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LHD BATTERIES 38 E&MJ; • JANUARY 2017 www.e-mj.com heat and hydrogen gas. The heat from either could initiate a decomposition re- action, leading to a thermal runaway en- hanced by oxygen gas." Lithium batteries require a specific tem- perature range, Nieto reported. "Thermal regulation is a larger concern with Li-ion batteries as storing above room temperature can cause irreversible self-discharge of the cell. Thermal runaway becomes increasing- ly more probable as the cell temperature in- creases past 60° C. The battery will exhibit increasingly unpredictable behavior the greater the deviation from its operational temperature range of -40°C to 60°C." Overcharging can lead to thermal run- away, fire and explosion, Nieto reported. "Li-ion cells are not very tolerant of being overcharged. Upon overcharging, the cell experiences expansion, which is signifi- cant enough, in some cases, to cause a cell breach. The cell temperature increas- es rapidly upon overcharge, which if un- checked would lead to thermal breakdown of metastable components releasing heat and oxygen. This positive feedback leads to a thermal runaway." Kasaba said Artisan has answered these challenges. Artisan battery packs are engineered "such that they stay close to whatever the ambient temperature is in the mine," he said. "So for an air tempera- ture of 35°C to 40°C, we are trying to keep our batteries in that same range too." Artisan has developed a battery man- agement system that prevents the possi- bility of overcharging. "Our battery system controls the charger so the battery system knows exactly what its state of charge is and it tells the charger how much charge it wants, when to start reducing the cur- rent levels as it approaches 100% charge, and when to shut off. So the battery is always in full control of the charge itself." The battery management system fac- tors in overall mine design to prevent overcharging due to regenerative brak- ing. "We look closely at any scenario where there might be a chance to get to full charge and then have to go downhill. We find that this is an extremely limited event that rarely ever happens, but if it ever happens, our system is designed to dump that power out in heat through the hydraulic system versus trying to charge the battery," Kasaba said. Battery packs are designed to withstand abuse, and Artisan reportedly does not use the more volatile chemistries in their de- signs. "Anything like that, that creates a risk of a lithium fire, we stay away from those chemistries completely. The lithium iron phosphate is much safer in that regard." Headlines reveal lithium battery tech- nology has made marked gains in reliability despite some noteworthy setbacks. While in September Samsung was ramping up a recall of one of its lithium battery-pow- ered phones on the basis of reports of it igniting, Jaguar was planning to unveil its first "fully electric," 90-kWh lithium bat- tery-powered car. In December, Apple be- gan offering replacements for 6S batteries after a number of reports of them igniting. Meanwhile, the state of Colorado green lighted infrastructure for and road testing of battery-powered transit trucks. Shortly thereafter, Amazon delivered a 14-lb pack- age by battery-powered unmanned aerial vehicle to a rural U.K. residency within 15 minutes of order placement. At roughly the same time, the United Parcel Service be- gan road testing battery-powered trike ma- chines for deliveries in Portland. These and other battery-powered technologies and machines are esteemed because of their utility and operability, and because they are emissions-free. In mining, battery-powered equipment, now beyond the testing phase, shows a propensity to save companies money while expanding capabilities and improving public and investor relations. Real and Hypothetical Savings The bottom line could drive the switch to battery-powered LHDs and underground hard rock mining machines, said Pierre Mousset-Jones, Ph.D., professional engi- neer, professor emeritus of mining engi- neering, Department of Mining Engineer- ing, MacKay School of Earth Science and Engineering, the University of Nevada at Reno. Nonetheless, those savings are diffi- cult to generalize and project because the market share for battery-powered mining machines remains comparatively minute. "There is no question that capital and operating cost savings may well be quite significant in an all-electric mine, but it is difficult to generalize since each mine is unique," Mousset-Jones said. Typical- ly, proponents of battery-powered mine machinery accurately say ventilation cost savings justify the switch. For example, he reported, reducing fan speed from 100% to 80% reduces electricity consumption by 50%. Generally, the equation results in savings, but the variables are numerous, Mousset-Jones said. "In a particular mine, there are oth- er reasons for requiring airflow to be at a certain level, such as to keep the miners breathing, reduce dust levels and poison- ous gases (other than diesel particulate matter and exhaust gases) below regula- tion limits, provide sufficient cooling in hot mines, dilute radon daughters and ra- diation levels," he said. "Certainly, elec- tric-powered equipment produces much less heat than diesel power, hence in hot mines they can also reduce the need for airflow or refrigeration in the mine. This can be a significant savings." Nonetheless, electric vehicles pro- duce some heat. Further, where virgin rock temperatures are high and the break- ing of rock is fast, a significant portion of the total heat load in the heading may be unrelated to diesel machinery usage, Mousset-Jones reported. "In such a case, GE's electric LHD offers 'gradient control engine technology,' the company reported. 'We see GE as unique because we're the ones who have the heavy-duty electric propulsion expertise,' said Pat Jansen, senior engineer, under- ground mining. (Photo: GE)