Direct AC Drive Puts You in Control
by Adam Hailey - Director of Global Design Engineering On Feb 2, 2017, 03:00 AM
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Ever wonder why some electric booms perform differently as compared to hydraulically driven diesel units? The short answer is the limitations of DC drive systems. Conventional DC motors with brushes offer limited speed range, forcing low gear ratios and high motor torques. They are also slow to reverse torque, since the field of polarity has to change. The end result – a long lag time before the machine throttle-ups to full speed and aggressive slowdowns.
We have pioneered new AC drive technology for electric and fuel-electric booms with direct AC drive featured on the Genie® Z™-60/37DC and FE, Z-40/23 N and NRJ and Z-33/18 models. Our direct drive design allows operators to take advantage of both indoor and outdoor jobs to increase machine utilization rates without sacrificing drive performance. These models handle just as well as hydraulically driven diesel units without the expense or fuel consumption of larger Tier 4 final engines.
For over a decade, Genie has continually advanced our AC direct drive systems, improving efficiency to maximize battery life. With our latest design, the maintenance-free system integrates the motor, brake and gearbox into one unit. There are no brushes to replace or commutators to service, reducing time in the shop and increasing operating time in the field.
Our system is 50% more efficient than DC electric-over-hydraulic drives. In these systems, the DC pump motor drives a hydraulic pump that powers both lift and drive functions, which also require additional valves and hoses to manage speed. This results in efficiency loss and heat generation, and heat leads to wasted battery capacity. This is the primary reason why an electric 13,500-lb competitive unit with electric-over-hydraulic drive requires 300 amps of current, while the 17,100-lb Z-60/37DC and FE boom featuring direct AC drive requires only 125 amps to operate on a flat surface. This substantially extends battery life.
Our new AC direct drive also features a simplified mechanical braking system, designed to last the life of the boom, with no brake pads to wear or change. Featuring speed sensors, the efficient regenerative braking system helps to maintain consistent speed and returns some energy back to the battery, further lengthening operating time on a single charge.
One primary advantage to the AC direct drive system is much more precise low-speed control than DC drives. No more jerky back-and-forth start-ups with electric booms; just effortless positioning like with hydraulically driven units.
Traction on electric units like our all-wheel drive Z60/37DC and FE boom – which is the largest electric all-wheel drive unit on the market – is actually better than that of most hydraulically driven diesel models. Our AC direct drive system balances torque to each wheel, even at maximum steering angle, while hydraulic drive units cannot. Additionally, it applies full torque to all four wheels. So even if one wheel breaks traction, torque is not affected on the other three wheels. Conversely, wheel slippage on a hydraulically driven unit results in oil leakage to the spinning wheel and traction suffers.
If you’ve ever wanted to use an electric boom with DC drive outdoors, it would have to be in a clean and dry location. With an Ingress Protection rating of IP40 common to many DC drive units, dust and water can infiltrate the drive system, which can negatively impact performance of the drive and control systems. The sealed AC drive design that Genie uses on its models, on the other hand, offers an IP67 rating, so the system is completely protected from dust ingress and safeguards against immersion in water up to 1-m deep.
The bottom line for many boom customers is flexibility and savings, and our AC direct drive system delivers both. The drive’s sealed design allows these electric and Fuel-Electric booms to be used on both indoor and outdoor jobs equally as well, offering a high rate of return on invested capital. And, since even the fuel-electric models require only small engines of less than 25 hp, contractors save significantly on fuel every day and don’t have to service complex after-treatment systems.