Battery LHD loader with a charging window that does not close
An underground copper mine is trialling one 14 t battery-electric LHD loader against two diesel units. The loader carries a 120 kWh LFP pack and an 80 kW on-board charger fed from a 1,000 V trailing cable at a cut-out. The haul ramp is 1:7 and 400 m one way, and regenerative braking returns roughly 22% of the energy used on the climb. The stope has 34 °C dry-bulb and 28 °C wet-bulb temperature and 12 m³/s of airflow, and the loader's pack derates charging from 80 kW to 45 kW when cell temperature reaches 48 °C. In the first week the loader finished its 10-hour shift at 16–19% state of charge, and operators lose about 25 minutes of the single 30-minute crib break handling and coupling the trailing cable. Diesel exhaust from the two diesel units is the main source of NO2 and ventilation is the mine's largest single power cost.
1. Quantify whether the crib-break charging window is adequate, and state the minimum change needed.
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Start at 100%, finish at 17%: about 100 kWh net consumed across ten hours, an average draw near 10 kW with regeneration already netted off. The single crib break is 30 minutes, but 25 minutes is lost to cable handling and coupling, so at most 5–10 minutes of actual charging remains at 80 kW - roughly 7 to 13 kWh.
Even a perfect 30 minutes at 80 kW returns only 40 kWh against 100 kWh used, a deficit of 60 kWh per shift. That matches the observed downward drift to 16–19% and explains why the trial appears almost viable in week one.
Minimum changes, in order of cost: add a second charging window of at least 75 minutes at 80 kW; move the connection to an overhead pantograph or fixed docking point so the break is not consumed by cable work; or increase usable pack size to about 180 kWh to keep a 20% reserve across the shift. Battery swapping is technically viable but needs a second pack and a handling system, so scope it against the cost of lost production.
2. Explain the thermal derate to 45 kW and what you would check and change.
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80 kW into a 120 kWh pack is about 0.67C. That is within the pack's charge capability at moderate temperature, but the cell heat must be rejected, and at 34 °C dry-bulb with a 28 °C wet-bulb the cooling circuit has very little sink to work with, which is why the BMS pulls back to 45 kW at 48 °C cell temperature.
Check coolant level and concentration, pump flow, radiator cleanliness and airflow path in the cut-out, chiller setpoint and whether the derate threshold has been configured for surface rather than underground duty. Confirm temperatures with the BMS log rather than the operator's recollection.
Operationally, a longer period at 60 kW may deliver more energy than a short burst at 80 kW that derates partway through, so model the two profiles against the actual charging window. Relocate the charging point to a well-ventilated cut-out on the fresh-air route, and keep the pack in the 20–80% band where heat generation is lowest.
3. Management wants to justify converting more units on ventilation savings. What evidence would you require before supporting that claim?
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A diesel loader in this class is commonly ventilated at roughly 0.05 m³/s per engine kW, so a 250 kW unit implies on the order of 12 m³/s - comparable to the 12 m³/s currently measured at the stope. That is a plausible saving but not a demonstrated one, and removing one diesel unit does not automatically release air for other workings.
Require paired sampling on diesel and battery shifts: NO2, CO, diesel particulate matter and heat at the operator position and in the return airway, taken by the mine's ventilation officer under the ventilation plan and submitted to the regulator. Treat the battery's own heat load as an offset: charging loses 5–8% of energy as heat, released underground, plus motor and inverter losses.
Only after the trial report shows the credit should the mine re-baseline its ventilation model, and any plan to redirect air must be re-checked against dust, blasting fumes and heat stress before conversion of further units.