Electric Bikes: How Watts, Volts, and Amp Hours Impact Performance
If you want to know how fast or powerful an electric bike will be, you need to understand watts (W), volts (V), and amp-hours (Ah) as these energy measurements apply to ebike motors and batteries.
Otherwise, “attempting to compare ebike power ratings is a great way to lose your sanity. That’s because ‘rated power,’ the metric some manufacturers use, doesn’t equal a motor’s actual power output.
Rather, as an electric bike owner or shopper, you need to understand how these electrical measurements impact an ebike’s performance. This is especially helpful if you are comparing electric bikes for a new purchase. Let’s look at a brief definition of each of these electrical measurements and describe how the motor or battery impact performance.
Electric Bikes: Watts
In most cases, the watt rating on an electric bike motor describes how much energy the motor can handle (or consume) continuously. This continuous watt rating is different from a peak watt rating that describes how much energy the motor can manage (or, again consume) for short periods of time.
An electric bike motor might reach its peak watt rating when under stress, climbing a steep hill or similar.
So, when you compare electric bikes first be certain whether continuous or peak watts are being reported. In some cases, you will see both, as an example, the motor on the Electrified fat tyre electric bike is rated for 2500 watts of continuous power but has a peak rating of 3,000 watts.
CONFIGURATION IMPACTS POWER
While there can be a relationship between the wattage rating for the electric bike motor and how “powerful” an electric bike may feel, the amount of power at the wheel can differ greatly for motors with identical watt ratings depending on the ebike’s configuration.
In fact, a wattage rating may be the least indicative measurement of the those we are considering in this article since an ebike’s controller and battery can have a lot more to do with how an electric bike feels when ridden.
One of the best examples of the difference between a motor’s wattage rating and how an electric bike will perform can be found when you compare mid-drive and hub-drive electric bikes.
“A hub motor is situated in the hub of one of the bike’s wheels, providing propulsion by spinning whichever wheel to which it’s attached. As electric bikes first began gaining popularity, these were the most frequently used type of motor,
In contrast, “mid-drive motors drive power to the bike’s drivetrain, typically at the crankset. By directly powering the bike’s cranks, mid-drive motors work in tight coordination with the bike’s already existing gears, amplifying the mechanical advantage they provide. This becomes particularly helpful when it comes to climbing steep hills or navigating extended inclines,
Thus, an electric bike with a mid-drive motor rated for, perhaps, 350W of continuous energy may have more “power” than a 500W or even 750W hub-drive electric bike in some cases.
Electric Bikes: Volts
“Volts are a measurement of tension. How much pressure can be contained in the battery,
The electric tension is really the potential power (electromotive force) in an electric bike system. If you can imagine how water pressure builds up in a pipe, you can understand the voltage. Imagine that all the parts of an electric circuit have a water-flow analogy. In terms of electric bikes, “batteries usually have volts in sequences of 12 such as 12, 24, 36, 48, so volts pretty much means power — how powerful a battery can be, but it also leads to top speed.”
“A 48V battery will not likely propel an electric bike 100 km's per hour because it simply doesn’t have enough pressure to rotate a wheel that many revolutions. If you climb up steep hills, a 48V battery will outperform a 36V because the 36 [volt] system will be working harder to produce the same results,”
It is possible to have too many volts. “If you have a 72V battery that is only propelling a system at 20 miles per hour then that means that you have unused voltage or really underutilized
Given what you now know about volts, you should understand why it can become very important to look at the number of volts in an electric bike battery relative to the bicycle’s entire configuration. You want the battery and motor to work together to get the desired performance.
Electric Bikes: Amp Hours
Amp-hours are an indication of the capacity of the electric bike’s battery. You might even think of amp-hours as the fuel tank or the range for the bike.
First, an ampere or amp is the base unit for measuring electrical current or load.
“A battery with a capacity of 1 amp-hour should be able to continuously supply a current of 1 amp to a load for exactly 1 hour, or 2 amps for 1/2 hour, or 1/3 amp for 3 hours, etc., before becoming completely discharged, In an ideal battery, this relationship between continuous current and discharge time is stable and absolute, but real batteries don’t behave exactly as this simple linear formula would indicate. Therefore, when amp-hour capacity is given for a battery, it is specified at either a given current, given time, or assumed to be rated for a time period of 8 hours (if no limiting factor is given),
For an electric bike “higher amp hours generally means higher range,. But it “is not an exact mathematical formula for volts and speed and amp-hours and distance…bikes and especially riders are not that precise.”
Here is an example.
“They do a few rides here in Heidelberg where you get to choose from a 19km ride, a 38 km ride, and a 60km ride, and I did the 38km ride on my 2500W fat tyre eMtb and still had battery juice leftover because I did a lot of the work myself because I wanted a really good workout,
I effectively got more range out of my electric bike by pedaling more. Range and even speed then is not completely based on the electric bike alone but includes the pedal power (many adults produce between 150W and 200W with their legs) and the electric bike’s drive system.
When you compare amp hours for one electric bike against another you need to understand how amp-hours are expressed, and you need to consider range as a function of the entire electric bike system.
Hopefully, this write up has helped you to better understand watts, volts, and amp hours as they impact the speed, power, and range of an electric bike.