Relay in the electric car: the principle of operation, types and diagnosis of malfunctions

When the cooling fan, headlights or starter suddenly ceases to work in the car, many drivers immediately sin on fuses or wiring breaks. In 70% of cases, it is the fault. relay A small but critically important device that controls high currents in the onboard network. Without the relay, the modern car simply could not function: it protects thin control circuits from overloads, ensures stable operation of powerful consumers and prolongs the life of buttons, switches and even ECUs.

In this article, we will analyze what is a relay in the electric car in practice - without abstruse formulas, but with specific examples. You will learn how it works inside, what types of relays are used in machines (and why they should not be confused), how to check the performance of a multimeter or “by ear”, as well as what symptoms indicate its failure. We'll pay special attention. quirky Replacement of relays that lead to short circuits or even fire. If you have ever encountered a “clinking” starter or flashing headlights – this information will save you time and money on diagnosis.

What is a relay and why is it needed in a car

Relay is electromechanicalA system that allows you to control powerful electrical circuits (such as a starter or radiator fan) using weak signals (such as pressing a button or command from the control unit). Imagine: to start a starter, you need a current in 200-400 ABut no ignition button can withstand such a load. Relay solves this problem by separating control circuits and power circuits.

A simple example: when you turn the ignition key, the current does not go directly to the starter, but first to the relay coil. It attracts contacts that are already in place. lock-in from battery to starter. So, through the ignition contacts, everything happens. 0.2-0.5 ANot hundreds of amps. The same thing happens with headlights, wipers, glass heating and other powerful consumers.

• 🔋 Protection of control chainsThin wires and buttons are not designed for high currents. Rele takes the load.
• ⚡ Managing powerful devicesStarter, fans, fuel pump – all require relays.
• 🛡️ Preventing overheatingWithout a relay, the contacts of the switches will quickly burn.
• 🤖 Automation: The ECU may turn on/off the relays on sensor signals (e.g., a fan when overheated).

In most cars, the relays are installed in safety-lock (under the hood or in the cabin), but some (for example, the starter relay or the main injection system relay) may be separately located. They are easily recognized by the characteristic click when triggered – this sound means that the contacts have closed or opened.

The device and principle of operation of the relay

Classical. electromechanical relay It consists of three key parts:

1. Coil (winding) Creates a magnetic field when applying voltage. Usually designed for 12 V (in trucks) 24 In).
2. Anchor (movable core) It is attracted to the coil and moves the contacts.
3. Contacts (force group) Close or open the high-current chain.

When a voltage is applied to the coil (e.g. from a button or ECU), it creates a magnetic field that attracts the anchor. He, in turn, closes the power chain - for example, gives 12 V from the battery to the starter. When the voltage is turned off, the spring returns the anchor to its original position, and the chain opens. All of this happens in a split second.

The relay is usually applied to the body connection with contact numbers. Standard numbering:

• 85 and 86 - conclusions of the coil (they are supplied with a control voltage).
• 30 General power contact (usually connected to the battery plus).
• 87 - normally open contact (closes when the relay is triggered).
• 87a - normally closed contact (opens when triggered; is rarely used).

In cars, they are also used. solid-state (on semiconductors) that have no moving parts. They are more reliable, but more expensive and more sensitive to overheating. They are often installed in systems. xenon lighting or seat-heating.

How to distinguish a normally open relay from a normally closed one?

A normally open relay (HP) in the off state does not allow current to pass through the power circuit (pins 30 and 87 are open). Normally closed (NZ) – on the contrary, passes current until the coil works. In cars, NZ relays are rarely used, for example, in some alarm systems or emergency shutdowns.

Types of relays in automotive electrician

Depending on the purpose and design, relays in the car are divided into several types. Here are the most common:

Type of relay	Appointment	Examples of application	Features
Starter switching relay	Controls the supply of current to the starter retractable relay	System system for engine start-up	Often fails due to high currents
AKB charging relays	Controls the supply of voltage from the generator to the battery	Charging system	It can be built into a relay regulator.
Relay of the cooling fan	Turns on the fan when the temperature is exceeded	Cooling system	Controlled by a signal from an ECU or temperature sensor
Direction indicator relays	Provides flashing lamps with a given frequency	Light alarms	Often combined with a safety lock block
Main relay (ignition relay)	Supplies power to the ECU and fuel pump	Injection system	When the engine fails, the engine will not start.

In addition, the relay is classified by fixation:

• 🔌 Plug-in They are in the most common type of snails.
• 🔩 Flanched - are fastened by bolts (for example, the starter relay in the classic "Zhiguli").
• 🧲 Printed - for installation on boards (used in control units).

In modern cars, they are also found. timer-relay (e.g. for the control of headlamp washers) and diode-protected relay (Prevents surges of voltage when the coil is turned off).

Signs of relay malfunction

The relay can fail for several reasons: wear-and-wear, burnout, oxidation. You can recognize the malfunction by the following symptoms:

• 🚗 The starter is not spinning or spinning intermittently Often the starter relay or retracting relay is to blame.
• 💨 The cooling fan is not switched on Check the fan relay and temperature sensor.
• 💡 Headlights or turn signals flash chaotically - possible malfunction of the pointer relay or the main relay.
• ⚡ Loss of power in the onboard network If the lighter, tape recorder and other devices are not working, check the main relay.
• 🔥 Smell of fumes from the fuse block - a sign of burning contacts relay.

One of the most obvious signs is click-free when the device is turned on (for example, when turning the ignition key). If the relay doesn't click, it could mean:

• Break in the control circuit (wires, fuse, button).
• The relay coil burned out.
• No power on contacts 85 or 86.

If the relay clicks, but the device does not work, the problem is most likely in the power-chain (contacts) 30 and 87): they may have burned or oxidized. In some cases, the relay can “stick” – the contacts remain closed even after the coil is turned off. This is dangerous because it can lead to battery discharge or even fire (For example, if the fan relay is stuck).

How to check the relay multimeter and without instruments

Checking the relay does not require complex equipment - a multimeter or even a conventional light bulb is enough. 12 V. Let's look at both methods.

Multimeter check

1. Coil vertebra:

• Set the multimeter in resistance measurement mode (200 ohm).
• Connect the probes to the contacts 85 and 86.
• Resistance of a working coil: 50-120 Om. If he shows 0 (short circuit) or ∞ (cliff) - the relay is faulty.

2. Efficiency check:

• Connect. 12 V battery-to-contact 85 and 86 (Polarity doesn't matter).
• A click must be heard, which means that the coil and anchor are in good working order.
• Check the multimeter in the vertebral mode contacts 30 and 87: They should close after clicking.

Checking without devices (“by ear” and “by spark”)

If there is no multimeter at hand, you can use the available means:

• 🔊 Hearing testWhen the device (e.g. headlights) is turned on, the relay should click. If there is no click, the problem is in the control circuit or coil.
• 💡 Light bulb check:
  1. Put the light on. 12 V contact 30 and 87.
  2. Serve. 12 V on 85 and 86 - The light bulb must go on.

🔥 Checking for a spark (extreme case!):

1. Get in touch. 87 to the mass (body).
2. Submit short. 12 V on 85 and 86.
3. If 30 And the spark will pass by, and the relay is good (but this method is risky for contacts!).

If the relay doesn’t work, try clearing the contacts. 85 and 86 from oxidation (a frequent cause of malfunction). Use it for that. alcoholBut not sandpaper, it's going to damage the coating.

☑️ Multimeter relay check

Set up 200 ohms.Check the resistance of the coil (85–86)Serve 12 V at 85-86Check the 30–87 closure after clickingCall the chain on the cliff

Done: 0 / 5

Common mistakes when replacing the relay

Replacing the relay seems like a simple operation, but even here drivers make mistakes that lead to serious consequences. That's what don't:

⚠️ Attention.Never replace the relay with other parameters (for example, the fan relay on the starter relay), even if they are externally identical. The difference in switching current can lead to overheating or a device failure.

• 🔄 Ignoring the catalogue numberRelays with the same housing may have different characteristics (for example, the actuation current) 30 A vs 40 A). Always check with repairman your car.
• 🧲 Upside-down relay installation: Some relay contacts 85/86 They are asymmetrically positioned. If you confuse polarity, the coil may not work.
• 🔥 Use of soldering iron for repairHomemade repair of the relay (for example, soldering contacts) is unacceptable - this will lead to unreliable contact and the risk of fire.
• 💧 Replacement without cleaning nestsOxidized or contaminated connectors in the fuse unit can cause poor contact even with a new relay.

Another common mistake is load-check. For example, if you test a starter relay by plugging it into the battery only, it may work, but under real load (see below).200 A) contacts will start to burn. Always check the relays in conditions close to the workers.

If the device does not work after replacing the relay, check:

• Integrity of the safety lock in the control chain.
• Contact tension 85 and 86 (should be) 12 V when included).
• Mass condition (often problems with the "minus" simulate a malfunction of the relay).
💡

Before buying a new relay, take a picture of the old one and show the seller – this will help avoid compatibility errors. Pay attention to the marking (e.g., TYCO 12V 40A or Bosch 0 332 019 150).

How to extend the life of the relay

Relays in the car are not eternal, but their resource can be significantly increased if you follow simple rules:

• 🛠️ Regular cleaning of contactsOnce a year, remove the relay from the fuse block and clean the contacts 85, 86, 30 and 87 from oxidation. Use it. WD-40 or contact-cleaner.
• 🔌 Checking the reliability of the attachmentVibration can weaken the contacts in the connectors, which leads to sparkling and burning.
• 🌡️ Temperature monitoringRelays located next to the heating elements (for example, with the cylinder block) fail faster. If possible, move them to a cooler place.
• ⚡ Moisture protectionWater in the fuse block is the main cause of corrosion of contacts. Check seals and process contacts if necessary silicone-grease.

Pay special attention starter and fan relay They work with the highest currents and most often fail. If you notice that the starter began to “tightly” twist, and the fan turns on with a delay, do not wait for a complete failure – replace the relay prophylactically.

In modern vehicles with CAN bus and complex electronics, a faulty relay may cause errors in the ECU (e.g., P0562 Low voltage on-board network. If the dashboard caught fire check engine After replacing the relay, reset the errors with a diagnostic scanner or shut off the battery for 10 minutes.

FAQ: Frequent questions about relay in the car

Can I replace the relay with a similar one from another car?

Yes, but only if they match. coil-stress (12 V or 24 In), switching-current (e.g., 30 A or 40 Aand contact (normally open/closed). The appearance of similarity does not guarantee compatibility. It is better to use the relays of the same manufacturer (for example, Bosch, TYCO, Hella).

Why does the relay click, but the device doesn't work?

This means that the coil and mechanical part of the relay are in good working order, but the problem is power-chain. Check it out.

• Contact tension 30 (should be) 12 V from the battery.
• Integrity of the wire from contact 87 to the consumer.
• The mass state of the device (e.g. body "minus" for the fan).
• Fire up contacts 30 and 87 inside the relay (need to be disassembled or replaced).

How to check the relay without removing it from the block?

We can use it. vertebrate:

1. Turn on the device (e.g. headlights) that is controlled by this relay.
2. Check the multimeter voltage between contacts 30 and 87 - must be 12 V (if the relay worked)
3. If there is no voltage, but the relay clicks - the problem is contacts 30 or 87.

You can also change a suspicious relay with a knowingly serviceable (for example, turntable relays) - if the problem has disappeared, then the relay is to blame.

What happens if you put a relay with a lower switching current?

Lower current relays (e.g., 20 A instead 40 Awill heat up It'll be out of order quickly. In the worst case, the contacts will be “cooked” (stick), which will lead to:

• Constant operation of the device (for example, a fan), even when it is not needed.
• Battery discharge.
• Fire wiring due to overheating.

Always use the relay with stock-stock (e.g., 40 A instead 30 A).

Can I repair the relay with my own hands?

Theoretically, yes, but not recommended. In most cases, repairs are reduced to:

• Clearing contacts 85, 86, 30, 87 from oxidation.
• The stains of the stains (if they are broken).

However, if the coil is burned or the power contacts are melted, the relay can only be replaced. Replacement or replacement of parts can lead to cock-up and fire.