03.01.2015 Views

handbook of modern sensors

handbook of modern sensors

handbook of modern sensors

SHOW MORE
SHOW LESS

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

224 5 Interface Electronic Circuits<br />

Leclanche (Carbon–Zinc) Batteries. These batteries use zinc as the anode. They are<br />

<strong>of</strong> two types. One uses natural manganese dioxide as the cathode with an ammonium<br />

chloride electrolyte. A “premium” version uses electrolytic manganese<br />

dioxide as the cathode and a zinc chloride electrolyte. These batteries are still<br />

the most popular worldwide, especially in the Orient, being produced by over<br />

200 manufacturers. Their use is about equal to that <strong>of</strong> the alkaline in Europe, but<br />

is only near 25% <strong>of</strong> alkaline batteries in the United States. These batteries are<br />

preferred when a high power density is not required and shelf life is not critical,<br />

but the low cost is a dominating factor.<br />

Alkaline Manganese Batteries. Demand for these batteries grew significantly, especially<br />

after a major improvement: the elimination <strong>of</strong> mercury from the zinc anode.<br />

The alkaline batteries are capable <strong>of</strong> delivering high currents, have improved<br />

power/density ratio, and have at least 5 years <strong>of</strong> shelf life (Table A.20).<br />

Primary Lithium batteries. Most <strong>of</strong> these batteries are being produced in Japan. The<br />

popularity <strong>of</strong> lithium–manganese dioxide cells grows rapidly thanks to their<br />

higher operating voltage, wide range <strong>of</strong> sizes and capacities, and excellent shelf<br />

life (Table A.21). Lithium iodine cells have a very high energy density and allow<br />

up to 10 years <strong>of</strong> operation in a pacemaker (implantable heart rate controller).<br />

However, these batteries are designed with a low-conductivity solid-state electrolyte<br />

and allow operation with very low current drain (on the order <strong>of</strong> microamperes),<br />

which <strong>of</strong>ten is quite sufficient in cases for which passive <strong>sensors</strong><br />

are employed.<br />

The amount <strong>of</strong> lithium in the batteries is quite small, because just1gissufficient<br />

for producing a capacity <strong>of</strong> 3.86Ah. Lithium cells are exempt from environmental<br />

regulations, but are still considered hazardous because <strong>of</strong> their flammability.<br />

5.10.2 Secondary Cells<br />

Secondary cells (Tables A.22 and A.23) are rechargeable batteries. Sealed lead acid<br />

batteries <strong>of</strong>fer small size at large capacities and allow about 200 cycles <strong>of</strong> life at<br />

discharge times as short as 1 h. The main advantages <strong>of</strong> these cells are low initial<br />

cost, low self-discharge, on the ability to support heavy loads and withstand harsh<br />

environments. In addition, these batteries have a long life. The disadvantages include<br />

relatively large size and weight as well as potential environmental hazard due to the<br />

presence <strong>of</strong> lead and sulfuric acid.<br />

Sealed nickel–cadmium (NiCd) and nickel–metal hydrate (Ni-MH) are the most<br />

widely used secondary cells, being produced at volumes <strong>of</strong> over 1 billion cells per<br />

year. The typical capacity for an “AA” cell is about 800 mA h and even higher from<br />

some manufacturers. This is possible thanks to the use <strong>of</strong> a high-porosity nickel foam<br />

or felt instead <strong>of</strong> traditional sintered nickel as the carrier for the active materials. The<br />

NiCd cells are quite tolerant <strong>of</strong> overcharge and overdischarge. An interesting property<br />

<strong>of</strong> NiCd is that charging is an endothermic process, (i.e., the battery absorbs heat),<br />

whereas other batteries warm up when charging. Cadmium, however, presents a potential<br />

environmental problem. Bi-MH and <strong>modern</strong> NiCd do not exhibit a “memory”<br />

effect; that is, partial discharge does not influence their ability to fully recharge. The

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!