Electric SLC: Which for You: Batteries or Supercapacitors?

People have been interested in electric SLC's for a decade.

. . . I think a really "sick" drive train might be a pure electric or hybrid. I have searched these forums and there is very little mention of hybrid or pure electric builds. I live in MA and we have a quite a few people here that are doing Tesla conversions on a number of platforms. They are getting 600+ HP/ 480 ft/pound from a single stock tesla drive unit, conversions are getting almost plug and play now with the new generation of standalone controllers. Pretty sure it would fit in place of the trans on a SLC, leaving lots of room for batteries where the motor usually goes. . . . The technology is progressing really fast at this point, and its probably only a matter of time before with see a dedicated EV "kit" car.

Some on this board have actual experience installing electric drivetrains in vehicles.
. . . There are a number of really great forums that are dedicated to building EVs. A plethora of knowledge in those forums can save you a lot of money and work for nothing.
You will mostly find that those who chose to run their motors through a transmission found that they would select one of two gears - around town with a top speed of say 60mph and highway with a top speed limited only by their motors operating limits.
Electric motors generate a lot of heat when worked hard. A brushed motor can start throwing solder from its commutator to armature winding joints when worked too hard or run too fast.
Brushless is the way to go for dependability, but the complexity of the systems to control them are far greater..
Fran has experienced in electric SLC conversions.
We have been involved in three fully electric SLC's
One in Switzerland, Australia and now the USA.
Batteries have been the traditional source of electricity.
Much more expensive....batteries alone were well over $25,000..then charger, BMS system, coolers, heaters, charging system etc.....even more expensive than an LF engine
And now supercapacitors have come along. This from Lamborghini's press release.
Lamborghini Sian Roadster Powered by Hybrid Technology Revealed
A 48-volt e-motor, delivering 34 hp, is incorporated into the gearbox to provide immediate response and improved performance. The e-motor also supports low-speed maneuvers such as reversing and parking with electric power.

The Sián Roadster sports Lamborghini’s innovative supercapacitor application: a world-first technology storing ten times the power of a lithium-ion battery. Located in the bulkhead between cockpit and engine it ensures perfect weight distribution. Three times more powerful than a battery of the same weight and three times lighter than a battery producing the same power, the electric system with the supercapacitor and e-motor weighs only 34 kg, thus it delivers a remarkable weight-to-power ratio of 1.0 kg/hp. Symmetric power flow ensures the same efficiency in both charging and discharging cycles: the most lightweight and efficient hybrid solution.
. . .
The Lamborghini Sián Roadster incorporates a highly sophisticated regenerative braking system, especially developed by Lamborghini. The symmetric behavior of the supercapacitor, which contrary to normal Li-Ion batteries can be charged and discharged with the same power, fully charges the Sián’s energy storage system every time the vehicle brakes. The energy stored is an instantly-available power boost, allowing the driver to draw immediately on increased torque when accelerating away, up to 130 km/h when the e-motor automatically disconnects, improving the elasticity maneuvers and making it more than 10% faster than a car without this system.
But why supercapacitors?
What Are ‘Supercapacitors’ And What Are They Doing In Lamborghini’s New Sián Supercar?
What Are ‘Supercapacitors’ And What Are They Doing In Lamborghini’s New Sián Supercar?
Bill Roberson

But there won’t be a battery hiding inside the rumored $3.6 million Sián, of which only 63 units will be made available (oops, spoke too soon, they’re all sold). Instead, the car will use a 34-horsepower electric motor that gets fed electrons from something called a “supercapacitor.”

Okay, a little science 101 (or maybe 201) first. What makes a capacitor “regular” or “super?” And what does a capacitor do? Basically, it’s an electrical component that stores energy, but not really in the same way as a battery. And it’s not rare: You’re surrounded by regular capacitors right now. They’re in almost everything: Smartphones, computers, stereo equipment, microwave ovens, pretty much anything with a circuit board. Capacitors are great at storing and releasing energy at a rapid pace - as in thousands of times per second, and they can do it millions of times without degrading like a battery typically does. You can go more in depth here, but the bottom line is that they’re crucial for the proper operation of complicated electrical equipment - and they’ve been around since the dawn of electricity itself: 1745. So they’ve had some time to develop as it were.

But back to the Sián and those “supercapacitors.” It’s pretty much what is sounds like: Really BIG capacitors that store a lot of energy and are then able to dump it quickly into something like an electric motor, or the amplifier section of your stereo. In the case of the Sián, the supercapacitors power a small electric motor that’s connected to the engine . . .

But why just 34 measly horsepower? And how are those supercaps charged up if there’s no battery? Here’s where capacitors and batteries sort of part company (despite the fact they both store energy). While big batteries take many minutes or even hours to charge, big capacitors take mere seconds, and they can dump all their power in seconds as well. But, capacitors (at present) don’t hold a charge over time very well. A big supercapacitor array like that in the Sián will likely bleed off all of its stored energy in just a few days while parked. Also, capacitors don’t have the energy storage density of batteries, so they don’t store nearly as much power as a battery of the same physical size. At least, they don’t right now.

The Sián’s trick to charge up its supercapacitors is to use regenerative braking. When the driver slows, the Sián’s brakes work like generators, and quickly fill the capacitors with electricity. When the driver then accelerates, that energy is dumped into the small electric motor, which helps accelerate the Sián more quickly: Lamborghini is claiming it can hit 60 miles an hour in about 2.8 seconds. The reason the motor is so small is two-fold: The overall electrical energy system is small, likely to save weight (batteries are far heavier than capacitors) and it's more like an assist system than a full-on hybrid power plant. The Sián will not be able to move under electrical power alone.

Physics tells us that an object at rest requires a lot of energy just to get moving, but once underway, not nearly as much power is required to maintain a cruising speed (that’s why you get such good gas mileage on the highway). The small electric motor in the Sián, with its supply of essentially free energy from the car’s brakes stored in the capacitor system, helps get the car moving in tandem with the V12. It gives it a sort of free energy boost, either from a stop or from a lower speed when acceleration is called upon (like coming out of a corner). If this sounds like the KERS (Kinetic Energy Recovery System) device in race cars, it is indeed very similar in principle. Lamborghini says the system will also be used to smooth gearshits in the Sián.

So why doesn’t every car use this “supercapacitor” system to improve power and efficiency? Likely because it’s expensive and complicated to make and integrate, but now that it’s appeared in a (barely) civilian production car, the tech will likely be refined and start to trickle down to more affordable vehicles if economies of scale can be brought to bear.

Additionally, capacitors continue to be developed, with the hope that someday, perhaps some sort of battery/capacitor hybrid can be developed that will give the benefits of both systems: The ability to store large amounts of power long-term, quickly, and the ability to dump the power into motors for extreme performance. It could be a step on the road towards the ultimate battery technology: High-capacity solid state batteries that hold enormous power, charge quickly and last far longer than current “wet” batteries.

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So, electric SLC enthusiasts, what will be your chocie? Batteries or Supercapacitors?
Supercapacitors...ultarcapacitors....they are still aways away form being suitable for a primary drive ev, even in a hybrid capacitor/lithium pack. Just take up too much volume. If you custom designed a chassis with them built into the frame, maybe, but unlikely. They work ok as source for a small electric drive in a hybrid ev, but really only as interta absorption/regeneration source. There are batteries now that can take very large amounts of amps during regen, so I'm not sure of the current usefulness. Double their current energy density and they become interesting.