"Energy" is much in the news today, with good reason. Until the early 70s, the cost of electrical energy was not considered to be very important, and sometimes even went unstated in evaluating the cost of material handling operations. The "payback" of capital outlay and labor costs were the major considerations completely overshadowing the relatively miniscule costs of energy.

No longer, however, does capital outlay, or the cost of borrowed money, or of labor, etc., overshadow the cost of energy. Indeed, now, many engineering and purchasing decisions begin with an analysis of energy costs.

The reasons are obvious. Just as the shortages of gasoline and diesel fuel to operate combustion-engine vehicles have drastically increased their per-mile operating costs, so have the increased cost of generating and delivering electrical energy raised the cost of operating battery powered fork lift trucks. Every fork lift truck is a user of energy, whether that energy is derived from gasoline or from an electric grid fed by hydro-power, nuclear power, or fossil fuels. With all three categories of energy displaying strong tendencies to increasing costs in the foreseeable future, it is entirely reasonable to expect increasing concern for improving the overall efficiency with which battery-powered fork lift trucks are operated.

As developers and manufacturers of several proprietary instruments for monitoring the performance of batteries, we at Curtis have actively pursued the subject of efficiency in battery-powered vehicles.

An early example was our design of the battery state-of-charge indicator for NASA's Lunar Rover vehicle. The object in that case was to warn the astronauts so that they would not drive too far from their base station there being no means available for recharging the Rover's batteries,

A parallel program is our 933 Fuel Gage for battery-powered fork lift trucks. Here, the instrument is used to warn the driver when the truck's battery has reached the safe limit of discharge. Tens of thousands of these units are now in use on fork lift trucks throughout the world.

As we work with and listen to industry people using electric fork lift trucks, one theme emerges over and over again. "How can we minimize our energy costs?"

The purpose of this book is to assist those people in minimizing their energy costs:

        By helping them to correctly select batteries for their trucks.

        By showing them how to control the use of electrical energy in recharging their batteries.

        By helping them to avoid damaging batteries and trucks by over-discharging batteries.

The material in this book was compiled from numerous standard reference sources, from data published by manufacturers of lead acid traction batteries, from published technical papers, and from various engineering investigations carried on by Curtis as part of our ongoing study of batteries and their applications. There are, of course, no direct references to particular makes or models of truck, battery or charger. Of necessity we have generalized our examples to give them the widest possible application. Thus, where estimates of energy use, etc., are given, they are approximations based on our experience in the field and confirmed by reference to published product data. Note also that we have avoided placing specific values on capital equipment, labor, and energy.

Whenever feasible we have used nomenclature and abbreviations that conform to industry standards. In case of doubt we have relied on the standards promulgated by the IEEE/ANSI.

The text of this book has been reviewed for us by several well-known specialists in the field, and we would like to thank them individually:

Dr. David P. Boden, Vice-President Engineering and Technology, Douglas Battery Mfg. Co., Winston-Salem, N.C.

Larry E. Heisey, Battery Charging Engineer, Hobart Brothers Co., Troy, OH.

R. T. Josey, Mark C. Pope Associates, Inc., Smyrna, GA.

Service Engineering Department, Caterpillar Tractor Co. (Tow Motor), Mentor, OH.

Dr. William Reinmuth, Professor of Chemistry, Columbia University, NYC.

Curtis Instruments, Inc. - Mount Kisco, N.Y.

December 1980

The staff of Curtis Instruments. Inc ., assumes sole responsibility for the accuracy of the information in this book. In no way should it be assumed that the reviewers endorse the products referred to by company name and model in the text.