Picking a scissor lift: in the final analysis, a new machine pays for itself in long-term savings and reliability.
Published in: Electrical Contracting Products
Date: 4/1/2006
By: Jobes, Jim
If your jobs require overhead work and you are still using ladders or scaffolding, it’s time to consider the efficiency and safety of a scissor lift. With an electric-powered scissor lift, you’ll provide a safer work environment for your employees and make it easier for them to meet OSHA requirements that call for people working more than six feet above ground level be protected from falls. The guardrails on a scissor lift fulfill those requirements. However, some manufacturers also recommend the use of personal fall arrest equipment when operating a scissor lift.
Another feature of scissor lifts is their versatility. Most frequently they are used inside, but they are also suitable for outdoor use as long as they are operated on a firm, level surface. They can also be driven from one location to another and positioned to resume work without a lot of set-up time.
Scissor lifts’ maximum platform height for overhead work normally ranges from 19 feet to over 40 feet. In the shorter 19- to 20-foot range, machine width for most scissor lifts is usually 30 inches, which means they can be driven through standard 32-inch doorways or into freight elevators when working on multi-story projects.
In larger units, the machine’s body is wider (up to 46 inches) with higher platform heights. Standard capacity for most 20-foot platform height machines is 500 pounds, while larger scissor lifts’ capacity can go up to 1,000-pounds or more.
A feature that helps increase versatility is fold-down rails on the platform. When a 20-foot model with a normal stowed height of 87 inches is fitted with folding rails, its overall machine height becomes just under six feet, making it capable of being driven through pedestrian doors.
Another feature that has become standard on lift machines is a platform extension. This is a rollout platform extending about three feet, with a capacity of 250 pounds. The advantage of extensions is that they overcome the access limitation of scissor lifts. Since scissor lifts normally only lift vertically, the platform extension provides some horizontal reach to extend over obstacles.
Cost Considerations
For most electrical contractors, a scissor lift with a 20-foot platform height is the most useful size to own. If more height is required for a particular job, a larger scissor lift can be rented. In the 20-foot range, a used machine can be found on the Internet for as little as $4,600–but be careful! Batteries do wear out and they are costly to replace, hydraulic hoses can deteriorate or have loose fittings resulting in fluid leakage problems and electronic controls can be at the end of their useful life and need replacing.
A new 20-foot platform height scissor lift lists around $16,000 and will have new features that can make this investment worthwhile such as improved controls, lighter weight aluminum platform decks, re-engineered drive systems that use electric motors rather than hydraulic motors and a hydraulic lift cylinder combined with the hydraulic reservoir. Other advantages to the newly designed scissor lifts include reduced maintenance, significantly extended battery life and less chance for hydraulic leaks since some models have only four hydraulic connections versus the 40 or more on some older machines.
Duty Cycles
After considering where you will most likely use the scissor lift, the height you need to reach, and the amount of weight you need to lift, another important factor in choosing a lift is its duty cycle–a measure of how long the machine can be operated before the batteries are discharged. The longer the duty cycle, the fewer times the batteries need recharging. Each time a battery is recharged, a portion of the plates are consumed until the battery pack is no longer functional. When batteries aren’t charged as frequently, they last longer and don’t have to be replaced as often.
The duty cycle has become a basic method to measure battery life for electric powered aerials. For scissor lifts, the test starts with a fully charged machine on a clear level surface with the platform in the stowed position. The machine is then driven 100 feet forward, stopped and the platform is raised to its full extension. The platform is then lowered and the machine driven back 100 feet along the same path to complete one duty cycle. The procedure is repeated until the machine no longer functions, i.e. the batteries are discharged.
The number of times a machine can complete the test is its duty cycle rating. It’s not a perfect test because there are many factors that can influence the outcome. Ambient temperature, time between tests, area surface and speed of operation are among the elements that can affect the test. Nonetheless, it’s a good indicator of how long you can use a machine on the job without having to stop to re-charge the batteries. Obviously, contractors need a lift that will operate throughout their work shift so the batteries can be re-charged overnight. In general, the longer the duty cycle, the better machine.
Additional Benefits
Another benefit of newer scissor lifts is the smaller size of the battery pack installed. Newer machines use lighter but stronger alloys, consolidated operating systems and incorporate more precision bearings and more accurately machined scissor pins. As a result, frictional drag is reduced and machines can operate more efficiently, so smaller battery sizes can be used. Today, the most popular machines use 220 ampere-hour batteries rather than older, heavier 245 ampere-hour size. Smaller batteries mean the machine has less weight and lower battery replacement costs.
The design innovation that delivers the greatest improvement in the number of duty cycles is the use of direct drive electric motors instead of hydraulic motors. Using direct drive eliminates inefficiencies of pumping hydraulic fluid through hoses to and from the reservoir to the hydraulic motors driving the machine.
Electric drive motors power the wheels more efficiently than hydraulic motors. The efficiency of an electric drive is 65 percent versus hydraulic drive at 30 percent. In other words, scissor lifts with electric drive motors operate at twice the efficiency of machines that use hydraulic motors for their drive function.
Another innovation in new scissor lifts is industry specific workstations that integrate most of the tools needed by electricians into the scissor lift platform. The workstations for electricians include a work bench with compartments for components and tools, a conduit rack and a wire tree that can hold up to six spools of wire. A 12V plug can be added for recharging battery-powered tools.