Chargers series Kedr-Auto For several decades they have remained one of the most popular among car enthusiasts due to their simplicity, reliability and maintainability. These devices, produced back in Soviet times, are still actively used to charge batteries of cars and trucks. However, over time, even the most reliable equipment breaks down, and the original documentation is lost. In this article we will look in detail electrical diagram of the Kedr-Auto charger, we will explain the principle of its operation and show how to diagnose and eliminate typical faults.
The peculiarity of "Kedr-Auto" is its versatility: the device is suitable for charging lead-acid batteries with voltage 12V and 24V, and can also be used as a power supply for other purposes. But in order to properly operate or repair this device, you need to understand how its circuit is structured, which elements are responsible for what, and how they interact with each other. We will not only provide a complete circuit diagram, but also explain the purpose of each key component: from the power transformer to the protection circuit.
If you are faced with the fact that Kedr-Auto does not charge the battery, heats up, sparks, or produces low voltage, this article will help you understand the reasons and eliminate them without contacting service. We will also look at modifications to the circuit to improve the functionality of the device, such as adding an ammeter or adjusting the charge current.
Design and principle of operation of the Kedr-Auto charger
Charger Kedr-Auto built according to the classical scheme with transformer power supply and a diode rectifier. Its main components:
- 🔌 Power transformer - reduces mains voltage
220Vto the level required for charging (15–18Vfor 12-volt batteries). - ⚡ Diode bridge — converts alternating current into direct current, necessary for charging the battery.
- 🔄 Thyristor regulator (in some modifications) - allows you to smoothly regulate the charge current.
- 🛡️ Protection circuit — prevents overload, short circuit and polarity reversal.
- 📏 Measuring instruments — ammeter and voltmeter (not found in all versions).
The principle of operation of the device is quite simple: the mains voltage is supplied to the primary winding of the transformer, where it is converted into a reduced alternating voltage. Then it is rectified by a diode bridge, smoothed (in some models by capacitors) and supplied to the battery terminals. The charging current can be adjusted either by a transformer tap switch or by a thyristor unit (depending on the modification).
It is important to understand that Kedr-Auto is not a pulse charger, but a transformer charger. This means that it is heavier and bulkier than modern compact chargers, but it is less sensitive to power surges and easier to repair. In addition, transformer devices are better suited for “reanimating” severely discharged batteries, as they can produce a high current at the beginning of the charge.
Complete electrical diagram of "Kedra-Auto" with explanations
Below is a schematic diagram of the most common modification Kedr-Auto on 12V. For convenience, we have divided it into functional blocks and added explanations to each element.
Main components of the circuit:
- Surge filter and fuse — protects the device from power surges and short circuits. The fuse is usually rated for
1–2A. - Power transformer - has several taps on the secondary winding to adjust the output voltage. For example, to charge
12VThe battery is used with a tap on15–16V. - Diode bridge - assembled on diodes KD202 or D242, which rectify the current. Some circuits use a ready-made diode bridge like KTs405.
- Thyristor regulator (not present in all models) - allows you to smoothly change the charge current. Controlled by a variable resistor.
- Protection circuit - usually implemented on relays or transistors, turns off the output in the event of a short circuit or incorrect polarity.
A critically important point: in the original Kedra-Auto circuit there is no voltage stabilization, so during long-term charging it is necessary to control the process to avoid overcharging the battery.
Below is a table with the main parameters of the transformer and diode bridge for popular modifications:
| Modification | Mains voltage, V | Output voltage, V | Max. charge current, A | Diode type |
|---|---|---|---|---|
| Kedr-Auto (12V) | 220 | 15–18 | 6–8 | KD202, D242 |
| Kedr-Auto-2 (24V) | 220 | 28–30 | 4–6 | KD203, D232 |
| Kedr-Auto with thyristor | 220 | 12–24 (adjustable) | up to 10 | KTs405 + thyristor KU202 |
Ammeter connection diagram
The ammeter is connected in series to the charging circuit, between the diode bridge and the positive terminal of the battery. It is important to use a device with a shunt rated for current up to 10A. A parallel connection (like a voltmeter) will result in a short circuit!
Typical faults and their diagnosis
Like any electrical device, Kedr-Auto can fail over time. Below we list the most common faults and how to diagnose them.
- 🔥 The device does not turn on — check the fuse, power cord and primary winding of the transformer for an open circuit. Often the problem lies in oxidized contacts or a blown fuse.
- ⚡ No output voltage — inspect the diode bridge for broken diodes (test them with a multimeter). Also check the secondary winding of the transformer.
- 🔋 The charger heats up, but does not charge — a breakdown of the thyristor (if it is in the circuit) or a short circuit in the battery circuit is possible. Also check the condition of the battery terminals.
- 📉 Output voltage too low — the cause may be an interturn short circuit in the transformer or a network sag. Try connecting the device through a voltage stabilizer.
- 🔄 Charge current is not adjustable — the variable resistor or thyristor unit is faulty. In some cases, cleaning the resistor contacts helps.
For diagnostics you will need a multimeter. Start by checking availability 220V on the primary winding of the transformer. Then measure the voltage on the secondary winding - it should correspond to the selected tap (for example, 15–16V to charge a 12-volt battery). Next, check the diode bridge: in one direction the diodes should pass current (resistance ~500–700 Ohms), in the opposite direction they should show an open circuit.
⚠️ Attention: If, when connecting the battery, the device immediately turns off, this is a sign of a short circuit in the charging circuit or reverse polarity protection has tripped. Don't try to bypass the protection, first find the reason!
☑️ Diagnosis of "Kedra-Auto" faults
Do-it-yourself repair of the Kedr-Auto charger
Most of the Kedra-Auto malfunctions can be fixed on your own, with minimal skills in working with a soldering iron and a multimeter. Let's look at step-by-step instructions for repairing the most common breakdowns.
1. Replacing broken diodes in the rectifier bridge
If the diode bridge is broken, the device either does not output voltage or heats up and sparks. To replace:
- Disconnect the device from the network and discharge the capacitors (if any).
- Solder off the old diodes. Commonly used KD202 or D242, but you can install modern analogues, for example, 1N5408 (for current up to
3A). - Install new diodes, observing polarity (cathode is the side with the stripe).
- Check the operation of the bridge with a multimeter in dial mode.
2. Transformer repair
If the transformer hums or gets hot, the following problems are possible:
- 🔧 The core plates are loose - tighten the tightening bolts.
- 🔥 Interturn closure - rewinding of the windings is required (a rather complicated procedure, it is often easier to find a replacement).
- 🧲 Insulation breakdown - check the resistance between the windings (must be at least
10 MOhm).
If the transformer is completely out of order, it can be replaced with a similar one from an old TV or power supply, selecting the power (at least 150–200 W for 12 volt version).
3. Restoring the thyristor regulator
If the charge current is not regulated, the problem may lie in the thyristor or control circuit. Most often the thyristor fails KU202 or a resistor in its base. For repair:
- Test the thyristor with a multimeter (in the closed state the resistance should be infinite).
- Check the control circuit: the variable resistor should change resistance smoothly, without jumps.
- Replace faulty items. Instead KU202 can be used BT151 or TIC206.
⚠️ Attention: When working with thyristor circuits, be careful - even after disconnecting from the network, capacitors can retain a dangerous charge. Discharge them by shorting the terminals with an insulated screwdriver.
If you cannot find original diodes or thyristors, use modern analogues with similar parameters. For example, instead of KD202, 1N5408 is suitable, and instead of KU202 - BT139. The main thing is that the operating current and reverse voltage are not lower than the original ones.
Modernization of the Kedra-Auto circuit: adding an ammeter and protection
The original Kedra-Auto circuit is quite simple and lacks some useful functions, such as precise current control or overcharge protection. Let's look at how you can upgrade the device.
1. Installation of ammeter and voltmeter
To control the charging process, it is convenient to have instruments on hand that show current and voltage. Connection:
- 🔋 Ammeter turns on sequentially into the charging circuit (between the diode bridge and the positive terminal of the battery). Use the device on
10Awith a shunt. - ⚡ Voltmeter connects in parallel battery terminals. Measuring range -
0–20V.
For convenience, you can use a ready-made digital module from AliExpress (for example, DSN-VC288), which combines both an ammeter and a voltmeter.
2. Adding reverse polarity protection
To prevent damage to the device if the terminals are connected incorrectly, add a relay or a powerful diode (for example, 1N5408) into the gap in the positive wire. If the connection is correct, the current will flow through the diode; if the connection is reversed, the circuit will break.
3.Automatic shutdown when fully charged
To do this, you can use a circuit based on a voltage relay or a specialized microcircuit (for example, LM393). When the battery voltage reaches 14.4V the charging circuit will automatically open.
The upgraded device will not only be safer, but also more convenient to use. For example, adding an LED indication will allow you to visually monitor the charging process without constant measurements with a multimeter.
When upgrading a circuit, always use elements with current and voltage reserves. For example, if the original diode is rated at 5A, get a replacement for 10A. This will extend the life of the device.
Safety when working with the Kedr-Auto charger
Working with homemade or retrofitted chargers requires precautions. Here are the key rules:
- ⚡ Always unplug your device before connecting or disconnecting the battery. This will prevent sparking and possible damage to the circuit.
- 🔌 Use wires with sufficient cross-section (no less
2.5 mm²for currents up to10A). Thin wires may overheat. - 🧤 Wear gloves and goggles, especially when testing a live circuit. Battery acid and sparks are hazardous to health.
- 🔥 Do not leave the device unattended for a long time. Transformer chargers do not have precise stabilization, which can lead to overcharging.
- 📋 Keep a charge log: Record the starting and ending voltage of the battery, as well as the charging time. This will help track battery degradation.
Pay special attention fire safety. Do not place the device near flammable materials and ensure good ventilation - when charging, the battery may release hydrogen, which is explosive when mixed with air.
⚠️ Attention: If you smell something burning or see smoke coming from the device, immediately unplug it and disassemble it for inspection. Do not operate the charger if it shows signs of overheating!
Comparison of Kedra-Auto with modern chargers
Despite its reliability, Kedr-Auto is inferior to modern pulse chargers in a number of parameters. Let's look at the main differences:
| Parameter | Kedr-Auto | Modern pulse memory |
|---|---|---|
| Weight and dimensions | Heavy (3–5 kg) | Compact (0.5–1.5 kg) |
| Efficiency | 60–70% | 85–95% |
| Current stabilization | None (manual adjustment) | Automatic (multi-stage charging) |
| Protection | Minimum (fuse, relay) | Full complex (from short circuit, polarity reversal, overheating) |
| Price | Low (you can find a used one for 500–1000 rubles) | High (from 2000 rubles for high-quality models) |
However, Kedr-Auto also has advantages:
- 🔧 Maintainability - any malfunction can be eliminated independently, whereas modern chargers often come in a non-separable case.
- 🔋 Resistance to voltage surges — the transformer circuit is less sensitive to the quality of the network than pulse units.
- 💰 Low cost - even taking into account modernization, it will cost less than a new pulse memory.
The choice between Kedr-Auto and a modern device depends on your tasks. If you need a reliable and simple solution for periodic battery charging, as well as the ability to do it yourself, Kedr remains an excellent option. If automatic charging with multiple protections and compact dimensions is required, it is better to pay attention to pulsed devices.
FAQ: Frequently asked questions about Kedr-Auto
Is it possible to charge gel batteries with the Kedr-Auto charger?
No, this is not recommended. "Kedr-Auto" does not have voltage stabilization and can produce too high a current at the beginning of the charge, which will damage the gel battery. For such batteries, specialized chargers with a mode IUoU (initial current, then voltage stabilization).
Why does Kedr-Auto get very hot during operation?
Heating can be caused by several reasons:
- Overload (charging current is too high for the transformer).
- Breakdown of diodes in the rectifier bridge (they begin to pass current in both directions).
- Interturn short circuit in a transformer.
- Poor ventilation (device operating in an enclosed space).
Disconnect the charger, let it cool and check each element of the circuit.
How to increase the charge current in Kedr-Auto?
There are two ways to increase the current:
- Switch the transformer taps to a higher voltage (if any).
- Replace the diode bridge with a more powerful one (for example, diodes KD2999 with current up to
30A).
However, remember that the increase in current is higher 10A It also requires replacing the transformer with a more powerful one, otherwise it will overheat.
Is it possible to use Kedr-Auto as a power supply for other devices?
Yes, but with reservations:
- The output voltage is not stabilized, so to power sensitive electronics (for example, radios) you will need to add a stabilizer (for example, LM7812).
- Make sure that the connected device is designed for the current that Kedr can produce (usually up to
8–10A). - Do not connect a load that consumes a current higher than the rated current - this will lead to overheating of the transformer.
Where can I find spare parts for Kedra-Auto repair?
Most circuit elements (diodes, thyristors, resistors) are sold in radio stores or on AliExpress. The transformer can be taken from old equipment (for example, from a Soviet TV Horizon or computer power supply). It is also useful to search at flea markets or in amateur radio groups - they often sell used Kedras for spare parts.