Beatrice Lang
In electrical engineering, impedance refers to the opposition to alternating current (AC) presented by the combined effect of resistance and reactance in a circuit. It is a measure of the circuit's opposition to the flow of AC, taking into account both the resistance and reactance. Low impedance, in simple terms, indicates a lower opposition to the flow of AC electricity. In the context of electric fence chargers, low impedance means that the charger operates with medium to high voltage and much greater currents, allowing it to deliver a powerful shock that can penetrate through weeds while remaining safe due to the extremely short duration of each pulse.
Characteristics and Values of Low Impedance in Electrical Engineering:
| Characteristics | Values |
|---|---|
| Definition | Low impedance refers to modern electric fence chargers that use high voltage and high amperage to deliver a powerful shock. |
| Output | Medium to high voltage with greater currents compared to high-impedance chargers. |
| Pulse Duration | Extremely short pulses of about 3 milliseconds, or about 330 pulses per second. |
| Safety | Delivers a strong but safe shock due to the short pulse duration, reducing the risk of fires or electrocution. |
| Efficiency | Low-impedance chargers lose only 20% of their shocking power over five miles of fence, making them suitable for long or overgrown fences. |
| Type of Current | Relates to AC (alternating current) and is the equivalent of resistance in DC (direct current) circuits. |
| Units | Measured in Ohms (Ω), the same units as resistance. |
| Reactance | Inversely proportional to capacitance and directly proportional to inductance. |
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What You'll Learn
Low-impedance electrical fence chargers can power very long fences
In electrical engineering, impedance is the opposition to alternating current presented by the combined effect of resistance and reactance in a circuit. Low-impedance fence chargers have less resistance in the charger, allowing more power to be pushed through the wire. This means that low-impedance fence chargers can maintain a high energy output on the fence even as power is drawn by weeds or other forms of vegetation. The output from a low-impedance fence charger is medium to high voltage, but at much greater currents. This means that low-impedance fence chargers have a large reserve of current and are able to power very long fences or fences that are overgrown by green growth.
The amount of weeds touching a fence line is directly proportional to the draw from the charger. Therefore, if there are heavy weeds near the fence line, a low-impedance fence controller is recommended. This is because low-impedance fence chargers can maintain high energy on the fence even as power is drawn by weeds. Low-impedance fence chargers are also able to regulate their output and maintain a constant voltage supply to the fence even as the grounding and fence conditions deteriorate due to increased vegetation contact.
The size of the fence charger needed is determined by factors such as the length of the fence, the number of wires, the power source, and the type of animal being contained or excluded. Low-impedance fence chargers are the best and latest technology for powering long fences with weeds. The recommended and most reliable choice for powering fence chargers is AC power, which typically has greater energy output and more flexibility for future expansion.
Low-impedance fence chargers are available in several dual-purpose models. For example, the Power Wizard Ultra low-impedance model can be used for any type of livestock and can be connected to a 110-volt line input or powered by a 12-volt battery.
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Low-impedance circuits have high voltage and high amperage
In electrical engineering, impedance is the opposition to alternating current presented by the combined effect of resistance and reactance in a circuit. The SI unit for impedance is the ohm (Ω). In simple terms, impedance is the ratio of voltage to the current flowing through it.
The opposite is true for high-impedance circuits, which are low current and potentially high voltage. High impedance means that a node in a circuit allows a relatively small amount of current through per unit of applied voltage.
It is important to note that the terms "low" and "high" in this context are relative and depend on the specific application and range being considered. For example, in the context of electric fence chargers, older models with high-impedance outputs had high voltage but low current. The new low-impedance chargers have medium to high voltage and much greater currents, allowing them to power very long fences or those overgrown with vegetation.
Amperage, or the volume of electricity flowing through a circuit, is independent of voltage, or the force or pressure moving the electrons. Therefore, it is possible to have a circuit with very high amperage but very low voltage, or vice versa. The relationship between the two is described by Ohm's law, which states that voltage multiplied by amperage equals watts, or power.
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Impedance is the AC equivalent of resistance
In a direct current (DC) circuit, the relationship between voltage and current is commonly called resistance, as defined by Ohm's Law. However, in an alternating current (AC) circuit, this relationship is called impedance. Impedance can be defined as the ratio of the phasor voltage across the element to the phasor current through the element, as determined by their relative amplitudes and phases.
The impedance of a device can be calculated by complex division of the voltage and current. This can be done by applying a sinusoidal voltage to the device in series with a resistor and measuring the voltage across the resistor and the device. The impedance phase and magnitude can be found by sweeping the frequencies of the applied signal.
Impedance can be represented as a complex number, with the same units as resistance, for which the SI unit is the ohm (Ω). Its symbol is usually Z, and it may be represented by writing its magnitude and phase in the polar form |Z|∠θ. However, Cartesian complex number representation is often more powerful for circuit analysis purposes.
In a pure ohmic AC resistance, the current and voltage are both "in-phase", meaning there is no phase difference between them. The current flowing through the resistance is directly proportional to the voltage across it, with this linear relationship in an AC circuit being called impedance.
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Impedance is calculated by the ratio of voltage to current
Impedance is a fundamental concept in electrical engineering that represents the opposition to the flow of alternating current (AC) in a circuit. It is calculated as the ratio of voltage to current. In other words, it is the ratio of the complex representation of the sinusoidal voltage between the terminals of a two-terminal circuit element to the complex representation of the current flowing through it. The impedance of a circuit element can also be defined as the ratio of the phasor voltage across the element to the phasor current through the element, as determined by the relative amplitudes and phases of the voltage and current.
The notion of impedance is particularly useful for performing AC analysis of electrical networks, as it allows relating sinusoidal voltages and currents by a simple linear law. It is important to note that impedance is distinct from resistance, which opposes both direct current (DC) and AC, while impedance only opposes AC.
In RLC circuits, which consist of resistors (R), inductors (L), and capacitors (C), the impedance formula combines resistance, inductive reactance, and capacitive reactance. This formula is expressed as Z = R + j(XL + XC), where XL and XC represent the inductive and capacitive reactance, respectively. By understanding and calculating impedance in these circuits, engineers can effectively analyse, design, and optimise various electrical systems and components to ensure optimal performance and efficiency.
The accurate calculation of impedance is crucial in optimising the performance of circuit boards and systems. It is typically represented by the formula Z = R – j/ωC + jωL, where ω= 2πf. There are various methods to calculate the impedance of a circuit, including circuit simulation, online impedance calculators, and practical formula-based approaches. These calculations help ensure efficient signal flow and minimise disruptions.
In the context of low impedance, such as in electric fence chargers, low impedance output means medium to high voltage but at much greater currents. Low-impedance devices have a large reserve of current and can power very long lengths or those obscured by overgrown vegetation.
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Impedance is measured in ohms
Impedance is a vital concept in electrical engineering, and when measured accurately, it can significantly improve the performance and reliability of circuits and systems. It is defined as the total opposition a circuit presents to alternating current, encompassing both resistive and reactive components. Impedance is measured in ohms (Ω), and its symbol is usually Z.
In a two-terminal circuit, impedance is the ratio of the complex representation of the sinusoidal voltage between its terminals to the complex representation of the current flowing through it. It depends on the frequency of the sinusoidal voltage and is influenced by both resistance and reactance. By understanding impedance, engineers can design circuits and systems that require specific resistance, capacitance, and inductance values for optimal performance.
There are several methods for measuring impedance, each with its own advantages and applications. The bridge method, for example, uses a bridge circuit to compare the unknown impedance with a known reference. The current-voltage (I-V) method involves applying a known voltage to a circuit and measuring the resulting current or vice versa to calculate impedance. This method is straightforward but can be less accurate if the phase relationship between voltage and current is not correctly considered.
The choice of measurement method depends on the specific application and the required test frequency, impedance parameter, and preferred display parameters. Impedance analyzers and network analyzers are tools used to measure electrical impedance accurately.
In the context of low impedance, let's consider electric fence chargers. Older fence chargers were high-impedance, which means they output high voltage but low current. As a result, poor insulators or grass and weeds touching the fence could drain much of the shock. On the other hand, low-impedance fence chargers output medium to high voltage but at much greater currents. They have a large reserve of current and can power very long or overgrown fences effectively.
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Frequently asked questions
Impedance is the opposition to alternating current presented by the combined effect of resistance and reactance in a circuit. It is the AC (alternating current) equivalent of resistance, which is a concept used for DC (direct currents).
Low impedance circuits use very high voltage and very high amperage, delivering electricity in short pulses. This allows for a powerful shock that can punch through weeds and other obstacles while remaining safe due to its short duration.
Early electric fence chargers were high-impedance, delivering long pulses of high-voltage, low-amperage power. While the shock was strong, these chargers were prone to short-circuiting when tall grass or tree branches touched the wire. They also had a higher risk of causing fires and electrocution. Low-impedance chargers, on the other hand, have a large reserve of current and can power longer fences effectively, making them a safer and more reliable choice.
