What Makes a Good Motor? Key Factors to Consider for E-Motorcycle

When it comes to electric motors, the question of which one is the best is a common inquiry. Should you choose Motor A or Motor B? Which one is more energy-efficient? The production of an electric motor involves several physical components: magnets, core iron, coils, motor housing, Hall sensors, insulating paint, and phase wires. Let's analyze each one.

Magnets have five indicators: grade, height, thickness, width, and quantity. The grade reflects the magnetic flux density per unit volume, which is the level of the magnet, not visually discernible and often subject to manufacturer claims. Height, thickness, width, and quantity are generally better when higher, thicker, wider, and more numerous. Larger magnet volume means higher costs for manufacturers but greater power for users, albeit with slightly higher power consumption.

Following the principle that higher costs for manufacturers equate to greater benefits for users, under the premise of meeting power requirements, the larger the product of height, thickness, width, and quantity, the better. However, users typically cannot determine thickness, width, and quantity; they only know the motor's height rating, such as 30, 40, or 45.

Core Iron is often considered better when imported, a belief that may not be visually verifiable but is currently accepted.

Coils are characterized by copper purity (brass or red copper, as long as it's not copper-clad aluminum), number of turns, thickness, and slot fill rate.

The Motor Housing, once determined, sets the upper limits for space-related indicators involving quantity and volume. However, users have no choice in this matter, and neither do manufacturers.

Hall Sensors are electronic components whose quality is often distinguished by price, with Honeywell being a reputable brand in the market.

Insulating Paint is graded by the state, with higher temperature resistance being preferable.

Phase Wires should be as thick as possible; generally, 1 square millimeter (without rubber) can meet a 10A current limit. For example, if your controller's current limit is 20A, the phase wire should be over 2 square millimeters.

Power is a critical motor specification. For instance, if your original motor is 48V 500W with a speed of 36 km/h, and you over-voltage it to 72V, you'll find that the speed can reach 54 km/h. Dividing the motor's speed by its voltage gives a more accurate result. For example, if your current speed is 45 km/h and your voltage is 72V, the speed per volt of your motor is 0.625. Another motor with a speed of 40 km/h at 48V has a speed per volt of 0.83333. Comparing these will reveal which is faster.

Efficiency (Energy Saving) - The efficiency of electric bike motors is generally around 82%. For regular products, the difference is only about 2%. If you claim your motor is excellent, using top-notch technologies like high-temperature superconductivity, the efficiency might increase by up to 3 percentage points, but the perceptible difference should not be significant.

This is why many people do not feel a noticeable energy saving with certain motors (energy-saving versions). Of course, if someone insists they feel a real energy saving, they might be a genuine enthusiast or their previous motor was subpar.

However, it's understandable that some motors are indeed power-hungry. Increasing efficiency by 1% is challenging, but there's plenty of room to decrease it. Creating a motor with only 50% efficiency is quite easy.

Optimal Efficiency Point - The Key to Over-Voltage

We've discussed that efficiency is an indicator with a wide lower limit but an almost capped upper limit. Does this mean we should completely disregard the motor efficiency indicator? Absolutely not.

We should be more concerned about another crucial indicator—the optimal efficiency point.

The optimal efficiency point refers to the point of maximum efficiency. For example, if a manufacturer claims their motor has an optimal efficiency of 93%, you should ask, "When does this 93% efficiency occur?" If they say, "When the motor is at around 100W at 48V," you might be disappointed because you won't maintain a power output of 100W, which is too slow. Of course, if a manufacturer wants to deceive you, they won't tell the truth, or they might not know it themselves.

In the motor industry, the optimal efficiency point refers to the power around the rated voltage and rated power where the efficiency is best. For instance, a 48V 1000W motor tested at 48V, if you see the highest efficiency value of 82.5% at around 960W, while at the 1000W power point, the efficiency is only 81%, this indicates that the motor's optimal efficiency point is at 960W.

Of course, for most reputable manufacturers, the optimal efficiency point is around the rated power, with no more than a 5% difference. However, some manufacturers might have a highest efficiency value of 83%, which is at the 48V 500W power point. They claim the motor is 72V 1500W, but when you use it at 72V, the efficiency at the 1500W point drops to only 65%.

The above discussion is merely to illustrate the point. Later, we will have a simple method to understand the true performance of your motor.

Firstly, determine your usage requirements. It's not about going as fast as possible. If you want a motor that can break 100 km/h at 72V, then you shouldn't consider the quality of the motor, as safety and quality cannot be guaranteed.

For normal use, once the speed exceeds 50 km/h, it enters an unsafe zone.

Here's a simple power-speed comparison chart for reference:

So, when ordering a motor, consider your usage range, especially if you plan to over-voltage, don't go too high.

To summarize, don't just look at power. When buying a motor, how should you choose it?

First, determine your speed requirements, operating voltage, and power requirements. If you plan to over-voltage in the future, it's best to determine the desired maximum speed after over-voltage as well.

Then, divide the required speed by the operating voltage. For example, if you plan to buy a motor over-voltaged to 72V and hope for a maximum speed greater than 75 km/h, then 75/72 = 1.0416. You should look for a motor where the speed divided by voltage is just greater than 1.0416 to meet your requirements. Be careful not to exceed this significantly, as it would consume more power.

Calculate the following for the listed motors:

• Motor A: 48V 500W at 36 km/h
• Motor B: 48V 800W at 42 km/h
• Motor C: 60V 1200W at 45 km/h
• Motor D: 60V 1500W at 52 km/h
• Motor E: 48V 1000W at 45 km/h
• Motor F: 48V 1500W at 52 km/h

Among these, only Motor F meets the requirements.

Remember, stating the voltage for a motor is meaningless without context, as is stating speed or power alone. If you can order a motor, specify the motor size and magnet height first, as this sets the internal physical space of the motor, maximizing the material usage by the manufacturer. This is what I mean by motor size (for ordering e-bike motors) and magnet height. Of course, higher magnets come at a higher price, which is a matter of personal trade-off.

Next, specify the highest voltage and speed requirements, informing the motor manufacturer how much over-voltage you want and the speed you aim to achieve. Then, you can demand that the rotational speed at 48V should not exceed 42 km/h, or else you should return it. Once the motor housing is set, the slower the motor, the higher the cost.

The Above Points Highlight Key Considerations for a Product Manager When Selecting a Suitable Electric Motor for an E-Bike Development. I Hope This Is Helpful to You, Who Are Interested in E-Bikes. Dear Fans, What Else Would You Like to Know About E-Bikes? Please Feel Free to Comment