Browse Prior Art Database

THERMISTOR HEAT SINK FOR NiMH CHARGE CONTROL

IP.com Disclosure Number: IPCOM000007837D
Original Publication Date: 1996-Aug-01
Included in the Prior Art Database: 2002-Apr-29
Document File: 2 page(s) / 81K

Publishing Venue

Motorola

Related People

Edward Decker: AUTHOR

Abstract

Nickel electrode NiMH cells typically heat significantly at the beginning of fast charge. This early heating can cause chargers to trip early if the primary termination is AT Ifthe charger cannot be modified to accommodate this early heating (by ignoring AT for, say, the first five minutes of fast charge) then the solution needs to be in the battery. The heat sink, placed between the cells and the thermistor, delays and smooths out the initial heating so that early trip will not occur. As the battery con- tinues to charge the heat sink temperature saturates and the thermistor will accurately reflect the cell temperature so that at the end of fast charge correct AT charge termination will occur.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 56% of the total text.

Page 1 of 2

Technical Developments

THERMISTOR HEAT SINK FOR NiMH CHARGE CONTROL

by Edward Decker

  Nickel electrode NiMH cells typically heat significantly at the beginning of fast charge. This early heating can cause chargers to trip early if the primary termination is AT Ifthe charger cannot be modified to accommodate this early heating (by ignoring AT for, say, the first five minutes of fast charge) then the solution needs to be in the battery. The heat sink, placed between the cells and the thermistor, delays and smooths out the initial heating so that early trip will not occur. As the battery con- tinues to charge the heat sink temperature saturates and the thermistor will accurately reflect the cell temperature so that at the end of fast charge correct AT charge termination will occur.

  NiMH charging is an exothermic process. Foam type nickel electrodes may aggravate this early heating phenomenon. Early fast charge tripping results in a battery grossly under charged which in turn will provide a short run time. This is very fius- trating to the battery end user and will result in held returns and loss ofhrture business.

  Preferred charge termination for NiMH batter- ies is based on the rate of temperature rise of the cells at the end of charge. The temperature is meas- ured by a thermistor in the battery circuit. The foam nickel NiMH cells were causing early termination because ofthe initial rise in temperature.

Woven copper strips were placed between the battery thermistor...