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CAP-XX introduces supercap modules to support batteries in stop-start applications

CAP-XX stop-start system architecture. The company says that the cost of a 14V, 6-cell supercapacitor module for stop-start would be around US$60. Source: CAP-XX. Click to enlarge.

Australia-based CAP-XX Limited, a developer of thin, prismatic supercapacitors, has developed a supercapacitor module which supplies the cranking current to start the engine in Stop-Start vehicles (also known as start-stop, idle-stop, or micro-hybrid vehicles), reducing wear on the battery and eliminating the need for larger, more expensive ones.

Stop-Start technology, which turns the engine off when stopped in traffic and restarts it when the driver releases the brake or engages the gears, is gaining momentum worldwide as a means to save fuel and reduce emissions. The downside is the increased number of starts over a Stop-Start vehicle’s life—potentially more than 100 per day—which means a standard car battery may last less than 18 months, the company notes.

CAP-XX’s prototype Stop-Start supercapacitor module supports the battery by supplying the peak current (up to 300A) needed for each engine start. Containing six of the company’s thin supercapacitors, the module is about the size of 6 DVD cases , enabling easy integration into a vehicle’s floorpan, engine bay, or other tight spots. With 150F at 14V, and an ESR of 4.5 milliohms, the CAP-XX module offers the best power density available today, the company claims, and the energy necessary to support frequent start cycles in all weather and traffic conditions. It includes the control electronics to manage Stop-Start functions, balance the voltage across each supercapacitor cell, and limit the battery current during each restart.

With the supercapacitor module installed, the vehicle battery only needs to support continuous power functions such as air conditioning, navigation and lights, enabling longer battery life or smaller batteries. The battery also charges the supercapacitors for their first start, but once driving, the alternator keeps them charged.

Additionally, the supercapacitor module will start the engine in low temperatures (cold cranking) where a battery would falter, and can store energy in vehicles with regenerative braking systems (also known as Kinetic Energy Recovery Systems or KERS).

In testing under the New European Drive Cycle (NEDC) standard, the CAP-XX supercapacitor module completed more than 110,000 Stop-Start cycles at room temperature, successfully maintaining the battery voltage above 11.8 volts.

NEDC testing: battery alone. Click to enlarge.   NEDC testing: battery plus supercaps. Click to enlarge.

CAP-XX identifies the battery as having failed when voltage falls below 10 volts because, based on input from a leading European automaker, batteries at this state of charge can no longer operate vehicle electrical systems reliably.

Comparative tests of a battery-only system, also at room temperature, saw the battery fail after 44,000 cycles.

CAP-XX aims to partner with Tier 1 automobile parts suppliers to manufacture the modules, and will design and prototype the control electronics and modules to suit their requirements. CAP-XX estimates its module would cost approximately US$60 in mass production, and is already in negotiations with a leading Chinese automotive component company to commercialize the technology in China.

Anthony Kongats, CEO of CAP-XX, is scheduled to speak on the use of supercapacitors in Stop-Start systems at the EV Battery Forum in Barcelona, Spain, 21 - 22 March.

CAP-XX is the only supercapacitor member of the Cooperative Research Centre for Advanced Automotive Technology in Australia (AutoCRC), a government-sponsored group formed to develop and commercialize smarter, safer, cleaner vehicle technology.




This makes so much sense for Stop-Start equipped vehicles that it makes you wonder why it is not already installed as standard equipment.

A larger unit would also be beneficial for HEVs, PHEVs and BEVs.

When will the car industry wake up?


The car industry has alreeady woken up.
The Peugoet group is installing capacitors in their stop/start Valeo system using Maxwell capacitors, so CAP-XX will have to start from behind:

Other car companies source from Peugeot.

Unfortunately the market leader, Johnson Controls, simply uses an AGM battery, and so personally I would not specify stop start for cars which use them, as replacing the battery is likely to be expensive.
VW for instance uses them in their Bluemotion cars.
Avoid them.


With hydrogen fuelcell cars or battery cars we don't need this costly inneficient gadjet.


It is marketing, if people are not interested then NO sale. Some in Europe may be interested in start/stop but not in the U.S. In America, the only time they want it to stop is when they turn the key off in the garage.


This type of supercaps should be used as a complement to the 12 VDC regular car battery, not as a replacement.


?? It is supplementary as the article clearly says.


Yes, supplementary may be better description.

However, a supplement is also a complement?

In both cases, it would mean, 'in addition to' regular or other batteries.

Dave R

Seems like you could also then downsize the lead-acid battery and save weight overall, too.


Yes you could, but it is cost. When an OEM battery for a car goes for about $40, there is no need to change.

Nick Lyons

Sounds all good to me--small, cheap & saves money in both the short run and long run. Idle-stop is the lowest of the low-hanging fruit for reducing fuel consumption (apart from using your bicycle more and car less). Anything that speeds adoption of idle-stop is a good thing, IMHO.

Dave R

@SJC "Yes you could, but it is cost. When an OEM battery for a car goes for about $40, there is no need to change."

True - but if it can cut the weight of the lead-acid battery in half (say 15-20 lbs) - how much does it normally cost to reduce a pound of vehicle weight?


DaveR you win the internets today. That's a great perspective: it's not the cost of buying a Li-ion (or NiMh) battery, it's the cost of saving an equivalent amount of weight via another method, such as switching the hood and trunk lid to aluminum. That's especially true when you consider the design, sourcing, tooling, fabrication and testing load that attaches to changing body parts, as opposed to simply switching out one battery box for another. Great point.


The good thing about capacitors - they can deliver a lot of power very quickly even if not for very long. They should be useful in diesel-hybrids and other high compression engines that take more power to start.


So I can get 10 pounds out by adding $100 to the cost. Now the car gets .01 mpg better and costs $300 more. I don't think that would sell in most car company marketing departments.


A lot of these "low hanging fruits" cost as much or more than they save.

The point is - - a 20% smaller battery will save 10 to 20% cost (small, cheap lead-acid batteries already exist) and the weight savings adds more MPG.

Why do cars have $10 jacks?
They ran out of $5 jacks.

Like it or not; COST IS KING.


If the idea is to use caps for starting, then use a smaller lead acid battery to save weight, it sounds like a "solution" in search of a problem.

I suppose a case could be made for such and arrangement, I just don't see many car companies going for it...but that is just MO.


SJC, I think you underestimate how much weight has become a barrier to improvement in vehicle efficiency. Look at the Mazda SkyActive or Kia Rio/Hyundai Accent press release materials to see how much those companies have invested to make their cars 2-3% lighter than their class competitors. Kia/Hyundai actually bought their own steel plant so they could develop more advanced high strength steel formulations.

Dropping 20 lbs by just reworking the energy storage device is very, very cheap by comparison.

And ToppaTom, to your point, cost is king, but the customer's cost of fuel is also king. These weight reductions are how Kia and Hyundai are hitting the magic 40 MPG Hwy number with class leading performance and features.


Getting rid of non-essential weight such as spare wheel-tire, heavy lead battery, heavy steel wheels, ICE, metal radiator, heavy inefficient A/C, transmission, heavy drive shafts, steel brakes, heavy steel frame and body, doors etc is the way to 2X+ current efficiency for our personal cars while maintaining the same inside cab size.

A 1000/1500 lbs HEV, PHEV or BEV would require a lot less batteries than the current 4000 lbs units and would cost a lot less to build and to operate.

Common sense will eventually prevail but buyers will have to go through an attitude change first and accept that lighter and more efficient is better instead of bigger and heavier is better.


You have a 3300 pound mid sized sedan (typical) and now you want it to weigh 3000 pounds. This will get you maybe 0.5 mpg more on average. (optimistic)

So now you save 10 pounds on a battery, but the cost to make the car increases $100, for every 100 pounds you take out it costs $1000 more at the retail level.

People look at total cost of ownership for the first 5 years, those numbers are posted online. You are going to need expensive fuel to justify a significant increase in vehicle price.


SJC....during the last 24 years, our average car and small truck fleet has gone from 22 mpg to only 22.6 mpg because our manufacturers have built heavier and heavier vehicles, from about 2800 lbs to over 4000 lbs. All the gains from more efficient ICE, transmissions, tires, etc went up in smoke.

During the same 24 years or so, our Junk Food industries have also been very successful . We went form less than 20% to over 40% obese.

In a way, bigger-fatter (300+ lbs) drivers and passengers seem to justify heavier vehicles. If so, both problems may have to be fixed. otherwise, we may seriously need to revive the 8000 lbs Hummer I.


They have build heavier vehicles because the cars are bigger. Look at the Corolla and Civic versus the same models years ago. They are approaching mid sized and not compacts any more.

A compact will weigh about 2700, a mid sized will weigh 3400 pounds. A compact will have 85 cubic feet of passenger room and 12 cubic feet of truck. A mid sided will have 100 cubic feet of passenger space and a 16 cubic foot truck.

A compact will have 104 inch wheel base and a mid sized 108 inch wheel base. The point being, a bit more wheel base, rear leg room and trunk space adds 600 pounds to the car. They don't add 20% to the weight just to get worse gas mileage, they add it for size and comfort and NO it is not the twinkies that caused it all.


SJC....Some 100 years ago a 5-passenger Ford Model T had a 100 inch wheel base, a 120 cu. ft. cab, weighted about 1200 lbs, sold for less than $500 ($260 in 1922) and could drive off roads with its very large diameter wheels. Many farmers used it as an early tractor.

A similar car today weights almost 4000 lbs, cost $30K+, carries the same 5 passengers on roughly the same 21 mpg. All the gain in ICE efficiency went to propel the added weight. A 1200 lbs, 5 passenger car could probably do 80 mpg or about 4 times as well as a Ford Model T.


what do you think of this (concept) car:

Volkswagen L1 Concept

When carbon carbon fiber price drops significantly, it will be economical to build.

With width of just 1.20 m (or 1.25m in model from 2002), it could use just about half a lane, or convert a current wide HOV lane into two narrow lanes for this narrow cars, mark the dividing lane with a color different from other road colors (say blue). Reduces road congestion too, like an extra lane is added. Could be made as single seater, or with tandem seats (one behind the other).


“Additionally, the supercapacitor module will start the engine in low temperatures (cold cranking) where a battery would falter, and can store energy in vehicles with regenerative braking systems (also known as Kinetic Energy Recovery Systems or KERS).”

Well, the cold cranking has some value but the module’s contribution to regenerative braking would be rather minor, but not insignificant at lower speeds, since its amount of energy storage is about 4 Wh [ ½ (150) x 14^2 /3600]. The kinetic energy in a 3,000 lb. car traveling at 60 mph is about 150 Wh; and, at 30 mph, about 16 Wh.

So, at $60 per module ($15,000 per kWh), regenerative braking would not be the raison d’ȇtre for supercaps. However, if the module is already available, then use it so long as the cost of its integration is less than $2.00, $500 per kWh, or whatever the battery cost is.

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