As sales manager who has been engaged in the motor industry for over 20 years, when we asked customer for  the technical requirements, we all hope to make clear the four performance points on the motor torque-speed  curve, which is including 1. Free Load, 2. Max. Efficiency, 3. Max. Output Power, and 4. Stall Torque. The  performance curve is very important for motor design, as it can show out the performance changes of motor  under different loading points, as well as what kind of performance needs to be achieved when designing the  winding and whether there is a margin to pass the safety test. Here is a brief introduction for the differences  between these four performance points. 

 1. Free Load Point: From the moment the motor is powered on and starts running, there is no load yet and the  speed is at its highest point. The input current/power/output power/torque of the motor are at their lowest  values, just like a person who has just started running, transitioning from a static state to a dynamic state, and  the body has not warmed up yet. The human body functions and muscle strength exertion have not entered  the state of play. In mass production motors, due to manufacturing tolerances, the range of no-load speed  would be wider. Some customers are much concerned about whether the no-load starting current is too high  affecting the PCB control, whether the no-load speed is too high caused excessive noise, or whether the starting  torque is too low making it difficult to start with a load, and so on. 

 2. Max. Efficiency Point: As the loading increases gradually from no load state to reach its maximum efficiency  point, the overall heating and mechanical losses of the motor continue to increase which drawing more current,  the output power increases rapidly, in contrast the speed decreases along with increased load. However,  afterward the growth rate of output power would be slow down. It is generally recommended that designed  load by customer is in front of the Max. Efficiency Point, as the energy which input into the motor can be  maximized for driving the rotor, and it is also the safest operation range. It is like a person who has fully warmed  up during running and is in good condition, without feeling tired, as well as suitable for motor continuous  operation without the risk of premature failure.  

3. Max. Output Power Point: It is not recommended to operate motor continuously within the range from the  max. efficiency to the maximum output power. Intermittent and short-term operation, in co-operated with  good condition airflow, it is rather safe for motor. The far away from the max. efficiency point, the higher input  current, the increased chance of premature failure. Need to avoid operating motor consistently at this period,  as accelerated aging of insulating materials by high temperature accumulation. It is important to be aware of  any unusual odors or slight smoke when the motor is running long time. Do not increase load closer to this  loading point any more, just like a person feeling fatigued and experiencing muscle soreness during the middle  and later stages of running, which feel very strenuous. 

 4. Stall Torque Point: This refers to the point where the increasing load on motor reaches a locking state which  torque and input current reach the maximum value, the speed reduces to zero, stop running. From the point of  maximum output power to the stall torque, this is a dangerous zone, and it is highly advised that do not running  the motor at stall torque point. If the temperature protector has not tripped and cut off the power in advance,  when the temperature of the live parts of the motor exceeds the maximum heat-resistance temperature of the  insulation material, the insulation layer will melt and cause short-circuited. There is also a risk of ignition, which  could damage the motor coils, commutator, carbon brush etc. It is similar to running until the body's physical  capabilities reach their limit, causing collapse and inability to walk, lead to falling to the ground finally. Some  customers may use stall torque value for judging motor overall performance. 

These four motor performance points are very important for motor design. Engineers need to choose a suitable  motor platform based on the specific application requirements and working conditions to ensure that the motor  can achieve high efficiency, high output power and stable operation under normal load. In consideration of  these performance points can indicate engineers to design suitable outline dimensions, motor parameters and  control method, to achieve the best performance and energy efficiency. If customers can also learn the  performance curve and have a deeper understanding of their own product corresponding performance, do  simulation test such as end user overload using or long period continuous running before launching the product  to the market, do improvement on the motor for reaching higher quality and reducing market return rates.  

Shenzhen Power Motor has an experienced sales and R&D team who is always ready to assist you for project  initiation, with our reasonable, reliable and scheduled development proposal. Let we work together with you to  launch your good products into the market and gain a foothold in the market.  Please contact us immediately, Tel: 86-755-3689 9898/400-622-3329, Email: info.power@power-motor.com 

Note: This article is contributed by sales team