EV Fuses – Special Requirements for Electric Mobility

Electrical vehicles are gaining popularity and market shares stronger than ever before. Especially hybrid electrical vehicles (HEV) are being sold in high quantities lately, but also purely battery electric vehicles (BEV) are considered having good prospects. This is not only explained by falling material costs and subsidies, but also by the growing environmental awareness of the people.

Protecting Essential Electric Components

Just as every other car, electrical vehicles contain electrical components which need to be protected from dangerous overcurrent and short circuits. On top of these lower-voltage components, EVs also have high voltage DC parts like high-capacity battery packs, power conversion devices, air conditioning and other auxiliary circuits. Being direct current, fuses for these applications must meet special requirements for a safe and reliable operation.

The same applies to EV fast charging stations which are able to deliver high DC currents. They are an important pillar of e-mobility and the appropriate protection is important for making them reliable and available.

Unfortunately, currently there is only a very limited number of international standards defining the fuse selection for EVs and charging stations. Thus, EV or charging equipment manufacturers tend to use “off-the-rack” semiconductor or even AC fuses by only looking for the needed current/voltage rating. These may be less expensive than proper DC fuses and work well for the purpose they have been designed for, but do not meet automotive requirements at all. Considering the high value of the high voltage EV components such as battery packs, they should be protected the best way possible. It is reasonable to spend a little more on the correct fuse than having your expensive equipment damaged in case of a fault current that the cheaper, wrongly selected fuse couldn’t handle.

Special Requirements in a Special Application Field

Since they are built into moving vehicles, EV fuses must follow automotive standards. As long as there is no explicit standard, current general standards should be applied as close as possible, for example ISO 8820-8 and JASO D622. These concern fuse links for road vehicles in general and “Automotive parts - Bolt-in type high-voltage fuse-links”, respectively.

When the aforementioned standards were established, BEVs were not yet considered. They only cover the use of fuse links with a rated voltage of 450 VDC, which is enough for HEVs, but not for higher-voltage circuits found in BEVs. As a result, fuses have to comply with even higher requirements than these standards. These requirements are generally self-defined and self-tested by the fuse manufacturers or in accordance with the customer’s wishes.

The aR characteristics found in many ready-made fuses don’t provide the needed electrical requirements, as it lacks overcurrent protection. To prevent long-term damage on electrical equipment, the fuses must have relative low minimum interrupting ratings of about 1.3 times of the rated current. A high breaking capacity serves the purpose of withstanding and breaking short-time short circuit currents.

Also the construction has to be customized into the automotive environment. The limited space favors compact fuse formats which have high capacities to withstand mechanical stresses and still have the required electrical properties. Instead of ceramic fuse bodies, whose mechanical hardness doesn’t suffice, laminated glass fiber bodies provide a steady shape to integrate the fuse in. For highest precision and an ideal arc quenching, fuse elements completely made of silver are recommended. Contact links made of silver-plated copper conduct the energy with a low power dissipation.

Providing Protection Equipment and Support for Customers

Fortunately, there are fuse manufacturers supplying customers with application-oriented EV fuses matching for different situations. Not uncommonly, they also provide their customers with guides or assistance at choosing the right fuse. For them it is also more easily possible to fulfill the clients’ wishes than for companies only offering mass-produced goods.  

Considering the expected market growth of electric vehicles, the demand for mandatory guidelines on using EV fuses is already noticeable in the industry. It is just a question of time that an international standard will be established. Possibly, it will be based on the existing JASO D622 and ISO 8820 standards. So manufacturers such as ADLER, who already design their EV fuses according to these standards, are paving the way for a practical worldwide standard.

Copyright © ADLER Elektrotechnik Leipzig GmbH 2017