Mark Fowler has built himself an electric sports
car. The IT professional has done what many people dream about but few seldom
achieve. The car’s based on an off-the-shelf kit Clubman, but Mark has added an
electric motor, control gear and batteries.
And if the end result isn’t quite what he
expected, well, the project’s not finished...
The Birkin PRB S3 Clubman uses an epoxy-coated
steel frame fitted with aluminium panelling. The rear suspension comprises a solid axle located by four trailing links and a Panhard rod. Front suspension
uses unequal length upper and lower wishbones, an anti-roll bar and coil-over
dampers.
Brakes are discs front and rear, with four-spot
front aluminium calipers. Steering is non-power rack and pinion, and the kit
also includes an adjustable aluminium pedal box.
But of course it’s the non-standard parts that are
the most interesting.
The underbonnet scenery comprises a clear plastic
panel on which are mounted a throttle position potentiometer connected by cable
to the accelerator pedal. The pot talks to a 1000 amp Zilla DC motor speed
controller that works with an Advanced DC ‘9 inch’ electric motor, located
beneath these components. Mark says the continuous output of the motor is 20kW
but that short term, it’s good for something like 100kW.
The motor is bolted to a 5-speed gearbox that in
turn drives a conventional tailshaft to the standard kit differential.
Near the speed controller you’ll find an 800 amp
main fuse, and a mains-powered battery charger capable of outputting 20 amps at
the full 144V battery voltage. A DC/DC converter keeps a tiny 12V SLA battery
charged – this is primarily for safety in powering lights and instruments should
the main battery pack need to be shut down.
All fine and good so far – so what’s this about
the project not turning out as expected? Batteries... ah batteries...
Batteries are located in the nose of the car,
under the boot and (when fitted), either side of the pictured electric motor.
Unlike the other electric cars we’ve covered in AutoSpeed, Mark’s car uses
lithium ion batteries. But in this case, it looks very much as if going to the
new technology has not been the expected success. Lithium ion batteries are far
lighter than lead acid batteries of the same capacity. They also have better
performance characteristics in terms of being able to continuously supply high
current.
But the lithium ion batteries in Mark’s car have
proved to be a complete flop. The first generation ThunderSky lithium cobalt
designs have turned out to have an instantaneous current rating far lower than
claimed. In fact, Mark told us that while the original data suggested that the
batteries would be able to generate 300 amps in short bursts, the actual figure
is more like 30 amps! The battery voltage also sags hugely (and stays low), the
two aspects resulting in a massive shortfall in car performance.
To a degree, Mark is philosophical about the
battery disaster. While recently in North America he attended electric drag
racers and saw what real high performance lithium ion batteries are
capable of. ThunderSky also now has a new range of lithium ion batteries, and
these are apparently a much better proposition. However, having already spent
around $11,000 on batteries, Mark is not looking at using the same supplier.
Instead, he’s considering spending $40,000 on state of the art batteries that
would give the car phenomenal performance.
But, as he wryly says, “I don’t have forty
thousand dollars lying around - I’d have to sell one of my kids!”
After spending around $50,000 all-up, the
frustration of having a car with everything but the expected performance must be
great. We went for a ride in the car and it felt taut, well suspended and was
eerily quiet. The quality of build finish is excellent, with the carbon fibre
dash panel featuring gauges for 80 – 160 battery volts, motor amps, motor rpm
and vehicle speed. But as soon as Mark put his foot down, the needle on the
battery voltage gauge sagged off the lower end... (Although it must be said that
Mark has currently only 86V of batteries installed.)
In addition to new batteries, Mark would also like
to give the gearbox the flick (he uses only 4th and reverse gears,
and reverse is easily catered for by changing the polarity of the DC motor feed)
and perhaps upgrade the DC motor and controller for something more powerful. But
the latter’s another unknown – because even with the current motor/controller,
decent batteries should give the 640kg car great performance.
It all really depends on where you’re coming from.
A high performance petrol engine with programmable engine management and perhaps
a turbo, new fuel tank and fuel pumps, and a new custom radiator could easily
tip the balance of fifteen or twenty thousand dollars. An engine with a
lot of power could go much higher in cost. In this context, shelling out,
say, $20,000 for a battery pack that would make the car go hard is reasonable.
An all-up cost of about $70,000 for a unique car
with strong performance, very good handling – and running costs of only cents a
day – could even be warranted.
And Mark’s struggling with just that
justification...
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