The debate about whether a capacitor is needed in car audio or not does not subside and will probably never subside. 12 years ago, when I was just starting to work on car audio, it was believed that this was practically the most necessary part of the audio system, that without a "drive" the battery runs out very quickly, and with it you can listen to music in nature for at least 2 hours or even longer, and then a car without problems start and you can go.

That is, it was believed that the capacitor is something like an additional battery. Now, of course, everyone knows that this is a myth and the capacity of the capacitor is several orders of magnitude less than the capacity of the battery. At the present time, it is believed that the capacitor is generally unnecessary, useless and only serves to legally take money from the population, now this is the most common point of view thanks to well-known video reviews on YouTube. Meanwhile, the capacitor included in the power circuits of powerful audio systems, as it was a simple banal smoothing filter, has remained so. The capacitance connected in parallel with the load, in principle, cannot be anything else.
Whether a capacitor is needed in the system or not, everyone decides for himself. But in order to do this, it is necessary to understand the function that it performs in the system, as well as the criteria for selecting its capacity.

Capacitor functions

So, first about the function. As mentioned above, the capacitor acts as a smoothing filter in the power supply circuit of amplifiers, and like any power filter, it has one task - to improve the sound of the system. If there is any interference in the power supply, they will certainly appear at the output of the amplifier, no matter how wonderful it is and no matter what effective methods anti-interference was not applied in his scheme. If you want a good sound - clean the food, it's an axiom. The use of a capacitive filter is the simplest but most effective solution in the fight against interference. The efficiency of the smoothing filter is very much dependent on both the capacitance of the capacitor and the power of the load - the greater the power of the system, the more capacitance is required to reduce the supply voltage ripple to an acceptable level.
At this point, the question usually arises: what kind of pulsations? we have in the car constant pressure. This is not entirely true. When the generator is running, pulsations are present in any case, this is due to the principle of operation of the rectifier in the generator. A smoothing filter is installed in the generator in the form of a capacitor not large capacity, which effectively copes only with high-frequency ripples and only at small loads. Under heavy loads, the efficiency of its work drops very much and interference from the generator can pass through the power supply and greatly spoil the sound. If the generator does not work (the engine is turned off), then there are no high-frequency ripples, but there are all of us "favorite" voltage drops in the system - "drawdowns". They appear at the moment of the bass attack. No matter what battery is in the car and no matter what cable the amplifiers are connected to, there are still drawdowns - large or very small, which the voltmeter does not have time to catch, but they are. If you listen to rhythmic music, say with a 4/4 rhythm - four quarters (4 bits per second), then drawdowns also appear at 1/4 second intervals, that is, ripples appear in the system power supply with a frequency of 4 Hz and an amplitude somewhere 0.5 - 1.5 V, who has it like. That is, the system itself becomes a source of interference at high volumes and rhythmic music. In order to extinguish these rather strong and low-frequency ripples, a large capacitor is used - "accumulator", "buffer capacitance", etc., there can be very many names. If you listen to the lowest and scariest blacks, then power ripples occur less often or not at all, because these guys very often use almost stationary signals, when the bass tone can sound for several seconds without changing.

Capacitor selection

Now about the selection of capacity. The method for choosing a smoothing capacitor can be studied in detail by clicking on this link - http://www.meanders.ru/sglazg_filters.shtml.
When choosing a capacitor capacity, it is customary to use the rule of thumb - 1F per 1 kW of power consumption. From
the technique I referred to earlier, we know that the smoothing filter works effectively if the inequality holds: 1/(2pi*F*C)"R where
R is the filter load resistance, in our case some generalized input impedance of our entire sound system,
F - the frequency of pulsations that must be dealt with depends on the nature of the musical signal
C is the capacitance of the smoothing capacitor. the sign """ means "significantly less", the concept is not entirely specific, it means that one value should be less than the other by about an order of magnitude, if I'm not mistaken.
Of course, the generalized resistance R cannot be measured, but it can be estimated: if the system consumes 1 kW, then the source "sees" it as a load of 0.15 Ohm. You can estimate the resistance if you know the current drawn.
In order not to worry about estimating the resistance and if the power of the system is known, you can convert the expression to the form C»P / (2pi*F*U 2) where

U - on-board network voltage
P is the power of the system. According to the last formula, you can choose the capacitance of the capacitor, which in a powerful system will neutralize the negative effect of "drawdown" on the sound quality.
For example, for a system with a power of 1 kW (P = 1000 W), with a voltage in the on-board network of 12V (U = 12V), if we listen to music with a four-quarter rhythm (4 beats per second, F = 4Hz), then to eliminate negative impact for the sound of emerging drawdowns, we need a capacitor with a capacity of C "0.27F. It is believed that a capacity of 1F is enough, but personally I think that 2.5-3F satisfies the condition.

conclusions

There are a few highlights from all of this:
1. The capacitor is needed in order to deal with interference resulting from "drawdowns" of the supply voltage,
generated by the system itself during operation. The capacitor in no way eliminates "drawdown" and does not stabilize the voltage and does not increase the capacity of the battery.
2. If the system reproduces a stationary signal, for example, a sinusoid during pressure measurement, then there is no supply voltage ripple, therefore, the capacitor is useless in such modes.
3. If the sound system is powered by a source consisting of a very powerful generator and several AGM batteries connected in parallel, then such a source has a very low output impedance, as a result of which the “drawdown” in the system can be negligible. In these cases, the use of a capacitor will also not give a noticeable result.

Many owners quite often find themselves in a situation where they need to connect a device such as a three-phase asynchronous motor to various equipment, which can be an emery or drilling machine. This raises a problem, since the source is designed for single-phase voltage. What to do here? In fact, this problem is quite easy to solve by connecting the unit according to the schemes used for capacitors. To realize this plan, you will need a working and starting device, often referred to as phase shifters.

To ensure the correct operation of the electric motor, certain parameters must be calculated.

For run capacitor

To select the effective capacity of the device, it is necessary to perform calculations using the formula:

• I1 is the nominal stator current, for which special clamps are used;
• Unetwork - mains voltage with one phase, (V).

After performing the calculations, the capacitance of the working capacitor will be obtained in microfarads.

It may be difficult for someone to calculate this parameter using the above formula. However, in this case, you can use another scheme for calculating the capacitance, where you do not need to carry out such complex operations. This method allows you to quite simply determine the required parameter based on power alone. induction motor.

It is enough to remember here that 100 watts of power of a three-phase unit should correspond to about 7 microfarads of the capacitance of the working capacitor.

When calculating, you need to monitor the current that flows to the phase winding of the stator in the selected mode. It is considered unacceptable if the current is greater than the nominal value.

for start capacitor

There are situations when the electric motor has to be turned on in conditions heavy load on the shaft. Then one working capacitor will not be enough, so you will have to add a starting capacitor to it. A feature of its work is that it will work only during the start-up period of the device for no more than 3 seconds, which uses the SA key. When the rotor reaches the level of the rated speed, the device turns off.

If, due to an oversight, the owner left the starting devices on, this will lead to the formation of a significant imbalance in the currents in the phases. In such situations, the likelihood of engine overheating is high. When determining the capacitance, one should proceed from the fact that the value of this parameter should be 2.5-3 times greater than the capacitance of the working capacitor. By doing so, one can achieve Starting torque the engine reaches the nominal value, as a result of which there are no complications during its start.

To create the required capacitance, capacitors can be connected in parallel and in series. It should be borne in mind that the operation of three-phase units with a power of not more than 1 kW is allowed if they are connected to a single-phase network with a working device. And here you can do without a starting capacitor.

Type

After calculations, you need to determine which type of capacitor can be used for the selected circuit.

The best option is when the same type is used for both capacitors. Usually work three-phase motor provide paper starting capacitors, dressed in a steel sealed case such as MPGO, MBGP, KBP or MBGO.

Most of these devices are made in the form of a rectangle. If you look at the case, then there are their characteristics:

• Capacitance (uF);
• Operating voltage (V).

Application of electrolytic devices

When using paper starting capacitors, you need to remember the following negative point: they are quite large, while providing a small capacitance. For this reason, for the efficient operation of a three-phase motor of small power, it is necessary to use a sufficiently large number of capacitors. If desired, paper can be replaced with electrolytic ones. In this case, they must be connected in a slightly different way, where they must be present additional elements represented by diodes and resistors.

However, experts do not advise using electrolytic starting capacitors. This is due to the presence of a serious drawback in them, which manifests itself in the following: if the diode does not cope with its task, alternating current will be sold to the device, and this is already fraught with its heating and subsequent explosion.

Another reason is that there are improved metal coated polypropylene launchers on the market today. alternating current SVV type.

Most often they are designed to work with a voltage of 400-450 V. They should be given preference, given that they have repeatedly shown themselves on the good side.

Voltage

Considering Various types starting rectifiers of a three-phase motor connected to a single-phase network, such a parameter as operating voltage should also be taken into account.

It would be a mistake to use a rectifier whose voltage rating exceeds the required one by an order of magnitude. In addition to the high cost of acquiring it, you will have to allocate more space for it due to its large dimensions.

At the same time, you should not consider models in which the voltage has a lower indicator than the mains voltage. Devices with such characteristics will not be able to effectively perform their functions and will fail pretty soon.

In order not to make a mistake when choosing the operating voltage, the following calculation scheme should be followed: the final parameter should correspond to the product of the actual mains voltage and a factor of 1.15, while the calculated value should be at least 300 V.

In the event that paper rectifiers are selected for network operation AC voltage, then their operating voltage must be divided by 1.5-2. Therefore, the operating voltage for a paper capacitor, for which the manufacturer indicated a voltage of 180 V, under conditions of operation in an alternating current network, will be 90-120 V.

In order to understand how the idea of ​​​​connection is implemented in practice three-phase electric motor to a single-phase network, we will perform an experiment using an AOL 22-4 unit with a power of 400 (W). The main task to be solved is to start the engine from a single-phase network with a voltage of 220 V.

The motor used has the following characteristics:

Keeping in mind that the electric motor used has a small power, when connecting it to a single-phase network, you can only buy a working capacitor.

Calculation of the capacity of the working rectifier:

Using the above formulas, we take 25 uF as the average value of the working rectifier capacitance. A slightly larger capacitance of 10 uF was chosen here. So we will try to find out how such a change affects the launch of the device.

Now we need to buy rectifiers; MBGO type capacitors will be used as the latter. Further, on the basis of the prepared rectifiers, the required capacitance is assembled.

In the process of work, it should be remembered that each such rectifier has a capacitance of 10 microfarads.

If you take two capacitors and connect them to each other in a parallel circuit, then the total capacitance will be 20 microfarads. In this case, the operating voltage indicator will be equal to 160V. To achieve the required level of 320 V, it is necessary to take these two rectifiers and connect them to the same pair of capacitors connected in parallel, but already using a serial circuit. As a result, the total capacitance will be 10 microfarads. When the battery of working capacitors is ready, we connect it to the engine. Then it remains only to run it in a single-phase network.

In the process of the experiment with connecting the engine to a single-phase network, the work required less time and effort. Using a similar unit with a selected battery of rectifiers, it should be noted that its useful power will be at the level of up to 70-80% of the rated power, while the rotor speed will correspond to the nominal value.

Important: if the motor used is designed for a 380/220 V network, then when connecting to the network, use the “triangle” circuit.

Pay attention to the content of the tag: it happens that there is an image of a star with a voltage of 380 V. In this case, the correct operation of the engine in the network can be ensured by fulfilling the following conditions. First, you will have to “gut” a common star, and then connect 6 ends to the terminal block. Search common point should be in the frontal part of the engine.

Video: connecting a single-phase motor to a single-phase network

The decision to use a starting capacitor should be made based on specific conditions, most often a working one is enough. However, if the motor being used is subjected to an increased load, it is recommended to stop operation. In this case, it is necessary to correctly determine the required capacity of the device in order to ensure the efficient operation of the unit.

Or a lathe, powered by 380 volts. It could be installed in a home workshop or in the country. Yes, that's the trouble, in these rooms there are only ordinary sockets.

In cases where it is necessary to connect a three-phase electric motor, and only a single-phase voltage source is available, you can get out of the situation by powering one of the windings through a phase-shifting element - a starting capacitor. So you can get a replacement for the third phase of the voltage shifted by 120 degrees.

In the ideal case, to accelerate the motor, a large capacitance is required, and upon reaching the nominal angular velocity, another, smaller one is required. To achieve this, a scheme is used that makes it possible to turn off excess capacity both manually and automatically, leaving only its working value.

In the event that the windings are connected by a star, the working capacitance of the working capacitor is determined by the formula:

Cp = 2800 (I/U)

In the case of a triangle connection, the dependence is different:

Cp = 4800 (I/U)

However, the connection of the motor windings with a triangle is undesirable, because in this case the voltage should be 380 volts on each of them, and in home network- only 220.

To simplify the calculation of the value of the capacitance of a capacitor, you can use the formula according to which

P - power, watts;

Cn is the capacitance of the starting capacitor, mF;

Cn is the capacitance of the starting capacitor, mF.

Thus, the capacity of the starting capacitor should be one and a half to two and a half times the working one.

The standard AC voltage is 220 volts. The question arises of how to determine the magnitude of the current appearing in the above formula.

It is not difficult. engine is known, it is indicated on a plate fixed on its body and serving as a kind of passport for it.

I \u003d P / (1.73 U cos φ),

I - current value, Ampere;

U - voltage (220 Volts);

φ - phase shift angle.

Having correctly calculated and selected a starting capacitor for an electric motor, almost all types of three-phase electric motors can be connected to a single-phase network. Some of them will work better, that is, their characteristics will be closer to the passport ones when they are normally turned on (for example, the AOL, UAD, APN series). Series MA, characterized in that their design uses a double cage scheme squirrel-cage rotor, will show the worst results.

When choosing a starting capacitor, one should take into account the fact that at the moment of start, current values ​​\u200b\u200bthat are many times greater than nominal value. Thus, it should be remembered that the cross section of the conductors that provide power to the motor must be chosen with a margin.

Now about which starting capacitor can be used to connect Electrolytic capacitances can be used, but the presence of rectifier diodes in the circuit will complicate it and reduce the overall reliability of the entire system. Even Henry Ford rightly argued that the fewer parts, the lower the likelihood of a breakdown.

It is easier and more reliable to install a starting paper capacitor. The voltage indicated on its case must exceed 220 volts.

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Why is a capacitor needed?

The sole purpose of using capacitors in car audio systems is to combat voltage drops, i.e. voltage stabilization.

Did voltage drops kill the sound? Charge the capacitor!

Rice. 1. Capacitors - projectiles with electricity.

What's wrong with voltage drops?

best quality sound and maximum power sound amplifiers demonstrate at a stable voltage of 13.5 - 14 V. But in practice, without the use of capacitors, the voltage in the power system is far from ideal, and most importantly, it is completely unstable and sags almost to the beat of the music. At the same time, any sound amplifier significantly reduces efficiency, sound quality and power.

Work efficiency, i.e. the power level and sound distortion of any sound amplifier directly depends on the voltage at the supply terminals.

Why do voltage drops occur?

First, regular car battery unable to deliver large currents fast enough due to its large internal resistance(from 30mOhm). As a result, instead of 13.5 - 14 V, even with the engine running, especially at moments of peak power, such as drumming or other bass impulse, the voltage can sag by several volts. Such a voltage drop unequivocally leads to a significant decrease in power and the appearance of sound distortions that are perceptible by ear even to an inexperienced listener.

Secondly, the significant remoteness of the battery from the amplifiers requires the use of rather long power cables. Any cable, even if it is made of copper and the most suitable section, has its own, albeit small, resistance. The longer the cable, the greater its resistance, the more it prevents the instantaneous transmission of large currents.

Thirdly, in electrical circuit there are many connecting elements: fuse holders, power splitters, terminals, etc. Each of these elements connects different metals, creating the so-called contact resistance. Of course, quality brass connectors have little effect on overall voltage drops. However, as a rule, in the pursuit of price, many use connecting elements made of low-quality zinc-based alloys. This leads to energy losses in these sections of the circuit.

How does a capacitor solve this problem?

A capacitor or storage is a power source that has an instantaneous rate of return of electricity. When a regular battery and cables “do not have time to provide” the next portion of energy, the amplifier instantly receives it from the capacitor. Having given up partially or completely its charge, the capacitor is also instantly charged. Thus, the capacitor stabilizes the voltage in the power system.

Let's draw an analogy. Let's imagine that electricity- This is water. Sound amplifiers need a lot of energy to work as efficiently as possible, i.e. water. Then a regular battery is a big bottle with a narrow neck. A lot of water cannot flow through the neck at once, which is required by audio amplifiers to process a powerful wideband signal or bass impulse. In this case, the capacitor is a bucket. A bucket can quickly scoop up and pour out a large amount of water. Thus, the capacitor instantly gives up and receives its charge again, stabilizing the voltage on the power cables of the amplifier.

Rice. 2. Capacitors and a regular battery like a bucket and a bottle.

Capacitor to capacitor - discord!

The vast majority of car audio systems simply cannot reach their potential due to the lack of capacitors in the power system. However, why are there so many disputes and myths about the need for their use? Unfortunately, a significant number of companies produce low-quality capacitors that do not have the declared capacitances and even less resistance. Such capacitors do not reduce voltage drops, but they have a beautiful package and a low price. Affordable goods always become mass. Hence the army of dissatisfied, who believe that capacitors are of no use. Read more about the "dummies" that eclipsed the caraudio market in the article.

Asynchronous motors received wide application in industry. But electric units of small power can be successfully used in everyday life. It needs a rotating magnetic field to function.

However single phase motors will not rotate without a phase shift created, which is organized using an additional winding and a phase-shifting element. As the latter, MAL2118 capacitors are suitable.

Capacitor can be connected various methods. There are three different schemes:

• launcher;
• working;
• mixed.

It is worth noting that the most common scheme is the first (launcher). Her distinguishing feature is that the capacitor is connected to the motor network only at the time of its start.

Then the electric unit independently maintains its rotation. Such a switching scheme allows not only saving money on installing a complete set (wires of a smaller cross section), but also saving on electricity.

It must not be forgotten that there is a very likely risk of overheating, which in most cases depends on the terrain in which the engine is used. As a protection, it is recommended to install a thermal relay.

The indicated scheme is beneficial primarily in that it allows you to correct distortions. magnetic field, thereby reducing eddy current losses and increasing efficiency.

The capacitor remains on for the entire period of engine operation. However, in this method there is a fly in the ointment. Switching on with a running capacitor significantly degrades the starting characteristics of an asynchronous machine.

It is for this reason that engineers advise to come to a compromise and use two schemes at once, combined into one.

Due to the use of two schemes at once, starting characteristics will be average (quite acceptable in terms of resource use).

Remember! Before switching on with a capacitor, it is imperative to evaluate the performance using a multimeter. electrical element(even if it's brand new).

Alexander Shenrok will clearly demonstrate the methods for starting an asynchronous motor using a capacitor: