10. Getting the Most from your Batteries

GUIDE: Batteries in a portable world. 10. Getting the Most from your Batteries

It appears that you are using AdBlocking software. The cost of running this website is covered by advertisements. If you like it please feel free to a small amount of money to secure the future of this website.

<< Previous page  INDEX  Next page >>

10. Getting the Most from your Batteries

A common difficulty with portable equipment is the gradual decline in battery performance after the first year of service. Although fully charged, the battery eventually regresses to a point where the available energy is less than half of its original capacity, resulting in unexpected downtime.

Text Box: In many ways, a rechargeable battery exhibits human-like characteristics.Downtime almost always occurs at critical moments. This is especially true in the public safety sector where portable equipment runs as part of a fleet operation and the battery is charged in a pool setting, often with minimal care and attention. Under normal conditions, the battery will hold enough power to last the day. During heavy activities and longer than expected duties, a marginal battery cannot provide the extra power needed and the equipment fails.

Rechargeable batteries are known to cause more concern, grief and frustration than any other part of a portable device. Given its relatively short life span, the battery is the most expensive and least reliable component of a portable device.

In many ways, a rechargeable battery exhibits human-like characteristics: it needs good nutrition, it prefers moderate room temperature and, in the case of the nickel-based system, requires regular exercise to prevent the phenomenon called ‘memory’. Each battery seems to develop a unique personality of its own.

10.1 Memory: myth or fact?

              <p><img width="236" height="141" src="/img/guide_bpw2/c10_02.gif" align="left" hspace="19" vspace="19" alt="Text Box: For clarity and simplicity, we use the word ‘memory’ to address capacity loss on nickel-based batteries that are reversible." v:shapes="_x0000_s1033" border="0" />The word ‘memory’ was originally derived from ‘cyclic 
                memory’, meaning that a NiCd battery can remember how much 
                discharge was required on previous discharges. Improvements 
                in battery technology have virtually eliminated this phenomenon. 
                Tests performed at a Black &amp; Decker lab, for example, 
                showed that the effects of cyclic memory on the modern NiCd 
                were so small that they could only be detected with sensitive 
                instruments. After the same battery was discharged for different 
                lengths of time, the cyclic memory phenomenon could no longer 
                be noticed.</p> <p>The problem with the nickel-based battery is 
                not the cyclic memory but the effects of crystalline formation. 
                There are other factors involved that cause degeneration of 
                a battery. For clarity and simplicity, we use the word ‘memory’ 
                to address capacity loss on nickel-based batteries that are 
                reversible.</p> <p>The active cadmium material of a NiCd battery 
                is present in finely divided crystals. In a good cell, these 
                crystals remain small, obtaining maximum surface area. When 
                the memory phenomenon occurs, the crystals grow and drastically 
                reduce the surface area. The result is a voltage depression, 
                which leads to a loss of capacity. In advanced stages, the 
                sharp edges of the crystals may grow through the separator, 
                causing high self-discharge or an electrical short.</p> <p>Another form of memory that occurs on some NiCd 
                cells is the formation of an inter-metallic compound of nickel 
                and cadmium, which ties up some of the needed cadmium and 
                creates extra resistance in the cell. Reconditioning by deep 
                discharge helps to break up this compound and reverses the 
                capacity&nbsp;loss.</p> <p>The memory phenomenon can be explained in layman’s 
                terms as expressed by Duracell: “The voltage drop occurs because 
                only a portion of the active materials in the cells is discharged 
                and recharged during shallow or partial discharging. The active 
                materials that have not been cycled change in physical characteristics 
                and increase in resistance. Subsequent full discharge/charge 
                cycling will restore the active materials to their original 
                state.”</p> <p>When NiMH was first introduced there was much 
                publicity about its memory-free status. Today, it is known 
                that this chemistry also suffers from memory but to a lesser 
                extent than the NiCd. The positive nickel plate, a metal that 
                is shared by both chemistries, is responsible for the crystalline 
                formation.</p> <table width="100%" border="0" cellspacing="0" cellpadding="3"> <tr> 
                  <td><img src="/img/guide_bpw2/c10_03.jpg" width="186" height="104" border="0" alt="" /></td> <td valign="top"><b><i><span class="caption">New NiCd cell</span></i></b><span class="caption">.</span> 
                    <br /> <span class="caption-sub">The anode is in fresh condition 
                    (capacity of 8.1Ah). Hexagonal cadmium hydroxide crystals 
                    are about 1&nbsp;micron in cross section, exposing large 
                    surface area to the liquid electrolyte for maximum performance.</span></td> </tr> <tr> 
                  <td valign="top"><img src="/img/guide_bpw2/c10_04.jpg" width="186" height="104" border="0" alt="" /></td> <td valign="top"><b><span class="caption">Cell with crystalline 
                    formation</span></b><span class="caption">. </span><br /> <span class="caption-sub">Crystals have grown to an enormous 
                    50 to 100 microns in cross section, concealing large portions 
                    of the active material from the electrolyte (capacity 
                    of 6.5Ah). Jagged edges and sharp corners may pierce the 
                    separator, which can lead to increased self-discharge 
                    or electrical short.</span></td> </tr> <tr> 
                  <td valign="top"><img src="/img/guide_bpw2/c10_05.jpg" width="186" height="104" border="0" alt="" /></td> <td valign="top"><b><span class="caption">Restored cell</span></b><span class="caption">. 
                    </span><br /> <span class="caption-sub">After pulsed charge, the crystals 
                    are reduced to 3 to 5 microns, an almost 100% restoration 
                    (capacity of 8.0A). Exercise or recondition are needed 
                    if the pulse charge alone is not effective.</span></td> </tr> </table> <p class="caption">Figure&nbsp;10-1:&nbsp; Crystalline formation 
                on NiCd cell.<br /> <span class="caption-sub">Illustration courtesy of the US 
                Army Electronics Command in Fort Monmouth, NJ, USA.</span></p> <p>In addition to the crystal-forming activity on 
                the positive plate, the NiCd also develops crystals on the 
                negative cadmium plate. Because both plates are affected by 
                crystalline formation, the NiCd requires more frequent discharge 
                cycles than the NiMH. This is a non-scientific explanation 
                of why the NiCd is more prone to memory than the&nbsp;NiMH.</p> <p>The stages of crystalline formation of a NiCd 
                battery are illustrated in Figure&nbsp;10-1. The enlargements 
                show the negative cadmium plate in normal crystal structure 
                of a new cell, crystalline formation after use (or abuse) 
                and restoration.</p> <p>Lithium and lead-based batteries are not affected 
                by memory, but these chemistries have their own peculiarities. 
                Current inhibiting pacifier layers affect both batteries — 
                plate oxidation on the lithium and sulfation and corrosion 
                on the lead acid systems. These degenerative effects are non-correctible 
                on the lithium-based system and only partially reversible 
                on the lead&nbsp;acid.</p>                  
     </blockquote><p align="center"><font size="2"><a href="/guides/electronics/bpw/c09_03">&lt;&lt; Previous page</a>&nbsp;&nbsp;<a href="/guides/electronics/bpw/00_toc">INDEX</a>&nbsp;&nbsp;<a href="/guides/electronics/bpw/c10_02">Next page &gt;&gt;</a></font></p>

© 1998-2023 – Nicola Asuni - Tecnick.com - All rights reserved.
about - disclaimer - privacy