Li-Ion Battery Cell Test System

April 30, 2015
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Many electronic systems rely on batteries, which must be tested after manufacture to ensure reliability of the systems that use them. Masanobu Kamata, one of our principal applications engineers, developed a Li-Ion Battery Cell Test System that was recently featured as one of the Whiteboard Power Chains of the Week. Here’s what he told us about his design.

 

Li Ion Whiteboard of the WeekCan you explain how this test equipment is used?

This test equipment is used by a leading manufacturer of Lithium-Ion (Li-Ion) batteries for Electronic Vehicles (EV) and Hybrid Electric Vehicles (HEVs) applications. The system provides a final test before shipment of the batteries: each battery undergoes a charge and discharge cycle to ensure it operates correctly before leaving the factory.

 

You have used a VTM as a bidirectional converter in this test application. What are the benefits of this approach?

The Vicor VTM Current Multiplier is built on an inherently bidirectional topology and can allow current to flow in both directions, stepping the voltage up or down as required. Using a VTM as a bidirectional converter is much simpler and more compact than having two separate unidirectional converters.

Other benefits include the inherent high efficiency of the VTM, which minimizes the need for cooling to remove heat generated by the converter.

 

The charge current is shown as 50A, which seems very high. Why is the current so high?

In the example, the actual battery cell is 20Ah and is tested at 2 – 2.5 times the rated current. When using the test system the maximum charge current of the battery is dependent on the specifications, and this system has been designed to support a wide range of batteries, some of which do require high charging currents.

 

How does the Vicor-based solution improve on the previous solution?

Efficiency increased by over 20% utilizing the Vicor design. In addition, there were density benefits that aided in the overall form factor.

 

Are there any other aspects of the design you would like to highlight?

The circuit is a part of an ATE system. The computer runs the circuit and controls the enable/disable events. As the system needs to be able to run continuously for a long period of time, reliability is critical. Fortunately the Vicor power components are extremely rugged and reliable.

 

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