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A Method for Preventing Lithium Battery Thermal Charge Terminations in a Lithium Battery Charger

IP.com Disclosure Number: IPCOM000029487D
Original Publication Date: 2004-Jun-30
Included in the Prior Art Database: 2004-Jun-30
Document File: 5 page(s) / 231K

Publishing Venue

Motorola

Related People

Marc B. Riley: AUTHOR [+3]

Abstract

Lithium battery chargers are intelligent chargers. When charging lithium battery packs, the charger can indicate a “waiting to charge” state to the end user. This “waiting to charge” state is often the result of a battery heating up beyond the maximum allowed threshold for charging. Ambient temperature has a significant effect on TCO “temperature cutoff”. However, there are often cases when the heat contributed by the charger causes the battery to TCO in slightly elevated ambient conditions. When a TCO occurs it can lead to increased charge times and user dissatisfaction. Currently there is no simple method to prevent a lithium battery from TCO when the heat from the charger is the culprit for the early termination. This technique is a method for preventing TCO without adding additional hardware or software to the battery pack.

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A Method for Preventing Lithium Battery Thermal

Charge Terminations in a Lithium Battery Charger

By:  Marc B. Riley

        Taneka Frazier

        Martin Ramsden

·            Abstract

Lithium battery chargers are intelligent chargers.  When charging lithium battery packs, the charger can indicate a “waiting to charge” state to the end user.  This “waiting to charge” state is often the result of a battery heating up beyond the maximum allowed threshold for charging.  Ambient temperature has a significant effect on TCO “temperature cutoff”.  However, there are often cases when the heat contributed by the charger causes the battery to TCO in slightly elevated ambient conditions.  When a TCO occurs it can lead to increased charge times and user dissatisfaction.  Currently there is no simple method to prevent a lithium battery from TCO when the heat from the charger is the culprit for the early termination.  This technique is a method for preventing TCO without adding additional hardware or software to the battery pack.

·            Description of Method and Device

As portable electronic devices grow more popular the need for portable energy solutions also grows.  Lithium Ion batteries are among the most popular energy providers for portable electronics because of their lightweight and high energy density.  Care must be taken in charging lithium ion batteries because of the inherent volatility of the chemistry.  Lithium Ion chargers must prevent the batteries from overcharging and from charging outside the manufacturer’s specified temperature range (typically 0C to 45C for most lithium ion cell suppliers).  Most lithium battery packs incorporate a thermistor that reflects the cell temperature via a thermally controlled resistance.  The Lithium Battery charger will terminate the charge current if the thermistor indicates a cell temperature outside the specified charging range.  The hardware used to monitor the thermistor may be identical to hardware used in existing lithium battery chargers.  Figure 1 illustrates the embodiment of hardware used to interface with a thermistor.


Since portable electronic devices have the ability to be used in a wide variety of ambient conditions, it is important that lithium battery chargers also operate without any nuisance charging indications in those same ambient conditions.  This method for preventing TCO in a lithium charger utilizes an algorithm that reduces the power dissipation of the lithium charger by...