Why should you choose Huanfang Electrical for high-voltage contactors in new energy vehicles?

Since its inception, Huanfang Electrical has remained dedicated to the manufacturing of automotive relays and electromagnetic switches. As a drafting unit for national industry standards in these fields, Huanfang has also played a key role in shaping industry norms. In recent years, with the rapid global growth of new‑energy vehicles, Huanfang has developed high‑voltage DC contactors tailored for internal circuit control in NEVs, as well as for EV charging piles and charging stations. These products incorporate numerous national patents, and the company is actively collaborating with world‑renowned automotive component suppliers to pioneer next‑generation high‑voltage DC contactors, thereby contributing our utmost to sustainable, green mobility.

The role of high-voltage relays in new energy vehicles

As an important component of new-energy vehicles, the main‑circuit voltage in such vehicles typically exceeds 200 V, significantly higher than the 12–48 V found in conventional cars. In addition to the low‑voltage relays and contactors required by traditional automobiles, new‑energy vehicles must also be equipped with specialized high‑voltage DC contactors.

New energy vehicles typically rely on high-voltage battery packs to power their electric motors. To ensure the proper switching of the electrical system, a high‑voltage DC relay must be installed between the vehicle’s battery system and the motor controller. This relay isolates the battery system when the vehicle is shut down and connects it during operation. In the event of a vehicle shutdown or a fault, it safely disconnects the energy storage system from the vehicle’s electrical network, thereby breaking the circuit. Consequently, the high‑voltage DC relay is a critical safety component in new energy vehicles; without it, the vehicle would be unable to start, drive, or come to a stop.

I. Applications of High-Voltage Relays in New Energy Vehicles

Depending on the vehicle model and powertrain configuration, the number and scale of relays used in automobiles can vary significantly. On average, each new‑energy vehicle is equipped with 5 to 8 high‑voltage DC relays: two main relays, one pre‑charge relay, two fast‑charging relays, two standard‑charging relays, and one relay for auxiliary high‑voltage system components.

II. Basic Functions of High-Voltage DC Relays

As a critical safety component in new‑energy vehicles, the high‑voltage DC relay must possess fundamental capabilities such as high‑voltage withstand, load‑handling, shock resistance, strong arc‑extinguishing performance, and robust breaking capacity.

1. High-pressure resistant

New‑energy electric vehicles operate at relatively high voltages, significantly exceeding the 12 V/24 V typical of conventional cars. Consequently, their associated high‑voltage DC relays must be capable of withstanding elevated operating voltages and reliably making and breaking circuits under high‑voltage load conditions.

2. Strong load-bearing capacity

The rated power of electric motors in new‑energy passenger cars and buses typically ranges from 30 kW to over 80 kW, with peak outputs exceeding 60 kW and 160 kW, respectively. Based on the voltage platforms mentioned above, the corresponding currents would be approximately 200 A and 300 A. Under the dual constraints of performance and cost, products are required to exhibit strong load‑handling capability within a given volume while also delivering transient overload capacity several times the rated current; alternatively, for a given load‑handling capability, the smaller the product’s footprint, the better.

3. Impact Resistance

High‑voltage DC relays for new‑energy vehicles must not only withstand high voltages and carry sufficient current but also endure the surge of inrush current from capacitive loads at switch‑on—typically several to dozens of times the load’s rated current. Conventional relays cannot tolerate such transient currents; the resulting contact welding, failure of contact separation, and uncontrolled power interruption can lead to catastrophic safety incidents, including vehicle damage and loss of life. Therefore, DC relays used in new‑energy vehicles must exhibit robust surge‑withstand capability.

4. Strong arc-extinguishing capability

Arcing is an unavoidable phenomenon during the make-and-break operations of relay contacts, significantly reducing their service life. By employing specialized rapid arc‑extinguishing techniques, the energy of the arc can be mitigated, thereby minimizing damage to the contacts and extending the product’s lifespan. Consequently, strong arc‑extinguishing capability is a fundamental requirement for relays.

5. Strong breaking capacity

Automotive operating conditions are highly complex, and in emergency situations—such as an electrical system short circuit—the current in the circuit can surge instantaneously. Under such circumstances, the relay must reliably interrupt the circuit at extreme current levels without experiencing contact welding or relay failure, thereby preventing safety hazards like battery over‑discharge, short circuits, or explosions. This necessitates that the relay contacts possess excellent shock resistance and anti‑welding performance.

III. Types of High-Voltage DC Relays

From the perspective of application type, vacuum‑type and gas‑filled relays currently account for the largest share of high‑voltage DC relay applications in new energy vehicles.

Vacuum is an ideal insulator. Since high‑voltage arcs arise from the ionization of insulating media, and vacuum itself contains no medium, it provides excellent isolation between contacts. However, a perfect vacuum is only an ideal condition; in practice, trace amounts of oxygen remain. In the presence of an arc, this residual oxygen reacts with the copper electrodes to form copper oxide, increasing contact resistance and posing a risk of relay failure.

At present, gas‑filled relays are predominantly used, with hydrogen and nitrogen serving as the primary arc‑extinguishing media. When pure hydrogen is employed, an auxiliary deflection magnet is added to enhance arc extinction; this approach outperforms vacuum‑pumping and nitrogen‑filling in terms of arc‑quenching effectiveness. Hydrogen exhibits excellent insulating properties and is difficult to ionize.

Introduction to the Principle of High-Voltage Relays:

A high-voltage relay, in simple terms, is an automatic switch that uses a small current to control a much larger current. It performs functions such as automatic regulation, safety protection, and circuit switching within the electrical system. The primary purpose of high‑voltage relay control is to ensure the proper energization and de‑energization of the battery system: it closes to apply power when the vehicle starts and opens to disconnect power when the vehicle is stopped and the engine is turned off. As part of the automotive electrical and electronic system, failure modes of the high‑voltage relay can pose a risk to driver safety; therefore, it should be developed in accordance with the ISO 26262 standard to meet functional safety requirements.

High‑voltage relay status monitoring primarily involves checking the contact states of the relay to determine whether its operating condition meets control requirements, thereby preventing the application of electrical loads to the high‑voltage circuit when the relay is open and avoiding the disconnection of the relay under substantial load conditions. Contact inspection of the high‑voltage relay can accurately detect sticking or welding of the contacts, thus preventing inadvertent operation that could damage components in the high‑voltage circuit; at the same time, proper switching (opening/closing) of the relay helps extend its service life. For contact detection, either a high‑voltage relay equipped with auxiliary contacts is used, or an independent auxiliary‑contact detection circuit can be designed; by measuring the voltage across the relay’s contacts, the open/closed state of the contacts can be determined.

Two typical technical approaches for high-voltage relays (ceramic sealing and epoxy resin sealing)

Ceramic sealing—this technological approach is exemplified by Panasonic; the other is epoxy resin sealing, represented by TE.

Why are high‑voltage DC relays filled with gas? What is the arc‑extinguishing principle of gases? Why do ceramic‑encapsulated relays (e.g., Panasonic) use hydrogen, while epoxy‑encapsulated ones (e.g., TE) use nitrogen? The key difference between DC and AC lies in the absence of zero crossings in DC; once an arc forms, it does not self‑extinguish and will persist, causing severe damage to the contacts. What, then, is the nature of an electric arc? It is the emission of electrons under the influence of an electric field—an extreme form of discharge. Consequently, there are two primary methods for arc extinction: one is to increase the contact gap (magnetic blowout essentially uses the Lorentz force to deflect the arc path, effectively widening the gap; if the gap is merely enlarged mechanically without magnetic blowout, the required magnetic air gap becomes excessively large, resulting in unacceptably bulky and heavy devices for the same load‑carrying capacity). The other approach is to introduce a substance between the contacts that can block the electron flow; the most effective solution is to fill the gap with a gas. Gas filling must meet specific criteria: first, the gas should be highly reactive, as reactivity enhances collisions with electrons emitted by the arc, producing a blocking effect and efficiently carrying away heat. Second, the gas’s molecular structure must be stable, preventing its own electrons from escaping easily. Based on these requirements, hydrogen emerges as the preferred choice for arc extinction: it has the lowest molecular weight among all gases, exhibits exceptional reactivity, and possesses a sufficiently stable molecular structure. This explains why manufacturers like Panasonic and Hongfa adopt ceramic encapsulation, as they rely on this technology. Why does TE opt for nitrogen instead of hydrogen? Because their products use epoxy resin encapsulation. Hydrogen is indeed the optimal arc‑extinguishing gas, but its low molecular weight makes it difficult to contain within an epoxy housing without leakage. Thus, TE settles for nitrogen as a second‑best alternative.

At present, Huanfang Electrical offers two product lines: ceramic-sealed high-voltage relays and epoxy-resin-sealed high-voltage contactors.

Initial selection of high-voltage relays:

1. Understand the customer’s preliminary requirements, such as rated voltage, rated current, peak charge/discharge current, duration of the peak current, seismic performance, operating environment specifications, altitude, and vehicle‑specific operating simulation conditions, among others.

2. Common parameters of high-voltage relays include: contact ratings, normally open contacts, normally closed contacts, performance specifications, insulation resistance, dielectric strength, operating current, operating voltage, mounting hole dimensions, and mounting hole size, among others.

3. First, select a compatible model based on the rated voltage. Most high-voltage relays have a wide voltage range, making them suitable for a broad array of applications; this is provided for reference only.

4. Based on the rated current, further narrow down the selection to choose a model; select a high-voltage relay with a rated current that is higher than and closest to the specified value. For example, if the rated current is 200 A, and a particular manufacturer lists a 200-A-rated high-voltage relay with a nominal rating of 250 A, temporarily select the 250-A version.

5. Estimate the expected service life based on the peak current provided by the customer.

6. Estimate the short-circuit current based on the battery pack’s electrical performance; use this estimated short-circuit current to further assess the short-circuit current; and, based on the circuit current, estimate the failure time of the high-voltage relay.

7. A relatively important step: Compare the failure times of the high-voltage relay and the fuse during a short circuit. The relay’s failure time should be longer than that of the fuse; you can perform this comparison yourself or have your company conduct it.