There are different types of circuits in an EV. Choosing the appropriate fuses depends on each circuit’s requirements. In the circuit for numerous auxiliary applications such as heater, air conditioner and ECU, various requirements are assumed. The fuses for this circuit must withstand the maximum current at normal use without melting, and quickly interrupt the accidental fault current not to affect the upper circuit.

The following characteristics should be considered when selecting EV fuses. The fuse must be able to withstand rush current or transient current during normal usage, and must prevent the circuit devices from smoke or fire caused by abnormal current. Therefore, the rated current of the fuse is evaluated in reference with the I-t /I²t-t and temperature re-rating curves. To avoid nuisance fusing, a sufficient margin should be considered, which differs depending on fuse types or fuse manufactures. The voltage of EV batteries has increased in order to reduce power loss and charging time. The higher voltage tends to prolong the arc current, which can increase the risk of damaging the fuse itself. The maximum voltage that the fuse can safely interrupt should be considered together with the rated breaking current. The rated voltage must be larger than the circuit voltage. Since the size of fuse is closely related to the rated voltage or interrupting capacity, it is important to select an appropriately sized fuse. Large current flows may generate heat due to the contact resistance at the junction, therefore, we recommend bolted-connection-type fuses to ensure solid mounting. Fuses are affected by ambient temperature. The inside of an EV has a relatively higher temperature compared to other electrical appliances. The ambient temperature should be within the range recommended by the fuse manufacturer. This may require careful review of the margin or rated current. The I-t curve of a fuse is used to select a fuse which will successfully operate under the given conditions of the short circuit withstand of relays or the fuming characteristics of wire. In the high-voltage EV circuit, the fuse element will melt to interrupt the small accidental current as indicated in the relevant I-t curve. However, there is a possibility of the arc current continuing if the melted part of the element is too narrow to interrupt the current. Therefore, the minimum breaking current should also be considered.

The conventional current waveform, which consists of the inrush current at power-on and the constant current at normal use, can be used to select an appropriate fuse in reference with the conventional I²t-t curve and I-t curve. However, the current waveform in the EV circuit is usually complex and may not always be properly evaluated by I²t-t curves readily available. This evaluation requires extensive work. SOC can assist with selecting appropriate fuses for each customer’s application. Please feel free to contact us.

EV relays are used to open and close high voltage circuit. To prevent secondary damages caused by the burning of the relay contact, the evaluation of the protection coordination matching between fuse and relay will be critical. SOC can provide a matching test for EV relays and fuses. Please do not hesitate to contact us. (more information is available in our Technical Paper: How We Test Our Fuses).

SOC manufactures various EV (BEV/HEV/PHEV/FCV) fuses. For example, the PT series, which is designed for main circuit, has large rated voltage and rated current, excellent pre- arcing characteristics, and high durability to protect EV circuit (more information available in our Application Note: PT Series). We have other EV fuses which are not shown on our website, so please feel free to ask us.

Selecting appropriate EV fuses for each application is critical for the safety and reliability of the system. This guide provides some key points useful in choosing fuses, and we strongly recommend contacting us on specific points that interest you. SOC has highly experienced engineers who are more than happy to explain how to select the best fuse for your circuit. We also provide fuse seminars tailor-made for our customers. Please feel free to contact us by phone or e-mail.