Battery-powered machines, unlike their power-cord-tethered or trolley-connected cousins, have unlimited range of motion, the freedom to work in development areas without outlets, and few exposed fragile parts. Finding the right battery has been challenging enough to limit the use of this technology to specific, light-use vehicles. But two manufacturers, General Electric (GE) and RDH, have pushed battery power into a new, more intensive, application: load-haul-dump vehicles.
From scoops to LHDs
The closest relative of the battery-powered LHD would be the scoop, which is the norm for utility applications in underground coal mines, where regulations designed to prevent methane fires have discouraged diesel use. Typical scoops have a flat profile suited for low coal seams.
“Scoops, as utility machines, operate intermittently,” explained Mark Sprouls, spokesperson for Caterpillar, one of several manufacturers of battery-powered scoops. “Battery power is quite efficient in such applications, as there is no need to allow an engine to come up to operating temperature or to cool down before turning off.”
According to Sprouls, a typical coal mine has a scoop for each continuous mining section. The scoop will have four lead-acid batteries in circulation: two in the vehicle and two charging. At every shift change, the scoops pull up to a charging station near the operating area, where a hoist or a specialized transfer system is used to swap out the depleted batteries.
These batteries are extremely heavy – in the several-ton range – and large. That is why their use is limited to less demanding utility applications. But battery technologies have improved in recent years. When GE acquired the underground equipment manufacturer Fairchild in 2012, it immediately set about adapting the frame of a Fairchild battery-powered coal scoop for use as a hard-rock production LHD. Concurrently, RDH Mining Equipment developed its own battery-powered LHD.
LHDs are a different animal from scoop trams. Designed to lift and drop loads into trucks and hoppers, they have the higher, narrower profiles suited to the geometry of a hard rock mine and they come in a wider range of sizes to meet more varied needs. At their largest, LHDs can get over 20 tonnes of tramming capacity; at their smallest, they carry under two tonnes.
Building better batteries
GE decided to use 240-volt lead-acid batteries in its first models, providing customers with a familiar technology from other mining applications. Lead-acid is also a more economical battery solution than lithium-ion, which costs three to four times more per kilowatt hour, according to Sid Gaitonde, senior product manager of underground propulsion at GE Mining.
Although batteries of any type are heavy – adding as much as 20 per cent to the LHD weight – that can actually be an asset for machines during mucking operation, said Gaitonde. He explained that they get more traction when the bucket engages the muck pile. The operator does not have to let the wheels slip to ensure the bucket is completely filled. GE’s choice to power the wheels and hydraulic functions with separate AC motors provides extra efficiency, added Gaitonde. Having a dedicated motor gives the machine more traction on inclines, and the operator has better control during the different modes of operation.
Further, the more power that can be packed into that added weight, the better. Competitor RDH decided to build its prototypes with 470-volt lithium iron phosphate battery cells from the outset. Among their numerous advantages over lead-acid, lithium batteries weigh about half as much for the same power. They also live longer; whereas lead batteries last about 1,500 cycles before they need to be discarded, lithium can get up to 5,000.
Gustavo Portalier, COO at RDH, said it took about a year of testing batteries to come up with cells that provided sufficient power and that did not overheat. “This is a big learning curve with batteries,” said Portalier. “It’s why not many companies do it.”
Kirkland Lake Gold
RDH won its first customer through field tests at the Macassa mine in Ontario, where a deepening mine plan led owner Kirkland Lake Gold to find ways of reducing ventilation needs. The first battery-powered LHD went underground in 2012, followed by three 18-tonne trucks the year after. Batteries are now powering 12 LHDs at Macassa, each with buckets that hold about 2.3 cubic metres.
The mine keeps three batteries available for each vehicle at any given time: two on board – one in use and one spare – while a third is charging. A single battery can operate the machine for up to four hours, and each takes up to an hour and a half to recharge. When one of the vehicle’s batteries runs low, it stops by a battery station and an overhead crane switches it out for a spare. When the spent battery has finished recharging, the vehicle comes back and gets another switch-out. It is also possible to replace all the batteries at once – but that requires about 1.5 hours of downtime for the LHD.
Making sure the batteries stay charged and fully operational is something that Kirkland Lake has been learning to do over time. “We recently set up a maintenance crew dedicated first and foremost to the batteries and their respective infrastructure,” said CEO George Ogilvie. “Keeping that equipment and infrastructure running efficiently is essential to our production.”
GE tested its own prototype at Iamgold’s Westwood mine in Quebec. “Westwood was very helpful, very eager to try it,” said Rémi Desrosiers, an application engineer at GE Mining.
In continuous operation, one lead-acid battery supplies six to eight hours of power while one or two additional batteries charge. At the end of each shift, the battery can be changed in 10 to 15 minutes using a proprietary swap-out system that does not require a crane or other permanent infrastructure. “The lead-acid takes about eight hours to charge, so if you want a battery available at all times, we recommend three batteries,” said Gaitonde. When GE fulfills its plans to introduce a lithium – or a similarly efficient – battery, customers who take that option would use two batteries per vehicle.
Cost and benefits
Any prospective customer will ask how much, exactly, batteries cost. Portalier said RDH’s LHD is 30 per cent more costly than a diesel model, but the reduction in diesel consumption and ventilation required to clear exhaust from the work area gives batteries a short payback. A complete battery charge for the 2.3-cubic metre LHD – providing three to four hours of work – is about 120 kW, according to Portalier, who says a diesel LHD of the same size would consume 12 to 16 litres of fuel an hour.
Kirkland Lake introduced the battery-powered LHDs when oil was more than $120 a barrel. Given a strong differential between the cost of diesel and the cost of electricity, the new equipment paid for itself within a year. With oil on its more recent downswing, said Ogilvie, Kirkland Lake is still saving money, but the greatest benefits are in ventilation. “Most importantly, our workforce in these areas is working in cleaner air,” he pointed out.
Desrosiers said the main focus of GE’s marketing was to address the problem of diesel particulate matter, which the World Health Organization deemed carcinogenic in 2012. But what he has discovered is that some customers are more interested in the heat-reduction aspects of battery-powered vehicles. “Electric machines have much, much higher [heat] efficiency than a diesel counterpart,” he said. “For many customers, the heat management is sometimes more important than the diesel particulate matter (DPM) concentration. Whether the need is to reduce DPM or heat, we can help reduce the ventilation cost.”
Learning how to use it
Seasoned operators can make the switch to electric easily, according to GE’s Desrosiers. “There was one operator who actually got the hang of the vehicle controls within 45 minutes,” he said. The machine is simpler in some ways. For example, there is no starter for the engine.
There is also less operator involvement in braking. “Normally, the operator would use the brakes quite a bit if he had to go down a hill,” explained Desrosiers. “In our case, the brake usage is reduced because as you’re going down, the system automatically engages the motors to slow the unit and transfers that energy to the batteries. Effectively, they’re recharging the batteries when going down the slope, and this is transparent to the operator.”
Equally, operators will not have much to relearn on RDH machines, said Portalier. While they could theoretically let the battery run down unintentionally, the machines have a warning system. At 20 per cent battery life, a yellow light comes on and the machine shuts down long enough to alert the operator that it is time to get to a charging station. GE has a similar system on its LHDs.
Remote battery monitoring, maintenance and troubleshooting can be done by the mine, with support from manufacturers if needed. RDH machines can connect to a wireless network for remote assistance; GE provides over-the-phone or in-person support.
The most striking difference equipment operators will find is the relative quiet of the battery-powered units. The roar of diesel LHDs can put out a lot of decibels, sometimes requiring operators to wear double hearing protection. The battery-powered models only produce around 50 to 60 decibels – so little that both RDH and GE customers have requested an audible warning to alert workers in the vicinity when the machines move.
Orders and expansions on the way
Following successful trials, GE and RDH have orders in place for their respective LHDs. The GE commercial model to be launched at the end of 2015 has been dubbed the
LHD-7-HB, indicating its seven-ton hauling capacity. The bucket is four cubic yards (three cubic metres).
GE is also planning to expand its battery choices in 2016. Gaitonde said the company is evaluating lithium against other materials, including GE’s own Durathon sodium nickel batteries.
RDH sells its machine under the name Muckmaster 300EB. Portalier said the company will have a two-cubic yard (1.5-cubic metre) machine ready by the end of July in addition to the three-cubic yard to 3.5-cubic yard (2.3 to 2.67-cubic metre) and six-cubic yard (4.6-cubic metre) models it has already sold to miners. The company is also working on a more powerful lithium phosphate battery that would operate for six hours.
Those plans could go some way to address the desires of the current user. Asked what improvements he would like to see in the technology, Ogilvie answered: “We’d like to see longer life in the batteries before a change out is required. In addition, we’d like to see individual cells last longer before having to be discarded or refurbished.” Macassa’s first cells are expected to reach the end of their useable life shortly.
The Macassa mine could also use smaller equipment, having recently prioritized grade over tonnage and narrowed the scope of its mining activities. Ogilvie said the current LHDs require a minimum 2.1-metre mining width; there are areas where a 1.5-metre width would be preferred.
With battery-powered trucks and LHDs already in operation at one mine, more orders on the way, and plans for expansion, these manufacturers have broken a path for the rest of the industry. When it comes to scaling up, said Portalier, “There’s no limit. Everything depends on the battery technology you’re using.”