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Battery Isolator and Switch



Technical Challenge:

Safely combining multiple batteries with high efficiency and give a "Gas Gauge" of remaining battery power.


High-energy batteries can be dangerous. Mishandling of modern batteries has caused fires and explosions, not to mention serious personal injury. Putting multiple batteries in parallel to increase operating life is a common battery design error. The most common method for safely connecting parallel batteries, "Diode Isolation", is inefficient because of the diode's forward voltage drop. It also has no easy way to tell how much energy remains in the battery. The BIAS system uses a low loss analog switch, to connect one battery string at a time. This prevents dangerous circulating currents. The system can report which batteries have been used and which are still fresh, giving a rough "Gas Gauge" of how much energy remains.

Demonstration Capability:

While there is no existing demonstrator, several test and development models were built. A new test and demonstration model could be built within one day.

Potential Commercial Application(s):

Any system which needs reliable battery power could benefit from this system, such as: Systems where power failure would be catastrophic like Radio controlled model aircraft, where the main battery would last for several flights, and the backup battery would need only the energy to finish the present flight. An interlock would be added in this case to prevent taking off again until the batteries were charged or replaced. Medical uses could include I.V. Pumps and portable defibrillators. Unattended systems such as weather stations and sonobouys could use both the high efficiency and the "Gas Gauge" function. Finally, Emergency response vehicles often have redundant ignition systems; this would give them a redundant battery supply.

Patent Status:

Issued - United States Patent Number 6,144,189

Reference Number: Roc-1

If you are interested in exploring this technology further, please express your interest in writing to the:

National Security Agency
NSA Technology Transfer Program
9800 Savage Road, Suite 6541
Fort George G. Meade, Maryland 20755-6541


Date Posted: Jan 15, 2009 | Last Modified: Jan 15, 2009 | Last Reviewed: Jan 15 2009