Relay vs. MOS for High-Current BMS: Which Is Better for Electric Vehicles?

When selecting a Battery Management System (BMS) for high-current applications [https://www.dalybms.com/high-current-bms-products/] like electric forklifts and tour vehicles, a common belief is that relays are essential for currents above 200A due to their high current tolerance and voltage resistance. However, advancements in MOS technology are challenging this notion.

In terms of application coverage, modern MOS-based BMS schemes now support currents from 200A to 800A, making them suitable for diverse high-current scenarios. These include electric motorcycles, golf carts, all-terrain vehicles, and even marine applications, where frequent start-stop cycles and dynamic load changes require precise current control. Similarly, in logistics machinery like forklifts and mobile charging stations, MOS solutions offer high integration and fast response times.Operationally, relay-based systems involve complex assembly with additional components like current transformers and external power sources, requiring professional wiring and soldering. This increases the risk of virtual soldering issues, leading to failures like power outages or overheating over time. In contrast, MOS schemes feature integrated designs that simplify installation and maintenance. For example, relay shutdown requires strict sequence control to avoid component damage, while MOS allows direct cutoff with minimal error rates. Maintenance costs for MOS are 68-75% lower annually due to fewer parts and quicker repairs.

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Cost analysis reveals that while relays seem cheaper initially, the total lifecycle cost of MOS is lower. Relay systems need extra components (e.g., heat dissipation bars), higher labor costs for debugging, and consume greater than or equal to 5W of continuous energy, whereas MOS consumes less than or equal to 1W. Relay contacts also wear out faster, requiring 3-4 times more maintenance annually. Performance-wise, relays have a slower response (10-20ms) and can cause power "stuttering" during rapid changes like forklift lifting or sudden braking, increasing risks like voltage fluctuations or sensor errors. In contrast, MOS responds in 1-3ms, providing smoother power delivery and longer lifespan without physical contact wear.

In summary, relay schemes may suit low-current (



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