Unlike batteries, ultracapacitors maintain a more consistent power output in the face of extreme cold or hot temperatures.
Ultracapacitor starting is a technology that has been around for two decades, used extensively as standby power in electronics and power generation. Now, this technology looks ready for primetime. Fully productionized systems, with widespread distribution and mainstream installation, are making the battery-replacement capacitor starter system (CSS) a reality.
It’s taking off in automobile engine stop-start systems as carmakers are seeking ways to reduce emissions and increase fuel economy by automatically shutting off the engine when the vehicle is at rest and restarting it when the driver lifts off the brake.
Engine start-stop systems depend upon battery power to restart the engine as well as to keep electrical accessories. A CSS supplements battery power with ultracapacitors.
Also known as supercapacitors, these are electrical components capable of holding hundreds of times more electrical charge quantity than a standard capacitor. What’s more, ultracapacitors are generally lighter than batteries.
Heavy truck OEMs have begun investigating the adoption of ultracapacitor starting technology in their efforts to meet the final Phase 2 Greenhouse Gas Emissions Standards and Fuel Efficiency Standards for Medium and Heavy Duty Engines and Vehicles which takes effect next year.
Ultracapacitors, when paired with batteries, immensely improve the reliability, efficiency and power of diesel engines, say officials with Ioxus (www.ioxus.com), a developer and manufacturer of ultracapacitors and energy storage products. Ultracapacitors help assure engine starting with no dependence on the state of charge of onboard batteries and perform well under less-than-ideal weather conditions, making the vehicle’s operation more reliable.
Moreover, they say the application of ultracapacitors is economically beneficial because they extend the service life of a diesel engine’s starting system and lessen maintenance expenses and fuel waste.
Ultracapacitors are partially taking the place of batteries for their light weight, high current delivery and ability to store energy for extraordinarily long periods. Now, big ultracapacitors are a reality for replacing some of the lead-acid batteries for starting heavy duty diesel engines.
Currently, two manufacturers in the U.S. are in production, applying ultracapacitor starting systems to heavy trucks. One is Maxwell Technologies (www.maxwell.com), a developer and manufacturer of ultracapacitor-based energy storage and power delivery solutions. It uses its symmetric ultracapacitors, developed for a wide range of applications, including those used in the Lincoln Continental stop-start unit.
The KAPower starting system uses asymmetric ultracapacitors and its internal cells are combined in series or parallel to achieve the desired voltage and power, with no internal electronics needed.
The other company is Kold Ban International (www.koldban.com), a provider of engine starting solutions for heavy trucks and locomotives. It takes a different approach and uses asymmetric ultracapacitors.
Together, these two are pioneering and popularizing CSS in the heavy duty truck industry.
Asymmetric capacitors have a higher energy density than their symmetric counterpart due to increased capacitance and higher cell operating voltages.
Essentially, the ultracapacitor is a different type of electrical energy storage. A lead-acid battery uses reversible chemical reactions when charging and discharging. It generates heat in both directions, and generally, it is around 70 percent efficient. Because the batteries wear out with cycling, they last only around two to five years. Since the charge/discharge is chemical, batteries are temperature dependent.
A capacitor stores electrical energy physically as a charge on a plate. This physical process is around 98 percent efficient, can cycle millions of times and has a life of15 years or more. The voltage at -40 degrees F is only a few percent less than at 80 degrees F.
Because the charged plates can discharge almost instantaneously, the ultracapacitor storage is perfect for starting systems that have a very high current demand over a short duration. Conventional lead-acid batteries are much better at steady, moderate current over long durations.
One of the problems today is that in their manufacture, lead-acid batteries must be compromised and over-sized to be able to provide high starting current.
The ideal setup with CSS is to substitute one or even two of the vehicle batteries with an ultracapacitor setup for starting and use the remaining lead-acid batteries – preferably an Absorbent Glass Mat (AGM) deep-cycle battery – to handle the other electrical loads like ECUs, lights and hotel loads in the sleeper.
Maxwell’s Engine Start Module (ESM) is sized to do just that. Housed in a blue plastic box, the ultracapacitor stack and associated electronic controller are integrated and it has the standard Group 31 battery footprint. Weighing just 21 lbs, it offers a weight savings of approximately 40 lbs by replacing only one battery.
Rated at an equivalent 1,800 CCA (cold cranking amps), it can promptly start up a big-bore diesel engine, even down to -40 degrees F, in half the time a lead battery can.
In a Maxwell webinar, Jeff Brakley, the company’s senior product manager, said that during the 2013 Polar Vortex that saw all 50 states experience temperatures from freezing to -40 degrees F, many customers using the Maxwell product found that ESM-equipped trucks would start when others with all-battery starting systems simply would not.
For many truckers, a winter no-start or a Monday morning no-start after leaving some sleeper hotel load on over the weekend is a familiar and expensive scenario.
KBi’s KAPower starting system has been designed from the beginning to be an ultracapacitor starting system for heavy trucks, says company vice president Jim Burke. Having been in the cold-start business for many years, “we really understand the demands of starting deep cold-soaked diesels."
The KAPower used to be slightly larger than Group 31 batteries because early ultracapacitors were sourced from Russia, because, he notes, Russians have been cold-starting big locomotive diesels for two decades using this technology.
That created some issues for KBi. One was that some customers didn’t want to deal with a unit with Russian-sourced components. Another was that truck battery boxes have become so tight that accommodating the KBi unit has had its problems.
The company has switched to a North American Saft-built nickel ultracapacitor and has a newly tooled unit with a Group 31 footprint. Saft (www.saftbatteries.com) designs, develops and manufactures high technology batteries for the industry.
The KBi unit’s asymmetrical ultracapacitors are simple, have no internal computer controls and use nickel carbon technology for its storage system. This means the complete unit is nearly twice as heavy as Maxwell’s, acknowledges Burke, but it still saves around 20 to 25 lbs over a Group 31 lead-acid battery.
He says that the technology is robust and there is no issue with overcharging. Also, because of its simplicity, the battery will recharge in only 10 to 30 seconds even when fully depleted, which “is a big plus."
Maxwell’s solution has a stack of modular ultracapacitors that are controlled by an electronic DC/DC converter. Providing there is at least 9V on the vehicle batteries, the capacitor stack can be charged to between 14.5V and 16.2V for a guaranteed start – which is more than the 11.3V a battery-based start requires. Less than 9V would disable ECUs, notes Maxwell’s Brakley.
Both the Maxwell and KBi systems are recommended to be isolated from the main vehicle batteries once they have received their charge. The Maxwell ESM has a third terminal on the top which connects directly to the starter or the mag switch in the starter circuit.
In both cases, a completely discharged main battery will not affect the ability to start the vehicle. However, because of the difference between the symmetrical and the asymmetrical ultracapacitors, the Maxwell setup will drain down in three weeks, whereas the KBi setup may go as long as a year. The KBi ultracapacitor has no toxic materials or unstable Li-ion batteries inside, so it creates far less of a problem in shipping and handling.
It should be noted that in both the KBi and Maxwell setups, the ultracapacitors are available in a 24V configuration. Burke of KBi says that currently 24V accounts for the lion’s share of his company’s business for use in other applications, but he sees trucking as a huge market for 24V.
According to Brakley of Maxwell, since the starter is isolated in an ultracapacitor system, it’s possible to make that part of the electrical architecture 24V while keeping everything powered by the battery side at 12V. This same thought was shared by KBi’s Burke.
Brakley says the idea is gaining traction at the truck OEMs who are looking at 24V start systems as the current draw is half for the same power. There are enormous savings in copper to be made in the downsizing of the cabling to the battery box if the starter cranks on a 24V circuit. Add to that weight savings – especially if ultracapacitors are used – and it becomes an attractive proposition.
Several years ago, a number of papers were presented at SAE (Society or Automotive Engineers) meetings on the need and benefit of going to a 42V architecture. The proliferation of electronics, electric power steering and other systems taken off the engine and powered electrically indicated that a shift to 42V (three-battery – three times the nominal 14Vof a conventional six-cell lead acid battery) power may become necessary.
Improved electrical efficiencies, LED lighting and a lot more has taken the pressure off on the passenger car side. But in interviews with Russ Sukouski, manager of global innovation, Navistar International, on the topic of future fuel economy, he mentioned some of the technologies for 2017 and beyond would drive car the truck manufacturers towards 42V to 48V electrical systems.
Navistar (www.navistar.com) is a holding company whose subsidiaries and affiliates produce International brand commercial and military trucks, proprietary diesel engines and IC Bus brand school and commercial buses.
With the high electrical-demand passenger cars, this could be as near as 2017.
Looking ahead, it seems that the passenger car engine stop-start will drive towards a hybrid battery that has lead-acid, Li-Ion or another battery chemistry to drive the majority of electrical loads, possibly combined with an ultracapacitor module that could be integrated into the same case to handle the starter duties.
In heavy trucks, AGM lead acid batteries may be around for a long while yet, combined with a Group 31 ultracapacitor setup and maybe a 24V starter circuit. After all, with the starting load taken off the lead-acid batteries, they will have – at a minimum – double their life today and remain the economic best-bet.
Lastly, the application of ultracapacitors is very environmentally and economically beneficial because they prolong the diesel starting system’s service life, reduce maintenance expenses and fuel waste, reduce CO2 and unrecyclable waste, plus increase engine life.
Steve Sturgess is a long-time automotive journalist who specializes in the transportation industry. www.stevesturgess.com.