Voltage regulator is a device that allows you to maintain a constant voltage in the consumer circuit. Depending on the conditions of use and tasks, the designs differ. There are a number of groups: electromechanical, electronic, induction, compensated transformers.
Voltage Regulators of Electromechanical Type
Consider how current is generated in a car. Here, the electromechanical voltage regulator detects a curious principle of operation that differs from that described above. On board is a three-phase generator, the voltage of which is rectified by the Larionov scheme( see the review about the diode bridge).The circuit is assembled with an excitation winding that is powered by the device. The motor rotates the shaft, already at a frequency of 800 - 1000 revolutions per minute, the voltage is exceeded over the nominal. The amplitude of the EMF depends on:
- Current supply of the excitation winding.
- Anchor Speed.
- The current consumption of the onboard network.
The speed is constantly variable, and the gearbox, as a rule, is not adjustable. The current consumption is changed by an order of magnitude. It is clear that in the described conditions it is necessary to ensure the stability of the parameters. What and does the voltage regulator, changing the current supply winding. Exceeding the voltage over the optimum one by only 10 percent leads to a 2–2.5-fold reduction in the service life of the battery. As a result of the regulator's work, the deviation from the nominal does not exceed three percent and remains normal.
The voltage should be slightly higher than the battery voltage. The specified parameter depends on the ambient temperature. It is clear - changing the density of the electrolyte. Additionally, the voltage should be increased by 0.2 - 0.5 V for old batteries, where the active layer of the plates is destroyed due to sulfation. The electrolyte level does its bit: with a decrease it is supposed to reduce the charge voltage by 0.2 - 0.3 V. There are a lot of requirements, each failure leads to unpleasant consequences.
The voltage regulator allows you to maintain the parameters at the right level, set the voltage through a rheostat. Some motorists even carry the device into the cabin to adjust the device without leaving the cabin. However, under optimal conditions for charging the battery, disadvantageous modes of operation of lighting devices are created, the service life is reduced by 2 to 3 times. Consistently in the chain of lamps, it is advisable to include resistors that make up 10% of the nominal illumination. It is possible to determine the correctness in the operating mode by the voltage drop across the resistance( 1.2 V).
When operating from a battery, the headlights will glow a little dimmer. Automotive voltage regulator is a tandem:
- The executive mechanism in the form of a relay with a maximum and reverse current limiter.
- Tracking circuit.
The principle of operation of the automotive voltage regulator is simple. In the initial state, an additional current passes through the device to the excitation winding of the generator, the contact is held by the spring. When the voltage exceeds the threshold value set by the potentiometer( rheostat), the induction coil pulls the tension force, and the relay switches. The current in the circuit of the excitation winding is fed through a resistor, due to which the system goes back to mode.
The relay is constantly turned on and off, providing the necessary parameters. It works like a key, it is advantageous to replace the relay with electronic keys to increase the service life. Sudden voltage surges are smoothed back EMF in the excitation coil. Therefore, changes occur smoothly, which, in fact, is required. Note that if the difference increases strongly( due to the absence of a resistor in the field of the excitation winding), sparks occur, caused by the back EMF.
The considered type of regulators belongs to electromechanical. Despite all the tricks( increase in the frequency of operation, thermal compensation), such devices are unable to provide excellent parameters. The adjustment process is complicated, in addition, the parameters change for at least three reasons( preventive maintenance is required after 10–15 thousand km of run):
- shaking gradually changes the settings of the potentiometer;
- relay contacts burn from sparking, which increases the resistance by changing the excitation winding current of the generator;
- stretch stabilizer spring.
Limiters of maximum and reverse current
When filling a highly discharged battery or simultaneously turning on all consumers of a car, the excitation winding or armature may be destroyed. In the usual case, the current does not exceed 18-20 A, which at a voltage of 12 V is equivalent to a power of just over 200 watts. The protection scheme is performed on an electromechanical pattern. This is a spring-loaded relay, at the moment when the current exceeds the maximum threshold, throwing contacts, pulling the core into a magnetic field of inductance.
A resistor is switched on in the excitation winding circuit, absorbing a part of the potential difference on its resistance. This causes a decrease in current. Then the flow naturally decreases, the contacts are closed again. The relay works similarly to the previous one, but is configured differently and functions less frequently.
Such protection can fail when a short circuit is formed or a sharp increase in speed. The electronic circuit of current limiters is relieved of the indicated disadvantages.
Reverse Current Relay blocks battery discharge through generator windings. Turns off the battery when the generator voltage is too low( 11.8 - 13 V).All the time while the generator is running, the current flows through the parallel winding. When the voltage exceeds the threshold, the battery is connected to charge. The relay is cleverly arranged, it contains two windings:
- Serial connected along the circuit between the generator and the branch wiring to the battery.
- Parallel winding is turned on after branching, but before loading.
As a result, when the generator is turned on, the battery is separated from it by an open contact. As the current flowing through both windings increases, the coil field increases. When the threshold is reached, the relay closes and the battery begins charging. If the voltage drops, the battery is discharged. Moreover, in a serial winding, the current is now directed to the generator( the potential is lower there), and in a parallel winding it flows in the same direction. As a result, half the effort is not able to hold the core, and he breaks the connection with the generator. The onboard power supply comes from the batteries.
As you gain momentum, the situation repeats again. At some point, the potential of the generator exceeds the battery voltage, and the network starts to feed from here. Through both windings a full direct load current flows, the contacts are closed, the battery is charging. And so on. In addition to the above disadvantages inherent in an electromechanical relay, the regulator is affected by the variability of the battery voltage. Voltage sags sharply when starting a starter due to obvious reasons.
A negative effect is observed when driving around the city. Opening a relay requires a current of 6 A, which is a third of all costs. As a result of frequent operation, the battery discharges extremely quickly. This reduces battery life.
Electronic voltage regulators
Electromechanical voltage regulators for domestic use are slightly different from those described above, but the essence is the same: controlled switching of multiple relays. In this case, the number of turns of the transformer winding changes. A plus of electromechanical regulators is the speed of the signal change processing and accuracy. This is the only reason for the discovery of devices on the market today. Sometimes they are called vibratory.
We now consider electronic models. We list the brief component steps:
- Reverse Current Relay. In the simplest case, this is an ordinary diode placed between the pluses of the generator and the battery. Reverse current in this case is by definition impossible. When this charge on the diode voltage drops 0.5 V, if the device is germanium, and 1 V, if - silicon. The output power can be calculated by multiplying this value by the consumed current of 20 A( total 10 - 20 W).Separate diodes have to be cooled, as is the Larionov bridge. Of course, it is not bad to apply in this case a typical solution for pulsed power supplies: put a Schottky diode. But even without this, it is noted that the relay drops more - from 1.5 to 2 V( if the contacts are clean).
- A resistor and a zener diode are used as the sensitive element, setting the transistor switch mode. This is a parallel type stabilizer, the main drawback is the constant waste of energy. A current will flow through the divider from the beginning to the end of the generator, and the value does not correspond to the firing current of the transistor base. But the chain differs amazing simplicity. It should be noted that the voltage drop across the transistor switch is considerable, and it will require forced cooling, for example, of the radiator.
It is obvious that the maximum current limiter can work according to the voltage regulator circuit. A similar divider will set the operating mode of the transistor switch, which determines the power supply of the excitation winding. Often, simple diodes are used through which the load current is passed. The operating point of the transistor is chosen so that when the current exceeds 18–20 A and the voltage drop across the diodes increases to 1.5–2 V( along the current-voltage characteristic), the corresponding resistive divider. The transistor controls the other power switches, which directly limit the current of the generator excitation winding. The described scheme does not protect against short circuits, but positively fulfills the increase in engine speed.
With parallel connection of two or more diodes, the current through each individually decreases, reducing and the voltage drop. Sometimes it is profitable. And not everything is so bad with the differential resistance of the diodes. Sometimes a significant drop in silicon diodes can be used simultaneously to limit the maximum current( instead of resistance).For the use of this material says a higher permissible temperature. Silicon can withstand heat up to 150 degrees Celsius. By the way, with increasing temperature decreases the resistance of the diodes.
For thermal compensation of the stabilizer, it is allowed to use the successive switching on of two zener diodes. In this case, the temperature coefficients are opposite in sign and equal. In addition, we note that often clicking relays are used in the automotive network not by accident. This is required so that the eye does not notice the flicker from switching. Therefore, the frequency is not lower than 25 Hz. And given the smoothing due to the presence of winding induction, the butterfly effect becomes insignificant.
We hope that the obtained information on voltage regulators turned out to be useful and interesting. We also believe that the list of funds given is far from complete. Not told about the use of thermistors and varistors, but any knowledge is limited, and only ignorance is limitless.