Overcurrent Protection for Electric Hybrid Electric Vehicles

by with Comments Off on Overcurrent Protection for Electric Hybrid Electric Vehicles
October 28, 2012

Hybrids and EV’s are becoming increasingly popular. Not just the passenger vehicles you see on the road, but also smaller vehicles such as NEVs (Neighborhood Electric Vehicles), LSVs (Low speed Vehicles), ESVs (Essential Services Vehicles), and the myriad of other small utility vehicles being imported or imported and finished in the US. Despite this increase, few options are available for these vehicles for overcurrent protection due to their unique challenges. Some of these challenges are:

  • Automotive reliability. These vehicles may not always fall under the strict requirements of 4-wheel passenger vehicles (NEVs, LSVs, and any 3-wheel vehicles do not), but they still are subjected to the same environment.
  • Medium voltage. While 72V, 144V, 288V may be considered medium voltage to those in the circuit protection industry, this is an extremely high voltage compared to the rest of the 12V (and less) systems normally found in an automotive environment. This may sound minor but it can be very hard to find fuses (and holders) that fit these voltage levels.
  • Unique activation current requirements and curves. Unique solutions for the EV world have unique requirements. Many Battery Electric Vehicles (BEV) and larger hybrids will run motor currents as of 300A, 400A, or higher. To avoid damage to high-cost items, and reduce the risk of fire, a very sharp time-current/I2t curve is needed. Also, the high cost of DC-DC converters to drive 12V accessories, and the lack of an internal combustion engine to power things like AC compressors or power steering, pushes many of these high power items to the traction battery. This means that overcurrent protection is needed that can handle large initial surges (such as with PTC heating elements), as well as repetitive surges.
  • Environmental requirements. Again, with the environment of the automobile, many different requirements come into play, primarily heat, moisture, and chemical or salt. This is typically not an issue for lower current devices operating at 12V, but for higher voltage branch or accessory circuits, or higher current devices (such as a 400A main fuse), there are fewer options available.

The “Big 3” and other established automakers already have strong relationships with existing suppliers. Even if they are working on a new product, prototype, or low-volume production vehicle, they can leverage that relationship to develop new devices. Many such devices exist that are often hidden in different supplier catalogs and can be very hard to find.

For the industrious engineer, devices can be found for higher voltage systems by searching for these devices simply by voltage. Devices made for forklifts, telecom (their battery systems), and light rail can be a good source of devices. Often, finding a viable fuse holder becomes an issue, as is the case with ATC/ATO types. High-current ANL/ANN fuses for the forklift industry are plentiful but holders are typically open to the environment. Mega, Maxi, J-Case, and Mini varieties have similar issues. Interestingly, glass fuses, which have seen a huge drop in popularity, provide a fair number of options for higher DC voltages than just 12V (usually rated at 32V) automotive fuses.

Far too many engineers simply ignore the voltage requirement which may risk delayed opening times, overheating, or fire. Even worse some engineers neglect to put circuit protection at all on their circuits, which can be disastrous. Some EV batteries can run as high as 400VDC and provide thousands of amps of current. Do you know what sort of welding you can do with that energy?

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