The Basics
Fuses are protection devices that protect electrical circuits against undesired high currents. We can use passive fuses and pyro fuses in battery design.
Selecting a Fuse
- Select a fuse rated double as continuous current (e.g. initially take 400A fuse for 200A continuous current) and draw the load profile next to 50% of the fuse breaking current-time chart to check if pulse currents can be carried by the fuse without aging.
- Calculate the components and the fuse breaking energy (I2Rt) to ensure that the weakest component is the fuse.
- Identify the minimum breaking current for the failure cases when the contactor cannot switch-off.
- Analyze the short circuit clearing time and check if the contactor can withstand until the fuse breaks the circuit.
- Check the contactor-fuse coordination for normal operation, overloads and failure currents.
Manufacturers
The fuses in a battery pack protect the battery and the other electrical components against high currents. There are special off-the-shelf components similar to 12V starter battery fuses. However, EV fuses are rated for high voltage and traction currents. The page has a list of EV fuse manufacturers.
Cell Level Fusing
When we connect cells in parallel to increase the capacity we might also want cell level fusing. This fusing being by definition designed to disconnect a cell that for some reason is sinking or delivering high currents.
The fusing can be inside the cell and sealed or external to the cell, sometimes both internal and external fuses are used.