Chapter 7: Electric Braking and Energy Regeneration
AC electric technology allows precise and aggressive electric braking in which mechanical friction from a physical brake is not used as the sole means of slowing or stopping the lift truck but in addition, it ‘pours’ energy back into the battery. This process is known as ‘regenerative braking’ or ‘regen braking’ for short. In addition, because this process reduces wear on the lift truck’s conventional brake components, regen braking can lower operating costs over the life of the lift truck.
With most tier 1 AC electric lift trucks, lift truck speed precisely corresponds to the degree of travel of the accelerator pedal and won’t vary unpredictably, even on ramps. There is no longer a need for the operator to constantly switch a foot back and forth between accelerator and brake pedals in such situations, creating a much more pleasant and ergonomically pleasing working environment for the lift truck operator. ‘Regen braking’ occurs primarily with the release or easing up of the accelerator pedal and during changes of direction (e.g., going into reverse following a forward motion and vice versa). The controller senses a request to stop or slow down and creates a counter-electric force, or “back EMF,” in the motor. Essentially, this turns the drive motor into a generator and sends current in the opposite direction back toward the battery for regeneration.
With these modes of regeneration working as the lift truck carries out its normal tasks, a great deal of otherwise wasted potential energy can be, under ideal circumstances, fed back to the battery on a continual basis. Lift trucks can achieve more working cycles per charge, and users can sometimes even reduce the size of their charging stations or battery exchange areas. It is not out of the question to get two shifts of work from a lift truck with just one charge. The process for energy regeneration in electric AC lift trucks serves to top off a battery “on the run” and extend the time between charges, though regeneration is not intended to be an outright substitute for a full battery charge. The characteristics of an electric AC system allow for potent regeneration with a large amount of energy transferred back to the battery.
An AC lift truck can electrically brake and regenerate battery charge all the way down to zero mph, giving it essentially “infinite” speed control. The ability of an AC lift truck to regenerate down to zero mph allows for very smooth direction changes, which become evident in a smoother operation and more productive shuttling overall. In addition, the use of aggressive regenerative braking allows for a more level battery discharge rate during peak battery draw periods, resulting in longer battery run-times.
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HCO Innovations is publishing this eight-part series as an in-depth comparative analysis and discussion on Compressed Natural Gas (CNG) Internal Combustion (IC) motors and Alternating Current (AC) Eletric lift truck engines, Comparison Analysis of CNG (IC) vs. AC Electric Lift Trucks, by Will Van Ness, VP of Fleet Management at HCO Innovations.
Comparison Analysis of CNG (IC) vs. AC Electric Lift Trucks (AC)
The materials handling industry continues to evolve at a rapid pace, particularly in the area of motive power propulsion. Tremendous technological advancements have been made over the past decade to directly address the rising cost of petrol (fossil fuels) along with stricter emission standards. Today’s MHE acquirers have more choices than ever when it comes to motive power propulsion and with the success seen amongst fleets utilizing alternative fuel sources such as lithium ion (LION) and Hydrogen Fuel Cell (HFC), the choices will most likely increase as time goes on. For the purpose of this discussion document, our focus will be on comparing AC Electric (AC) to Internal Combustion powered lift trucks (IC), specifically compressed natural gas (CNG).