48 September/October 2023 | E-Mobility Engineering eBTM provides up to 10 kW of heating power and 8 kW of cooling power to keep water-cooled battery packs at their optimum temperature, despite any extremes of ambient heat or cold. “Webasto provided a nice, rounded package and we did not have to do a lot of shopping to find additional components,” Legtenberg says. Getting into a technology so new to the company, and still evolving, brought what Legtenberg calls a forest of uncertainty regarding the standards and norms they would have to comply with. This is another area in which working with Webasto was helpful, he says, as its battery systems already complied with a lot of standards relevant to electric powertrains for mobile machinery and road vehicles. He also points to the extensive environmental testing that Webasto carried out on the battery system, particularly shock and vibration tests using shaker rigs. Christian Kiemer, e-mobility applications engineering manager at Webasto, points out that the company’s facility in Hengersberg, Bavaria, has a very large shaker rig that can generate accelerations up to 50 g. “The shaker is in a climatic chamber, so you are not only shaking test items but doing so in harsh conditions such as very low and very high temperatures, so you can simulate a lot of use cases,” he says. “There are not many of these shakers in Europe, maybe two or three, and one is in our facility. This helps a lot to make the batteries as robust as possible, especially for the off-highway market.” NMC over LFP Legtenberg emphases the importance of cooling the battery pack, which is based on lithium nickel manganese cobalt oxide (NMC) cell chemistry and is inherently more vulnerable to thermal runaway than lithium iron phosphate (LFP). “There was a lot of discussion about whether we should use LFP or NMC batteries,” he says. “We decided that the Webasto NMC batteries would be best for off-road applications, because they have a high energy density, are highly certified [including for control of thermal runaway] and can also run in freezing temperatures. On the construction site, you need robustness and high energy density, and in winter you need to start in the morning after a cold night.” The only part of the battery system not supplied by Webasto is the twin 12 V battery used during start-up for the high-voltage system, powering the BMS and closing the contactors on the 800 V packs. As the whole system runs on DC, the power electronics boxes perform the DCDC conversion and voltage regulation. Nominally rated at 800 V, the battery supplies the DC bus with 790-670 V over the course of the working day. Legtenberg explains, “This DC bus voltage is converted to 840-890 VDC by the DC-DC converter to a central DC bus voltage. The voltage drops more than an LFP battery would, so we need the converter. With this set-up, we can still use the maximum power of 613 kW at the end of a heavy working day, even when the batteries are nearly empty.” Although the 90DRe is a very large machine, space and weight are at a premium because of packaging and transport constraints, and the high voltage allows the size and weight of the conductors to be reduced for a given power draw, Kiemer says. The battery system also supports charging from the mains during operation. While not needed to provide maximum power, this simultaneous charging and discharging provides the ability to top up the battery pack if the machine has to use more energy because of heavy ground conditions. Electro-hydraulics Each of the two Danfoss PM motors drives its own hydraulic pump. When the rig needs to move under its own power between piles, the smaller of the two motors draws power from the smaller battery pack installed on the machine deck to power the hydraulic motors that drive the tracks and the smaller winches. When the rig is in position, the larger motor draws from the main pack in its container attached to the back of the machine deck to power the big winch and whichever tool is fitted to the leader. When maximum power is required, however, both motors draw from both sections of the battery, and all the hydraulic flow from both pumps can be directed to the winches and the tooling. Together, the low and high-pressure pumps can deliver hydraulic fluid at up to 350 bar. Two permanent magnet DC motors are mounted above the hydraulic pumps powered by them. They can operate separately or together to run the tracked propulsion system and the machinery and tooling
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