Red Bull KERS: Floor Mounted Super Capacitors?

In the second year of their use of RenaultSport’s KERS, Red Bull appear to have found a new mounting position and format for their KERS energy storage with what appear to be floor mounted super capacitors.  Super Capacitors (Supercaps) are an alternative energy storage to Lithium Ion batteries, using very much the same technology as smaller capacitors used in electronics

2011 was Red Bulls first year with KERS, having chosen not to run it in 2009 as it compromised their design too much. As is typical for Newey, Marshal and their design team the KERS installation was unique and uncompromising, with its energy storage in two packs either side of the gearbox and a smaller unit inside the gearbox. Reliability issues plagued the team throughout the year, with the batteries succumbing to heat and vibration.

Floor mounting

So with a year’s understanding under their belt and the newly confirmed status as the RenaultSport factory team, the RB8 has taken a step forwards in KERS packaging. Now the energy storage appears to be slightly revised, with the unit inside the gearbox swapped for floor mounted units. In this exclusive picture from MichaelD in Melbourne, we can see the units remain fitted to the floor when it’s removed. The two carbon fibre cases are closed with aluminium tops and are provided with electrical and cooling connections. They sit in the final section of flat floor known as the boat tail.
Having the units placed on the floor, as opposed to between the gearbox and engine, means they can lower the Centre of Gravity. Also being quite heavy they are placed near the rear axle line to suit the mandatory weight distribution. As mentioned the units are supplied with a common cooling circuit, one pipe routes around the back of the floor to link the devices. There are also a number of electrical connections for both connecting to the KERS Power Control Unit and for monitoring their status. Quickly detachable connectors are used to allow rapid removal of the floor keeping the units in place.

What are they?
While trying to confirm these items as part of KERS, I’ve learnt some new facts about KERS in F1, which might help to explain these devices. It might convenient to call these units ‘batteries’; however their actual design and purpose might not accurately tally with that term.
It’s possible they could be part of the energy storage system for the KERS, either as Li-ion Batteries or Super Capacitors (supercaps), or they could be an energy dump used to reduce the load on the battery when harvesting power under braking.

Energy dump
The way the FIA F1 KERS rules are written there is a limit on the amount of energy that can be stored and reused. These limits are not in line with what is actually achievable with current technology. Teams are effectively capped on energy, as they could store and re-use far more. Part of the problems is that under braking, the energy harvesting is capable of producing more power than they are allowed to put into the battery. So the teams control the harvesting rate according the driver’s style and the circuits demands. Even then the harvesting potential is hard to predict. Rather than stopping the harvesting mid braking, which would unsettle the car. The teams keep the same harvesting rate, but dump the energy through a series of fixed rate resistors. Obviously these resistors quite large and create a huge amount of heat. This would explain their low position and cooling requirement.
These floor mounted devices might be the energy dumps, but they are particularly large and with increased experience of KERS teams are getting better at controlling the harvest rate, so shouldn’t need such a large dump. So it’s possible, but unlikely these are energy dumps.

Energy storage solutions

Li-ion batteries
Typically current F1 cars use dozens of Li-ion cells packed into an array forming a ‘battery’ pack. This KERS Battery Pack is commonly a single part sat under the fuel tank. Although often used as a single battery, the unit can be broken up into a set of batteries in series.
In 2011 Red Bull clearly split this part up into several smaller Battery Packs, there being the two aforementioned units either of the gearbox and another in the gearbox. Although interconnecting these parts with cooling pipes, high current cable and sensor cabling adds some weight, this does provide a nicer packaging solution. It’s logical to explain these new floor mounted parts as batteries. However they do not look like the battery packs seen in the gearbox last year, or on other cars. Being on the floor of the car they are subject to even more danger from impacts as well as the heat and vibration that caused issues last year.

Supercaps
As their design does not tally with existing Li-ion battery packs, then they might still form part of the energy storage element of KERS. So if not Li ion batteries then they might be the next bet alternative ‘super capacitors’. Supercaps have far more energy storage than the capacitors we common see on household electronics. They are far more efficient in storing and releasing energy quickly, with less losses and do not degrade as quickly as Li Ion batteries do. However they are not as efficient in storing larger amount of energy for longer periods.
A link between Red bull and supercaps is RenaultSport. Renault already uses supercaps as onboard storage for both formula Renault 2.0 and 3.5. In the 2012 FR3.5 series, the KERS only uses Supercaps, not a conventional battery.
So it’s possible the Red Bull RenaultSport KERS uses hybrid storage with a mix of Li ion cells and Supercaps, using the supercaps for short term storage and for more immediate bursts of acceleration. While the Battery provides the longer term storage between corners and for more sustained discharges of energy.
It’s believed that other teams are already using a mix of supercaps in their KERS Battery Packs to reduce the unit’s size and provide the option for a quick storage\release of energy.  So I believe that most likely these devices are Supercaps.  With revised KERS regulations coming for the new Powertrain in 2014, more use canbe made of Supercaps in both the Kinetic and Thermal Energy Recovery systems.  Experience of these componenents now, will be an important part of the development of the 2014 systems.

More on Supercap KERS via Race Engine Technology Magazine