Last updated 23rd January 2002

A technology, which can generally be referred to as 'voltage optimisation', has been around for a number of years and offered to the injection moulding industry by a number of suppliers.
The original idea to reduce motor running costs by lowering the voltage supplied to them when they are lightly loaded was patented by a NASA scientist in 1974.
He needed to make some cost reductions in the jet-propulsion laboratories to help offset budgetary cuts in the space program.
He discovered that by electronically regulating the voltage supplied to motors driving large ventilation fans he could reduce their internal 'losses'.
This was good news for him and earned him a couple of patents. However he couldn't possibly have envisaged how his discovery would be misused.
Whilst many companies have developed products based upon his original idea and achieved genuine savings of typically 10%, many have found ways of misinterpreting the effects of applying this type of technology.
We regularly come across moulding companies who have either been offered or have even installed this type of technology on the understanding that they will achieve savings as high as 30-40%!
Amazingly it is not too difficult to 'hook-up' a power-measuring device to a motor fitted with an 'optimiser' and demonstrate apparent savings of this level. To the uninitiated it can be made to look very plausible. The trick lies in how the 'power' is measured.
The only savings that can actually be made using this type of technology with an injection-moulding machine are reductions in motor losses. These losses are relatively small (<10%) when compared with the energy required to operate the machine.
Standard 4-pole induction motors much above about 15kW offer a full load efficiency of at least 93% i.e. they waste up to 7% of their full load power. For a 55kW motor this is equivalent to less than 4kW.
The losses can be generalised into three main areas: 'Iron losses', 'Copper losses' and 'friction losses'.
Iron losses occur in the magnetic circuit of the motor and are not dependent upon motor load. Some of the iron losses arise from hysteresis losses which are determined by the physical characteristics of the steel used in the motor construction.
The remainder come from 'eddy current' losses which are determined by the construction and assembly of the steel laminations. Typically Iron losses account for about a fifth of the total full load losses.
Copper losses, also known as I²R losses, stem from the electrical resistance of the stator windings and the rotor 'bars'. These losses are proportional to the square of the load current and predominate at heavy load.
Friction losses include 'windage' losses and are constant for a given speed irrespective of load.
The magnetic circuit of an induction motor is designed to produce a sufficiently strong magnetic field to support full load operation. The field produced is independent of motor load and influenced only by motor design and supply voltage.
When a motor is not operating at full load the magnetic circuit still produces the same field strength even though the motor could actually operate with a reduced field.
'Optimisers' capitalise upon this fact and reduce the magnetic field when a motor is operating at less than full load by reducing the voltage supplied to the motor. They do this by chopping pieces out of the mains sinusoids with thyristors.
The inductance of the motor acts to integrate the supply waveform so it can tolerate operating on a 'chopped-up' sinusoid, though the process does produce a significant amount of harmonic distortion on the mains supply.
By reducing the voltage supplied to a motor during light load, called 'field-weakening', the losses associated with the magnetic circuit i.e. the 'Iron losses' can be reduced.
By doing so the magnetisation current falls-off quite dramatically, as can be demonstrated by a current clamp, but since this is purely reactive current it doesn't affect the amount of energy being consumed by the motor by much at all.
The 'Copper losses' actually increase with 'field-weakening' since the motor has to 'slip' more to produce the same output torque. However at light load the increase in 'Copper losses' is quite small and can largely be ignored.
As you might expect the 'Friction losses' are not affected by 'field-weakening'.
As an example, a 55kW motor might typically have iron losses amounting to 2kW. When a moulding machine driven by this kind of motor is 'idling' (e.g. during 'cooling') the motor might see a load of around 14kW. This would make the iron losses around 14% of the idling power.
Whilst the iron losses could never be totally removed using 'voltage optimisation' a good implementation of the technology might save you around 10% of the idle power.
However, when the machine is moulding, the load on the motor is significantly increased and the field cannot be weakened as much and hence the saving opportunity is dramatically reduced.
Since 'voltage optimisers' do not change the speed of motors they cannot reduce any system inefficiencies other than internal motor losses. These typically account for less than 10% of the overall power consumed by an injection-moulding machine.
The Powermiser system is different!!
It modifies the way the hydraulic oil is pumped by varying flow-valve settings, motor speeds and pump selections in real-time to ensure the hydraulic system operates at near maximum efficiency at all times.
See the How it Works page for more details.
We remove losses in the hydraulic system that can typically account for 30-40% of the overall power consumed by an injection-moulding machine. In an extreme case the losses were as high as 73%.
Powermiser reduces losses in the hydraulic system by varying motor speed. 'Voltage optimisers' reduce losses in the motor by varying supply voltage only.
Note: If you want to evaluate the energy savings of a 'voltage optimiser' product yourself make sure you use a 3-phase power meter that measures true electrical power in kilo-Watt-hours (kWh).
Do not be fooled by measurements taken with current clamps that measure only apparent power (kVA).
If you are unsure about the differences between kW and kVA then take a look at our Measuring Motor Power page.
Understanding the difference is crucial when it comes to making measurements of true power consumption and evaluating the benefits of energy saving products.
Also, be sure to connect your power measuring equipment to the input side of the 'optimiser'. The output side (i.e. the cables feeding the motor) contains non-sinusoidal voltages which can easily 'fool' power meters.