The EV/HEV High Voltage Fuse applications market ecology is mainly composed of manufacturers such as Eton, Littelfuse, Sensata, Mersen, EV/HEV fuse tube from wellele.com and fusestube.com Pacific Engineering, Siemens, ON Semiconductor, etc. In order to select the right high-voltage fuse for EV/HEV development models, it is necessary to understand the performance parameters of the fuse itself (voltage drop, temperature rise, breaking characteristics, temperature shock, vibration resistance, etc.) and the key characteristics of DC protection (e.g. L/R time constant), in addition to the actual application engineering of the high-voltage electrical platform of the model (considering collaborative protection, etc.).
Fuse selection key parameters are as follows: Table 1. Fuse parameter base requirements
[Rated Voltage] The rated voltage rating of a fuse determines the magnitude of the ability to suppress arc discharge. If a fuse is used below the maximum voltage of the circuit, it may not clear the risk of overcurrent under some overcurrent conditions. Therefore, fuses for EV/HEV must have a voltage rating greater than the maximum circuit voltage. Among others
It is worth noting that:
a) the maximum circuit voltage is not the nominal or maximum operating voltage of the vehicle’s power cell, but the actual peak voltage of the circuit that may occur under various operating conditions (including fault voltage).
b) The DC nominal operating voltage of the protection device given by the manufacturer usually corresponds to a circuit with a specific inductance, and if the relative inductance in the circuit increases (L/R time constant increases), the rating must be reduced.
c) The sinusoidal characteristics of AC (natural past zero) help the fuse to extinguish the residual arc, which is not the case in DC systems where the EV/HEV voltage is kept constant. Some AC fuses are also suitable for DC circuit applications, but there is no “rule of thumb” for safely converting the AC voltage rating on a fuse to a DC voltage rating, so testing is the only reliable way to determine the DC voltage capability of a calibrated AC voltage fuse. In view of this, manufacturers based on traditional industry fuses need to be tested for specific applications to launch new DC fuses for EV/HEV.
[Current Rating] The fuse current rating is the RMS current it can carry continuously. In the EV/HEV environment, the fuse current rating value needs to be re-evaluated for each specific application to ensure that the selected fuse does not exceed its current carrying capacity resulting in premature aging or false operation. a) The actual RMS steady-state load through the fuse, without considering the effects of overload and cyclic load current shall be less than or equal to the calculated maximum allowable load current rating – the basic selection criterion for fuse current rating. Under the conditions applicable to IEC60629, UL248 industry standard, the fuse application characteristics have been extensively tested in practice and there is a consensus that derating is required in environments affected by different conditions (e.g. temperature derating, thermal connection derating, high altitude derating, etc.). For automotive applications, the performance of parameters such as rated voltage levels and current-time fusing curves provided by the fuse manufacturers are derived under specific test conditions, so selection corrections are also required under different environmental conditions. Table 2. Fuse test conditions and vehicle application environment