The car battery relay acts as a "control unit" for the battery. It manages the flow of electric current, ensuring the safety of both the battery and your vehicle's entire electrical system. It is widely used in cars, trucks, and is especially in the RVs for dual-battery systems, enhancing the efficiency of the electrical setup.

Battery Relay Functions

Unlike a regular relay(starter relay), a battery relay controls the flow of the high electricity. It uses a small current in the control circuit to switch the high current on or off. The relay can be operated manually or automatically. For instance, in some electric vehicles or RVs with dual-battery systems, the ECU controls the battery relay; in other cases, the driver turns the key on/off to switch the battery relay. Whether it’s in single-battery or dual-battery systems, the battery relay prevents the overloaded devices from draining the battery, which extends the battery life.

Battery Relay Parts

Coil

A coil made of copper wire carries current and then generates a magnetic field that attracts the armature.

Armature

When activated, the armature moves to connect or disconnect the contacts, allowing the flow of electricity or not.

Contacts

The contacts inside the battery relay are usually made of copper alloy or silver alloy, which are wear-resistant and heat-resistant.

·Common Contact: Based on different conditions, the armature moves the common contact to connect either the NO or NC contact.

·Normally Open (NO): When the relay is not powered, the common contact and NO contact are separated, meaning the circuit is open.

·Normally Closed (NC): When the relay is not powered, the common contact is closed with the NC contact, meaning the circuit is connected.

Yoke

The magnetic field from the energized coil is spread out. Magnetic materials can guide the field and strengthen the magnetic force to move the armature. So the yoke, often made of soft iron or silicon steel, provides a path for the magnetic flux.

What are the Types of Battery Relay

Based on application requirements, battery relays have been developed with multiple functions, leading to standard relay, latching relay and smart relay. Each has its own advantages in cost, power use, and automation.

Standard Relay

It’s simple and cost-effective. Once you turn off the car, the relay cuts off the circuit. However, the relay consumes more power since the battery supplies the power continuously for it.

Latching Relay

It is activated by a pulse signal. Once activated, it can stay in position by magnetic force even after power is cut off. So when your vehicle is in standby, the relay’s energy consumption is much lower than a standard relay.

Smart Relay

It’s designed for complex applications and low-energy consumption. Controlled by the microcontroller, the smart relay can be programmed for self-monitoring. Relatively, it costs more than the other relays, which requires a larger initial investment.

Battery Relay vs Other Relays

Current Load

Battery relays are designed to switch the battery current, which can handle higher electricity compared to other relays.

Material Quality

As the battery relay is used for the battery, it often requires better materials than other relays, including the insulation. Also its contacts with thicker silver alloy layers are designed for heavier-duty.

Smart Features

Especially in smart relays or dual-battery systems in RVs, battery relays distribute current between the primary and secondary batteries to prevent either battery from draining

What are the Right Specification of the Battery Relay

The battery relay controls the power from the battery. Even a small mistake, an incompatibly low-quality relay can cause a short circuit and damage other electrical components. It’s vital for you to consider major factors while choosing the right battery relay.

Voltage rating

The battery relay’s voltage should match your vehicle’s electrical system, which can properly transfer power between the battery and the electrical system.

Current rating

It’s crucial for the battery relay to handle the current safely. The maximum current is more than the steadily operating current of the highest electrical load of your vehicle. So the battery relay can protect its parts and electrical components from the peak current.  

Coil resistance

The coil resistance of the battery relay should be kept in a safe range. If it’s too low, the current spikes and exceeds the current rating of the battery relay, causing damage. If it’s too high, there isn’t enough current to activate the relay and the connected electrical components may fail to operate.

What are the Battery Relay‘s Features？

If a battery relay operates reliably under the strong vibrations in the engine bay, it should handle the battery’s high current or high voltage, along with the risk of overheating. A reliable battery relay features are following:

Durable: It can endure up to 100,000 switching cycles, resist high-frequency engine vibrations and heat caused by high electricity.

Fast response: It balances the spring tension, uses a low-pulse copper coil and a low-friction armature to react quickly to your commands. Modern vehicles even use automatic sensing systems to intelligently control the relay.

Environmental Resistance: It protects against the tough conditions inside the engine but also blocks outside dust and moisture, making it suitable for use in various regions and climates.——

Battery Relay Advantages & Disadvantages

Maintenance

In addition to purchasing the high-quality battery relay based on the current ratings, you should also use a battery relay fuse for added protection. It’s important for you to regularly check the relay during its service life.

·Check if the housing is deformed or cracked.

·Look for signs of corrosion or oxidation on the terminals.

·Use a multimeter to measure whether the coil resistance is within the normal range.

For minor oxidation, you can gently remove the impurities with a scraper. Conversely, replacing it with a new one is better for the safety of the vehicle’s electrical system.

The outside environment also greatly affects the battery relay performance. Conditions like high humidity, salt, or corrosion can shorten its lifespan. To reduce environmental impact, choose a battery relay with stronger sealing or a protective cover.