Dismiss
There will be a system update on Friday, May 5th, 6 PM ET. You may experience a brief service interruption.
Browse Prior Art Database

NICKEL METAL HYDRIDE (Ni-MH) CELL THERMAL BALANCE DURING PARALLEL CHARGING

IP.com Disclosure Number: IPCOM000007375D
Original Publication Date: 1995-Mar-01
Included in the Prior Art Database: 2002-Mar-20
Document File: 2 page(s) / 79K

Publishing Venue

Motorola

Related People

James L. Tidwell: AUTHOR [+2]

Abstract

Due to design form factors and space limitation it is sometimes desirable to utilize cells in a parallel configuration to increase the available capacity of a battery pack.

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 50% of the total text.

Page 1 of 2

0 M

MOTOROLA Technical Developments Volume 24 March.1995

NICKEL METAL HYDRIDE (Ni-MH) CELL THERMAL BALANCE DURING PARALLEL CHARGING

by James L. Tidwell and Robert E. Richter

  Due to design form factors and space limitation it is sometimes desirable to utilize cells in a parallel configuration to increase the available capacity of a battery pack.

  Wth Nickel Cadmium (Ni-Cd) technology this works very well due to the thermal characteristics and voltage characteristics of this technology. Typi- cally the cells are self balancing. Current will nor- mally divide appropriately between the cells during charging not adversely affecting the thermal char- acteristics or rapid charge termination.

This is not the case with Ni-MH cells.

  Due to the voltage differences, impedance dif- ferences and due to the relative difference of the cell voltage as the cell is heated, Ni-MH cells will not effectively charge in a parallel configuration. Ther- mal balance of Ni-MH cells is not automatic. The cell receiving the most current will heat more since the Ni-MH chemical reaction during charge pro- duces heat proportional to the rate of charge. They will continue to heat depending on the rate ofcharge and their ability to dissipate the heat which is depend- ent on the construction of the battery pack. This effect will allow one cell string to thermally domi- nate the cell pack. This will prematurely terminate rapid charge since most Ni-MH rapid chargers uti-

lize heat to control rapid charge.

  This thermal problem is solved by the add...