overview of power relay

What is a power relay

A power relay is a switch that uses an electromagnet to open or close a circuit. The basic design of a relay uses a solenoid, armature, spring, and one or more contacts. If the power relay is designed to be normally open, the circuit is incomplete in the off state.

When power is applied to the power relay, usually from battery power, the electromagnet attracts the armature, which is usually a movable arm made of iron. The armature, held in place by the spring, is pulled in the direction of the coil until it reaches a contact, closing the circuit. If the relay is normally closed, the coil pulls the armature away from the contacts, opening the circuit.

What is a power relay used for?

You can use power relays in different industries. These switches are useful in audio amplification and telephone systems. You can also use them in automotive electronics and computer systems.

The goal is to relay any signal from one circuit to another. Additionally, cars have many electrical systems and devices. They both use a 12-volt battery for power. Therefore, power relays may be ideal in these applications.

Some cars will have more than 20 power relays that manage everything from windshield wipers to horns to drivetrains.

Power Relay Applications and Uses

When using relays in electronic circuits, pay attention to the following aspects:

1. Coil working voltage

Coil operating voltage refers to the voltage applied to the relay coil (not the contact loop voltage). When determining the working voltage of the coil, it is strongly recommended to select it according to the rated voltage (if not, you can refer to the temperature rise curve for selection, which is generally not recommended). Using any coil voltage below the rated operating voltage will affect the operation of the relay. Especially when using the transistor amplifier circuit to drive the relay coil, the coil voltage value must be guaranteed; otherwise, when the rated voltage is exceeded, the product performance will also be affected. Excessive working voltage will make the coil temperature rise too high, which will damage the insulating material. , will also affect the working safety of the relay.

For magnetic latching relays, the excitation (or reset) pulse width should not be less than 3 times the pull-in (or reset) time, otherwise the product will be in a neutral state. When the coil is excited with a solid state device, the withstand voltage of the device should be at least 80V, and the leakage current should be small enough to ensure the release of the relay.

2. Transient spike suppression

When the coil is powered off, a reverse peak voltage that is more than 30 times higher than the rated working voltage of the coil will be generated, which is extremely harmful to the electronic circuit. It is usually suppressed by paralleling transient suppression (also known as peak clipping) diodes or resistors so that the reverse peak voltage does not exceed 50V. But the parallel diode will prolong the release time of the relay by 3~5 times. When the release time is required to be high, a suitable resistor can be connected in series with one end of the diode.

3. Parallel and series connection of multiple relay coils

When multiple relay coils are powered in parallel, the relay with high inverse peak voltage (ie large inductance) will discharge to the relay with low inverse peak voltage, and its release time will be prolonged. Therefore, it is better to control each relay separately and then parallel to eliminate mutual influence. ;Relay coils with different coil resistance and power consumption should not be powered in series, otherwise the relay with a larger coil current in the series circuit cannot work reliably. Only relays of the same specification and model can be connected in series, but the reverse peak voltage will increase and should be suppressed. The part of the power supply voltage higher than the rated voltage of the relay coil can be tolerated by the voltage divider ratio in series with the resistor.

4. Contact load

The contact load should meet the rated load and performance requirements of the contact, otherwise problems are likely to occur. Products designed for use with DC loads only should not be used for AC applications. A relay that can switch single-phase AC power is not necessarily suitable for switching two asynchronous single-phase AC loads; products that only switch AC 50Hz (or 60Hz) should not be used to switch 400Hz AC loads

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