- Contact plates
- Armature
- Pins for coil wire
- Switch contacts
- Coil made of Cu wire
- Iron core (in the coil)
- Blade terminal (load) made of E-Cu (electrolytic copper) with tin-plated surface
- Blade terminal (coil) made of CuZn (brass)
with tin-plated surface - Base plate
- Coil body
- Yoke
Functional principle
Relays are basically electrically operated switches which use an electromagnet to move a switching mechanism by switching one or more contacts. They are used where one or more load circuits need to be switched on or off by means of a control signal. Characteristic of the electromechanical relay is the complete (galvanic) isolation between the control and controlled circuits.
Make relays
Make relays are used to close an electric circuit between a power source and one or more electrical loads, i.e. the loads are switched on. Relays are operated by means of switches, pulse generators or control devices. Typical vehicle applications are headlamps, auxiliary headlamps as well as fog lamps, horns, heaters, air conditioning systems and many other applications.
How make relays work
The control circuit (86/85) is inactive and the return spring keeps the armature open. The make contacts are open and the load circuit (30/87) is interrupted.
The control circuit (86 / 85) is active and the current flow in the magnetic coil (copper wire) induces a magnetic field, which pulls the armature down onto the magnetic core. The make contacts are closed and the load circuit (30/87) is therefore also closed.
Change-over relays
Change-over relays switch the load circuit over from one electrical load to another. These relays can be operated by a dashboard switch, for example. Change-over relays are used for switch applications with two stages/speeds such as heated rear windows or fan motors etc.
How change-over relays work
A change-over relay operates on the same principle as a make relay. The only difference is that the armature is connected to a second (alternative) output (87a) when released. As soon as the control circuit is active, the armature is pulled in, opens the break contact (87a) and switches over to the make contact (87). A change-over relay can be used as either a make or a break relay. By design, the switching current of the make contact is always higher than that of the break contact.
Rated voltage
12V: for passenger cars, agricultural and construction machinery etc.
24V: for commercial vehicles, buses, municipal vehicles etc.
Rated load
Resistive load:
The current remains around the same from switch-on to switch-off (e.g. rear window heater).
Inductive load:
The inrush current increases to the rated current with a specific delay time due to the build-up of the inductor’s magnetic field and then levels off (e.g. switching on a solenoid switch). During switch-off, a voltage of up to several thousand volts is (theoretically) induced, resulting in an electric arc between the relay contacts just opened.
Capacitive/bulb load:
The inrush current of a capacitive load or a lamp can rise to ten times the rated current before leveling off to the rated current.
Coil circuit
In order to prevent voltage spikes caused by mutual inductance when switching off the coil current, our relays are in part equipped with resistors or diodes parallel to the coil.
Contacts and connector configurations
The connections of the relays are each labelled with numbers. The corresponding assignment is enclosed.
30: Load current +, terminal 15 (input)
85: Relay coil – (input)
86: Relay coil + (input)
87: Load current, make contact (output)
87a: Load current, break contact (output)
Mini relays according to ISO 7588-1, blade terminals according to ISO 8092-1. Contact configurations: Normally open contact, changeover contact, max. 50A rated switching current (normally open contact), rated voltage: 12 V, 24 V
Areas of application include: headlights, starters, fuel pumps, fan motors, horns and fanfares.
Micro relays according to ISO 7588-3 (1988), blade terminals according to ISO 8092-1. Contact configurations: Normally open contact, changeover contact, max. 35A rated switching current (normally open contact), rated voltage: 12 V, 24 V
Areas of application include: fuel pumps, air conditioning systems, windshield washer systems, wiper motors.
Mini relay version with enlarged dimensions, flat connector according to ISO 8092-1. Contact configuration: Normally open contact, changeover contact, max. 60A rated switching current, rated voltage: 12 V, 24 V
Areas of application include: battery disconnect relays, starter motors, glow plugs, ignitions, windshield heating.
Hella Relay OE numbers
