Lightweight Electric/Hybrid Vehicle Design

Viable energy storage systems 31
Fig. 2.2. The performance issues of these cells are complex. Amazingly there are 14 different
types of sealed Ni–Cad cells in four main product groups: (a) standard, (b) high discharge current,
(c) fast charge and (d) high temperature.
It is the double-sintered fast charge cells that are used in model aeroplanes and in the world
championships the Sanyo Cadnica is specified using a 1.7 Ah cell. A Tamiya connector can deliver
up to 32 amps. Battery packs of 7.2 V six packs are usually fitted. In the power tool area, Black
and Decker have the Versapack, a three cell string. Two or four strings are used in series with
larger cordless power tools. One problem is that sealed Ni–Cad cells cannot be connected in
parallel. At the end of the charge cycle, the cell voltage falls, causing rapid charge/discharge
between parallel cells. On the face of it, the packaging problem is daunting, with more than 2000
cells in a pack.
Sony/Nissan battery pack
Specifications of prototype cell
Rated capacity 22 Ah
(4.0 V)
Cell shape Cylindrical
Dimensions, mm D50 x L250
Weight 1.2 kg
(b)
FR
Ventilation hole
Air intake duct
Rib
Battery case
Battery package
Air flow
Prototype module
Module case
Fans