Electric Vehicle Conversion/Battery disposition, security, and wiring

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Note the presence of hazardous materials and conditions that must be approached with proper precautions and procedures to avoid damaging, injurious, or even fatal consequences.

Separate from passenger compartment[edit]

It is considered highly desirable to separate the traction batteries completely from the passenger compartment. As the batteries form a substantial portion of the vehicle weight it is very desirable to place the batteries as low as possible in the vehicle as this enhances stability, greatly reducing the probability of rollover. Owing to the bulk of the batteries and particularly their height, this placement can be quite inconvenient in most vehicles. This is why light trucks are strongly preferred as conversion vehicles as they can offer substantial volume around the frame rails without adversely reducing ground clearance.

Protected from road hazards[edit]

For any vehicle the protection of the batteries from road contact or road debris must be carefully considered. While it is good to place the weight as low as possible the batteries should not be directly exposed to road hazards. The cases on modern batteries are relatively thin and if the plates of a cell are damaged they can overheat from the short circuit. The internal contents of most batteries are also hazardous.

Note that more than just the bottoms and sides of the batteries should be protected, since if it is possible for a conductive piece of road trash to be flipped to the terminal part of the batteries this could create a shock hazard or a short circuit and possibly a fire.

Battery security[edit]

The batteries must be well-secured to the vehicle. This is very important, since a loose battery might cause contact between the terminals and some part of the vehicle, causing a dangerous short circuit and potentially a fire or battery explosion. A pull-up security factor of 4g0 is recommended; that is, the battery mounts should withstand negative forces of four times the battery weight, for security in case the vehicle rolls over in an accident.

Battery access[edit]

The batteries must be accessible for testing, cleaning, replacement, tightening of connections, and periodic service where this is required (such as the addition of water to wet cells).

Weight distribution[edit]

Battery location is one of the most important factors determining vehicle functionality and safety. If the batteries are placed low in the vehicle it will have less tendency to tip and rollover. If too much weight is distributed to the front the vehicle will be hard to steer without power steering and the vehicle will be somewhat unresponsive. If too far to the rear the vehicle may be unstable in hard turns, tending to "swap ends", although for specialty performance cars (such as are used in autocross racing) this "oversteer" may be an advantage when controlled by a well trained and experienced driver.

Moment of inertia[edit]

For purpose-built vehicles and some electric truck conversions, it is advantageous for handling to concentrate the battery mass near the center of the vehicle. This may be done by placing the batteries in a tray between the frame rails, in a center console, or in a "saddlebag" configuration on each side of the passenger compartment. In a custom built vehicle a center console may also contain batteries.

For conversions of most common passenger and sports cars there is insufficient centrally located volume for batteries. As it is considered undesirable to place batteries within the passenger compartment this will usually lead to a "dog bone" configuration. Batteries will be placed both in the front compartment and a rear compartment (the latter created sometimes by raising the floor of the trunk, using the location of the original gas tank. This configuration can be particularly effective in earlier Volkswagen models such as the original "beetle" and the type 3, since separate compartments are built into the vehicle for luggage storage (in the front) and the motor and its cooling fan (in the rear). Owing to the distribution of mass the vehicle will have a high polar moment of inertia. This will assist it to track well on straight line highways but will reduce its nimbleness in other road conditions.

Height of center of mass[edit]

It is highly desirable to place the batteries low in the vehicle while protecting them from road hazards.

If a light truck is converted the batteries should be between the frame rails or in a dropped battery box setting atop the rails at their low point (not at the "kick up" over the rear axle) but with their bottoms below bed level. This is especially important if a truck with taller ride height is used. Most light trucks are available in a two wheel drive version that will sit fairly low and sometimes these are available in long frame models (such as the Mazda B-2000 "Sundowner"). Other examples include trucks from Mazda, Nissan, Toyota, Ford Courier (a re-badged Mazda), the Chevrolet S-10, and the GMC S-15. In long frame light trucks a long bed version, rather than a short bed—long cab is preferred unless extensive cab modifications are to be made for isolated battery placement. Note that it is important that the batteries be protected from road hazards and that the exposed connections at the tops of the batteries are not exposed to trash flipped up from road level.

Many light truck converters install a hydraulic bed lift - intended to convert the pickup into a light dump truck. This allows easy access to battery boxes below the bed.

Caution: If such a system is installed this must include a positive mechanical up lock, so that the batteries may be safely accessed without relying on the hydraulic system to keep the bed up.

Electric Vehicle Conversion Index

  1. Technologies
  2. Powertrain
  3. Battery disposition, security, and wiring
  4. Auxiliary systems and control
  5. Chassies, suspension, and running gear
  6. High power electrical
  7. Controls, interlocks, indicators, and alarms
  8. Conversion of concrete vehicles
  9. Resources