Magnets have five key indicators: model, height, thickness, width, and quantity. The model reflects the magnetic flux per unit volume, indicating the grade of the magnet. This cannot be visually assessed and relies on manufacturer claims. Ideally, the higher, thicker, wider, and more numerous the magnets, the better the performance. A larger volume means higher costs for manufacturers but greater power for users, which also implies higher energy consumption. In line with the principle that higher manufacturer costs lead to greater user benefits, maximizing height, thickness, width, and quantity is ideal, but users generally cannot ascertain thickness, width, or quantity, only that the motor is rated at 30, 40, or 45 high.
As for the core, imported ones are preferable. It’s widely accepted that foreign products are superior, although this is not easily discernible.
For coils, the critical parameters are copper purity (whether brass or copper, but not aluminum-coated), number of turns, thickness, and filling ratio. The housing determines the upper limits of volume and quantity, but users usually have no choice here, and neither do manufacturers. Hall sensors, as electronic components, can only be differentiated by price, with Honeywell being a reputable brand in the market.
Insulation varnish is rated by five classifications, with higher temperature resistance being better. For phase wires, thicker is better; generally, a 1 mm² wire can handle a 10A current. For example, if your current limit is 20A, you need at least a 2 mm² wire.
Power is another key specification. For instance, if your original motor is rated at 48V 500W with a speed of 36 km/h, increasing the voltage to 72V can raise the speed to 54 km/h. To compare speeds across different motors, divide the speed by the voltage. For example, if you’re achieving 45 km/h at 72V, your speed per volt is 0.625. In contrast, another motor achieving 40 km/h at 48V has a speed per volt of 0.83333, indicating it’s faster.
Efficiency (energy saving) is also crucial. Typically, electric motors operate at around 82% efficiency for legitimate products, with a variation of only about 2%. Even if a motor claims to use cutting-edge technology, the efficiency improvement is unlikely to exceed 3%. This explains why some users do not perceive significant energy savings with certain "energy-efficient" models; those who do may either be misinformed or simply used a poor-quality motor before.
It's understandable that some motors are indeed less efficient. Achieving even a 1% improvement in efficiency is challenging, but creating a motor with only 50% efficiency is relatively easy.
Optimal Efficiency Point: As we’ve discussed, while efficiency has a wide variance below its maximum, the upper limit is nearly fixed. So, should we disregard motor efficiency entirely? Absolutely not! We should pay attention to another important metric—the optimal efficiency point. This refers to the load at which the motor operates most efficiently. For instance, if a manufacturer claims an optimal efficiency of 93%, you should ask, “At what load is this efficiency achieved?” If they say it’s at 48V and 100W, you’ll realize that maintaining 100W is impractical for normal operation.
In the motor industry, the optimal efficiency point should be within the rated voltage and power range. For example, for a 48V 1000W motor, when powered at 48V, check the efficiency at around 1000W. If the highest efficiency is 82.5% at 960W and only 81% at 1000W, the optimal efficiency point is at 960W. Generally, reputable manufacturers have their optimal efficiency points close to the rated power, within a 5% margin. However, some manufacturers may claim an impressive efficiency at a much lower power level, misleading you about performance when used at higher power.
These factors indicate the considerations to keep in mind. We will soon provide simple methods to assess your motor’s performance. First, determine your requirements. It's not always about speed; if you're looking for a motor that can exceed 100 km/h at 72V, you might sacrifice safety and quality.
For normal usage, speeds above 50 km/h typically enter an unsafe zone. Here’s a simple power-to-speed reference table:
- 350W: 35 km/h
- 500W: 40 km/h
- 800W: 45 km/h
- 1000W: 50 km/h
- 1200W: 53 km/h
- 1500W: 55 km/h
- 2000W: 60 km/h
- 3000W: 65 km/h
- 4000W: 75 km/h
- 5500W: 85 km/h
- 7000W: 90 km/h
- 8500W: 95 km/h
- 10000W: 100 km/h
- 12000W: 110 km/h
- 15000W: 120 km/h
Thus, when ordering a motor, consider your intended usage, especially if you plan to increase the voltage.
Summary: Don’t focus solely on power when selecting a motor. Determine your speed, voltage, and power requirements. If you plan to overvolt in the future, define your desired maximum speed. Divide the desired speed by the voltage. For example, if you want a motor that reaches over 75 km/h at 72V, calculate 75/72 = 1.0416. Seek a motor with a speed-to-voltage ratio just above this.
Among various motors:
- Motor A: 48V 500W, 36 km/h
- Motor B: 48V 800W, 42 km/h
- Motor C: 60V 1200W, 45 km/h
- Motor D: 60V 1500W, 52 km/h
- Motor E: 48V 1000W, 45 km/h
- Motor F: 48V 1500W, 52 km/h
Only Motor F meets the criteria.
Simply stating the voltage a motor operates at or its power or speed is insufficient. If you can customize your motor, prioritize specifying the dimensions and height of the magnets, as this determines the internal physical space, which should be maximized for optimal material usage.
Next, communicate your desired maximum voltage and speed to the manufacturer. Specify the maximum speed at which the motor should operate. Keep in mind that, once the housing is established, slower motors may incur higher costs. Ensure that the motor’s speed does not exceed a specified limit, such as 42 km/h at 48V, to avoid having to return it. Slower speeds require adjustments to coil turns, filling ratios, and higher-quality cores to achieve.
Don't worry about increased magnet height impacting energy consumption; current parameters are determined by the controller.