The Truth About Electric Bike Wattage Claims

Understanding Electric Bike Terms:


Amp Hours (AH)

Ampere-hour(s): A measure of battery capacity.

Volts:
Volt (or Volts): Unit of measure for electromotive force (EMF), the electrical potential between two points. An electrical potential of 1 volt will push 1 ampere of current through a 1-ohm resistive load.
Using a common plumbing analogy, voltage is similar to water pressure and current is analogous to flow (e.g. liters per minute).
In equations, the symbol E is often used (as in: E = IR). V is the symbol for the unit of measure, Volt.

Watts:
Watt (W) is the unit for measuring power. In physics terms, one watt is one Joule of energy transferred or dissipated in one second. Electrical power is calculated as:

Watts = Volts x Amps

Amp: (Ampere)
Ampere(s), the unit of electrical current. Current is defined as the amount of charge that flows past a given point, per unit of time.
The symbol I is used for current in equations and A is the abbreviation for ampere.

Watt Hours: (Wh)
The watt-hour (symbolized Wh) is a unit of energy equivalent to one watt (1 W) of power expended for one hour (1 h) of time. The watt-hour is not a standard unit in any formal system, but it is commonly used in electrical applications. The E-Bike industry has become a “hodge-podge” of mis-claims, hype and mis-nomers when it comes to selling and marketing E-Bikes. The facts are that physics do not change and the actual “power level” of an E-bike is very difficult to put into perspective to most folks.

The facts are that the volts (48 in our case) x Amps (25 in our case) = Watts

Nearly every retail electric bicycle and E-Bike conversion kit is listed at a specific power level, such as a “500-watt electric mountain bike” or a “250-watt E-Bike conversion kit”, yet often this power rating is misleading or just plain wrong. The problem is that manufacturers don’t use the same standards to name their motors, and consumers often don’t understand the differences.

Let’s start with some definitions and a bit of a physics lesson.

A “watt” is a unit of power, named for Scottish Engineer James Watt.
Watts can be used to measure the instantaneous power output (or input) of a machine, such as the electric motor on your E-Bike. The number of watts used by an electric motor at any moment equal the voltage supplied by a battery multiplied by the current flowing from the battery to the motor. So an E-Bike motor connected to a 24V battery being supplied with 10 amps of current would be powered at 24*10=240 watts.

As you can see, calculating the peak power of an E-Bike is simple. You just multiply the voltage of the battery by the maximum current the E-Bike can handle. The maximum current is determined by the E-Bike’s controller, and is usually somewhere between 15-30 amps. An E-Bike with a 48V battery and a 20 amp peak controller would theoretically be capable of a nominal 960 watts of instantaneous power.

Nearly every retail electric bicycle and E-Bike conversion kit is listed at a specific power level, such as a “500-watt electric mountain bike” or a “250-watt E-Bike conversion kit”, yet often this power rating is misleading or just plain wrong. The problem is that manufacturers don’t use the same standards to name their motors, and consumers often don’t understand the differences.