Recovery of the car battery is a challenge that every motorist faces, especially after cold winter nights. The use of homemade or modified schemes based on thyristors allows not only to efficiently charge the battery, but also to desulfate it, which prolongs the service life. Thyristor chargers (TD) are valued for high efficiency, the absence of overall transformers (in pulse circuits) and the ability to accurately adjust the current.
Unlike simple transformer rectifiers, thyristor They allow the formation of a pulsed charging current, which many experts consider more useful for lead-acid plates. The principle of operation is based on phase control, when the thyristor opens not at the beginning of the sine wave, but with a delay regulated by the control circuit. This makes it possible to smoothly change the pore of pulses, controlling the average charge current without heat loss on resistors.
Compliance with safety rules when assembling and operating such devices is critical, since the work is carried out with a network voltage. A properly assembled circuit on thyristors can last for decades, providing stable charge parameters even when voltage surges in the network. In this article, we will discuss in detail popular schemes, methods for calculating components and nuances of configuration.
The principle of operation of thyristor charging schemes
The basis of any charger on thyristors is a phase-pulse control unit. The thyristor, being a semiconductor key, transmits current only in one direction and only after receiving a control impulse to its gate. In charging schemes for cars, this pulse is formed synchronously with the frequency of the 50 Hz network. Opening delay The thyristor relative to the beginning of the half wave determines how much energy will get to the battery.
If you open the key at the beginning of the half wave, the charge current will be maximum. By shifting the opening moment to the end of the half wave, we reduce the effective value of the current. This adjustment is much more efficient than using rheostats, which simply dissipate excess energy in the form of heat. That's why. thyristor regulators It is very popular among radio amateurs and professionals.
It is important to understand that the current through the battery in such schemes is pulsating. This is not a disadvantage, but rather a feature that can be used for good. The pulse mode prevents the active mass from settling at the bottom of the jar and helps break down lead sulfate crystals. However, to smooth out the pulsations and protect the electronics of the car (if charging is done without removing the terminals), sometimes it is necessary to install additional filter elements.
⚠️ Attention: Thyristor circuits create powerful radio interference. When such a charger is operating, noise in the radio receiver or interference on the TV screen is possible, so the control unit should be placed away from sensitive electronics.
The key element of management is often diode bridgeThe exit of which is a thyristor, or thyristors are included in the diagonal of the bridge. In both cases, it is necessary to ensure the electroplating of the control circuits from high voltage, if microprocessor control is used, although in simple analog circuits this is achieved by the correct selection of reference points.
Popular Charger Schemes
There are many variations in the construction of chargers, but the most common remain two main topologies. The first is a scheme with a thyristor in the secondary circuit of the transformer after the rectifier. The second is a scheme with a thyristor in the primary circuit, which allows the use of less powerful and cheaper components, since the current in the primary is much smaller.
Let’s look at the classic scheme of single-period rectifier. Here, the thyristor is on sequentially with the diode. The shutter is controlled via the RC chain and the dinistor (or transistor analogue of the dinistor). When the capacitor is charged in the control circuit, the voltage increases, and at a certain point there is a breakdown of the dinistor opening the thyristor. By changing the resistor resistance, we change the capacitor charge velocity and therefore the moment of opening the key.
More complex devices are used two-periodwhere the thyristors are included in parallel or in the shoulders of the diode bridge. This allows the transformer power to be used more efficiently and reduces the load on the network. Such circuits often use op-amps or specialized microsms (e.g., TL494, although more commonly for pulsed units) to form a stable cutoff voltage.
Special attention should be paid to the schemes with shutdown. They use a comparator that compares the voltage at the terminals of the battery with the reference. When the battery is charged to 14.4–14.7 V, the control circuit stops sending impulses to the thyristor shutter and the charge stops. This eliminates the boiling of the electrolyte and recharge.
- 🔌 Kuznetsov's scheme: Simple and reliable, uses affordable Soviet components, ideal for beginners.
- 🔋 Impulse RAM: based on voltage conversion and PWM-modulation, is low weight and high efficiency.
- 🛡️ Protected: includes nodes of protection against overpole and short circuit, which is critical for safety.
Calculation and selection of components
The correct selection of elements is the key to the durability of the charger. The thyristor must withstand the maximum charge current with a margin of at least 30-50%. For example, to charge with a current of 10 Amps, it is advisable to use a series of thyristors. T161 or T152, which are designed for currents of 10-16 Amperes and more. The use of "back-to-back" elements will lead to their rapid overheating and failure.
The transformer is selected based on the required charge current. For a standard car battery with a capacity of 60 Ah, the optimal charge current is 6 Amps (10% of the capacity). Therefore, the transformer must provide a voltage of about 14-16 volts on the secondary winding (taking into account the voltage drop on the diodes and thyristor) and a current of at least 6-8 Amps. Transformer power In this case, it will be about 100-150 watts.
| Component | Parameters | Example of marking | Appointment |
|---|---|---|---|
| thyristor | Current > 10A, U > 400V | T161-16, KU202H | Power key |
| Diode bridge | Current > 10A, U > 50B | KD213, D242 | Straightening |
| Transformer. | 14-16B, 5-10A | TN61, TPP270 | Power scheme |
| Resistor R1 | Power 2-5 watts | PEP-5, PBP-25 | Current adjustment |
Particular attention should be paid to the cooling system. Thyristors and diodes heat up when working. Even if the calculations show that the radiator is not needed "in theory", in practice it is better to install a plate of aluminum with an area of 50-100 cm2. Heat vent It will significantly extend the life of semiconductors, especially in summer heat or when charging deeply discharged batteries, when the current is maximum for a long time.
Control circuits often use variable resistors with a linear or logarithmic characteristic. For smoothness of current regulation, it is better to choose resistors with logarithmic dependence, although in simple schemes the difference is not so noticeable. It is important that the power of resistors in the gate circuit corresponds to the control currents, otherwise they can burn up when the thyristor breaks.
Assembly and configuration of the device
The assembly process begins with the preparation of the body. Ideally suitable old cases from computer power supplies or transformer charges. They already have vents and a sturdy design. Place the transformer at the bottom and the power elements (thyristor, diodes) on the wall or separate radiator for better air convection.
☑️ Checklist before first inclusion
The scheme is set up in several stages. First, the operation of the control unit without connecting the battery is checked. Connect the oscilloscope parallel to the load resistor at the output. When rotating the variable resistor handle, you should observe the change in the pulse pore on the oscilloscope screen. If there is no oscilloscope, you can use the multimeter in the mode of measuring the alternating voltage, observing the change in readings during the rotation of the regulator.
Then comes the calibration of the current. Connect the output equivalent of the load (for example, a powerful incandescent lamp 12V 55W) and the ammeter. When adjusting the resistor, make sure that the current varies within limits (e.g. 0.5 to 10 Amps). If the current is not controlled or "breaks", check the serviceability of the thyristor and the integrity of the shutter control circuit. Often the problem lies in the incorrect polarity of the connection of the control elements.
⚠️ Warning: Never try to adjust the current by simply closing the output terminals of the charger short! This can cause the thyristor or diodes to fail instantly, as the current is limited only by the transformer’s internal resistance.
To improve the ease of operation, you can introduce a digital voltmeter and ammeter into the scheme. They are connected to the shunt (to measure current) and parallel to the output (to voltage). Modern Chinese modules are compact and cheap, but require their own power supply (usually 5V), which can be taken from an extra transformer winding or through a miniature power supply.
Protection against gyrations and CZ
One of the main problems of thyristor schemes is the lack of built-in protection against user error. If you confuse the plus and minus when connecting the battery, the thyristor can open in the opposite direction (if the design allows) or burn the diode bridge, and in the worst case, the battery will lock through the diodes, which will lead to a fire. Therefore, the introduction of protection against pole-pole It is mandatory for a quality device.
The simplest way to protect is to install a high-power diode sequentially with the output of "plus". It will only pass current in the right direction. The disadvantage of this solution is the voltage drop on the diode (about 0.7-1 Volt) and heating. A more advanced option is to use a relay that only closes the circuit when the battery is connected correctly. In this case, the current flows through the contacts of the relay, and there is practically no voltage loss.
Protection against short circuit (SCC) in thyristor schemes is more difficult to implement. Since the thyristor, having opened, closes only when the current drops to zero (at the end of the half-period), then with KZ, it will simply pass the maximum current each half-wave. For protection, high-speed fuses or electronic circuits are used, which block the supply of impulses to the shutter with a sharp increase in current. Electronic protection preferably, since it allows you to resume work after eliminating the cause of the CC without replacing the fuse.
- 🛡️ Relay protection: It is reliable, not afraid of interference, but clicks and has a limited contact resource.
- ⚡ Electronic protection: fast-acting, silent, but requires accurate setting of the trigger thresholds.
- 🔥 Thermal protection: bimetallic plates that break the chain when the radiator overheats, save from overloading by current indirectly.
For example, when connecting a severely discharged battery (voltage 5-8 volts), some protection schemes may perceive this as the absence of a battery or KZ and not turn on. Therefore, the thresholds of operation should be selected wisely, taking into account the voltage of a fully discharged lead-acid can.
Recovery of ACB and desulphation
Thyristor chargers are ideal not only for planned charge, but also for resuscitation of old batteries. The desulfation process consists of breaking down the large crystals of lead sulfate covering the plates. The traditional charge with direct current is ineffective here, but the pulse mode created by the thyristor works wonders.
The essence of the method is to charge short pulses of high current with long pauses. During the pause, the chemical processes in the electrolyte are leveled off and the voltage at the terminals drops, allowing the next pulse to again deliver high current. Asymmetric current (when the charge current significantly exceeds the discharge current in pause) contributes to the dissolution of sulfate plaque.
During desulfation, the charge voltage is often raised to 16-17 volts, which is impossible on conventional RAMs. The thyristor circuit allows you to work safely in such modes, controlling the process. However, it is necessary to monitor the temperature of the electrolyte: it should not exceed 40-45 degrees Celsius, otherwise the plate may lead, and the battery will finally fail.
The duration of the recovery procedure can take from several hours to several days, depending on the degree of sulfation. Signs of successful completion of the process are abundant gas (boiling) in all banks and stable voltage at the terminals after disconnecting the charger. If after 10-12 hours the electrolyte density does not increase, and the voltage immediately falls after the charge is removed, most likely, the battery life is exhausted.
⚠️ Attention: During desulphation, active gases are released. Carry out the procedure only in a well-ventilated room or outdoors, away from spark sources, as rattlesnake gas is released.
Frequently Asked Questions (FAQ)
Can lithium-ion batteries be charged with thyristor memory?
Absolutely not. The thyristor circuits described in the article are intended only for lead-acid batteries (12B, 24B). Lithium-ion batteries require a completely different charge algorithm (CC/CV) with the most precise voltage control (up to a hundredth of a volt). Charging the Li-Ion with a thyristor device will cause the battery to ignite or explode.
Why is the transformer buzzing when the charger is working?
The buzzing can be caused by overloading the transformer, weakening of the core plates or saturation of the magnetic conductor due to the constant component of the current (in single-half-period circuits). Also, the humming is increased if the thyristor opens asymmetrically or magnetization occurs. Try to reduce the charge current or check the reliability of the transformer mount.
How do I know if the thyristor is faulty?
Call the thyristor with a multimeter in diode check mode. There must be an infinite resistance between the anode and the cathode in both directions. Between the gate and the cathode, the resistance should be small (tens to hundreds of ohms) in one direction. If the multimeter shows a short circuit or the thyristor opens from touching with probes without applying the control voltage - it is defective.
Do I need to remove the battery from the car to charge?
For thyristor RAM without high-quality filtering of pulsations and protection from voltage surges in the onboard network, it is desirable to remove. Pulse interference can damage the sensitive electronics of a modern car (ECU, alarm system). If you can not remove the battery, make sure that your ROM has a good galvanic decoupling and filtering.