There are a lot of questions around the subject of which motor shows the highest efficiency, in particular when talking about applications with limited power supply, such as a battery driven tool or a solar panel powered satellite. However, it is believed that it’s worth expanding the question to the full drive system consisting of controller, motor, gearhead and other mechanics.
Table 1 gives a rough guess about typical efficiencies of different energy converting devices.
A lot depends on how the mechanics is made. A high friction in the mechanical system costs a lot of the energy. Hence optimising the efficiency of a drive train should always start with the mechanical system.
Note that DC drive systems are very often powered by a fixed voltage. Hence, it is not really the overall efficiency that must be maximised. Efficiency is a relative parameter giving the losses per input power.
However, at fixed voltage it is rather the current consumption (as an absolute parameter) that needs to be minimised. Making good use of the full supply voltage reduces the current consumption – and enlarges battery life.
A few rules for high efficiency and low current consumption:
Rules for mechanical transformation
Rules for planetary and spur gearheads
Rules for motors
Rules for controllers
Here the rule is similar to gearheads. Load them well, don’t run them at too low a current. Don’t select controllers with too high a current rating. Match the size of the power stage with the required motor current.
Finally by ensuringgood use of the full supply voltage, will reduce the current consumption and save money; you will need a smaller power supply, a smaller controller, less cable shielding.