Bigger batteries. Bigger challenges?
18 June 2019
There is a growing trend to replace IC trucks with heavy duty electrics. These larger electric trucks need larger batteries, together with chargers capable of charging them efficiently, quickly and reliably.
These challenges can now be met using High Frequency (HF) technology modular chargers. Capable of supporting 96V and 120V operations, and ratings to 21kW, they allow charging of the largest electric materials handling vehicles. Below is a list of 12 key issues to overcome.
#1 Until now, a solution for charging 120V batteries at 21kW has not been available on the market from a large industrial charger manufacturer; the legislative and technology barriers have been too high.
Modular chargers with the correct HF technology can now overcome these barriers. This means that owners can support vehicles of all sizes with a single charger range. Additionally, the chargers’ modular design adapts to a wide range of battery capacities, allowing a potential reduction in the number of chargers on site; freeing-up space.
#2 As warehouse operations intensify, use larger-capacity vehicles and consume more power, improving power efficiency has become essential. Because of their high-frequency design and modular topology, modular chargers can achieve OPEX savings over the traditional ‘50Hz’ charger types. This can be further improved through the use of modern batteries with more advanced technology and lower input impedance.
#3 As a battery approaches full charge, its load on the charger reduces; this causes traditional chargers to operate less efficiently.
Solution: Modular chargers can have up to six modules sharing the load. These are progressively switched off as the load falls, so the modules remaining on line stay well-loaded and efficient throughout the entire charging cycle.
#4 Conventional chargers tend to overcharge their connected batteries by up to 20%; this wastes energy and can reduce battery life.
Using modular chargers with carefully designed charging profiles eliminates this tendency and prolongs battery life.
#5 In addition, modern, modular battery chargers provide energy savings potential. For example, internal tests have shown that, depending on locally prevailing energy costs, a 120V 1500Ah battery that would typically cost €50 to charge using a ‘50Hz’ charger would cost approximately €37 with the modular charger type. This represents significant possible savings when multiplied over the entire battery fleet’s daily operations.
#6 As warehouses face ever-increasing pressure to move stock fast, they cannot afford to lose productivity through an inoperable charger. Modular chargers share the load across their multiple modules. If one fails, the others continue to support the load at reduced power without stopping the charging process. For particularly critical operations, extra modules can be added for N+n redundancy.
#7 Chargers can adversely affect warehouse productivity through excessive charging periods as well as by failing. Using optimised charging profiles reduces charging times by one or even two hours, depending on battery type.
#8 Further loss of productivity arises if maintenance interval periods must be shortened. As each 60 litre water top-up can take 20 to 30 minutes, with the battery being unavailable for use, this is another strong consideration.
Intelligent charging can extend the maintenance intervals for some batteries to up to eight weeks, compared with just one week to 10 days for conventional chargers.
#9 Conventional chargers with a poor input power factor mean that supply cabling and switchgear must be upsized, while the mains supply is overloaded with reactive power and subjected to AC distortion.
These problems can be nearly, if not entirely eliminated, by using modern modular chargers that have a power factor close to one.
#10 Maintaining chargers can be time-consuming and labour intensive if each unit has to be inspected on the warehouse floor.
With the right infrastructure, battery chargers can have wireless devices installed to allow communication and easy visibility of charger status from a central location.
#11 While we have already seen how a modular design keeps the charger operational even if a module fails, it is still important to minimise the impact of a module failure if it does occur.
Self-diagnostic functions on modular chargers flag any failure, and fitting a new module is a simple plug-and-play operation. Standard modules are always available for rapid delivery and replacement.
#12 Batteries cannot be optimally charged if the charger is not set up correctly for them.
Today’s modular chargers can offer automatic identification of their connected batteries, together with automatic switching of the output voltage (within the charger’s specification). The control algorithm also enables increased efficiency and power factor control.
Martin Walsh, senior product manager motive and reserve power, EnerSys EMEA