Electronic Design

Ultracaps Solve Diesel-Cranking Problems

Putting big ultracaps to use can take some out-of-the-box thinking. Here's one that helps truckers who aren't allowed to leave their engines idling .

Large-capacitance ultracapacitors offer something of a design challenge. Providing tens or hundreds of Farads for potential power storage, they demand new ways of thinking about potential applications. They’re not simply another kind of battery. As a rule, they have 10 times higher power density (W/kg) than batteries, while batteries have about 10 times higher energy density (Wh/kg).

Maxwell Technologies has taken advantage of that difference to create two products that solve a problem common to both long-haul freight-carrying companies and operators of local delivery fleets. Laws and regulations prevent these companies from keeping their diesel engines running when they’re stopped for long periods.

That’s complicated by the amount of power it takes to crank diesel engines, which operate at much higher cylinder compression levels than gasoline engines. Compression, not spark, is what it takes to ignite a diesel-air fuel mix.

With a conventional battery array, that’s a problem for both long-haul and short-haul truckers. On mandated layovers, long-haul drivers use all kinds of appliances for light, entertainment, and climate in the cab, while the trailer can pull even more energy for refrigeration. That can leave scant power for engine cranking when it’s time to move on.

The problem is a little different for short-haul companies. There, the challenge is the requirement to shut down the engine at every stop. That leads to more frequent cranking, which may not give the batteries time to recharge between stops.

To deal with both problems, Maxwell’s ultracapacitor-based Engine Start Module (ESM) product line includes one version for class 3 through 6 medium-duty trucks and another version for class 7 and 8 heavy-duty diesel trucks. Each combines a charger/ultracap array and replaces one or more of the batteries in the truck’s battery box, but is devoted exclusively to cranking the engine during starting.

The original ESM product for long-haul trucks provides 1800 cold-cranking Amperes (CCA) and recharges in 15 minutes. It functions from –40°F to 149°F and weighs 21 lb. The ULTRA 31/900 is essentially half the larger version in a smaller package, delivering 900 CCA. It weighs 16 lb and matches the industry-standard Group 31 battery form factor. It stays fully charged even when the truck’s lead-acid battery is as low as 9.5 V.

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