Electric Vehicle

Next project, battery powered electric car.

My angle  You can't compete with petrol cars - so don't try; make a cheap vehicle with 20 mile range that will be used as a 2nd car; if it will do most fixed length known journeys (commutes, shops). When you limit your ambitions to 20 miles you don't need 1/2 a ton of batteries any more, 5 45Ah 12V lead acid UPS batteries will do nicely. Suddenly running costs are below 1/10 a petrol car. Many folk would only need such a vehicle and could hire a petrol car if a rare longer journey were undertaken.

Base vehicle   Reliant kitten. This has 4 wheels so it can be made to corner well. It is important that a vehicle which does not accelerate well should not have to slow down too much for the bends...

Drive    Single 4kW induction motor driving the propshaft via a toothed belt. Motor is a standard industrial TEFC motor re-wound with 1/5 as many turns (of thicker wire....)

Electronics    MOSFET based inverter. Power Shottky freewheeling diodes. Conduction and switching losses thus minimised. Controller based on hitachi H8 3048 micro does PWM, reads motor shaft encoder & provides all MMI.

Control system    Open loop V/f drive with motor shaft encoder feedback. Motor  base speed corresponds to ca 15mph, top speed around 55mph with 4:1 field weakening. Note inherent regenerative braking capability. Special control systems to facilitate hill starts.

Auxiliary electrical systems    A 12 volts supply will be chopped from the main 60V DC   bus. To save power this voltage will be made speed dependent, falling to 8  or 9V stationary but up to 13V at 50mph. When stopped the lights will thus automatically dim and the wipers slow down.

Charging   A 2kW charger should recharge the batteries in less than 2 hours. This can be timed to take advantage of economy tariffs at home. The charger can stay with the car to plug in en route! For longer journeys a small generator on a roof rack could keep things going! The charger can be incorporate PFC & fast charge algorithms - we'll see what's fashionable if I get that far!

Performance let's see what we get: aiming for range 20m Top speed 50mph. 0-30mph in 10s

EMC     relevant standards and approvals applied if project attracts any commercial interest.

more techie notes Drive and power design

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