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The 2008 AEVA Electric Vehicle Field Day by Leo Simpson T his year’s field day for the Australian Electrical Vehicle Association, held at Annagrove in western Sydney during late October, had a range of interesting electric and hybrid electric vehicles on show. Some were fully converted cars that are driven on a regular basis while others were “works in progress” which may be up to a year or more away from completion. There was also a Toyota Prius which had been modified with extra battery capacity and an on-board charger. At the outset it must be said that anyone who decides to convert any conventional vehicle to electric drive is taking on an ambitious project. Typically, the way they go about it has never been done before: to convert exactly that vehicle type or model, using that combination of motor, batteries, controller etc. So the AEVA annual field day is very much a display of DIY electric 78  Silicon Chip The AEVA field day at Annangrove was pretty basic in format – just a big open shed with lots of electric car enthusiasts poring over the cars. There was even an electric go-kart – with neck-snapping acceleration! siliconchip.com.au (Opposite): star of the show, Carmel Morris with her Mitsubishi Starion conversion, also shown above. It uses an array of lithium iron phosphate batteries in the boot and bonnet compartments. The DC motor is run by a Curtis controller. The sheet of Lexan over the engine compartment is to prevent any of the viewers touching the battery array – it could be quite lethal! vehicle conversions rather than an expo of the latest up-tothe-minute technology. And no doubt, all the owners would go about such a conversion quite differently if they were going to repeat the process – such is the value of on-the-job experience. As far as we could tell, all the electric conversions on display used DC motors with wound fields and they ranged in power up to about 70kW. Such a power rating may not sound numerically impressive compared with typical petrol motors which can be up to 200kW or more. But whereas the 200kW rating for a petrol motor is an absolute maximum rating which is rarely, if ever, likely to be delivered (or even available at the wheels), a 70kW motor is quite likely to be able to deliver three times the continuous power for short periods. As well, electric motors deliver close to their maximum torque at very low revs, so an apparently modestly-powered motor can give quite sparkling acceleration. Most, if not all the electric conversions on display used one or another model of motor controller made by the US company Curtis. These essentially have a bank of power Mosfets operated in PWM (pulse width modulation) mode This 2002 Holden XC Combo van had the usual DC motor and Curtis controller and was powered with 16kWh’s worth of Trojan wet cells. They occupy a fair amount of the cargo space, as shown in the photo below. It is used for daily commuting of about 35km each way and takes about 4.5 hours to recharge after each trip. There was even a VW Beetle EV conversion. There are more batteries inside the (front) boot, as well as those on view in this photo. While the batteries take up a lot of space in the Combo van, the all-up weight is not excessive at 1540kg. Best feature according to the owner is the electric power steering. siliconchip.com.au December 2008  79 Extra batteries added to this Toyota Prius give it an estimated electric-only drive range of 40km. The 256V battery pack is in the same voltage range as the existing battery and is disconnected by a big contactor (visible at one side of the boot) for charging via the 240VAC socket on the rear bumper bar. We liked the solid mounting for the batteries – you would not want them coming adrift in accident. Maximum measured fuel consumption for the Prius above in mixed petrol/electric mode is 2.3l/100km. That’s 122 MPG! Oops, did we mention MPG again? Silly us! under the control of a microcontroller. In every case, the cars had a throttle control potentiometer for speed control. None appeared to make use of regeneration under braking and all used some variant of lead-acid or lithium-iron phosphate batteries. Some motors were wired in series mode (ie, with armature and field windings in series) while others were wired in shunt mode with the field windings run at constant voltage while the armature voltage was varied (using pulse-width modulation). All on-road conversions need to pass inspection by the transport authority in the relevant state and these have comprehensive specifications which must be met before the vehicle can be passed. Electrical safety is most important, both from the aspect of avoiding electric shock as well as potential fire hazards if, for example, high voltage battery banks are shorted in an accident. Each of the cars on display had varying approaches to safely securing the batteries and they all had heavy-duty contactors to disconnect batteries when not in use. Providing heating is a problem when there is no waste heat from an internal combustion motor available. The common approach seems to be to use a hair-dryer running from the main battery bank. In a similar vein, power brakes must still be available and This Datsun 1200 EV conversion had a large array of batteries underneath the fibreglass canopy. Note the extra lead-acid battery in the engine compartment; necessary to run headlights and all the accessories. All EV conversions need a separate 12V battery or a step-down DC-DC converter, for this reason. 80  Silicon Chip siliconchip.com.au This Mitsubishi Triton EV conversion was perhaps the most impressive on display with a whopping DC motor. However, the rear ute section was chock-a-block with batteries, leaving little capacity to carry extra load. Again note the 12V battery in the engine compartment for lighting and accessories. a 12V vacuum pump connected to the original accumulator is the common approach. Some conversions are now using electric power steering, adapted from cars like the Honda Jazz. We did not see any cars with LEDs for stop/tail or traffic indicators – a little surprising perhaps. Our overall reaction? We salute those people who take on such a project. In each case it must be a very good learning experience with a great sense of accomplishment when it is finished. For more information, go to www.aeva.asn.au A video of AEVA field day is presently available at www.electriccarsforeveryone.com/blog/ SC This mini was an intriguing conversion with not a lot of installed batteries. The east-west DC motor is well hidden from view. Making a return appearance from previous years was this 1987 Toyota Camry station wagon. As the data sheet above shows, the Camry employs the standard 5-speed gearbox but no clutch is required. The large battery load means that it can only carry two people. siliconchip.com.au December 2008  81