Differences between High Voltage DC relay and solid relay
| Comparison item | High Voltage Dc Relay | Solid-state Relay |
| Core principle | Mechanical contacts are driven to close/open by the magnetic force generated by an electromagnetic coil, enabling circuit on/off control. | The on-off function is entirely achieved through semiconductor electronic components, with no mechanical moving parts. Electrical signal isolation and power control are realized via optocouplers, thyristors/MOSFETs, etc. |
| Rated voltage range | Typically designed for high-voltage DC applications above 1000V, some high-voltage models can accommodate DC systems at the 10kV level. | High-voltage DC systems typically cover the voltage range of 600V to 1500V, with fewer products available at higher voltage levels and consequently higher costs. |
| Static voltage drop | The contact resistance of mechanical contacts is extremely low (in the mΩ range), resulting in minimal power loss and heat generation under high current conditions. | Semiconductor devices exhibit inherent on-state voltage drops (approximately 0.3–1V for Si-type MOSFETs and 1–2V for IGBTs), leading to significant heat generation under high current conditions. Therefore, thermal management design must be implemented. |
| Switching speed | Mechanical contact movement requires millisecond-level time (typically 5–50 ms) and exhibits bouncing phenomena. | Microsecond-level response speed, contactless bounce, ideal for high-frequency switching applications |
| life span | Mechanical contacts experience arc erosion and wear, with a load-switching lifespan typically ranging from 10^4 to 10^6 cycles, while the no-load lifespan can exceed 10^7 cycles. | No mechanical wear is observed, with a theoretical lifespan ranging from 10^8 to 10^12 cycles. The lifespan is primarily influenced by temperature and overcurrent stress. |
| Isolation performance | Physical isolation after contact disconnection, high insulation withstand voltage, and almost zero leakage current in open state | Due to semiconductor junction isolation or optocoupler isolation, μA-level leakage current exists in the open state, making it unsuitable for safety scenarios requiring complete electrical isolation. |
| Overload capacity | Demonstrates strong short-term overload capacity, capable of withstanding 10 times the rated current for several milliseconds. | Semiconductor devices have weak overload capacity, typically only able to withstand 1.5 to 2 times the rated current, and overcurrent can easily cause damage. |
| Applicable scenarios | High-voltage energy storage systems, DC charging piles, high-voltage distribution circuits, and high-voltage distribution boxes for new energy vehicles require scenarios with high-reliability isolation and high-current switching capabilities. | Industrial automation control, low-power DC load regulation, explosion-proof environment, high-frequency switching scenarios, low-vibration requirement scenarios |
| Cost control | The cost is moderate for the same voltage and current rating, while the high-voltage and high-current model has a lower cost compared to solid-state relays with identical parameters. | High-voltage and high-current models incur higher costs, and the thermal management system further increases the overall solution cost. |
In the high-voltage electrical system applications of new energy vehicles, high-voltage DC relays are currently the mainstream and more suitable options. Solid-state relays are only used in a few specialized auxiliary scenarios, such as LED lighting groups on the vehicle body, small-power sensor arrays, and noise-free control of automatic doors/windows in low-voltage scenarios. They mainly take advantage of the advantages of solid-state relays, such as no mechanical noise, fast switching speed, and long lifespan.
The core of the power system of new energy vehicles is the high-current transmission between the battery and the motor. Compared to the 12V low-voltage system of traditional vehicles, the high-voltage platform of new energy electric vehicles is usually at 400V or even 800V. The current transmitted from the battery to the motor and control unit can reach tens to hundreds of amperes. Therefore, as the primary consideration for safety factors, the structural characteristics of high-voltage DC relays will fundamentally meet the vehicle safety standards:
High-voltage DC relays use high-conductivity materials and optimized terminal structures to reduce the risk of overheating. After the contacts are disconnected, high-voltage DC relays can achieve complete physical isolation. The insulation withstand voltage can reach above 30V, and the leakage current is almost zero, avoiding the hazard of high-voltage leakage to passengers and low-voltage systems. While solid-state relays rely on semiconductor junction isolation, they have micro-ampere-level leakage current and cannot meet the safety standards for complete disconnection of the high-voltage circuit.
When a short circuit occurs in the vehicle's high-voltage system, the instantaneous current can be more than 10 times the rated value. The maximum breaking current of high-voltage DC relays is generally several thousand or even tens of thousands of amperes. Combined with the hydrogen/hydrogen gas/magnetic blowout arc extinguishing structure filled in the ceramic sealed enclosure, it can extinguish the high-temperature arc in milliseconds and cut off the fault current, fundamentally avoiding the risk of short-circuit fire.
High-voltage DC relays generally adopt ceramic brazing or epoxy sealing structures. The ceramic breakdown strength reaches 18KV/mm, and the tensile strength exceeds 280Mpa. They can withstand wide temperature ranges (-40℃ to 125℃), high-intensity vibration, and impact under complex vehicle conditions. The protection level can reach IP67, and the long-term reliability is much higher than that of solid-state relays.