An intermediate relay is necessary to perform auxiliary functions. It is widely used in control and automation systems. The main purpose of the element is to distribute and switch loads in electrical networks. The relay is necessary for converting or transmitting one signal to another. It is used for both direct and alternating current. As a rule, the product is used to control more powerful devices: power contactors, actuators of automation and alarm systems. In this article we will tell readers of the site how to connect an intermediate relay, providing an installation diagram and video instructions.
Ways to turn on the device
How to connect the mechanism to the system? Connecting the device to the electrical circuit occurs in two ways:
When there is a normal stable voltage from the power source, it should work reliably. In addition, their reliable operation is provided during an emergency voltage drop to 40–60%. Due to the design features, such a conversion element can have one, two or three windings (the latter are extremely rare).
Connecting an intermediate relay is important for any equipment or device. After all, this allows not only to automatically interrupt the chain, but with its help you can expand the functional abilities of other relay that are located in this electrical circuit.
The durability of the device depends on the number of times it is triggered. That is, it is characterized by the number of operation cycles and a return to its original position. The degree of protection of the equipment from various undesirable factors that surround the structure is assessed by such a criterion as the time of transition of contacts from one position to another.
Connection diagrams
After the intermediate relay has been installed in the electrical cabinet, it should be connected to the electrical circuit. For this purpose, the contacts of the coil itself and direct contact elements are used. The relay usually has several pairs of NO normally open and NC normally closed contacts. The normal position is considered to be the absence of a signal to the coil. Since the coil does not have polarity, the contacts are connected arbitrarily.
Such a device is installed in control and automation circuits. Located between the actuator (for example, a contactor) and the reference source. The figure shows the electrical diagram of the device:
The picture shows an intermediate relay without voltage supply. If you apply it, the contacts will switch. The voltage in the coil can be different: 220, 24 and 12 volts.
How to connect the device is shown in the figure below: 
In some cases, an intermediate type relay is used as a contactor, then the installation diagram will look like this:
As you can see, the intermediate relay has three groups of contacts that control the load and one group to hold the current in the coil. You can install an additional contactor, then the device is connected first to the contactor.
This device can also be connected to a motion sensor. Thanks to it, it is possible to connect several powerful lamps to the motion sensor system. Installation occurs as follows: the winding of the device is connected to the sensor, and the power contact switches the load in the lighting system. How to install such a sensor is shown below:
Another option for installing an electronic starter is to a thermostat. The diagram is shown in the picture (click to enlarge):
In this case, the thermostat and starter are connected in sequential order to the first phase and neutral wire (in the diagram they are designated as T1 and K1, respectively). The installation of the remaining contacts of the starter is carried out evenly between other phases.
According to the rules of the road (traffic rules), a moving vehicle during daylight hours must be indicated by low-beam headlights, fog lights (PTF) or daytime running lights (DRL or in English DRL). We will learn about various options for connecting DRLs to car wiring via an electromagnetic relay in this reference material prepared by the site.
Example of connecting DRLs from a generator
Attention: do not forget to install a fuse in case of a short circuit. No one is safe from accidental short circuits during installation and operation!
DRL connection diagram via 4-pin relay
Some people buy DRL headlights and simply connect them to the headlights. But it is more correct to make them light up when you turn on the ignition and go out when you turn on the side lights of the car.
You can even connect the DRL lamps to the cigarette lighter, because voltage is supplied to it only when the ignition is turned on. This will be better than looking for the ignition wire in the wiring.
Connecting DRL lamps via a 5-pin relay
Many are in no hurry to install daytime LED headlights by simply turning on the low beam headlights, but you need to take into account that using DRLs instead of low beams will allow you to charge the battery faster while driving, since their power consumption is 5 times less.
15 watt LED DRLs DRL connection diagram using a control unit
Some daytime lights, the most expensive and modern models, have a control unit that allows you to automatically control their operation (brightness, switching on, and so on). In this case, the electrical circuit will look like this:
Some auto electronics manufacturers produce running light control units with the ability to turn off the DRLs when one of the functions is active: parking brake, reverse, or starter operation when starting the engine. So it’s better to overpay a little and buy just such a set of headlights.
Annex 1.A brief overview of domestic standard relays in housings as shown in the photograph below.
Below you will find information from one manufacturer; there are other manufacturers and foreign analogues. For this part of the article, the main thing is to make it clear to the average car enthusiast that relays can be interchangeable, have different circuits, different numbers of contacts, depending on their purpose.
Domestic relays of this series mark the normally closed contact as 88. In imported relays this contact is everywhere called 87a
Typical relay circuits. Tsokolevka.
 Scheme 1 |
 Scheme 1a |
According to scheme 1, the following 5-contact (switching) relays are produced:
With 12V control - 90.3747, 75.3777, 75.3777-01, 75.3777-02, 75.3777-40, 75.3777-41, 75.3777-42
With 24Volt control - 901.3747, 901.3747-11, 905.3747, 751.3777, 751.3777-01, 751.3777-02, 751.3777-40, 751.3777-41, 751.3777-42
According to scheme 1a with an anti-interference resistor:
With 12V control - 902.3747, 906.3747, 752.101, 752.3777, 752.3777-01, 752.3777-02, 752.3777-40, 752.3777-41, 752.3777-42
With 24Volt control - 903.3747, 903.3747-01, 907.3747, 753.3777, 753.3777-01, 753.3777-02, 753.3777-40, 753.3777-41, 753.3777-42
 Scheme 2 |
 Scheme 2a |
According to scheme 2, the following 4-pin (closing/closing) relays are produced:
With 12V control - 90.3747-10, 75.3777-10, 75.3777-11, 75.3777-12, 75.3777-50, 75.3777-51, 75.3777-52, 754.3777, 754.3777-01, 754.3 777-02, 754.3777-10, 754.3777-11, 754.3777-12, 754.3777-20, 754.3777-21, 754.3777-22, 754.3777-30, 754.3777-31, 754.3777-32
With 24Volt control - 904.3747-10, 90.3747-11, 901.3747-11, 905.3747-10, 751.3777-10, 751.3777-11, 751.3777-12, 751.3777-50, 751.3777- 51, 751.3777-52, 755.3777, 755.3777-01, 755.3777-02, 755.3777-10, 755.3777-11, 755.3777-12, 755.3777-20, 755.3777-21, 755.3777-22, 755.3777-30, 755.3777-31, 755. 3777-32
According to scheme 2a with an anti-interference resistor:
With 12V control - 902.3747-10, 906.3747-10
With 24Volt control - 902.3747-11, 903.3747-11, 907.3747-10
 Scheme 3 |
 Scheme 3a |
According to scheme 3, the following 4-contact (breaking/switching) relays are produced:
With 12V control - 90-3747-20, 904-3747-20, 90-3747-21, 75.3777-20, 75.3777-202, 75.3777-21, 75.3777-22, 75.3777-60, 75.3777-602, 7 5.3777-61, 75.3777-62
With 24Volt control - 901-3747-21, 905-3747-20, 751.3777-20, 751.3777-202, 751.3777-21, 751.3777-22, 751.3777-60, 751.3777-602, 751.37 77-61, 751.3777-62
According to scheme 3a with an anti-interference resistor:
With 12Volt control - 902-3747-20, 906-3747-20, 902-3747-21, 752.3777-20, 752.3777-21, 752.3777-22, 751.3777-60, 751.3777-61, 751.3777 -62,
With 24Volt control - 903-3747-21, 907-3747-20, 753.3777-20, 753.3777-21, 753.3777-22, 753.3777-60, 753.3777-61, 753.3777-62,
ATTENTION!!!
Relays of the 19.3777 series have a housing similar to the one above. The circuit of these relays has protective and decoupling diodes. Such relays have a polarized winding. These relays are not mentioned here in the article because they have limited use.
Relays of modern cars.
Differences and variety of relay numbers mean different mountings, housing design, degree of protection, coil control voltage, switched currents and other parameters. Sometimes when choosing an analogue it is necessary to take into account some parameters.
According to scheme 5, the following 4-contact (closing/closing) relays are produced:
With 12V control - 98.3747-10, 982.3747-10
With 24V control - 981.3747-10, 983.3747-10
According to scheme 5a with an anti-interference resistor:
With 12V control - 98.3747-11, 98.3747-111, 982.3747-11
With 24V control - 981.3747-11, 983.3747-11
It is often difficult for novice auto electricians and people modifying their car to understand the phrase “connect via a relay.” What does connecting via a relay mean and how to do it? Let's figure it out.
Before studying the wiring diagram for any automotive device via a relay, you need to know what a relay is in general and how it works. This has been written about in detail. Once you understand the operating principle of this simple device, it will be much easier to figure out how to connect it.
The general meaning of connecting via a relay is the load on the switch that controls the installed equipment. All powerful consumers of electricity in the car (for example, headlights, starter, fuel pump, heated rear window, electric power steering) are connected through a relay. Thanks to this, these devices can be controlled by small, beautiful buttons instead of rough and large switches. In addition, in some cases, the relay allows you to save on wires.
The relay is connected to an open circuit in the electrical circuit. Let's look at installing a relay using the example of a gas pump. Power is supplied to it by the engine control unit (hereinafter referred to as the computer) and in order for the computer board tracks to withstand the current consumed by the pump, they would have to be made too powerful. Passing strong current near sensitive electronic components of a computer can affect their operation. To avoid such problems, a relay is installed between the computer and the fuel pump and the computer is connected not to the pump, but to this little “helper”.
The relay, as it were, divides the wire going from the fuse block to the pump into two parts, which can close inside the relay when voltage is applied to the control contacts of the magnet. As already mentioned in the article about the relay device, the control current is very small and cannot damage the computer in any way. The computer supplies voltage to the control contacts of the relay, and it then “connects” the power circuit within itself and connects the fuel pump.
Using the same principle, the relay is installed on any other electrical consumers in the car. Let's consider connecting fog lights.
The wires to the fog lights come from the fuse box, but they go through a relay along the way. The process of turning the headlights on/off is controlled by a button on the dashboard. When it is pressed, voltage is supplied to one of the control contacts of the relay, and it closes the power circuit - the lamps in the headlights light up. The second control contact of the relay is “mass”, that is, voltage goes through it to the car body, creating an electrical circuit.
Using this circuit, you can connect almost any powerful device and control it with a small, beautiful key. In some cases, a relay can be a salvation from factory defects. So, for example, in a VAZ-2106, the current flowing to the starter solenoid relay through the ignition switch quickly leads to. They get rid of this trouble by installing an intermediate relay and changing the power supply of the solenoid relay. After modification, a weak control current begins to pass through the contact group of the lock, and the relay connects powerful power to the starter.
As is known, the dimensions and power of a switch switching a powerful load must correspond to this load. You cannot turn on such serious current consumers in a car as, say, a radiator fan or glass heating with a tiny button - its contacts will simply burn out after one or two presses. Accordingly, the button should be large, powerful, tight, with a clear fixation of the on/off positions. It must be connected to long thick wires designed to carry the full load current.
But in a modern car with its elegant interior design there is no place for such buttons, and they try to use thick wires with expensive copper sparingly. Therefore, a relay is most often used as a remote power switch - it is installed next to the load or in a relay box, and we control it using a tiny, low-power button with thin wires connected to it, the design of which can easily fit into the interior of a modern car.
Inside the simplest typical relay there is an electromagnet, to which a weak control signal is supplied, and a movable rocker arm, which attracts the triggered electromagnet, in turn closes two power contacts, which turn on a powerful electrical circuit.
In cars, two types of relays are most often used: with a pair of normally open contacts and with three switching contacts. In the latter, when the relay is triggered, one contact closes to the common one, and the second one is disconnected from it at this time. There are, of course, more complex relays, with several groups of contacts in one housing - making, breaking, switching. But they are much less common.
Please note that in the picture below, for a relay with a switching contact triple, the working contacts are numbered. The pair of contacts 1 and 2 are called "normally closed". Pair 2 and 3 are “normally open”. The “normal” state is considered to be the state when voltage is NOT applied to the relay coil.
The most common universal automotive relays and their contact terminals with a standard arrangement of legs for installation in a fuse box or in a remote socket look like this:
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The sealed relay from the aftermarket xenon kit looks different. The compound-filled housing allows it to operate reliably when installed near headlights, where water and mud mist penetrate under the hood through the radiator grille. The pinout is non-standard, so the relay is equipped with its own connector.
To switch large currents, tens and hundreds of amperes, relays of a different design than those described above are used. Technically, the essence is unchanged - the winding magnetizes a movable core to itself, which closes the contacts, but the contacts have a significant area, the fastening of the wires is for a bolt from M6 and thicker, the winding is of increased power. Structurally, these relays are similar to the starter solenoid relay. They are used on trucks as ground switches and starting relays for the same starter, on various special equipment to switch on particularly powerful consumers. Occasionally, they are used for emergency switching of Jeeper winches, creating air suspension systems, as the main relay for homemade electric vehicle systems, etc.
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By the way, the word “relay” itself is translated from French as “harnessing horses,” and this term appeared in the era of the development of the first telegraph communication lines. The low power of galvanic batteries of that time did not allow transmitting dots and dashes over long distances - all the electricity “went out” on long wires, and the remaining current that reached the correspondent was unable to move the head of the printing machine. As a result, communication lines began to be made “with transfer stations” - at an intermediate point, the weakened current activated not a printing machine, but a weak relay, which, in turn, opened the way for current from a fresh battery - and on and on...
What do you need to know about relay operation?
Operating voltage
The voltage indicated on the relay body is the average optimal voltage. Car relays are printed with “12V”, but they also operate at a voltage of 10 volts, and will also operate at 7-8 volts. Similarly, 14.5-14.8 volts, to which the voltage in the on-board network rises when the engine is running, does not harm them. So 12 volts is a nominal value. Although a relay from a 24-volt truck in a 12-volt network will not work - the difference is too great...
Switching current
The second main parameter of the relay after the operating voltage of the winding is the maximum current that the contact group can pass through without overheating and burning. It is usually indicated on the case - in amperes. In principle, the contacts of all automotive relays are quite powerful; there are no “weaklings” here. Even the smallest switches 15-20 amperes, standard size relays – 20-40 amperes. If the current is indicated double (for example, 30/40 A), then this means short-term and long-term modes. Actually, the current reserve never interferes - but this mainly applies to some kind of non-standard electrical equipment of the car that is connected independently.
Pin numbering
Automotive relay terminals are marked in accordance with the international electrical standard for the automotive industry. The two terminals of the winding are numbered “85” and “86”. The terminals of the contact “two” or “three” (closing or switching) are designated as “30”, “87” and “87a”.
However, the marking, alas, does not provide a guarantee. Russian manufacturers sometimes mark a normally closed contact as “88”, and foreign ones – as “87a”. Unexpected variations of standard numbering are found both among nameless “brands” and among companies like Bosch. And sometimes the contacts are even marked with numbers from 1 to 5. So if the contact type is not marked on the case, which often happens, it is best to check the pinout of the unknown relay using a tester and a 12-volt power source - more on this below.
Terminal material and type
The relay contact terminals to which the electrical wiring is connected can be of a “knife” type (for installing the relay into the connector of the block), as well as a screw terminal (usually for particularly powerful relays or relays of obsolete types). The contacts are either “white” or “yellow”. Yellow and red - brass and copper, matte white - tinned copper or brass, shiny white - nickel-plated steel. Tinned brass and copper do not oxidize, but bare brass and copper are better, although they tend to darken, making contact worse. Nickel-plated steel also does not oxidize, but its resistance is rather high. It’s not bad when the power terminals are copper, and the winding terminals are nickel-plated steel.
Pros and cons of nutrition
In order for the relay to operate, a supply voltage is applied to its winding. Its polarity is indifferent to the relay. Plus on “85” and minus on “86”, or vice versa - it doesn’t matter. One contact of the relay winding, as a rule, is permanently connected to plus or minus, and the second receives control voltage from a button or some electronic module.
In previous years, a permanent connection of the relay to the minus and a positive control signal was more often used; now the reverse option is more common. Although this is not a dogma - it happens in every way, including within the same car. The only exception to the rule is a relay in which a diode is connected parallel to the winding - here polarity is important.
Relay with diode parallel to coil
If the voltage to the relay winding is supplied not by a button, but by an electronic module (standard or non-standard - for example, security equipment), then when turned off the winding gives an inductive voltage surge that can damage the control electronics. To suppress the surge, a protective diode is switched on parallel to the relay winding.
As a rule, these diodes are already present inside electronic components, but sometimes (especially in the case of various additional equipment) a relay with a diode built inside is required (in this case its symbol is marked on the case), and occasionally a remote block with a diode soldered on the wire side is used . And if you are installing some kind of non-standard electrical equipment that, according to the instructions, requires such a relay, you must strictly observe the polarity when connecting the winding.
Case temperature
The relay winding consumes about 2-2.5 watts of power, which is why its body can get quite hot during operation - this is not criminal. But heating is allowed at the winding, and not at the contacts. Overheating of the relay contacts is detrimental: they become charred, destroyed and deformed. This happens most often in unsuccessful examples of relays made in Russia and China, in which the contact planes are sometimes not parallel to each other, the contact surface is insufficient due to misalignment, and point current heating occurs during operation.
The relay does not fail instantly, but sooner or later it stops turning on the load, or vice versa - the contacts are welded to each other, and the relay stops opening. Unfortunately, identifying and preventing such a problem is not entirely realistic.
Relay test
When repairing, a faulty relay is usually temporarily replaced with a working one, and then replaced with a similar one, and that’s the end of it. However, you never know what problems may arise, for example, when installing additional equipment. This means that it will be useful to know the elementary algorithm for checking the relay for the purpose of diagnosing or clarifying the pinout - what if you came across a non-standard one? To do this, we need a power source with a voltage of 12 volts (power supply or two wires from the battery) and a tester turned on in resistance measurement mode.
Let's assume that we have a relay with 4 outputs - that is, with a pair of normally open contacts that work for closure (a relay with a switching contact “three” is checked in a similar way). First, we touch all pairs of contacts one by one with the tester probes. In our case, these are 6 combinations (the image is conditional, purely for understanding).
On one of the combinations of terminals, the ohmmeter should show a resistance of about 80 ohms - this is the winding, remember or mark its contacts (for automotive 12-volt relays of the most common standard sizes, this resistance ranges from 70 to 120 ohms). We apply 12 volts to the winding from the power supply or battery - the relay should clearly click.
Accordingly, the other two terminals should show infinite resistance - these are our normally open working contacts. We connect the tester to them in dialing mode, and simultaneously apply 12 volts to the winding. The relay clicked, the tester beeped - everything is in order, the relay is working.
If suddenly the device shows a short circuit on the working terminals even without applying voltage to the winding, it means that we came across a rare relay with NORMALLY CLOSED contacts (opening when voltage is applied to the winding), or, more likely, the contacts from overload melted and welded, short-circuiting . In the latter case, the relay is sent for scrap.
