Kemet goes big on capacitors for EV inverters

  • 08-Dec-2011 04:21 EST
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Kemet CTO Phil Lessner holds a roll of metalized capacitor film, thin enough (as little as 3 µm) to be seen through. The film (polypropylene dielectric and aluminum-zinc electrode) goes through a machine to produce windings, which after further processing are packaged according to the customer’s design. (Patrick Ponticel)

The average car finds use for about 5000 capacitors, according to Kemet, one of the world’s largest suppliers of the types used in automobiles. They’re generally small and not noticeable.

A new Kemet capacitor product for vehicles employing electric traction motors is very large by comparison, and the company made sure it would be noticeable via a recent event to celebrate the product’s launch in the U.S. Involved in the grand opening celebration Oct. 17 at Kemet’s headquarters, research, and production facility in Simpsonville, SC, were several automotive Tier 1 suppliers, including Magna E-Car Systems, which makes inverters that incorporate large capacitors to convert the direct current generated by the vehicle’s battery into alternating current for use by the electric motor.

In Europe, Kemet already produces a similar product using the same manufacturing process, primarily for hybrid vehicles made there. It wanted a North American manufacturing and engineering presence to serve customers on this side of the Atlantic. A $15 million U.S. Department of Energy grant and a smaller one from the state of South Carolina helped make that a reality at the Simpsonville complex, where about half of Kemet’s global engineering workforce of 200-plus is based.

The Simpsonville complex consists mostly of research and development, not manufacturing. It serves as the company’s center of innovation for ceramic and tantalum capacitor technologies. The center of expertise for power film technology, which the new product uses, is Italy. Both the technology and processing equipment were developed there.

Kemet has carved out space at its Simpsonville complex for four manufacturing lines to make the new capacitors. By the time of the grand opening, only one line had been installed and it was being used for qualification work. The capacitors being qualified on that line were to begin shipping on Dec. 1 to an unnamed customer. Three additional lines will be added as demand for the product grows. Total investment, including the grants, will be about $34 million when the Simpsonville Power Film Facility is fully built out.

The active line is highly flexible to accommodate the diverse demands of customers in terms of capacitor capability and configuration. The other lines will be more automated and less flexible.

One of the more visibly compelling stations in the process is winding. As explained by Chief Technology Officer Phil Lessner, a Kemet-designed machine winds a roll of very thin (as thin is 3 µm) metalized film around a circular mandrel. The dielectric films used for the power film capacitors are made of a special grade of polypropylene and metalized with ultrathin layers of metal. The metal patterns are specially designed by Kemet to provide safe operation of the capacitor in these high-power applications.The resulting multilayer winding is then ejected from the mandrel and flattened. From there it undergoes additional treatment and processing (including application of terminals by means of spray technology) in other stations.

Among the final steps is stacking the completed windings in various configurations to fit into each customer’s own inverter design. “As the industry matures, we may have more standardization, but right now everyone has their own design,” Lessner said.

He noted that, in addition to helping the inverter convert current from dc to ac, the capacitor also “smooths the load between the input and the output. Sometimes the motor demands more energy than the battery can put out. The capacitor can store energy and give a little oomph to the motor to level things out.”

Ultimate plant capacity with all four lines running is 100,000/year, Lessner said. Though it’s the same technology already used in Italy, “each car is a different design and so different shape and terminal designs have to be taken into account. It’s a relatively engineering-intensive operation that requires close contact with the end customer.”

The process can also be used to make film capacitors for use in industries such as wind and solar energy, Lessner noted.

Industrial represents the largest customer base (26%) for Kemet wide product lines (48 billion units sold last year), which unlike some competitors produces nothing but capacitors. Transportation (including off-highway) accounts for 16% of sales, according to Kemet CEO Per Loof.

“The automotive guys are hardest to please, as we all know,” he said. “Their quality requirements are above most others'. And we price [our products] accordingly.”

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