Battery-powered motor applications need careful design work to match motor performance and power-consumption profiles to the battery type. Optimal motor and battery pairing relies on the selection of an efficient motor as well as a battery with the appropriate capacity, cost, size, maintainability, and discharge duration and curve.
By Scott McMillan • Senior Applications Engineer | Power Electric
Travis Lake • VP of Sales and Marketing | Power Electric
新的商业设备设计继续驾驶更小，更轻，更宽敞的移动解决方案。这使得从传统的有线设计到电池供电设备的加速过渡。当然，适当的电机选择是优化任何自动化设备性能的关键。然而，电池供电的应用需要考虑电动机和电池交互的额外因素。
This article reviews the process for selecting motor-battery combinations that are suitable for commercial equipment.
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电池and electric-motor power requirements
在任何电动机应用中，目标设备性能都决定了所需的电动机功率。电动机的额定功率是根据应用的速度，扭矩和占空比的组合计算的，又建立了电池的临界电压，电流和容量要求。
电源电压和电流直接与电动机产生的速度和扭矩相关联。除电压和电流外，容量是选择特定应用的适当电池的第三个关键因素。电池容量基于再充电循环之间的设备的所需操作运行时间，并且仅仅是电池可以保持的电荷量。
The standard measure for battery capacity is milliampere-hours (mAh) or amp-hours (Ah), which indicates how long the battery will last based on the current it outputs. The calculation of the battery life at a certain current draw is the battery capacity (Ah) divided by output current (A) = Battery life (hours). For example, an AA battery with a rating of 2,500 mAh outputting 100 mAh will last approximately 25 hours.
Battery performance considerations
One motor parameter that affects the performance of battery-powered applications is efficiency. Maximizing motor efficiency helps minimize required power capacity — in turn allowing for a smaller and less costly battery. For this reason, brushless dc (BLDC) motors are preferred over brushed DC motors despite their higher upfront price. Brushed dc motors have lower upfront costs and are simpler to integrate. However, their relatively low efficiency may necessitate a higher-cost battery solution — or a reduction in the operating time between battery recharging cycles.
Typical battery-discharging processes require consideration of several performance considerations — including that of motor speed. With most battery types, terminal voltage decreases as the battery discharges. Motor speed is directly proportional to the battery voltage, so the motor speed will in fact decrease with dwindling terminal voltage. In addition, batteries exhibit decreasing terminal voltage as the output current (load) increases, which degrades motor speeds at higher torque loads.
不考虑这些因素的特点f the motor winding itself, for which output speed decreases as load on the motor increases — even with constant battery voltage.
One method to address this potential speed-fluctuation problem is to incorporate speed control electronics into the system. Such controls can help the motor maintains the target speed as the battery discharges over time … or as the load on the motor changes.
还必须考虑电动机输出扭矩，因为电池的放电电流有限。因为电动机输出扭矩与所提供的电流成正比，所以电机的最大输出扭矩可能受电池放电电流额定值的限制。适当大小的电池应具有放电电流额定值，可满足或超过电机电流输入要求。
Other battery considerations for motor-driven applications
电池选择中的一个基本标准是确保电池在充满电量的情况下满足电机的电压和电流要求，并继续满足这些要求，因为电池接近完全放电。称重电池类型，尺寸和成本之间的权衡，同时仍然满足关键性能要求是过程中的下一步。
All rechargeable and non-rechargeable battery designs rely on the conversion of chemical energy into electrical energy. Today, most small and rechargeable batteries are made using Lithium-Ion (Li-ion) technology due to its high energy density. These rechargeable and low-maintenance batteries are more expensive than traditional technologies such as Nickel-Cadmium based cells. Larger batteries have traditionally been lead-acid designs, although Li-ion has become increasingly popular due to longer life, smaller size and weight, and overall ease of maintenance and rechargeability compared to lead-acid batteries.
| 可充电电池类型 | ADVANTAGES | DISADVANTAGES |
| Lithium-Ion (Li-ion) | 小而薄 Very high power density 更短的充电周期 Efficient • Environmentally friendly |
需要保护电路以防止过热 Overall capacity degrades over time Charger matched to battery |
| 尼斯镉（NICD） | 廉价 全部能力运行，直到几乎完全放电 |
降低保质期•使用有毒金属 Full discharge required before recharging Charger matched to battery |
| Nickle Metal Hydride (NiMH) | 高能量与体积比 环保 全部能力运行，直到几乎完全放电 |
Requires full charge before use Over charging diminishes battery life Discharges at high rate |
| 铅酸 | 容忍更宽的温度范围 Low self-discharge rate High tolerance to overcharge 广泛可用性•低成本 |
Bulky • low power density Long charge times Very toxic |
Battery size directly correlates to the energy storage capacity of a given battery. For product designs with minimal space available for batteries, like medical hand tools, utilization of a high energy density battery is beneficial despite the potential cost and capacity disadvantages.
The differing ways in which batteries discharge over time is another important factor in proper selection. While many of today’s energy-dense battery technologies maintain a relatively stable output voltage until they approach full discharge, traditional battery technologies offer a gradually decreasing voltage versus time curve until they reach full discharge.
As mentioned, the battery-discharge curve is important because output voltage directly affects the output speed of the motor … and understanding how close a battery is to full discharge can prevent damaging the battery and potentially the whole system. Allowing a battery to fully discharge during operation may ultimately damage the battery, rendering it no longer rechargeable. To prevent this, a preset cutoff voltage can disengage the motor once the battery voltage dips below the preset threshold. Determining and implementing the proper cutoff voltage is typically easier with a battery that has a gradual discharge curve than a battery with a flat curve.
Additional battery selection considerations include the number of recharging cycles the battery can endure, availability, and environmental factors.
Power Electric |www.powerelectric.com
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