As electric vehicles (EVs) proliferate, so to do the need for good and reliable charging solutions. At the heart of such charging systems — and many other power electronics applications — is the requirement for good electrical protection: fuses protect against overcurrent in devices such as EV chargers, power inverters or other power electronics, devices that could otherwise become damaged, start a fire, or otherwise enter a dangerous state.
In this article, we review the main fuse types for EV chargers and power electronics.
Key Considerations for Fuse Selection
In selecting fuses for use within EV chargers and power electronics generally, the following are considered:
Voltage Rating
Fuses must of course be rated for the voltage level that they will be seeing in that part of the application. For EV chargers, this might be in a low voltage gradient (for a residential charger), through to higher voltage for fast chargers and commercial charging stations. The voltage rating of the fuse must obviously be greater than the operating voltage of the circuit, to ensure correct operation.
Current Rating
Similarly, the current rating of the fuse should be approximately equal to or slightly greater than the maximum current that the system will be undertaking in normal circumstances: but the fuse must blow if the limit is exceeded, in order to avoid greater damage.Time-current Characteristics
Different applications require different time-current characteristics from fuses in this arena: a slow-blow fuse might be suitable for use in a motor driver, and thus can be found in the likes of high power inverters; yet a fast-acting fuse may be the order in the likes of a charging station, for example, where rapid protection is required in that manner.
Fuse Type
There are a number of types of fuse which might be applied in your power electronics applications: Cartridge fuses for use in relatively high current applications such as power inverters and EV chargers. These are available with all sorts of characteristics- some available with very large interrupting capacity suitable for dealing with short circuits and so on. Blade Fuses: These small blade-style fuses are used in low voltage applications, including many vehicle applications; however they may also be used in residential EV chargers to protect some smaller devices. Resettable Fuses (PTC): PTC( Positive Temperature Coefficient )devices protects against overcurrent, can depend on the requirement of the application etc, and often reset themselves automatically once the cause of the fault has cleared. Such devices can also be suitable for circuit protection. Interrupting Capacity: The ability of the fuse to “break” the current in a safe manner is pivotal in all applications, but at higher voltages and ampies particularly in a device like an EV charger.Interrupting Rating: The rating of the fuse must be sufficient for the application, with an extra margin of safety provided to eliminate the risk of further serious damage.
Environmental Conditions: The fuse may be used in environments where it is subject to extreme temperatures, and/or high humidity and other such potential risk factors, and therefore must be rated accordingly, as appropriate, for example in industrial and outdoor applications.
Common Fuse Types Used in EV Chargers and Power Electronics
Common high voltage cartridge fuses: This is a common fuse type that is relied on for proven protection, often comparatively very high voltage and interrupting rating, for overcurrent and short circuit protection for high voltages; including in vehicle and EV charging stations and including
Automotive Blade Fuses: Protecting low voltage circuits, for the high volume automotive and light vehicle application and for residential charging applications.The devices are easily replaced and less expensive and come in a very wide range of current ratings.
Fastacting fuses including fuses intended for DC voltage applications. Devices on circuits where a circuit must be instantaneously interrupted, which can include power electronics, power diodes, MOSFETs and other devices in an EV electrical system.Slow-blow fuses – fuses which are suitable for circuits where suddenly starting up or other transients may cause a spike in current; these fuses are allowed a short duration overcurrent without opening the circuit. This fuse is commonly used in an EV’s motor and battery control circuits.
Fuse Selection for Specific EV Charger Applications
Level 1 and Level 2 Charging Stations. Used at pretty low voltages of 120V and 240V, these stations usually require fuses which are designed to carry moderate levels of current, and also fuses which fit in small enclosures. Typical fuses are of the blade type, or small cartridge fuses with a proper current and voltage rating. DC Fast Chargers. Used for charging EVs at the best possible speed, these fast-charging stations operate at very high voltage (up to about 800V) and high current, requiring robust protection. High voltage cartridge fuses with high interrupting capacity can be typically found in such systems, protecting them from possible overcurrent conditions and of short circuits at the charging station. Onboard charging systems in EVs. The systems responsible for charging the batteries in an EV must be protected from overcurrent while it is being charged, with a suitable fuse necessary to protect the onboard charging systems. The best fuse in this application is one that is rapid-action, compact and offers high reliability. Summary Choosing a suitable fuse for EV chargers and other applications in public charging stations and can be a real challenge. It can be a challenge for manufacturers, as well as people who develop and build the electric vehicles themselves. Taking into consideration the voltage and current ratings and the characteristics of the fuse to be used, and the type of fuse can make all of the difference between safety and risk. With the proliferation of EVs on the roads, the boom in EV charging stations and power electronics systems simply cannot afford to use the wrong fuse.
