By replacing the powertrain and ancillary components of an excavator with compact electric motors and battery packs, the overall weight increase is minimal, if present at all. Positioning these heavy battery packs at the rear of the housing helps counterbalance the load and offers a practical location for easy replacement with fresh packs when needed. Depending on the specific machine and workload, battery life can typically range from four to five hours. However, with smart design strategies, battery swaps can be extended, and charging intervals can be reduced, enhancing overall machine efficiency.

Let’s be clear: these recommendations should be applied across all machines whenever feasible. Ignoring the impact of wasted energy on both the environment and your budget is shortsighted. Fortunately, leading manufacturers in the mobile machinery industry are well aware of both regulatory requirements and customer expectations, so modern machines are already quite efficient. However, if you’re new to the field, here’s what you need to understand.

While it might sound simple when said quickly, the goal is to complete your tasks using the fewest possible electrons. In essence, the power output required for the task must be closely aligned with the combination of voltage and amperage delivered by the battery pack. Maintaining this efficiency ensures your machine can perform as much work as possible before depleting its battery charge.

Idling machinery is never beneficial

To begin, we can draw valuable insights from advancements in vehicle technology, particularly in how motors only operate when necessary. Historically, it's been common practice for machine operators to start the engine at the beginning of their shift and let it run throughout the workday, regardless of whether the machine is actively working. This mindset contrasts sharply with modern passenger vehicles, where electric drive motors are engaged solely when there is a load to propel the vehicle. In fact, many new internal combustion engine (ICE) cars now include automatic stop/start systems that shut the engine off at stops, reducing RPMs to zero.

It’s worth questioning why similar stop/start functionality, which automatically halts the powertrain during idle periods and uses a high-voltage starter to resume operation, isn’t more widespread in mobile machinery. The same energy-saving principles should apply, especially as we focus on electric-only equipment. This shift in approach could significantly boost efficiency and operational sustainability.

Just as no current flows to the drive motors of an EV until the accelerator is pressed, the electric motor-driven pumps in a battery-powered machine remain idle until a button, lever, or joystick is engaged. This offers several advantages. Even when running without load, an electric motor consumes power inefficiently, operating outside its optimal speed and current draw range. Cutting power during idle periods conserves valuable battery life.

Running a hydraulic pump at idle is even less efficient. Just as engine stop/start technology conserves energy, shutting off the hydraulic pump when not needed does the same. A pressure-compensated pump, even at idle, still consumes energy due to its rotating mass, friction, leakage, and pilot energy, potentially using between 3-10% of its full capacity. Conserving battery power often comes down to fine margins, and this is no small measure—it’s significant.

If you doubt the energy drain of an idling pump, disconnect the case drain line at the reservoir, let it flow into a bucket, and observe how much fluid escapes without producing work. The noticeable heat radiating from the fluid is a clear indicator that energy was wasted as heat instead of being used productively.

Sophisticated electronics to the rescue

You might be surprised to learn that we can now replicate the functionality of a load-sensing, pressure-compensated hydraulic pump using advanced electronics. A pressure-compensated pump adjusts flow rates while maintaining pressure through a compensator—a small relief valve that controls the operation of the control piston, reducing pump volume to stabilize pressure at a given flow rate.

For example, if your pump is set to 3,000 psi and rated for up to 10 gpm of flow, when you activate a valve, the open flow path causes a slight reduction in outlet pressure as fluid is directed to the required actuator. The pump continues to supply fluid to maintain the potential of 3,000 psi, regardless of whether the load needs the full pressure. This is why these systems are sometimes referred to as "constant pressure" systems. If the flow demand exceeds 10 gpm, the pump will reduce to load pressure until the downstream flow is adjusted or halted.

Now, if instead of using a traditional pressure-compensated pump, we employ a fixed-displacement pump driven by a variable-speed electric motor, we can achieve the same result by incorporating a pressure transducer at the pump’s outlet. The ideal solution here is to use a compact, synchronous servomotor, known for its low inertia and precise control over both speed and torque. Instead of controlling the pump volume through constant motor speed, we can regulate the pump flow by varying the motor's angular velocity (rpm), achieving the same pressure and flow control without the complexity of a conventional pressure-compensated pump.

In this system, the machine controller (typically a PLC) continuously monitors the pressure at the pump’s outlet, aiming to maintain the set point of 3,000 psi. If the pressure dips below this threshold, the controller ramps up the pump speed to inject more flow into the system and raise the pressure. Similarly, if there’s a sudden drop in pressure due to increased flow demand, the controller adjusts the pump speed to match the new requirements, maintaining optimal performance.

The key benefit of this approach is that the motor only operates when necessary and at the speed required, improving energy efficiency. While servomotors might not be as efficient at partial loads and varying rpm as other types of motors, this setup is still a far more energy-efficient solution compared to running a traditional engine at constant high rpm, such as 2,500 rpm for an entire 12-hour workday. This dynamic control over motor speed ensures the machine uses only the power it needs, reducing overall energy consumption and extending battery life.

Variable displacement technology takes this concept even further

The astute fluid power enthusiasts will rightly note that we can take this approach a step further by using a load-sensing hydraulic pump instead of a variable-speed fixed-displacement pump. The advantage of a load-sensing pump lies in its ability to reduce waste, especially at the higher pressure end. Instead of constantly forcing 3,000 psi into the system when the application might require less, the load-sensing pump provides just enough extra pressure—around 300 psi, for example—to ensure flow potential.

The key feature of a load-sensing system is its ability to read the pressure at the work ports downstream of the valves. By doing so, it ensures that the pump only generates as much pressure as is needed to meet the highest load, and no more. This prevents unnecessary overpressurization, which in turn reduces energy consumption and minimizes wear on components.

In essence, a load-sensing pump adjusts to match the precise demand of the system, dynamically optimizing both flow and pressure for efficiency, rather than operating at a fixed high pressure that could be unnecessarily wasteful for most of the machine's tasks. This results in significant energy savings, improved battery life in electric machines, and a more efficient hydraulic system overall.

I’m sure the sharp-eyed fluid power enthusiasts have already caught on to the fact that we can achieve the same outcome using a network of pressure transducers rather than relying on check and shuttle valves. By placing pressure transducers at the outlet ports of the control valves, we can measure the pressure drop relative to the pump outlet sensor. This setup captures the pressure differential across the entire system—accounting for any valve or restriction in the flow path. The primary task is adjusting the control orifice to match the desired flow rate.

The beauty of using a machine controller is that it can handle all this complexity. You can even program individual pressure drops for each actuator. For example, with a differential cylinder, rather than feeding the same flow rate to both the rod and the cap sides, you can adjust the flow to maintain identical extend and retract speeds, all controlled electronically. While this can be done hydraulically, it’s far simpler and more precise when handled by electronics.

When we bring all this together, we’ve created an on-demand flow system that generates just the hydraulic energy required by the machine. When there’s no active function, the only power draw is for displays, lights, and controllers—leaving the battery to run at its most efficient.

With the engine no longer running constantly, we can also focus on reducing the overall electrical demand of the hydraulic system. Implementing low-wattage solenoid coils is an easy win here, as is using a high-voltage control system. These upgrades reduce the need for heavy-gauge wiring, which not only lowers the overall weight of the machine but also contributes to further energy efficiency.

I hope you sharp-eyed aficionados noticed in the previous paragraph that we can achieve the same result using a network of pressure transducers instead of relying on check and shuttle valves. By placing pressure transducers at the outlet ports of the control valves, you can measure the pressure drop relative to the pump outlet sensor. This setup will capture the pressure change across the entire system—any valve or restriction in the flow path is accounted for in the pressure calculation. The primary task becomes adjusting the control orifice to match the desired flow rate.

With a machine controller handling all this, we can go a step further: individual pressure drop programming for each actuator. This includes even differential cylinders. Instead of supplying the same flow rate (dictated by pressure drop) to both sides of the cylinder, you can regulate the flow to ensure the same extend and retract speeds, all electronically controlled. While this can be achieved hydraulically, it’s so much easier and more precise with electronics.

Now, bringing everything together, we’ve created an on-demand flow system that generates only as much hydraulic energy as the machine needs. When no active function is required, the system draws just enough battery power to run the displays, lights, and controllers.

Having reduced the need to keep an engine running unnecessarily for hours, we can also look at ways to further lower the electrical demand of the hydraulic system. Low-wattage solenoid coils are an easy win, as is adopting a high-voltage control system. These upgrades cut down on the need for heavy-gauge wiring, which not only reduces the weight of the machine but also increases overall energy efficiency.

It may be less obvious to make some of the tough decisions, such as limiting your options to piston motors. While inside gear pumps provide a solid alternative to piston-style pumps, the situation with actuators is a bit more challenging. Low-speed, high-torque motors, often budget-friendly, just don’t fit well in machines focused on efficiency. These motors suffer from significant leakage, which increases exponentially with pressure, making them poorly suited for battery-powered applications.

You might ask, "Why not just use electric motors?" In many cases, this is a great option because electric motors avoid the energy loss inherent in the motor-pump-motor sequence, where each transformation adds some waste. However, if you already have a hydraulic pump running efficiently with the help of smart machine controllers, hydraulic drive motors still offer significant advantages.

Many leading manufacturers now offer piston motors that achieve 95% efficiency. While I risk sounding hypocritical after advocating for low-wattage coils, these motors are too good to dismiss. If your machine demands the most powerful and compact motor possible, you can achieve twice the torque in half the size without breaking the bank.

That said, switching to an efficient electric motor may still improve battery life in many cases. As much as I can't believe I'm saying this, the times are changing. But be cautious: not all electric motors are created equal, and many fall short of the 95% efficiency mark. Pay careful attention to what you replace a hydraulic motor with, especially if your design requires weatherproof or submersible capabilities.

Big players in the construction and agriculture industries are already developing battery-powered electric machines. Much like electric vehicles (EVs), these machines are expensive and limited in capabilities with today’s technology. However, with intelligent design and a focus on energy-saving details, expect the market share of battery-powered electric machinery to grow.