Evaluating electric lift trucks
Electric rider counterbalanced lift trucks (Class I) have accounted for 15-20% of the industrial truck market for over 10 yr.
Electric rider counterbalanced lift trucks (Class I) have accounted for 15-20% of the industrial truck market for over 10 yr. For example, in 1998 this segment had a 17% share, which is less than the 24% piece taken by the Class I electric’s primary competitor-the Class IV internal combustion cushion tire truck. At the same time, the electric portion of the total vehicle market has increased to about 57%, with some growth realized in Class II narrow aisle and much more in the smaller Class III electric pallet trucks.
Class I manufacturers have always been, and currently are, extremely optimistic about the future of their product lines. They feel that their trucks have closed the performance gap often perceived between electric and internal combustion equipment, while offering a number of advantages. Increasing environmental concerns, along with advancements in electronic controls and battery technology, are helping fuel this positive feeling.
No emissions. Electric vehicles meet OSHA and other standards for indoor operation and do not emit combustion byproducts, which keep the plant air cleaner and reduce ventilation and cooling requirements. The electric vehicle is the only practical choice in a number of industries, particularly food processing.
Improved productivity. Class I lift trucks operate with a low noise level and reduced vibration to keep operators alert and less fatigued in applications that require extended periods of work. More productivity, at a safer level, results.
Less maintenance. Electric vehicles have fewer moving parts to wear out or fail, and require less preventive maintenance. Savings up to 40% in maintenance costs can result.
Lower operating costs. The amount of electricity used to charge batteries is almost always less than the fuel required by IC engines. Depending on local energy costs, electrics are up to 60% less expensive to operate.
Longer life. Electric vehicles last longer. Generally speaking, IC trucks operate 6-7 yr, while electric powered units usually run 10-12 yr.
Lower life cycle costs. An evaluation of total ownership costs over the vehicle’s life almost always favors electric lift trucks. Calculating annual equipment, fuel, and maintenance costs over the vehicle’s life determines the actual numbers. (See the “Cost comparison” sidebar for a typical scenario.)
Balancing these positive considerations are several disadvantages.
First cost . Electric vehicles (including batteries and chargers) cost up to 20% more than comparably sized IC trucks. Depending on the plant’s economic condition, this point could override all other factors.
Performance . Electrics might be impractical for long travel distances and in older plants with steep grades to negotiate, even though performance characteristics in these types of plants are improving. Also, electrics are not often considered if the vehicle is operating outdoors (particularly in northern climates).
User resistance . Many operators are just more comfortable using IC trucks. They have concerns with productivity and perceived power to do the work with electric lift trucks.
Batteries. Battery replacement and charging areoften considered a significant disadvantage. The batteries, which serve as the vehicle’s motive force and counterweight, basically operate one 8-hr shift/charge. Therefore, one battery is needed for each shift, or as many as three battery packages for use, charging, and cool down in a three-shift operation.
Changing is accomplished in a matter of minutes via a hoisting mechanism or a roller or slide arrangement where the batteries are simply pushed in and out. Floor space is required for the charging and storage area, and safety showers are needed because of the battery acid. Disposing of old batteries is a significant environmental concern.
Class I electric riders generally compete with Class IV internal combustion vehicles for inside applications at load capacities up to 6000 lb. Above that figure and for outside duties, combustion equipment usually dominates. However, electric lift trucks are available for inside and outside jobs in sizes up to 12,000 lb. In reality, though, few electrics are sold for these two situations.
Comparative performance between combustion (LPG, diesel, or gasoline) and electric lift trucks in the 2000-6000-lb range is quite similar. Combustion equipment initially moves and lifts a bit faster, but the top speed for both types is essentially the same. Both versions accommodate a wide assortment of attachments, and both are available with cushion, air-filled pneumatic, or solid pneumatic tires.
Electric rider lift trucks are available in three and four-wheel designs with the operator in a sitdown or standup position. Various price ranges and options are available in each category to match plant requirements.
Four-wheel sitdown trucks (Fig. 1) dominate the Class I market, with 57% of the 30,000 vehicles sold. These trucks are available in higher load capacities and lifts, and are perceived to offer greater stability than three wheelers.
Three-wheel sitdown vehicles (Fig. 2) are rear steered and limited to about 5000 lb. This type is more compact and turns in a much tighter radius, making the vehicles significantly more maneuverable for narrower aisle applications. The three-wheel lift truck is also lower in height and well suited for working in the dock area and in tight quarters, such as trucks or railcars. This version has 24% of the Class I market.
Three-wheel standup trucks (Fig. 3) are the most economical category. Vehicles are available in the 2000-4000-lb range. The operator faces forward or in a side position, both of which offer excellent front and rear visibility. Truck loading, maneuverability, and situations where the operator is on and off the vehicle frequently are the three-wheel standup’s forte. Standup equipment takes 19% of the Class I market.
Class I vehicles are applied in manufacturing, dock operations, warehousing, and distribution. Industries with particular concerns about emissions, such as food, beverage, and automotive, typically select electric vehicles.
Four-wheel sitdowns are concentrated in the 3000-6000-lb range. Less than 10% of the market falls into other size categories. Three-wheel trucks essentially serve 3000 and 4000-lb jobs, with over 90% of standup or sitdowns concentrated in these two sizes.
Lifting heights reach up to about 20 ft, but can go higher with special masts. Upward reach depends on mast arrangement, battery size, and weight of load lifted.
Travel speeds are about 10 mph, and lifting speeds exceed 80 fpm. Battery size and load determine the actual figures.
Because of their counterbalance, electric trucks with a battery pack weigh about twice what they lift.
Ergonomics and safety
The primary ingredient in lift truck performance, efficiency, and safety is the operator. Consequently, ergonomics play a major role in the design and operating characteristics of lift trucks. The human engineering features must be able to accommodate the changing concerns and physical sizes of the workforce.
Safety and comfort features incorporated into the trucks include adjustable seats, easy entry/exit, vibration isolation, improved control technology, and quieter operation. In addition, vehicles include power steering and brakes, tilt steering, improved operator visibility, overhead guards, seat belts, and safety interlocks.
Standup trucks present additional concerns. These vehicles include floor and hip pads, padded rear posts, and sloping sidewalls to reduce strain and fatigue on the back, shoulders, feet, and legs.
Electric lift trucks operate with 24, 36, or 48-V batteries, usually lead acid. The size depends largely on required load capacity, with 36-V found in about 75% of the vehicles. Higher voltages translate into greater lift and travel speeds, but come at a premium price.
Advancements in battery technology have allowed electric lift trucks to attain higher load capacities in the same amount of space, and longer cycle times before recharging. Maintenance-free and fast charging batteries are considerably more expensive and are becoming somewhat popular, but still used in only a limited number of vehicles.
Electric lift truck manufacturers do not make batteries.
Maintaining electric lift trucks is a fairly simple procedure. Regular checks of the fluids and controls through easily accessible locations are required on a daily basis. Battery watering is also necessary. Motor brushes are the major maintenance concern.
Onboard display panels feature diagnostic information in diagram and analog or digital form to pinpoint problem areas and facilitate maintenance and service.
-Ron Holzhauer, Managing Editor,
Plant Engineering magazine would like to thank Toyota Industrial Equipment for providing the cover photograph and other special contributions to the development of this article.
Class 1 lift trucks produce no emissions, need less maintenance, and have lower operating and life cycle costs than internal combustion vehicles.
Rider electrics are available in three and four-wheel versions with the operator standing or sitting.
The operator is the most important factor in lift truck performance, efficiency, and safety.
One of the concepts advocated for extending battery use is fast charging. This method, which has actually been around over 10 yr, slashes the time needed for charging from 8 hr to opportunity charging of 1 hr or less. Fast charging eliminates the need for multiple batteries, significantly reduces storage areas and charging rooms, possibly extends battery life, needs less personnel for swapping and charging, and minimizes some environmental and safety concerns.
The Electric Power Research Institute (EPRI) has undertaken several studies, working with battery and charger manufacturers, to examine the fast charging issue. The results to this point have been mixed.
Results of several demonstration projects revealed the positive results indicated above. On the other hand, several issues remain unresolved. These concerns include the possibility of the battery overheating, long-term effect on performance, watering needs, and power quality. Also, fast chargers are quite expensive, and there may be some impact on battery warranties.
DC to AC
Currently all electric lift trucks in the United States use dc power, with energy running from the battery pack through motors and brushes to perform motive and lifting actions. This exclusivity is soon to change as a concept found on vehicles overseas makes an introduction in this country-an ac powered lift truck.
In this four-wheel vehicle, dc energy from the battery travels through a controller and inverter. Three-phase ac power comes out of the controller. These trucks offer several advantages over a traditional electric: higher efficiency, greater acceleration and lifting, more compact motors, faster speeds, 20% longer operation/charge, tighter turning, quicker forward/backward direction changes, and lower operating costs. Some of the standard vehicle’s biggest maintenance expenses-forward/reverse contactors, motor brushes, and commutators-are eliminated.
The pneumatic tire truck is intended for outdoor applications, but could be used inside as well. Capacity ranges up to 6000 lb using a 48-V battery.
The key ingredient:Operator training
Regardless of the many safety and ergonomic features incorporated into a lift truck, the most important factor in a safe and efficient operation is the person driving the vehicle.
OSHA’s updated training standards, effective December 1, 1999, mandate that “Only trained and authorized personnel shall be permitted to operate a powered industrial truck. Operators of powered industrial trucks shall be qualified as to visual, auditory, physical, and mental ability to operate the equipment safely.”
Companies are responsible for providing training that meets these OSHA requirements. The training must include formal instruction, such as lecture, discussion, interactive computer learning, videotape and/or written material; demonstrations by the trainer; exercises performed by the trainee; and evaluation of trainee performance. The evaluation must include a written and driving test.
A 5000-lb capacity lift truck weighs about 9000 lb, or a total moving vehicle of 14,000 lb. This amount is as much as five or six automobiles. Impacts of a moving 14,000-lb load with people, materials, or equipment are often devastating, with several deaths resulting each year. Nearly half of the fatalities result from tipover accidents.
Besides the operator, a number of conditions around the plant might contribute to lift truck accidents. Check your facility for congestion (particularly in the dock area), poor lighting or blind spots, layout storage aisles and truck movement patterns, and uneven, damaged, or slippery floors.
Lift truck manufacturers offer a large assortment of safety training information.
For additional information related to this general subject, visit the “Material handling” channel on our web site: www.plantengineering.com.
A variety of factors should be considered when calculating lift truck costs, including capacity, number of shifts/day and days/yr, hourly salary plus benefits for maintenance and repair staff (or hourly labor rate if outside sources are used), and fuel costs.
This simple cost analysis compares 5000-lb capacity LPG and electric lift trucks. The vehicles operate 8 hr/day and 2080 hr/yr. Assume that maintenance labor is $26/hr, propane costs $1.09/gal., and electricity is $0.77/kWh
|Estimated life||7.5 yr||11 yr|
|Annual cost of ownership||$3224||$2386|
|(2 sets over 11 yr)|
|Annual cost of charger||NA||$171|
|Annual labor||$1040 (40 hr)||$572 (22 hr)|
Adapted from information provided by Yuasa, Inc.