Connecting two electrolytic capacitors in series with a polarity of plus-to-plus or minus-to-minus is the only reliable way to obtain a nonpolar analog from the available parts. This type of assembly is often required when there is no specialized equipment available. nonpolarIt is impossible to replace it with a conventional ceramic or film element due to the requirements for a large capacity in the AC circuit or pulsating voltage. The correct connection allows the use of standard polar components in circuits where the current direction changes periodically, preventing them from exploding or failing.
When creating a component element, it is important to take into account that the final capacity of the resulting bundle will always be less than the capacity of each of the used components separately. Electrolytic capacitors They have the property of passing current only in one direction, and when the reverse voltage is applied on the plates, a violent chemical reaction occurs with the release of gas. It is to block this dangerous process that a counter-sequential switching scheme is used, which ensures that in any half-period of alternating current, one of the elements will be turned on in the forward direction, and the second in the opposite direction, but under the protection of the first.
The principle of operation of a non-polar component
The physical principle underlying the operation of a homemade nonpolar capacitor is based on the properties of the aluminum oxide layer, which serves as a dielectric. Normal. polar-capacitor It only lets the leakage current through when the plus source is connected to the anode, supporting the oxide film. If the polarity changes, the film begins to break down, which leads to a sharp increase in current and heating. In a composite design, when two elements are connected in series by the same-named terminals, they work as two diodes included towards each other.
At the time of supplying voltage in one of the half-waves of alternating current, one capacitor is turned on in the forward direction, and the second in the opposite direction. The element turned on in the opposite direction behaves as a nonlinear resistance with very high impedance, effectively blocking the flow of large reverse current through the entire chain. It is critically important to understand that without such a connection, the supply of alternating current to a single polar capacitor will lead to its instantaneous failure.
The effectiveness of such a bundle depends on the symmetry of the parameters of the parts used. If you take two elements with very different characteristics, the voltage distribution can become uneven, which will reduce the overall operating threshold of the design. To ensure stable operation in high-frequency circuits or chains with large pulsations, it is often recommended to add resistors in parallel to each shoulder, but in most household cases, such as starting engines or filtration in audio equipment, competent selection of the capacitors themselves is enough.
- โก The sequential connection of the same conclusions creates a diode protection effect for each element.
- ๐ The total capacity of the prefabricated structure is always reduced and calculated by the formula for serial connection.
- ๐ The breakdown voltage of such a ligament is summed up, allowing you to work in chains with higher voltage.
Required materials and tools for assembly
For the manufacture of a high-quality non-polar analog, a pair of identical electrolytic capacitors will first be required. The ideal option is to use parts from one batch or even from one package, as their parameters, such as: ESR (equivalent serial resistance) And the current leaks will be as close as possible. If it is not possible to find the same models, it is necessary to select components with the minimum possible difference in the rated capacity and operating voltage.
In addition to the radio elements themselves, for installation, tools for high-quality soldering will be required. The use of cheap solder with a high lead content is not recommended, as it can create additional resistance and worsen contact at the connection point of the terminals. It is better to use solder with a rosifol in the core, providing a reliable connection and protection against oxidation. Flush is also needed if soldering is made on weight or to a printed circuit board.
โ ๏ธ Warning: Never use condensers with a swollen body or impaired tightness. Even if they show capacitance with a multimeter, their oxide layer is already damaged, and in an alternating current circuit, they can behave unpredictably.
To isolate the connection site and protect against mechanical damage, a shrink tube or insulation tape will be required. Since the connection is often performed by the โhingedโ method directly on the terminals, it is important to ensure the rigidity of the structure so that vibration does not lead to a break in the contacts. In some cases, especially in audio technology, the adhesion site is additionally filled with thermal glue for fixation.
For best results, use capacitors with a voltage margin. If the circuit is 25 volts, take parts 50 volts or higher, as in transient processes, voltage surges are possible.
Step-by-step instructions for connecting capacitors
The process of creating a non-polar element begins with the preparation of conclusions. If the capacitors have long legs, they must be shortened to a comfortable length, leaving a margin for twisting or soldering. The conclusions are then cleaned from oxides to metallic luster. The most important step is to combine two positive conclusions ("plus" with "plus") or two negative ones ("minus" with "minus"). The choice of the connection scheme (plus-plus or minus-minus) does not affect the electrical properties of the final assembly, the main thing is to connect the contacts of the same name.
After the twisting or pressing of the conclusions, the ration is made. The connection site should be heated evenly so that the solder flowed into all the voids, ensuring the monolithic contact. The remaining two terminals (one minus and one plus from different capacitors) will be the external contacts of the resulting non-polar capacitor. They can be irrigated for ease of installation in the board or soldered to them wires.
โ๏ธ Checking the condenser assembly
The finished structure must be isolated. Since the potentials may differ at the connection site, and to prevent short circuits on adjacent circuit elements, the joint is carefully wrapped with insulating tape or heat shrinkage is put on. If the assembly is intended to be installed in a high vibration device, it is recommended to fix the capacitor bodies relative to each other with glue or clamping to prevent breaking the terminals at the base.
Calculation of capacity and operating voltage
When combining two capacitors in series, their total capacity is calculated using the same formula as for a serial connection of resistors, but with the opposite result. If two identical elements are used with a capacity C1 = C2 = C, then the final capacity C_total It will be equal to half of the value of one of them. This is a fundamental rule that should not be ignored when selecting replacement components.
The working voltage of the component element also undergoes changes. Theoretically, using two identical capacitors designed for voltage V, assembly withstands stress 2V. However, in practice, due to the scattering of parameters and the possible asymmetry of leakage currents, the actual operating voltage may be slightly less than the amount. However, such a margin of safety is often an advantage, allowing the assembly to be used in higher-voltage circuits.
| Parameter | One capacitor (C1) | Two consecutive (C1+C2) | Note |
|---|---|---|---|
| Capacity | 100 ฮผF | 50 ฮผF | Capacity drops 2 times |
| Tension. | 25 V V | 50 V. | The voltage is summed up |
| Polarity | Polar | Nonpolar | It's in the AC circuit. |
| ESR | 1 ohm | 2 ohm | Resistance grows |
It is important to consider that an increase in ESR (equivalent serial resistance) can adversely affect the operation of a circuit if it is designed to operate at high frequencies. In pulsed power supplies or HF filters, doubling ESR can lead to overheating and reduced filtration efficiency. Therefore, for such purposes it is better to look for original non-polar electrolytes or use film analogues.
Features of application in audio equipment and filters
In audio engineering, especially in crossover acoustic systems and separation filters of amplifiers, the requirements for the quality of capacitors are extremely high. There are often situations where a large capacity (e.g., 20-50 ฮผF) is required when working with a variable signal. Conventional electrolytes are distorted by the nonlinearity of the dielectric, and specialized audiophile nonpolar capacitors (NPs) are very expensive.
Using a bundle of two high-quality polar capacitors allows you to get an acceptable result for less money. The sound becomes cleaner, the distortions characteristic of the polar electrolyte in the reverse turn on disappear. However, audiophiles often argue about which scheme is better: "plus to plus" or "minus to minus." Practical hearings sometimes show a difference in timbral color, although from the point of view of pure physics the difference should be minimal.
โ ๏ธ In high-quality audio equipment, avoid using cheap capacitors with high tangent loss angles. Even in non-polar inclusion, they can impair the dynamics of sound.
For separation capacitors in lamp technology is also often used this method. Lamp circuits operate at high voltages, and the ability to double the operating voltage when connected in series is a strong argument in favor of such an assembly. The main thing is to monitor the dimensions, since two capacitors take up more space on the board than one.
Typical errors and security measures
One of the most common mistakes is to connect different conclusions ("plus" to "minus"). In this case, you get just a serial connection of two polar capacitors, which, when applied alternating current will still be under reverse voltage at certain points in time. Such an assembly will not become non-polar and will fail as quickly as a single element.
Another mistake is to ignore the difference in capacity. If you connect a capacitor of 100 ฮผF and 10 ฮผF, the voltage will be distributed disproportionately between them. On a smaller capacitor, the voltage will be much higher, which can lead to its breakdown. After a breakdown of one element, the entire chain will cease to perform the protection function, and the second capacitor will also quickly fail.
Can more than two capacitors be connected?
Yes, you can combine three or more elements. When three identical capacitors are connected in series (plus-plus-plus), the total capacity will drop 3 times, and the operating voltage will triple. However, this increases the size and ESR, which is rarely justified.
When working with high-voltage circuits (for example, in old lamp TVs or amplifiers), it is necessary to remember about the residual charge. A composite nonpolar capacitor, like a conventional one, can retain charge for a long time. Before touching the conclusions, always discharge them through the resistor. Failure to comply with this rule can result in a painful electric shock.
The main conclusion: assembling a non-polar capacitor is a temporary or budgetary solution. For responsible units, it is better to use specialized non-polar electrolytic or film capacitors of factory manufacture.
FAQ: Frequently Asked Questions
Can capacitors of different capacities be connected?
Technically, it is possible to connect, but not recommended. With different capacity, the voltage will be distributed inversely proportional to the capacity. A smaller capacitor will take on more voltage and can break through quickly. Use items with the same denomination.
Will the capacity decrease with this connection?
Yeah, it's bound to shrink. When two identical capacitors are connected in series, the total capacity will be exactly half the nominal value of one of them. This should be taken into account when choosing a replacement.
Will this scheme be suitable for the engine of the washing machine?
Yes, for start-up and working engine capacitors (for example, in washing machines or pumps), this method is often used. The main thing is to choose capacitors with a margin of voltage (minimum 400-450V for a 220V network).
What is the life of a homemade non-polar capacitor?
The service life depends on the quality of the initial components and operating conditions. If the capacitors are new and operate below the limit, they can last for years. However, reliability is always lower than that of the factory non-polar counterpart.