How the world’s first large-scale electric excavator worksEric Olson | July 29, 2019
In the construction vehicle market, large-scale mobile machinery has largely been powered by internal combustion engines. But as electric powertrain technologies including motors and batteries advance, heavy construction machinery powered by electricity is becoming a reality.
The world’s first large-scale electric excavator, the 25 tonne Cat 323F Z-line, operates on battery power alone without the help of a diesel engine. The excavator is nearly identical to the diesel-powered Cat 323F excavator, except its diesel engine has been replaced with an electric powertrain.
The conversion was carried out by Pon Equipment, the official Caterpillar dealer in Norway, Sweden, Denmark and the Netherlands. The company was spurred by Norway’s pledge to become carbon neutral by 2030 along with a push by the country’s capital city, Oslo, for zero-emission construction sites.
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The electric excavator’s powertrain system — provided by Danfoss Editron, a subsidiary of Danfoss Power Solutions — eliminates the noisy, dirty diesel engine in the 323F and replaces it with a battery pack and electric motor to power the excavator’s hydraulic system.
The electric powertrain enables the 323F Z-line excavator to operate emission-free without sacrificing power or performance compared to the diesel version. With no combustion engine, the electric excavator also consumes no diesel fuel, produces no direct CO2 emissions and generates much lower noise than its diesel counterpart.
A key element of the powertrain is the 300 kWh battery pack that powers the 122 kW electric motor. On a full charge, the battery provides enough power for five to seven hours of excavator operation. The machine can also operate continuously if plugged into an external power source.
Weighing 3.4 tonnes, the battery pack has three times more capacity than the largest battery available for Tesla vehicles. The significant weight of the batteries required a redesign of the ballast block that balances the weight of the digging arm; the ballast was downsized from the massive 6 tonne version in the diesel excavator to a smaller steel block.
The batteries are ruggedized, heavy-duty storage cells rated for use in maritime applications, ensuring they can withstand the harsh vibrations and shocks of the construction environment. The batteries are also designed for longevity, rated to retain 80% of their charging capacity after 10,000 hours of operation.
One hour of charge over a 400 V mains connection provides one hour of operation. A fast-charge option fills the battery completely within two hours from a 1,000 V source.
How it works
In operation, the 323F Z-line electric excavator is powered by electricity according to the following steps:
- A DC distributor routes DC power from the battery pack to a DC/AC inverter.
- The inverter converts the DC voltage to AC voltage to power an electric motor.
- The electric motor drives a hydraulic pump that pressurizes hydraulic fluid for operation of the excavator’s arm, attachments and tracks.
- The main DC distributor also routes DC power from the battery pack to a second DC distributor.
- This second DC distributor directs DC power to an electric heater that warms a coolant fluid that circulates around the battery pack to regulate its temperature.
- The second DC distributor also sends DC power to a DC/DC converter that converts the voltage to 24 V DC to charge a 24 V battery that provides onboard power.
To recharge its battery pack, the 323F Z-line electric excavator draws power from the grid according to the following steps:
- The excavator is connected to grid power by attaching a power cable to a large power jack on the front of the excavator.
- 400 V AC power from the grid is filtered and routed to an AC/DC inverter, which converts it to DC voltage.
- The main DC distributor routes DC power to the batteries to charge them.
- The main DC distributor also sends power to the second DC distributor, which powers the electric heater to regulate battery temperature.
- The second DC distributor also sends power to the DC/DC converter to charge the 24 V battery.
Will it sell?
As the world’s first large-scale electric excavator, the Cat 323F Z-line has a price tag that reflects its innovative electric powertrain and sizable dimensions. The excavator costs approximately $680,800 (620,000 euros), around three times more than the diesel-powered Cat 323F.
The asking price is high, but the benefits offered by the vehicle are significant: no use of diesel fuel, no direct CO2 emissions, much lower noise and less maintenance than a diesel excavator. If electric excavators prove popular on the market, technology improvements and economies of scale could lower production costs, increasing their affordability.
In the meantime, regulations like those in Norway are driving adoption of environmentally friendly construction machinery. Norwegian construction company Veidekke has purchased eight of the electric excavators. The company estimates each 323F Z-line excavator will prevent the release of 52 tonnes of CO2. Replacing all of Norway’s approximately 2,500 excavators would offset carbon emissions equivalent to taking 60,000 cars off the road.