g., “CT” #381, www.ferra.ru/online/supply/5961, www.ferra.www/online/supply/9668 and www.ferra.ru/online/supply/20793). Here is another brief introduction to this problem.
I remember a friend of mine from the late 1980s complaining that his Spectrum was keeping the neighbors awake: the stepping motor of a five-inch floppy disk drive lying on the table (where did you see a Spectrum in a?), was in resonance with this very table and could be heard on the floor below just as well as an electric drill.
Later on, my neighbors were already enjoying the howling of the bearings of a five-inch Seagate 20-megabyte hard drive, and they had to wrap it in two layers of porous rubber. Nowadays the times are not that bad, the main computer components are “below the water, below the grass”, but for the people working at night, especially when the rest of the family is asleep, the noise of the computer is still the first priority. I have to choose a “soft” keyboard, to switch disk drives in Acoustic mode to the detriment of productivity (by the way, the sound of heads is very different: to my distinguished ear the dry “crackle” of IBM or Maxtor disks is much more pleasant than, for example, “canned” Seagate U-series, but in “soft” mode they are nearly silent), to refrain from installing pirated CD-ROMs with huge eccentricity.
However, there are components, the noise of which has to be reconciled with. these are fans. Usually there are two of them: in power supply unit and in processor. Both of them can be replaced by quieter ones, but if you can find at least some test results with indication of noise level for processor coolers, a power supply fan has to be chosen by “by eye” or by trying many variants. The only thing that can help is power information on the label: the higher it is the more productive and the noisier is the fan (“by eye” I can only note that straight “chopped” blades make more noise than curved sickle-shaped ones).
In most cases the airflow created by the CPU cooler’s fan is excessive, especially taking into account that it circulates in a confined space of the case. The air blown through the fins of the heatsink simply does not have enough time to heat up. Much more important is the surface area and material of the heatsink, the tightness of fit to the chip, as well as the temperature inside the case (or rather, the temperature difference between the heatsink and the air); the fan speed can often be halved, while the CPU temperature will only increase by a safe 3-5 degrees.
With power supply fans, the situation is more complicated. Contrary to popular belief, this fan cools not only and not so much the power supply, but provides air circulation inside the case (usually in ATX cases the power supply is placed on top, and the fan works as an extractor), which greatly affects the efficiency of the CPU cooler. Here the case itself also interferes: its volume and height, the placement of the power supply, the presence and location of ventilation holes. Owners of powerful processors who want to decrease the noise of the power supply fan, I can recommend to reduce its speed by compensating the air flow by installing an additional blower fan in the bottom of the case (it also can not be “turned on full blast”).
Now let’s move on to ways to reduce fan speeds.
One of the easiest is to switch to a lower voltage. Normally all the fans are powered by 12V, but most are quite usable even at 5V. For the CPU cooler just take the tip of the middle wire (usually red) from the three-pin fan jack and put it in the 5 volt free socket of the “chip” power (also a red wire). In the power supply. re-solder the red fan wire from its regular location to the 5V output (again, red power wires). The operability of the speed control circuit is maintained. Noise drops to almost zero, however, rpm is reduced too much, so this method is suitable only for low-power systems.
The best results are obtained by switching the power supply to 7 V. I hope, readers have already guessed: this is the difference between 5 and 12 volt power supply. It is done similarly to the first variant, except that the black wire of the fan is connected to 5 volt power supply instead of red. Disadvantage. speed control circuitry stops working.
clever solution. current reduction through the use of a resistor inserted in the gap of the fan power supply wire. Rating depends on the fan power and RPM reduction degree; resistors from 10 to 75 Ohm of 0,25 W are applicable for typical coolers. Similar way is used not only on amateur level: industrially produced adapters (on photo); usually 10 Ohm resistor is used there, which lowers revolutions only slightly. The disadvantage of this solution is that the fan inrush current is severely limited. At one point a dusty bearing may not allow the rotor to move.
The most proper solution, in my opinion, is to connect a 3-6V DC regulator in the fan’s power supply. By selecting the type of regulator you can choose desired speed, while maintaining both high inrush current and operability of speed control circuit.
When using such solutions don’t forget about monitoring programs, which control fans. If your motherboard monitor is not compatible with low-speed fans, update your BIOS: most manufacturers have recently added support for low-speed coolers.
One last story. A month ago I was buying the cheapest CD-RW drive and asked the seller: should I buy NEC or Mitsumi, what should I get for the same price?? And without any leading questions got the answer: of course, Mitsumi. it’s quieter, and the speed of what about the speed?
How to reduce the fan speed of the hood
Suppose that, in anticipation of hot summer days, you once bought a fan. Inexpensive and, as usual, Chinese. Designed for several modes of operation. But having plugged it in the network, found that even in the most minimal mode fan gives too much speed and quite strong noise. What to do in this situation?
So to refuse to buy and try to return the product to the manufacturer is absolutely not necessary. To reduce the noise from a household fan you can do yourself with minimal knowledge in electrical engineering and ability to work with the soldering iron.
How you can reduce the zeal of the fan?
Let’s start with the fact that the excessive efforts of Chinese fans are often explained by quite good reasons in the Celestial Empire the voltage in domestic electrical networks, as a rule, does not reach the declared 220 volts, and in Russia it often turns out even somewhat higher. Hence the excessive power of Chinese products in our conditions.
What to do in this case is clear: it is necessary to take measures to reduce voltage supplied to the fan motor.
The first way will be to attach to the fan by connecting in series some more load. In principle, you can do this with an ordinary 40-watt bulb. But the “fan with light” will look too original, so to reduce its speed will be more reasonable to use non-polar capacitor at 400 volts with a capacity of 1 to 10 microfarads. This capacitor for AC will play the same role as the resistance for DC.
But to tell in advance exactly what capacity will be suitable is difficult to say, it will depend on both the fluctuation of voltage in the network and the model of the fan. But the problem is not great such capacitors in radio stores are from 5 to 12 so you can pick up the necessary one by simple selection.
However, there is one subtlety: the motors in the fans can be different. If it is a single phase motor or a phasor motor, it will simply reduce the speed and make less noise when the operating voltage is reduced. But if the motor in the fan is asynchronous, then the noise reduction from the rotational speed will be “compensated” by its specific humming, which is undesirable.
Therefore, to regulate the speed of an induction motor you need a second way to regulate by changing the power.
To do this, a more complicated device is used, with a circuit diagram like this. This device is called a “stray power controller” or uses the principle of phase power control.
To collect independently such a device will need quite a bit of skill, but do it yourself and will not need such products can be purchased at radio parts stores at a price of 250-300.
Knowledgeable people advise how to reduce the speed of the fan in the sanitary unit by half. Parameters: 220 volts, 50 hertz, 16 watts. It’s howling all over the apartment.
No duplicates were found
You shouldn’t use a diode, the motor might not like the “half sine wave”.
I’d go for 400 volts (the mains peak voltage is 310 volts). I’m not sure what the rating on the case means. RMS or peak. Probably the first, but it’s better to have more).
and you can also get 5 μf. to see which one will attenuate your fan enough
What’s the result? Helpful? Greatly reduced speed and noise?
Return the fan to the store. Buy a less powerful, with an output adequate to the volume of your bathroom.
When choosing a fan pay attention to the noise level characteristic specified for almost all models.
Your particular model is a two-speed fan. The speed is changed by the connection diagram to the terminal block in the fan internals. Unfold the instruction (it’s a piece of paper with letters in a box with a fan) and read it carefully. Don’t mix up the inputs or you’ll burn your fucking engine.
Volage.220v Power 25w Electrical Frenguency 50Hz
What can you think of?? can put a light switch with a regulator in the circuit?
If the motor is asynchronous, then lower the voltage.Step-down transformer,LATR. Triac regulator may cause humming (current is not sinusoidal), you must check. Light regulators work from 0 to 220v and have mostly a linear variable resistor control characteristic.0V cutoff switch. Fan from 110 to 220 V, 220 V switch to start the fan from the maximum torque, and a logarithmic characteristic of the variable resistor (resistance is 2 or more times lower). Many induction fans don’t start from 140-150v so they use a resistor for the starting voltage of the fan.And the main adjustment occurs in the range of 160-200v, so this section of the adjustment should be stretched.
So convert the Turkish dimmer in the fan regulator is quite within the power of an amateur radio.
Light regulators can not be put. Triac regulator can be bought for 1500-2000rub the best option in my opinion. Type MTY 1.5 But there is one unpleasant thing about the fan at low rpm, it starts humming.к. The triac cuts the current sine wave. The lower the speed, the stronger the hum.
And the paper-metal capacitor in the gap wire forgot to offer? It’s a penny question. The main thing is that they should be rated at 400 volts. The capacitance should be selected from 0.5 to 2 uF.
I put a couple of 1 µF in series at 250 volts. In the old Czech phone sockets were. It’s a zero.5 uF, 500 volt. Helpful.
Also now wondered about this. Turkish dimmer tried the RPM is reduced, but, indeed, there is a hum. And it burned out after 3 minutes. I liked the idea of the condenser that, in fact, everything is so simple? Thanks, I’ll give it a try!
Vadim M ; I told you you can’t install a regular dimmer.)
Vadim M wrote: Turkish dimmer tried the speed is reduced, but really appears hum. And it burned out after 3 minutes.
And I’ve had a remodeled one for 5 years.What is there to burn??If the triac is 16A and the fan consumes milliamps and you don’t need a heatsink?Boo-ha-ha. The dynistor?Only if it’s defective. The hum is coming from triple price fan triac regulator. I have one too.The principle of operation is the same. the output current is not sinusoidal.
With a capacitor, it’s easy, but there’s no smooth regulation.I don’t care if it’s defective.
Ah yes, there is an ancient ancient dimmer circuit with which inductive loads such as induction motors and collector motors do not work. But it’s not used in modern circuits.
Gotman wrote : I told you you can’t put a regular dimmer)))
Don’t talk nonsense!Look at the diagram! You can’t get rid of the faults, the duds and the junk.
Popadopulos wrote : Capacitor is simple but there is no step regulation.
You don’t need a smooth one. I’ve chosen a capacitor that won’t make the fan howl.
FAV1976 wrote: I don’t need smooth. I picked it up so the fan doesn’t howl too much, but I don’t care.
Which one of these will fit my fan?? Googled it, it says that.Do NOT use electrolytic capacitors under any circumstances.
Both or as many as you like. Zero or phase doesn’t matter. You need MB capacitors. They’re not polar. It’s faster to use boards from monitors and TVs. You’ll find what you need by connecting capacitors in series and parallel.
FAV1976. For the uninitiated, can you tell me what brand of capacitors to use?? So you can come to Mitinsky Radio Market and say, “Give me a 1 microfarad 400 volt capacitor. I have no old TV sets and monitors on hand now, and Czechoslovakian telephone sockets last time I saw in my childhood (and then, I think, they were Polish and Bulgarian) Thanks for the help! PS: by the way, and trimmed such capacitors do not exist?
In the chip are mentioned here: “Only not in stock. And here’s a lot of pictures: “There are also. Look at the capacitance and voltage.
FAV1976 wrote: We need MB capacitors. They’re not polar.
I’d rather use a dedicated autotransformer for this purpose: “
Designman ; And the motor won’t hum like with a dimmer?
Designman. They would have offered a welding machine transaxle at once.
Vadim M. In all kitchen hoods for stepped fan speed control, the manufacturers use condensers. Mitinskii is working today. By lunch time you will be done.
Vadim M wrote : And the motor hum, as with a dimmer will not?
Bomfunk MC’s. (Crack It) Something Going On (Official Video)
FAV1976 wrote : Designman, you could have offered a welding machine transistor.
FAV1976 wrote : In all kitchen hoods, the manufacturers use condensers for stepped fan speed control.
Yes?I have a Fox that has a normal induction motor with 3 switchable windings. Even a lousy 6 dollar Chinese fan has 3 windings to switch speeds.
Vadim M wrote: There are no such trimmers?
No.You can use any non-polar capacitor.Tell me the parameters for the induction motor, they’ll understand.
Hobbyists with condensers! No one has suggested specially designed regulators? “
If I can reduce rpm with capacitors without prejudice to the engine, why not “kink it”? Thank you all for the practical help, as in Mitino for the condensers I will get out, be sure to report on the result of upgrading my noisy unit.
The Sovok still reigns supreme, even
Vadim M wrote: Thanks for the practical help, I will go to Mitino for the condensers
At least 400V, by the way. Better 660V. And what capacity will you take?
andrewkhv wrote : No one has suggested specially designed regulators?
They’re thyristor motors that make a lot of noise in partials. And the comrade needs to crush the fan. because of the noise. Even when the dB is not much, they are terribly annoying, because the spectrum is just in the nasty range of frequencies.
Vladimir_Vas wrote: They thyristor speed regulators make a lot of noise in partial load conditions.
Yes.Some induction motors hum, others not so much.Depends on the design.Others don’t even want to rotate.
“There are 2 models of fan speed controllers in the Vents catalog, with mounting in a standard socket:” Question: how do these controllers differ from conventional dimmers?”How they differ from the Turkish dimmer I described above and personally remade the Turkish dimmer on the model Ventsa (triac, diistor, 2 capacitors, 4 resistors, variable resistor switch, trimmer resistor, fuse, and a capacitor or varistor).Boo-hoo-hoo, it’s virtually the same as a dimmer. The shape of the sinusoid from the dimmer is just the same.
Ideal is not a sine-wave voltage regulator LATP or controlled laboratory autotransformer (there are small).Allows you to get 250v at the output and a little even increase the speed of the induction fan from the nominal.
For some very smart people.Speed of an induction fan depends on the resistance and torque on the shaft.And the torque depends. you’ll find out for yourself. So, yeah.speeds up.Yes, it does!
How to reduce the speed of a household fan?
Many people naively believe that they can use an ordinary dimmer as a domestic fan speed controller. After all, the device is essentially a triac regulator.
The fan to buy in Kiev is not difficult. But an ordinary dimmer is clearly not suitable for use. The use of a special triac regulator, which is suitable in terms of technical characteristics, is required.
Overview: How to connect an exhaust fan and reduce speed
Deciphering of parameter values in the marking of the main leading manufacturers of fan speed regulators:
- Index “E”. 1 phase (220 V). Shuft, VENTS, Polar Bear, Systemair, Luftmeer;
- Index “D” for three-phase (380V). Shuft, VENTS, Polar Bear, Systemair, Luftmeer;
- The digital value. the maximum current intensity;
- Index “T”. availability of fan thermal protection connection.
- Polar Bear OVTE 7 controller.5. single-phase, max. Current is 7.5A, with thermal protection;
- Regulator Shuft FSRD-A 3.0. three-phase, max. current strength. 3.0 A, without thermal protection;
- Systemair RTRD 14. three phase, max. current strength. 14,0 A, with thermal protection.
Reducing the noise and speed of the cooler
This is my first post, in the future I will talk about how to make video surveillance, liquid cooling system, automated (programmable) lighting and many other delicious things, we will solder, drill and flash chips, but for now we will start with the simplest, but nevertheless very effective method: installation of a variable resistor.
Noise from a cooler depends on RPM, blade shape, bearing type, etc. The higher the RPM, the more efficient the cooling is, the more noise it makes. Not always and everywhere you need 1600 rpm. and if we lower them, the temperature will rise by a few degrees, which is not critical, and the noise may disappear altogether!
Modern motherboards have integrated speed control of the coolers that are powered from it. In BIOS, you can set a “reasonable” cut, which will change the speed of the coolers depending on the temperature of the cooled chipset. But this is not an option on older, low-end boards, and what about other coolers, e.g. PSU cooler or cabinet cooler?? For this you can mount a variable resistor in the supply circuit of the cooler, such systems are selling, but they cost unbelievable money, considering that the cost of such a system about 1.5. 2 dollars! Such a system sells for 40:
You can make it yourself, using as a panel. a plug of your system unit (plug in the basket, where the DVD / CD drives are inserted), and the rest you learn from this post.
In the following I will describe the process of working with a PSU, but it is identical in all cases.
Т.к. I broke off 1 blade from the cooler on the PSU, I bought a new one with ball bearings, it’s much quieter than the regular ones:
Now we need to find a wire with power, in the gap of which we mount the resistor. This cooler has 3 wires: black (GND), red (12V) and yellow (tacho contact).
Now we need a variable resistor with a resistance of 100 ohms to 300 ohms and a power of 2 to 5 watts. My cooler is rated at 0.18 A and 1.7 W. If the resistor is designed for less power than the circuit, it will heat up and eventually. burn out. As exdeniz suggests, for our purposes, the PPB-3A 3W 220 Ohm will work fine. A variable resistor like mine has 3 pins. I will not go into details, just solder 1 wire to the middle contact and one extreme, and the second to the remaining extreme (details you can find out with a multimeter/ohmmeter). Thanks guessss_who for the comment).
Now install the fan in the case and find a suitable place for the resistor.
The resistor has a nut for attaching to the plane. Note that the case is metal and can short the resistor terminals and it will not work, so cut out of plastic or cardboard insulator. I don’t have the contacts shorted, fortunately, so no gaskets in the photo.
Now the most important thing. the field test.
I turned the system on, opened up the PSU case and used a pyrometer to find the hottest area(it’s an element, looks like a transistor, which is cooled by the heatsink). Then I closed it, twisted the resistor to maximum rpm and waited 20-30 minutes The element heated up to 26.3 °C.
Then set the resistor to half, The noise can no longer be heard, again waited for 30 minutes The cell heats up to 26,7 °C.
100 Ohm), waiting 30 minutes, do not hear any noise from the cooler at all The cell heats up to 28.1 °C.
I don’t know what kind of element it is and what its working temperature is but I think it can hold another 5 or 10 degrees. But if you consider that at “half” of the resistor the noise was already gone, then we don’t need anything else! =)
Now you can make a panel like the one I gave at the beginning of the article and it will cost you pennies.
UPD: Thanks to the gentlemen in the Комментарии и мнения владельцев, for reminding me of the watts. UPD: If you are interested in the subject and you know what a soldering iron is, you can easily assemble an analog reobassembly. As fleshy tells us, in the article Analog Reobassembly, this wonderful device is described. Even if you have never soldered a board, you can build a re-board. There is a lot of text in the article which I don’t understand, but the main thing: Composition, Schematic, Assembly(This paragraph has links to all the articles you need on soldering).
Varieties and features of devices
Transformer controls are ideal for situations where you need to control the speed of the hood blades manually. Their popularity is also due to their moderate cost, as well as the highest reliability among “colleagues.
The difference of step controllers from other types of controllers. the ability to operate continuously for a long time on unattended objects.
The main technical characteristics of the devices:
- voltage: 65-110-135-170-230 or 80-105-130-160-230 (figures differ depending on model)
- Single-phase and three-phase. 220 and 380 V, respectively;
- weight can be up to 30 kg (all devices are quite bulky)
- current frequency: 50-60 Hz;
- Device protection class: 00, 20, 54 IP.
Device housings are made of durable plastic and can withstand temperatures up to 40 degrees. Some groups of regulators are class B with up to 130 degrees of shutter speed reserve.
Some models are equipped with equipment operation signaling lamps and emergency indicators. There are also unique units with the option of galvanic isolation from the network. These controllers can be used in medical institutions.
As additional options, the controller may have terminals for connecting and controlling external devices (for example, actuators of air dampers).
By design and type of serviced fans controllers are divided into installed:
Some models are Din-rail mounted, controlled remotely.
If you need to control the speed of several fans, it is advisable to buy a multichannel controller. There are models that can serve up to four or more devices simultaneously.
But if the fans are located in different rooms, and there is only one controller, the parameters on the hoods will be set the same. In the case where you need a different microclimate in different rooms, it is more convenient to connect several controllers.
High weight and dimensions of such devices, complexity of external control are overlapped by their advantages in stationary positioning. The choice of a specific model depends on the technical features of the ventilation system.
Regulator of fan speed: types of devices and connection rules
Fan is one of the little-noticed, but extremely important devices that help to create favorable conditions for work, rest and just a pleasant stay.
Without it, computers, refrigerators, air conditioners and other appliances can not function. For maximum efficiency of various devices use the fan speed controller.
From our material you will learn about what regulators can be, features of their work. We will also tell you how to assemble the device with your own hands and what you need for this.
Wiring diagrams and the choice of the fan speed controller: overview of the best models and their costs
Fan very often used in many household appliances. To make this unit last a long time, a fan speed regulator is used. It helps to set the desired speed of rotation of the blades. This technique lowers the noise of the appliance and prolongs its service life.
What are fan speed controllers??
A speed regulator (also called a controller) helps to reduce speed when necessary or increase it. Basically, it changes the voltage applied to the device. This small-sized device is connected to the equipment by a special circuit.
If the fan is constantly running at maximum speed, this reduces its service life. The device wears out and breaks down quickly.
How it works: principle and principle of construction
The principle of the speed controller is to change the voltage and the speed of the motor. This affects the air exchange and changes the power of the airflow.
Different methods can be used to control the speed:
The second method is almost not used, because frequency drives are very expensive, many times more than the fan itself, and it is not always advisable to buy them. Mainly the first method is practiced.
Types of speed controllers
According to the principle of speed control there are several types of controllers:
Triac regulator is the most common, it can even cover not one but several motors. The main thing is that the current value should not exceed the limit value.
Frequency models can be used in any range from 0 to 480 V, they are used for three-phase fan motors up to 75 kW.
Transformer controllers are used for more powerful fans. They are single-phase or three-phase, allow you to smoothly reduce the speed of rotation, can regulate multiple fans.
Wiring diagrams of fan speed regulators
Let’s consider wiring diagrams of different regulators.
The most common device is a triac or thyristor controller. It can be wired independently using the diagram. Each thyristor reduces voltage. Adjustment is carried out with the help of a control unit. The capacity of the device is limited, it cannot withstand high voltages.
The transformer regulator has the following principle of operation:
Incoming supply voltage of 220 V. The winding has several branches in which the load is connected, and then the voltage decreases. As the voltage is lowered the power consumption decreases as well. With the help of a switch the motor is connected to the desired part of the winding and then the voltage changes.
A transformer with electronic control works according to a different circuit. It has a transistor circuit, and by modulating the pulses, can change the voltage smoothly. The shorter the pulses and the longer the pause between them, the lower the voltage.
Step transformer regulator
A transformer is used in the operation of this device. This is an ordinary transformer, but it has a single winding and part of the turns have taps.
The regulator is controlled by a step change in voltage. Noise levels are lower at low speeds.
Usually five voltage steps are used, which means the fan will have five speeds. Such a regulator can be used both for reversible fans and for several units at the same time. The maximum fan power should not exceed 80W.
Electronically controlled autotransformer
These models are among the most reliable and powerful. This is the most expensive unit in terms of price. It has small dimensions and weight.
Such a controller works on the principle of pulse-width modulation. Changes in pulses and pauses between them give a change in voltage and, accordingly, the speed of the fan.
The device has lowered noise level, the fan speed can be lowered or raised in steps according to the lowering or raising of voltage.
Thyristor and triac controllers
These are the most common devices for regulating the rotation of fans. They are used for single-phase AC fans. Thyristor controller changes the speed of rotation up or down depending on changes in voltage. Can be installed in appliances with overheat protection.
Triac regulator is a kind of thyristor regulator. It uses a triac, which is equal to two thyristors in parallel. The devices can be used for both AC and DC. The speed of regulation from the minimum required voltage to 220 V.
They are small and switch speed smoothly, have a simple design. Disadvantages include excessive noise and short life.
Fan operating principle
According to the technical definition, a fan is a device that moves gas by creating excess pressure or vacuum. It is divided into axial and radial in design. Virtually all fans, used in homes, are of axial type. The use of this type is characterized by the convenience of obtaining directional air of varying strength and pressure. Fans are divided by place of use, they can be:
Axial, otherwise known as axial, fans use an impeller as a basic unit. This wheel is located on the motor axis, contains the outer rotor and has blades angled for aerodynamic properties. This arrangement generates and shapes the air flow.
As an electric motor, a single-phase asynchronous motor is used, the axis of which repeats the movements of the air flow discharged or injected by it. Such an electric motor consists of a rotor placed inside the stator. The space between them is not more than two millimeters. The stator has the form of a core with grooves, through which the winding is wound. The rotor looks like a moving part with a shaft that contains a core with a short-circuited winding. This design is reminiscent of a squirrel wheel.
When alternating current is applied to the stator winding, according to the laws of physics, an alternating magnetic flux appears. On a closed conductor placed inside this flux, there is an electromagnetic induction (EMF), and so there is also a current. What makes a conductor with current appear in an alternating magnetic field. This causes the core, i.e. the rotor, to rotate.
So, to make a 220V fan speed controller, you need to change the magnitude of the magnetic field acting on the rotor. In turn, the value of magnetic field depends on the value of current, so when you reduce its value, the speed of rotation decreases as well.
Another parameter, on which the number of revolutions of the electric motor depends, is the frequency of the alternating voltage. Frequency converters that change frequency are complicated and expensive, compared to those that change voltage level. In domestic conditions are rarely used, although they can achieve the best results in the accuracy of adjustment.
According to the type of circuitry used, devices that control the speed of rotation are divided into: