Automotive relay introduction

1. Working principle, structure and classification of automotive relay

The working principle of automotive relay

When a certain voltage or current is applied to both ends of the automotive relay coil, the magnetic flux generated by the coil passes through the magnetic circuit composed of the core, yoke, armature, and the working air gap of the magnetic circuit. Under the action of the magnetic field, the armature is attracted to the pole surface of the core. Thus, the normally closed contact of the contact is pushed to open, and the normally open contact is closed; when the voltage or current at both ends of the coil is less than a certain value, and the mechanical reaction force is greater than the electromagnetic attraction, the armature returns to the initial state, and the normally open contact is disconnected. The normally closed contact is turned on.

Definition of automotive relay

Simply, it is a switch that uses weak electricity to control strong electricity. The electromagnetic attraction generated by the control current through the coil drives the movable part of the magnetic circuit to realize the contact opening, closing or switching function.

Structure of automotive relay

Automotive relay is generally composed of several parts such as magnetic circuit system, contact system and return mechanism.

The magnetic circuit system is composed of iron core, yoke, armature, coil and other parts.
The contact system consists of static reeds, moving reeds, contact bases and other parts.
The return mechanism is composed of a restoration reed or a tension spring.

Classification of automotive relays

There are many classification methods for automotive relays, which can be classified according to the principle of application, size, contact load, protection characteristics, contact form, and product usage.

Classified by principle of application

Power system relay
Power distribution, radiator delay control, oil pump delay control, fan control, A/C compression clutch control, preheat control, power management system, oil pump control, cooling fan motor control, cooling fan delay control, low temperature start.

Security system relay
Indicator light control, anti-lock brake, battery disconnect device, car light delay control, hazard light control, emergency brake light control, turn signal control, speed limit signal control, flashing light control, fog light headlight control.

Body system relay
Wiper control, rear window defogger, horn control, traction control system, seat belt pre-tensioning equipment, instrumentation control.The use of permanent magnets or parts with high remanence characteristics enables the armature of the electromagnetic relay to remain in the position when the coil is energized after the coil is de-energized.

Anti-theft system relay
Anti-theft device, electronic locator, central door lock.

Convenience system relay
Seat adjustment, air conditioning, car mirror adjustment, lighting control, heater, audio, sunroof control, automatic doors and windows.Anti-theft device, electronic locator, central door lock.

Classified by size

Sub-miniature relays – relays with the longest side dimension not greater than 10mm.
Miniature relays – relays whose longest side dimension is greater than 10mm but not greater than 25mm.
Small relays – relays whose longest side dimension is greater than 25mm but not greater than 100mm.

Classified by contact load

Low Power Relay – Relays less than 30A.
Mini Power relay – 30~100A relay.
High power relay – 100A and above relay.

Classified by protection characteristics

Sealed waterproof relays – using welding or other methods to seal the contacts and coils in a cover, which has a low leakage rate.
Dust cover relay – a relay whose contacts and coils are enclosed and protected by a cover.
Open Relay – relay without protective cover to protect contacts and coils, etc.

Classified by contact form

Normally open relay – only a relay with normally open contacts.
Normally closed relays – only relays with normally closed contacts.
Changeover relay – relay with changeover contact form.

2. Main technical parameters and terminology

Electrical parameters

Operate voltage, release voltage

The minimum value of the coil voltage required when all the contacts of the relay reach the working state from the released state – general-purpose relays are generally specified as 75% to 80% of the rated voltage.
The maximum value of the coil voltage when all the contacts of the relay are restored from the closed state to the released state – general relays are generally specified as 5% to 10% of the rated voltage.

Contact resistance

The resistance value between a pair of closed contacts is measured under the specified measurement conditions. Generally in the milliohm level.
The measurement conditions are divided into: 30mV, 10mA; 6V, 10mA; 6V, 100mA according to the contact application category;
6V, 1A; 24V, 1A

Coil DC resistance

The DC resistance value measured from both ends of the coil lead-out pin. (Generally refers to the value of the ambient temperature of 20℃).

dielectric withstand voltage

The dielectric withstand voltage of the relay refers to the ability of the insulating part between the disconnected conductive parts to withstand the specified voltage without breakdown and specified leakage current. (Under normal circumstances, the dielectric withstand voltage between normally open contacts, between contact groups, and between contact coils is different).

Insulation resistance

The insulation resistance of the relay refers to the resistance value of the insulating part between the disconnected conductive parts when a certain DC voltage is applied. (Generally, the insulation resistance between normally open contacts, between contact groups, and between contact coils is the same value).

Operate time

The relay in the released state (initial state), under the specified conditions, the time interval from the moment when the specified value of the input excitation is applied to the moment when the relay is switched (excluding the pick-up and bounce time).

Release time

The relay in the operating state (termination state), under the specified conditions, is the time interval from the moment when the specified value of the input excitation is turned off to the moment when the relay is switched (excluding the release and rebound time).

Bounce time

For a contact that is closing its circuit, the time interval from the moment when the contact circuit is first closed to the moment when the contact circuit is finally closed.

Mechanical parameters

Contact gap

When the contact circuit is disconnected, the gap between the moving contact and the static contact.

Contact pressure

Interaction force between two contacts in the closed position.

Armature overtravel

The gap between the armature and the iron core at the moment when the relay contacts are in contact.

Secondary Operate

When the coil voltage gradually increases, the relay stays at a moment when the normally closed contact has been opened and the normally open has not been closed, or the armature and the pole face of the iron core are not yet attached even though the normally open is closed. The coil voltage rises in one step, and the armature is attached to the pole surface of the iron core, forming a “two ring”.

Jet lag Contact

For relays with multiple conversions, the difference between the operating time of the slowest contact and the operating time of the fastest contact.

Normal open contact

A contact that is closed when the relay is in the operating state and opened when it is in the released state.

Normal close contact

A contact that opens when the relay is in action and closes when it is in the released state

Moving contact

The contact fixed on the mov-spring moves with the movement of the armature.

Static contact

Contact fixed on the static reed

3. Automotive relay parameter detection method

Based standard

GB/T10232-94 IEC255-7
“Electrical Relays Part 7: Test Procedures for With or Without Electric Relays”.

test condition Standard

Temperature: 15~35℃
Relative humidity: 25%~75%
Atmospheric pressure: 86~106Kpa

Measurement of operate and release voltage

The operating voltage, hold voltage, and release voltage of the relay are tested as shown in the following figure. The test procedure is a unified method that the production unit and the user must comply with. Its greatest advantage is the repeatability of the tested parameters. It does not mean that the relay must be magnetized first and then work in actual use.

Coil resistance measurement

The measurement of the coil resistance can use the voltage-current method and the bridge method. When using the voltage-current method to measure, try to avoid or reduce the influence of the internal resistance of the voltmeter and ammeter, and the test process should be as short as possible to avoid the temperature rise of the coil.
The test value Ra should be converted to the value under the reference temperature (generally 20℃), the conversion formula is: Ra=R0[1+a(Ta-20)]

In the formula: Ta is the ambient temperature (℃)
a is the temperature coefficient of resistance (the temperature coefficient of copper wire is 0.004/℃)

 

Measurement of contact resistance

The relay is in the non-excited state when measuring the contact resistance of the moving-break contact; when measuring the contact resistance of the moving-closing contact, the relay is in the rated excitation state. The measurement of contact resistance generally adopts the voltage-current method (four-terminal method). When measuring, the load added to the contact should meet the requirements of the product standard.
The test site is within 4mm of the leading end from its root. The load should be applied after the contact is closed stably and cut off before the contact is opened.

Insulation resistance

The insulation resistance test generally uses a megohmmeter. The tested relay should be placed on a high-quality insulation board. The test voltage should meet the technical requirements of each product. Generally, the minimum value after applying the voltage 2s is the measured value.

dielectric withstand voltage

The dielectric withstand voltage test generally uses a special dielectric withstand voltage gauge, which can be maintained at the highest voltage (110% test voltage) for 1s during the test. In case of dispute, the test voltage should be maintained for 1 min. The leakage current is generally 1mA.

Time parameter measurement

The time parameter measurement circuit is as shown in the figure. It can also be replaced by other suitable electronic instruments and meters, but the contact load should be resistive. The measurement action, release and rebound time should be 10mA × 6v (resistive load), Measure the stabilization time load as 50μA × 50mV (resistive load). The resolution of the instrument is 1μS.

4. Introduction to the production process of automotive relay

Spare Parts production

Stamping-heat treatment-electroplating of metal parts such as armature, yoke, dynamic and static reeds. Injection molding of plastic parts such as coil formers, bases, shells, and push cards.

Parts production

Coil plug terminal – winding – dip tin.

assembly

Riveting contact, riveting armature, riveting iron core, mounting pins, mounting push block, mounting armature moving spring, mounting base.

Correction

Mechanical parameter correction-contact gap, pressure. Correction of electrical parameters-pull-in and release voltage, overtravel.

Parameter test

Mechanical parameters, electrical parameters

Cover

Soot blowing cover, sealing glue curing, sealing hole, leak detection, printing logo.

Final inspection

Detect contact resistance, pull-in and release voltage, coil resistance, dielectric withstand voltage, insulation resistance, appearance size.

package

Inner and outer packaging

Assembly line

Manual assembly line 50~100 people
Semi-automatic assembly line 30~50 people
Fully automatic assembly line 25 people or less

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