Checklist: Verifying Servo Drive Efficiency in Molders

Why Verify Servo Drive Efficiency Before Purchase

Servo-driven blow molding machines are often sold on the promise of lower energy draw than older hydraulic systems. The gap between marketing claims and shop floor results is where budgets get hurt. A new machine may look efficient on paper but underperform once cycle times, material viscosity, and operator habits are factored in.

Buyers need a practical way to confirm that the stated efficiency matches real operation. This checklist groups the technical checks by theme. Each item includes what to look for and the red flags that suggest the machine may not deliver the expected energy savings.

Verify the Servo Drive and Motor Specifications

The core of the efficiency claim sits in the servo drive and motor pair. Check the nameplate data for rated power, peak power, and rated efficiency percentage. The drive controller should show efficiency at rated load, not just maximum output. Ask for the efficiency curve, not a single number.

Ask the supplier to provide the drive manufacturer’s data sheet. The nameplate efficiency is usually measured at 100 percent load. Real blow molding cycles rarely hold 100 percent load continuously. The actual average efficiency is often lower. If the supplier only gives a peak figure, treat the energy savings claim with caution.

Red flags to watch for:

1. Only peak motor power is listed, with no rated efficiency percentage.
2. The drive manufacturer is unnamed or obscure.
3. The efficiency curve is unavailable or shows a steep drop above 75 percent load.
4. The control software does not log efficiency per cycle.

A drive that holds efficiency above 85 percent across the typical load range is a better indicator of real savings than a high peak rating.

Compare Electric and Hydraulic Power Units

The power unit type changes the efficiency story. Electric servo drives convert electrical energy into mechanical work with relatively low losses. Hydraulic power units pump fluid under pressure and transfer it to actuators. Each has different loss points and different ways to measure draw.

For electric units, check the inverter efficiency and the motor winding losses. For hydraulic units, check the pump efficiency, the relief valve pressure setting, and the accumulator sizing. An electric unit may have a lower idle draw, but a hydraulic unit with a well-sized accumulator can reduce peak power demand.

Use the table below to compare the two types under common test conditions.

Parameter	Electric Servo Drive	Hydraulic Power Unit
Idle energy draw	Typically lower	Can be high if pump runs continuously
Peak power demand	High during clamp or necking	High during pressure phase
Efficiency at partial load	Varies with drive tuning	Depends on pump and valve settings
Maintenance impact on efficiency	Lower, no fluid leaks	Higher, fluid degradation increases losses
Best for	Steady cycles with low duty	High peak demand with intermittent duty

The choice depends on your cycle. If your production runs long, steady cycles with low duty, an electric unit may save more. If your cycles have sharp peak demands, a hydraulic unit with a large accumulator may reduce grid strain.

Measure Energy Consumption Under Real Conditions

Energy consumption is not a single number. It changes with material type, cycle time, and ambient temperature. Ask the supplier to run the machine under a defined test protocol. The protocol should include a set number of cycles, a specific material, and a fixed cycle time.

Record the total energy in kilowatt hours over the test run. Divide by the number of parts to get energy per part. Compare that against the supplier’s stated figure. If the supplier only gives a per cycle number, ask for the total energy over a full shift.

Red flags to watch for:

1. The test is run with the machine idle or with no material.
2. The energy meter is not connected to the main power feed.
3. The supplier does not provide the test protocol in writing.
4. The energy per part varies widely between runs.

A reliable measurement uses a power analyzer on the main circuit. A multimeter or a simple clamp meter may not capture the full draw, especially if there are multiple motors and heaters running.

Check Control Logic and Duty Cycle Settings

The servo drive does not work in isolation. The control logic determines when the motor runs and how hard it pushes. A poorly tuned control loop can cause the motor to run at low efficiency even if the drive itself is efficient.

Ask for the control logic documentation. Look for the pressure profile, the speed profile, and the duty cycle settings. A machine that holds pressure longer than needed wastes energy. A machine that ramps up too quickly can spike the draw.

Red flags to watch for:

1. The control software does not allow custom pressure profiles.
2. The default settings are not adjustable.
3. The duty cycle is fixed at a high percentage.
4. There is no way to log the pressure and speed over time.

A good control system lets you tune the profile to your material. It also logs the data so you can see where the energy goes. If the supplier will not show you the control screen, walk away.

Review the Power Quality and Grid Impact

Energy savings are not just about the machine. They are also about how the machine affects your plant’s power quality. A servo drive that draws power in short bursts can cause voltage dips. Those dips can trip other equipment or increase losses in the transformer.

Check the inrush current rating. Ask for the power factor correction method. A machine with a power factor correction capacitor will draw less reactive power from the grid. That reduces losses in the feeder and can lower your demand charges.

Red flags to watch for:

1. No power factor correction is installed.
2. The inrush current is high relative to the rated power.
3. The machine causes voltage dips on the plant bus.
4. The supplier does not provide the power quality data.

A power quality audit is not optional. If the machine causes voltage dips, the energy savings may be offset by other plant losses.

Confirm Documentation and Test Protocols

The final step is paper. Ask for the test protocol, the energy data, and the control logic documentation before you sign. The supplier should be able to provide a written test report that matches the machine you are buying.

Red flags to watch for:

1. The test report is not signed by an engineer.
2. The data is from a different model.
3. The protocol does not match your production cycle.
4. The supplier refuses to run a trial cycle on your site.

A trial cycle on your site is the best way to verify the claim. Run the machine for a full shift. Record the energy. Compare it to the supplier’s figure. If the numbers do not match, do not sign.

Final Checklist for Buyers

Use this numbered list to verify the machine before purchase. Keep it on your clipboard.

1. Request the servo drive efficiency curve, not just the peak power.
2. Confirm the power unit type matches your cycle profile.
3. Run a test cycle with your material and record the energy per part.
4. Check the control logic for adjustable pressure and speed profiles.
5. Verify the power factor correction and inrush current data.
6. Obtain the signed test report and the control documentation.

If the supplier cannot provide these items, the energy savings claim is not verified. A machine that looks efficient on the brochure may not be efficient on your floor. The checklist above gives you the technical basis to decide.