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FIA Formula E…Batteries Included

November 20, 2014

What exactly drives a Formula E car if it has no internal combustion engine? We know it’s battery powered, but what kind of battery? What does it look like? Where is it in the car and how does it compare to the batteries we know from around our homes?

I recently spent a morning with the clever folk of Williams Advanced Engineering, the division of the Williams Group that we all know and love for their Williams Formula One Team, that take knowledge and technology gained through F1 and develop it for use in other markets.

Williams is an impressive company. They, together with my old team McLaren, have led the way in diversifying from their core Formula One businesses and putting their impressive skills, knowledge base and competitive natures, together with the ‘can-do’ attitude prevalent in the very top level of open wheeled motorsport, to use across a variety of sectors.

Through five years of developing high end battery technology for Formula One’s KERS and now ERS programs, Williams Advanced Engineering were well placed to extend that know-how into meeting the unique demands of a fully electric race car battery.

FE Battery Box

FE’s battery box. Weighing in at around 320kgs, containing cells connected in series, cooling system & electronic & thermal management system.

The company was approached late in the day when another partner pulled out of the project after getting nervous of the tight timescales involved. The Williams Group however, are very used to dealing in impossibly tight and immovable deadlines and reacted quickly to design, develop and produce the forty car batteries, plus a number of spares to deliver to the teams

The Spark-Renault SRT_01E Formula E car was already well under way when Williams got the call and so the battery had to be designed to fit into a structural box, designed by chassis manufacturers, Dallara, and meeting the energy, power, weight and safety requirements mandated by the FIA.

The battery box, a large carbon fibre structure with bolt on lid, sits in the space most single seater racing cars use for the engine and fuel cell, just behind the driver.

It’s what’s known as a ‘stressed member’ of the car and that means it bolts structurally directly to the back of the chassis or monocoque and transmits all of the torsional, or twisting, forces from front to rear and vice versa as the car’s on track. The electric motor housing and gearbox casing bolt directly to the back of the battery box, continuing the structural nature of the car’s main assemblies.
This is common practice and is the same basic layout as a Formula One car, just swapping the engine and clutch housing for the electric drive components in Formula E.


The large FE battery box, with electric motor housing & gearbox bolted to the rear, motor control unit on top and sidepod mounted radiators to each side. Drawing by @scarbsf1

The reason racing cars are designed this way is to avoid the excess weight of having a separate chassis frame, where the engine (or battery box) would drop in, much like a road car, but also to maximise the stiffness and structural integrity of the car.
This means designers are able to more efficiently control and utilise the loads going through the vehicle with suspension design, rather than having a flexible chassis, that twists and contorts over bumps and through corners, giving an unpredictable feel to the driver at racing speeds.

FE battery cell v F1 KERS cell

A large FE lithium-ion battery cell, here compared to a much smaller early F1 KERS cell

The FE battery box contains over 150 individual lithium-ion cells, each one roughly between the size of an iPad and an A4 padded envelope and stacked upright in rows.
Lithium-ion batteries are nothing new, they’re what we all have in the back of our mobile phones and laptops, but whilst all part of the lithium-ion family of batteries, the cell chemistry is designed specifically for the needs of each application and that’s a closely guarded secret at Williams. With all those cells connected together in series, the FE battery is capable of delivering 200kw, or around 270hp.

An innovative cooling system is integrated into the battery box to help maintain stable temperatures across the entire unit.
A non-conductive fluid, known as a dielectric, is pumped around the inside of the battery case and around each cell, before being circulated through a traditional style, sidepod mounted, cooling radiator and back into the box.

As energy is transferred from the battery into the car’s electric motor at varying levels, depending on the driver controlled, steering wheel mounted map switch position and of course the accelerator pedal demand, the chemical reaction in the battery cells generates a considerable amount of heat.
Equally, during the rapid charging process with the cars in the garage, the reverse chemical reaction, transferring lithium ions in the opposite direction between one side of the cell and the other, also heats up the battery considerably.

With the car stationary inside the garage, powerful blowers and dry ice are used to cool the radiators and consequently the battery while it’s recharged, a process which takes around 45 minutes, but one that can only begin once the unit has been pre-conditioned, or brought into the optimum temperature window by the team.

Batteries have to be strictly maintained and their cell temperatures are carefully monitored at all times by a sophisticated battery management system (BMS), sitting inside the box on top of the cell modules. The system has the ability to shut down cells if required, or switch to a reduced power failsafe mode if things get a little too hot.
Williams have given detailed guidelines to the teams on how to operate the battery within its performance parameters, but are well aware that the competitive nature of motorsport means that they’ll always be looking to find ways to gain advantages through areas like the car’s regenerative system, or ‘regen’, over each race weekend.

Pushing too hard lap after lap will overheat cells, so efficient and strategic deployment of the energy available is absolutely crucial to performance in Formula E.

More than one driver in Beijing hit temperature limits, resulting in the system reducing power until normal levels were reached, so teams will be well aware that the high ambient temps in Malaysia need to be respected.

Williams engineers have also programmed new, slightly reduced, limits for the amounts of energy regenerated by the motor/generator unit under braking, that can be fed back into the battery whilst the cars are on track for the Putrajaya race. The reduction won’t cause any noticeable difference in the spectacle, but is simply an extra measure to make sure batteries maintain their performance under these tough conditions.

Looking towards the coming years of Formula E, it’s hoped competition will drive innovation, particularly in battery technology and electric motors as technical regulations are opened up to manufacturers.
Williams Advanced Engineering are already assessing a number of options, including the possibility of becoming an electric motor supplier, again utilising their expertise gained in F1 with ERS.

There are various battery development paths the series could take, ranging from increased power or energy density, to rapid charging or even battery swap technology, all of which will help to accelerate progress in the key areas of electrical energy storage and deployment, something Williams hope to be able to benefit from as they look to transfer their own learning into the automotive world and beyond.

Whilst it may be easy for the cynics to criticise the shortcomings of battery technology today, the opposing view and the one I hold, is that the battery we’re using in Formula E is already an incredibly advanced piece of kit, but the competitive nature of motorsport should help to push forward development much faster than in the ‘real world’.

I hope we might look back in a few years, using today as a benchmark and marvel at how the technology’s progressed, citing the fact that if Formula E and Williams Advanced Engineering hadn’t taken the plunge in 2014, we might never have got there at all.

Marc Priestley


You can catch me on this weekend’s ITV4 Formula E show, starting at 5am on Saturday, with highlights on the same day at 6pm.


From → Cars, Formula E

One Comment
  1. Great know you have provide . In a series that is unique and groundbreaking, the most innovative component of all is Williams’ battery. Built to a specification determined by the FIA in terms of power, charge time and longevity, the work that has gone into powering the world’s first all-electric racing series could only have been performed by a company with the racing pedigree of Williams – from being awarded the tender to running on track for the first test took just six months!

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