Have you ever wondered what the difference is between nominal power and peak power? Nominal power output is measured in watts and refers to the rated power that a motor can produce without damaging itself. Peak output of an electric hub motor is the maximum power that a motor can generate for short periods of time before overheating or other issues occur, e.g., “nose dive” or “cut out”. Knowing this information can help with choosing which type of electric unicycle is right for you, and how hard you may be able to push your EUC when riding.
This article will look at the definition of both, what they useful for, and what their main differences are. We’ll also talk about what these terms mean in regards to electric unicycle use.
1. What You Need to Know about Electric Hub Motors in an EUC
I’m not what you would call a “hardcore electric unicyclist,” but I do know what it’s like to get out and have some fun on an EUC, e-bike, or e-scooter. I have several! To be specific, though, I’ll tell you that hub motors are what power every electric unicycle, and this post’s going to tell you all about them.
First things first: what is a hub motor? A hub motor is what provides the torque needed to move the wheel of an electric unicycle. They come in a variety of shapes and sizes that depend on what type of electric vehicle they’re powering up. There are larger ones that produce more overall power than smaller hub motors.
If I’m looking for a high performance electric unicycle then it will be fitted with larger hub motors that produce more power than smaller hub motors which may not provide enough power to keep up with what I need.
But, what is power? Torque? Let’s quickly clarify what we mean by power. When we talk about power in a hub motor, we usually mean torque, which is a rotational force that causes rotation. The larger the torque, the faster an object will rotate. Sure, there are multiple ways to think about torque in an EUC. Torque can refer to the force the entire tire, wheel rim, and motor exert, or only the motor power. For simplicity, I refer to the torque generated only by the hub motor.
When discussing hub motors, this is what the primary axis of rotation of a hub motor’s rotor (or what may be called its winding) can provide. Many hubs have several shafts that are geared together, which results in an increase in available torque when more than one shaft turns at a time. These geared hubs are common in e-bikes and e-scooters. But, in EUC, hub motors are not geared in this manner; they are gearless. Rather, the hub motor designed for electric unicycles have multiple windings, which dramatically improves efficiency as each winding carries part of the load while others rest.
People often wonder why “gearless motors” are a better choice for some applications. Geared hub motors, which have the motor and gears enclosed in one shell, tend to be smaller than their counterpart (gearless), but that doesn’t make them superior. Gearless motors can last longer due to fewer moving parts. They also regenerate energy through regenerative braking when you decelerate or come downhill on your electric unicycle!
2. What is Nominal Power and What Does it Mean for Electric Unicycles?
Nominal power is the standard measure for electric unicycles and what typically what is what the manufacturer states. This is what the electric motor will use in addition to what it has to work with from the terrain or what other resistance it encounters as it moves along.
A hub motor can also be given what is called a “rating”, usually termed in wattage or watts (W). For reference with a combustion engine, like in your lawn mower, a 750W electric motor has a 1 horsepower rating. The watt rating of a hub motor reflects what the internal winding(s) are capable of (more about this below) and not how much power they draw from the EUC battery. What the motor actually needs to run normally may be significantly less than what’s stated on the rating label of the hub motor.
Instead, what this does mean is that what a hub motor is rated for in watts is called the “nominal” rating. The nominal ratings are used when estimating how much torque there will be available to propel an electric unicycle during continuous steady state use, e.g., riding at moderate speed over flat terrain. The term may also refer to what you might otherwise call the “continuous” power rating of an electric hub motor.
3. What’s the Difference Between NOMINAL POWER VS PEAK POWER?
Nominal ratings are what the motor will provide in continuous use (as described above), and what’s called “peak” or termed its “instantaneous” power. The peak power rating of a hub motor is what it can actually produce when required for short periods of time. In practice, the peak motor power should be what you rely on when estimating how much torque there will be available to propel an electric unicycle when you are riding hard, fast, uphill, or offroad.
The peak or instantaneous horsepower of a hub motor should only be relied on for short periods of time, such as what might be required to accelerate from a dead stop. If you go beyond what the hub can provide, excess electrical current with no or less rotational movement of the wheel will draw energy that has no place to go escape, except through heat production. The heat can build up and you may experience reduced electrical efficiency, shortened motor lifespan, or simply “overheating”.
Here’s the real problem with going beyond the power rating of a hub motor. Overheating leads to what’s called what we might otherwise call “thermal runaway” or what is when temperatures increase so much that what the hub does then turns what it has to work with into something else, such as an insulator. This can lead to what’s termed “frying” where not only will there be a reduction in how well the motor works but what it will also be what we might otherwise call “dead” because what this does is destroy the windings. Yup, dead motor and cut out.
I’ll note that modern battery management systems (BMS) along with their controllers (or “boards) have ways to cut off or reduce electrical power to an overheating or overpower motor. This is your “cut-out” or what may be what we might otherwise call “over-voltage protection” and what this does is prevent the motor from being damaged by what it’s asked to do.
What you can’t rely on for long periods of time however, are what could be called peak or instantaneous power ratings which should only be used when starting a hub in order to get what the motor up to what it needs to be for what we might otherwise call “full speed”.
4. Two Hub Motor Types Suited for Different Riding Styles
Knowing the rated power output of your electric unicycle motor is important for a few reasons related to your suited riding style. If you’re not careful, you could seriously injure yourself by riding on an overpowered machine. Sure, there are safety features built into EUC, such as tiltback, audible alarms, and other devices that may tell you that you’re reading “the end” of the power.
In general, you can divide the current electric unicycle offerings into two categories:
- Speed hub motor
- Torque hub motor
With a speed motor, the cables, magnets, and other components in the electric motor are configured for the electric unicycle to run continuously and efficiently at lower-torque (less peak output) at higher rotational speed. An EUC with a hub motor with “speed” in mind will have higher maximum top speed and likely better range than the 2nd configuration (below).
With a torque motor, even if it is rated with the same nominal power output (in Watts), than a speed motor hub, an EUC will have more torque, or peak instantaneous power. This gives the EUC stronger acceleration from stop, mid-ride speeds, and gives the EUC much better hill-climbing ability.
A torque hub motor will also run at generally cooler temperatures, as it is designed to more efficiently accept additional electrical current and use it. The limitation of course of a torque wound hub motor is that the top speed of the EUC will usually be much less than the speed hub motor.
5. How do I know if my hub motor needs replacing or not?
See this article about signs your hub motor may need repair or replacement.
6. What is the lifespan of a typical hub motor?
The lifespan of a hub motor can vary anywhere from 5,000 to 10,000 hours (source). It depends on what the motor is being used for and what kind of load it’s under.
Conclusion
Your hub motor is what drives your electric unicycle, and it’s what will determine how quickly you can accelerate from stop to full speed. It also determines what the top speed of your EUC will be.
Whether you’re riding for leisure or are a veteran rider who needs peak power output while maintaining speed or off road capability, understanding what nominal power vs. peak power means should help you decide which type of hub motor best fits your specific needs in order to get the most out of every EUC ride.
I hope you found this article helpful! Let me know with a comment what you think.