| Relay is a kind of automatic controlling component with isolation function, which is mainly used in circuit controlling and switching, and widely used in telecom, automotive, traffic, electric, industrial control, etc. It is an essential component in automatic control.
Generally, relays have the inductive organ (input organ) that can reflect the input value (such as current, voltage, power, impedance, frequency, temperature, pressure, speed, light,etc.); have the executive organ (output organ) that has the capacity of switching the controlled circuit “on” or “off ”; between the input and output parts, there is the medium organ (actuator) that can make the input value do the function dealings, input and output value coupling-isloation and drive the output part.
As a kind of controlling component, generally, relay mainly has the following functions:
a) To enlarge the range of control. E.g., when the input value of a multi-contacts relay reaches a certainvalue according to the different forms of the contacts, it can synchronously change over, close or open several circuits.
b) Enlargement. E.g., sensitive relays and medium relays can control a high-power circuit with tiny controlling power.
c) To integrate signals. E.g., when several controlling signals are put into multi-winding relay in the statedform, the relay can realize the expectant controlling function by analyzing the different signals.
d) Automatization, remote control and monitoring. E.g., in automatic equipments, the relays and othercomponents can constitute program-controlled circuit, realizing the automatic operation.
The automotive relay is the relay specialized in the field of automotive. It is regards as a dedicated category as the automotive electronic components, and other electric products develop. It is widely applied for several controlling system, such as vehicle start control, warm-up device, air conditioner, lamp, wiper, electrical sprayer, fuel pump, anti-theft, audio system, communication device, orientation system, electrical fan, power door & window, securityairbag, anti-lock braking system, suspension control and vehicle electrical meter & failure diagnosis system. Just next to the transducer, the automotive relay is the second popular electrical component of the application of electrical automotive components.
CHAPTER 1 The Selection Guideline of Automotive Relay
1 Automotive Relay Classification
Although there are various of automotive relays, the automotive relays can be divided into four kinds according to the mounting modes and functions of the terminal:
● PCB Mounted Automotive Relay: ?the relay welded on PCB. E.g.:HFKA/HFKA-T, HFKB, HFKC/HFKC-T, HFKD, HFKDV, HFKE, HFKM/HFKS, HFKP, HFKW, HFKW-SH, HFV4, HFV6, etc.
● Plug-in Automotive Relay:the relay plugged in the special socket. the size of the terminal are 2.8mm, 4.8mm, 6.3mm, 9.7mm. E.g.: HFV4, HFV6, HFV7, HFV7A, HFV8, HFV9, etc.
● Combined Automotive Relay:the relay that is combined with PCB type relay and other logical electric wires to achieve some specialized function. E.g.: flasher such as JA3501, JA3501A, JA3506, JA3506A, JA3508, JA3508A; fog-lamp controller such as JA3505, JA3505A; wiper controller such as JA3502, JA3504, JA3504A, JA3507, JA3507A; delaying relay such as JA3503, JA3503A, JA3503D, JA3503F, JA3503G, etc.
2 Input Parameter Principle
The following parameters should be considered when applying the input parameter:
● Coil Rated Voltage
● Coil Power Consumption
● Pick-up Voltage/ Drop-out Voltage
● Max Continuous Current
● Coil Resistance
● Pulse Width of Impulse Input Parameter(Magnetic Latching Relay)
a) Ambient Temperature: According to the ambient temperature of the automotive relay, its ambient location can be divided into engine cabin (Max. limit temperature should be 125℃) and cockpit (Max. limit temperature should be 85℃) . The rise temperatue of the ambient temperature and the coil would effect its operation voltage and pick-up voltage; The coil resistance may change with the ambient temperaure. When it rises by 1℃, coil resistance will rise by 4‰. Once the coil resistance changes, the operation and pick-up voltage will also change. When the coil is energized for a long time, the coil temperature will rise, or the ambient temperature will rise. And if switching the contacts , the pick-up voltage will be more than when the coil is cold.
b) Pick-up voltage: When the relay is driven by the transistor and integrated circuit, because of the voltage drop inside them, it may cause the voltage in the coil's both sides too low so that fails to drive the relay.
The counter EMF caused by breaking coil may damage the transistor and the integrated circuit. If it is necessary, the coil designer had better design the protection circuit or choose the realy with the resistane or the diode.
c) Coil Rated Voltage: When the relay operates, if reducing the holding voltage (or reducing the voltage in the coil), it may weaken the vibration resistane of the products, thus, the false operation may take place when the automobile badly bumps. The recommended holdingvoltage should be higher than 80% of rated voltage.
d) Coil Max. Pick-up Voltage: To meet the requirement of low pick-up voltage (60% of rated voltage), the power consumption of automotive relay is designed relatively higher and the impressed voltage to the coil should be less than 120% of the rated voltage. If it would be more than 130% of the rated voltage, please contact Hongfa for the technical support. Especially when the relay is applied in high ambient temperature, the coil temperature will be too high, which will accelerate aging--- in the end, the insulation of coil will be damaged, which will result in short circuit and the relay will be failed.
e) Drop-out voltage: Generally, the drop-out voltage will be 10% of rated voltage. When the residual voltage in the circuit is too high, it will result in the failure of the relay performance.
3 Out-put Parameter Selection Principle
The following parameters should be considered when applying the output parameter:
● Amount of Contact Poles
● Contact Arrangement
● Contact Load
● Contact material
● Electrical endurance
3.1 Contact Load
The power of automotive system applies direct current, which does not have pass zero point as alternating current has. When the contact breaks, it will generate the electric arc. Meanwhile, as the impressed voltage keeps, the electric arc will draw out, until it can not withstand and extinguishes. The arc heat will burn the contacts badly, meanwhile, the contact material transfer will become more severely, as the DC transfers in the one direction.
Regarding the load capability, most of automotive relays indicate resistance load, however, generally automotive relay does not apply for resistance load, but inductive load, lamp load, motor load. Therefore, relatively high impulse current exists, the contact stable load should be applied according with the impulse current, based on the principle that the impulse current doesn't exceed the resistance load labeled.
It should be emphasized that the contact fault is the key reason of relay failure. Different types of loads and different power volume of load may result in different contact statistics, failure phenomenon and failure mechanism. Let is explain as follows:
a) Headlight：Since the resistance of the automotive headlight in cold state is small, at the moment when the circuit is connected, the surge current will be 15 times than stable current. Such high current will burn the contact quickly, even result in the failure of fusion welding.
b) Motor Load：When the motor rests, the input impedance is very small, when it works, the surge current will be so big. When the motor runs, the motor will generate the electromotive force (EMF), which will make the contact current become less. Moreover, when the motor is off, it will generate the Counter EMF. Usually, it will generate arc, then burn the contacts.
c) Inductive load：At the moment when the electromagnet is energized, it will emerge the surge current. When it breaks, electromagnetic energy remained in the coil will be consumed by the arc between the contacts. This will result in the contact burning, material transfer and contacts lock.
Applying contact protect device, such as RC network, diode, resistor may lesson the contact burning.
d) Low Level：Low Level refers to the open circuit voltage in amount of 10mV to 100mV , and the contact switching current during microampere level to 10mA. Since the organic substance and the compound on the contact surface can not be eliminated when switching load, the contact resistance will be so large and unstable, the current will be unstable, contact voltage drop increases, in the end the contacts fail. We usually apply telecom relay to switch the low level signal such as vehicle communication, audio system and GPS signals in automotive relay.
Out-put Selection Principle:
a) The Max. switching voltage, max. switching current, max. switching power and the load switching frequency should not exceed the specified value. Please contact Hongfa for technical support if exceed.
b) Usually, the load voltage of automotive is 12VDC, however, it will be 24VDC for the vehicle of diesel engine. We should make sure if the automotive relay has the specification of 24VDC.
c) The contact load should be larger than the min. allowed load to avoid incorrect signal transport. The contact load of automotive relay is usually 1A 6VDC.
d) When relay apply for the circuit, we shouldfull consider any kind of contact short circuit, circuit break failure,and design essential circuit to avoid of power short circuit or any serious accident which may affect traffic safety.
e) Choose relay according to load shock current and latest version of catalogue, then do actual load test on relay.
f) Please select the relay not only according to the load value on the cover, but also the parameters specified in the latest catalog. Make sure the contact rated voltage (12VDC or 24VDC), and what the operation life is.
g) In the case that the relay will be apply for the low level load, such as vehicle communication, audio system, positioning system etc., the telecom relay will be applied. The telecom relay possesses divaricable contacts, high contact reliability, but we should make sure whether the proper capability of anti-vibration and anti-shock.
h) For general usage, relay can be applied without arc-control circuit, however, when the impulse current and impulse voltage generates at the moment of switching the load (see Table
i) Check if the life cycle of relay duration is equivalent with the one of vehicle parts.
j) Check if the contact material and the load are coincident, especially in the case that the flasher load and low level load are applied.
k) The environmental stress may shorten the relay life. Make sure the automotive relay should meet the requirement of environmental stress.
3.2 Contact Material
Contact material is the vital material of relay application, its characteristic may refresh the quality of relay. Following table indicates the different characteristics and the application occasion of different contact material:
4 Time parameter selection Principle
The following time parameters should be considered when selecting relay:
● Pick-up Time
● Drop-out Time
● Pick-up Bound Time
● Drop-out Bound Time
Following chart indicates the relay time parameter:
5 Ambient Environment Selection Principle
The following parameters should be considered when selecting relay:
5.1 Ambient Temperature
a) The insulation material may intenerate and melt easily in the high ambient temperature. While, it may crack easily in the low temperature environment. However, when you select engineering plastic, the above requirement can be satisfied.
b) When the exchange of high temperature and low temperature occurs, it will easily make the structure flexible, the placement of movable parts may change, which may lead the pick-up and drop-out out of control, even the contact fails.
c) In low temperature, the vapor inside may condense or freeze, which may result in the failure of the relay.
d) In high ambient temperature, the coil resistance will increase, and the pick-up voltage will increase as well. When the power of automotive accumulator is inadequate, it will result in the failure of relay.
e) In the high temperature, when contacts switch the power load, the capability of arc resistance will depress, and the contact corrosion and contact material transfer will become more severely, the operation life will be shortened.
5.2 Humidity
The humid environment will affect the relay performance, the details listed below:
a) Long-time humid environment may decrease the electrical resistance of insulation, even result inthe total failure.
b) Regarding the relay without sealed in humid environment, the coil may break off due to the electrochemical corrosion or mildew. In this manner, the electrochemical corrosion and oxidation of contacts will become worse, and the corrosion of metal parts will obviously speed up, thus, the performance of relay will be worse, reliability of application become worse, even result in relay failure.
c) In the humid environment, when the contacts switch load, the arc phenomenon will become worse, which will shorten the electrical life.
5.3 Shock & Vibration
Shock and vibration will result in the following negative effects.
a) The structure will become flexible, damage, crack even lose the capability.
b) The NC contact will separate momentarily, which exceeds the one specified.
c) Relay may conduct false operation.
Pay attention to following points when using:
a) The actual temperature should be lower than the max. temperature. When the relay runs in high temperature, the power of switching load should lower relatively.
b) Sealed relay should be applied in the high humid (+85%RH) and corrosive atmosphere.
c) The capability of relay vibration and shock should meet the parts or assembly requirement. Relatedtests are required as well.
6 Security Parameter Selection Principle
The following parameters should be considered:
6.1 Insulation Material
The insulation material should possess nice temperature endurance capability, the temperature for long-time application should reach 125℃.
6.2 Insulation Voltage Withstand Level
The voltage withstand of relay divide into voltage withstand and insulation resistance between contacts, and between contacts and coil.
6.3 Electromagnetic Compatibility (EMC)
EMC refers to the capability of noninterference or susceptibility for the automotive relay in electromagnetic environment.
EMC has become one of the most important standards for determining products quality. EMC divides into Electromagnetic Interference (EMI) and Electromagnetic Susceptibility (EMS). Since the automotive relay applies the sole power, when the coil breaks, it will generate high voltage, which will interfere other system or parts, in this manner, PCB type automotive relay usually will be parallelly connected with resistors or diodes fortransient suppression, which will make the coil Counter EMF< 100V.
When the relay contacts open, it will generate arc, and send out electromagnetic wave, which will affect IC performance. In such case, we may add arc suppression circuit. Or we may extent the distance between relay and IC.
7 Mounting and Application Principle
7.1Mounting, Storage
a) The terminals should match the holes on PCB board. Any improper match may result in danger by relay, and the performance and reliability of relay will affected.
b) After relay is mounted into the PCB, don’t bend the terminals, or it will affect the sealing characteristics or other characteristics.
c) In the process of plug in, don’t press the cover too hard, or the cover may crack and the switching characteristic may change.
d) The insert and pull force for quick-connected terminals will be 10kg. Too large force may destroy the relay, while, too little force may affect the contact reliability of terminals and socket and current carrying capability.
e) It should be emphasized that if the relay drop or shock, although the electrical parameter is qualified, the mechanical parameter may change a lot, this will result in serious hidden trouble, so the relay hereby can not be applied.
f) Relay should be stored and mounted in clean ambient environment.
7.2 Flux Coating
The relay with wash tight type for PCB mounting are easy to be polluted, so the relay types of wash tight and flux proofed are recommended to prevent the flux gas entering into relay through the terminal or slot between base and cover. If the relay of flux free type can be drying(100℃, 1min), it will further prevent the flux from leaking inside.
7.3 Seal Technology
Be careful to use flux or auto soldering, not to destroy the performance of relay. The relay with the flux free and sealed type can be applied for the technology of solder dip and Wave Soldering. The soldering temperature should be 240℃ to 260℃, and the time should last 2s to 5s. However the soldering tin should not exceed PCB. Manual soldering temperature should be around 350℃, and last 2s to 3s, avoiding soldering the relay too many times.
7.4 Cleaning Technology
The cleaning-free soldering flux is recommended for sealing, avoid entire cleaning. And the cleanser should not enter into relay, which may result in failure of relay. The ultrasonic cleaning agent is prohibited, as it may result in contacts cold joint, coil break and other structure damage.
7.5 Protective Agent Coating
Sometimes in order to ensure the PCB board is dampproof or to improve the insulation requirement, protective agent is used on PCB board after assembling. Flexible protective agent with no organic silicon shall be used. Sealed relay is used in such application. In process of coasting, relay shall not be under high temperature to avoid protective agent absorbing into relay due to pressure and cause relay failure. Recommended coasting tempertature is room temperature, and dry it under high temperature.
CHAPTER 2 The Application of Automotive Relay
The automotive relay should be applied according to its mounting positions and its functions, meanwhile, the destroy strength it can endure is also different, e.g. temperature, humidity, temperature punching, impulse current etc. If the relay is not selected and validated properly, it will result in unexpected failure. In such case, the relay should be tested and evaluated according the actual application conditions.
For example, when the relay is applied with the parameters beyond rated voltage, rated contact voltage, rated contact current, switching frequency etc., and the coil will generate abnormal heating and the contact may lock.
The relay should be mounted according the mounting drawing. Connect the wire according to specific polarity. According to the load current, the cross-section area of lead wire should be applied properly to meet the current carrying requirement. To connect proper linker is another option. However, the unreliable linker may result in failure of relay due to the high temperature generated.
If the contacts lock, fail, or the coil breaks off, it will affect the security of vehicle. The necessary security devices are required to design.
1. Application of Relay
1.1To apply relay properly, we should be familiar with the characteristics of relay and make sure that the application condition and ambient environment can meet the requirement of assembly.Please pay attention to the following points:
a) To keep the initial capability, the relay should not drop or be shocked.
b) The relay with dustproof or sealed relay should be applied in the dust environment.
c) Don’t use the silicon-contained colophony or protective agent, which will result in the contact failure, even the sealed relay will be affected.
d) According to the specific polarity, the relay should be connected properly with the coil power and contact power. Regarding the contacts, the mov. spring should be connected with anode (+).
e) Pay attention that, the voltage impressed should not exceed max. allowed voltage or the coil temperature rise should not exceed the insulation system specified.
f) The rated load and duration is defined in the rated conditions prescribed. It does not covering all of the aspects of actual automotive application requirement. The actual contact load and duration will be obviously different according to the load type, ambient condition, switching frequency or other condition. Please test or contact Hongfa for technical support.
g) The ambient temperature should meet the requirement of automotives, if wave soldering should be used, sealed relay should be applied, and the ultrasonic cleaning agent should be prohibited.
h) Insert force of ISO plug-in automotive relay is 10kg, don’t bend the terminals of PCB relay when using.
1.2 Coil Input Cautions
a) The rated voltage is the guarantee for the reliability of relay performance.
The contacts will switch improperly in the condition of high impulse, as If the coil voltage exceeds the switching voltage, although the relay can work.
In the case that the actual coil voltage exceeds the max voltage, it will result in the characteristic of coil insulation declining, short circuit, even burning.
b) The resistance of the coil may change by 0.4% per centigrade due to the change of ambient temperature and the heating of the relay. So if the coil temperature rises, the pick-up voltage and drop-out voltage may raise.
c) Since the automotive relay is driven by the accumulator, and big load power may result in the drop of power voltage, the duration of relay may be affected. Please be aware of that the voltage change may affect the reliability of relay application.
d) The max. continuous impressed coil voltage: the max continuous coil voltage affects the stability of relay performance, and is limited by the insulation performance of coil. Therefore the insulation grade should be studied. For the relay of F grade in 40℃ ambient temperature, the temperature rising limit should be 115℃ (according to the resistance method). However, considering that the parameters outside and inside of coil are uneven, the recommended temperature is 105℃.
e) Coil electrical corrosion: the automotive relay run in the environment of cycling temperature and humidity,
when the coil is connected the anode of the power (break the cathode), the coil will ‘break’ due to the electrical corrosion, therefore, the relay coil can not be connected with high electric potential, the coil, and mov. spring and the power anode should be disconnected when using.aspects of actual automotive application requirement. The actual contact load and duration will be obviously different according to the load type, ambient condition, switching frequency or other condition. Please test or contact Hongfa for technical support.
1.3 Notes about the Contact Application
Contact is the key part of relay. The reliability of contact application is determined by the contact material, contact voltage & current (esp. voltage, current wave when on and off), load type, switching rate, and ambient condition.
a) Contact Voltage: the inductive load may generate very high counter voltage, the higher voltage, the more power, which will accelerate the electrical corrosion, contact material transfer. Please pay attention to such points.
b) Contact current: When the contact ’make’ or ‘break’ the current will affect contact performance. Especially when the load is a motor or a front lamp, once the contact closes, the impulse current will be so large, thus, the contacts will be damaged, contact material transfer become worse, which will result in the contact lock, even failure. Tests should be taken to evaluate.
1.3.1 Contact Protection
a) Counter Voltage:
When breaking the coil circuit in series or any inductive load such as motor, electromagnet, the diodes should be applied to absorb surges to protect contacts. When breaking the inductive load, it will generate hundreds ?thousands of counter voltage, in such case, the electrical corrosion will become worse and the duration of relay will be shortened. Meanwhile, If the current in these loads is relatively small at around 1A or less, the arc generated by the counter voltage may decompose the organic gas sent out by coil and plastic, and then cause the black deposits (acid matter, oxides) to develop on the contacts. This may result in bad contact of contacts.
b) Contact metal transfer:
Contact material transfer means that the direct current will make the material of contact transfer in one direction, as the amount of switching increases, the concave on one side of contact set will take place gradually, meanwhile, the convex will be on another side. And the concave and convex will generate the mechanical lock even the contacts may weld. Therefore, the contact material with transfer resistance or the protect circuit should be applied.
c) Contact protection absorption circuit:
The protection component or circuit can be applied to reduce the counter voltage. However, if they are not applied properly, the negative effect will take place. table 1 indicates the typical protection circuit.
1.3.2 Contact Connection
Load and impulse current: the type is related with the switching frequency, esp. for lamp load. Switching frequency is the vital factor in creating contact stick. The impulse current of various loads is shown below:
The impulse current of load is 1 time than stable current (equivalent).
The impulse current of solenoid is 10 to 20 times than stable current.
The impulse current of motor is 5 to 10 times than stable current.
The impulse current of lamp load is 10 to 15 times than stable current.
The impulse current of capacitor is 20 to 40 times than stable current.
1.4 Ambient Environment
1.4.1 Environment
The ambient temperature should not exceed the value specified to relay.
In the environment with dust, sulfide gas (SO2, H2S)and other organic gas, please use the sealed relay.
1.4.2 Silicon Environment
The colloidal matter with silicon can not be contained in the relay application environment. Otherwise it will generate the silicon gas, which will make the silicon to attach to contacts and result in bad contact effect.
1.4.3 NOx Generation
It will easily generate arc in the environment with high humidity. With the arc processes, N2 and O2 may produce NO2,
Table 1 Typical contact protection circuits
1.4.4 Vibration & Shock
The capability of vibration and shock of automotive relay should meet the automotive requirement, please take notice that the instability and insufficient hardness can magnify the acceleration of vibration.
1.4.5 External Magnetic Field
The automotive relay can not be applied near the speaker, or it will be affected by the magnetic field, then affect its performance.
and then the nitric acid will be generated with H2O. The nitric acid may erode the metal parts even affect the performance of relay. The recommended environment is the one in which the humidity is less than 85%RH (at 23℃).
2. Carriage Storage, Transportation
2.1 Storage and Transportation Environment
Avoid direct sunlight and maintain normal temperature·normal humidity·normal pressure
Temperature: 10℃ to 35℃
Humidity: 5% to 85% RH
Air Pressure: 86kPa to 106kPa
a) Under the environment of high temperature and high humidity, once the temperaturechange sharply, it may coagulate inside the relay. Especially in the process of transport by sea, it will be easily condensed, please take attention to the transportation environment. Condensation refers the phenomenon that in the environment of high temperature and high humidity, the temperature drop from high point to low point very suddenly or rise from low point to high point very sharply, the vapor turn into drip. Condensation may result in insulation decline, coil corrosion and break, rust etc.
b) Freezing may lead the movable parts to stick, delay operation or contact failure if the ice generated between the contacts.(Freezing: it refers to the phenomenon that in the environment of condensation and high humidity, when the temperature drops down below zero point, the moisture on the relay may freeze.
c) In the environment of low temperature and low humidity, the plastic may become brittle.
d) When the relay is stored in the environment of high temperature and high humidity, and the atmosphere containing organic gas and sulfide gas, the surface of contacts may develop sulfide film and oxide film, which may result in contact instable even failure. Please pay attention to the package, try to diminish the blight by humidity, organic gas, sulfide gas etc.
2.2 Storage and Transportation Stress
If the relay drop down or is shocked badly in the process of transportation, it may result in relay fault. Please check whether the outline of package is perfect before removing the package.
When the relay is packed by tube, if the amount is not enough for full tube, and lacking limit, the relay may slide. This may affect the outline and capability of relay.
3. Usage of Wash tight Relay
The PCB relay can be divided into two types: wash tight and flux proofed. The wash tight relay possesses nice environmental endurance. It can prevent flux and cleanser from entering into relay.
When cleaning PCB, the alcohol type of cleaning agent is recommended. The ultrasonic cleaning agent is prohibited. If the ultrasonic cleaning agent is applied, the coil may break off, and the contacts may lock.
4. Mounting
4.1 Mounting direction
If the mounting direction is same with the direction of relay shock, and the relay performance can be fully take place. The recommended mounting direction of the relay is perpendicular to the movement direction of the contacts and armature, then it can improve the capability of vibration and shock without magnetic excitation state.
Mounting the relay that the axis direction is parallel with the ground, so the surfaces of its contacts prevents scattered contact material or charing matters, in this manner, it can improve the contact reliability. Regarding the multiple poles of relay, avoid mounting the relay with its low level load contacts located below the large load contacts.
4.2 Adjacent Mounting
In the case of adjacent mounting common relays, it will result in abnormal heating. The recommended space is 2mm. when mounting the polarity relay or the magnetic latching relay in a small distance, the switching voltage will be affected and the recommended space is 5mm or more than that.
4.3 For the relay of cover fixed mode, it can not be mounted without cover. To avoid flexibility, damage, deformation, please utilize the spring gasket. The moment should be during (0.5 to 70) N·m.
4.4 Please use mounting pressure of 40N to 70N for plug-in relay.
.4.5 Area of Lead Wire (As shown in the following table)
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