When you are looking at electric bikes there is a lot of new terminologies you aren’t used to seeing. What do electric bike voltage, amps, and watts mean? Will a 48volt e-bike go much faster than a 36volt e-bike? What about a 1000 watt e-bike versus a 500 watt e-bike? Let’s take a look at some basics of electric bike power systems to clear up all the confusion.
Electric Bike Voltage, Amps and Watts. What do they mean?
Volts, Amps and Watts are the units electricity. Volts are pressure, Amps are volume and Watts are power.
What is a volt?
Volts are a measure of electric potential. Think of them as water pressure in a hose. The higher the voltage, the higher the pressure of the electrons flowing in a circuit.
What is an Amp?
Amps are a measure of electric current. This is the volume of electrons flowing in a circuit. Think of this as the same as how much water is flowing in a hose. A fire hose has a much higher volume of water flowing through it than a 1 inch garden hose. A 50 amp circuit has many more electrons flowing through it than a 10 amp circuit.
You can only push so much water through a hose before a hose will burst. In a similar manner, you can only push so many electrons through a piece of wire before the wire burns up. Circuits and wiring have a maximum amount of current they can handle before overheating and burning up. Circuit breakers and fuses are put in the circuits to prevent damage from over current. This is why you should never replace a fuse with a higher amp fuse if that’s all you have available.
What is a Watt?
A Watt is a unit of power similar to Horsepower. 745.7 Watts are equal to 1 hp. Your 300hp internal combustion car engine is also a 223,710 watt engine. Watts is equal to Volts * Amps. A 36volt bike pulling 20 amps is producing 720 watts of power.
- A 250 watt e-bike is a 0.33 horsepower e-bike
- A 500 watt e-bike is a 0.67 horsepower e-bike
- A 750 watt e-bike is a 1 horsepower e-bike
- A 1000 watt e-bike is a 1.34 horsepower e-bike
If you have a high voltage but really low current it is like having a very thin stream of high pressure water. It’s not going to push anything. If you have very low voltage and high amps it is like a 6 inch pipe with water trickling out. It won’t push anything out of the way. If you have high voltage and high amps you will have very high watts. This is similar to a fire hose opened full blast. You can use that water to blast anything out of your way. With an electric bike more watts is more power. More power will be more fun.
For reference a professional cyclists can produce a sustained 400 watts of power from their body and can generate 1000 watts in short bursts. A 500 watt e-bike is giving you a professional cyclist amount of pedal assist. To learn more about human power output go here.
The below video shows an analogy between water/hydraulic systems and electric systems to make it easier to understand.
How do Watts compare to MPH (miles per hour)
How many watts do I need to go 25mph on an e-bike? How fast is 250watts in MPH? How fast is 500watts in MPH? These are common questions from people looking for electric bikes.
There is no direct conversion from Watts to MPH just like there is no direct conversion from HP to the max speed of a car. An ocean going cargo ship has thousands of horsepower in engines but has a top speed under 50mph. A high performance motorcycle might have 200 horsepower but a top speed of 200mph.
It generally takes more power to go faster. You need power to overcome drag and friction. In general a higher powered e-bike will go faster.
To learn more about watts go here.
What is an Amp-hour?
An Amp-Hour is a measure of how much electricity a battery can hold. This is similar to how many gallons of gas fit in your cars fuel tank.
A 36 volt 8amp hour battery is common battery for a 250 watt E-bike. A 36 vole 8 amp hour battery will be able to deliver 36 volts of electricity at 8 amps for 1 hour before it runs out. It can deliver 36 volts at 16 amps for 30 minutes or 1/2 an hour. It can deliver 36 volts at 32 amps for 15 minutes.
The battery in your electric bike is made up of several cells. Each cell has a fixed output voltage. For Lithium batteries this is 3.6 volts per cell. It doesn’t matter how big the cell is. It still outputs 3.6 volts. Other battery chemistries have different volts per cell. For Nickel Cadium or Nickel Metal Hydride cells the voltage was 1.2 volts per cell.
The output volts from a cell varies as it discharges. A full lithium cell outputs closer to 4.2 volts per cell when it’s 100% charged. As the cell discharges it quickly drops to 3.6 volts where it will remain for 80% of it’s capacity. When it’s close to dead it drops to 3.4 volts. If it discharges to below 3.0 volts output the cell will be damaged and may not be able to recharge.
If you force the cell to discharge at too high a current, the voltage will sag. If you put a heavier rider on an e-bike, it will cause the motor to work harder and draw higher amps. This will cause the battery voltage to reduce making the scooter go slower. Going up hills has the same effect. The higher the capacity of the battery cells, the less it will sag under current. Higher capacity batteries will give you less voltage sag and better performance.
Watch the below video to learn more about Lithium batteries and how they work.
Electric motor basics
Let’s look at a few electric motor basics. How do Volts, Amps and Watts of an electric bicycle relate to the motor.
All electric motors have something called a “Kv value” or motor velocity constant. It is labeled in the units RPM/volts. A motor with a Kv of 100 RPM/volt will spin at 1200 RPM when given a 12 volt input. This motor will burn itself up trying to reach 1200 RPM if it has too much load on it to get there. This motor will not spin faster than 1200 RPM with a 12 volt input no matter what else you do. The only way it will spin faster is to input more volts. At 14 volts it will spin at 1400 RPM.
If you want to spin the motor at more RPM with the same battery voltage then you need a different motor with a higher Kv value. You can learn more about motor constants here.
Motor controllers – how do they work?
How does an electric bike throttle work? If a motors kV determines how fast it will spin, then how do you make it go faster or slower?
It won’t go faster than it’s kV value. That is the upper range. Think of this as the gas pedal pushed to the floor in your car.
How does an electric motor spin slower? The motor controller takes care of this. Motor controllers slow down the motor by rapidly turning the motor on and off. They are nothing more than a fancy on/off switch. To get 50% throttle, the motor controller will be switching on and off with off occurring 50% of the time. To get 25% throttle, the controller has the motor on 25% of the time and off 75% of the time. The switching occurs quickly. The switching can occur hundreds of times a second which is why you don’t feel it when riding the scooter.
The below video gives an explanation of how motor controllers work.
Class 1, 2, and 3 e-bikes
California has developed a system of 3 classifications for electric bikes. Several other states and federal organizations have adopted it as well. The classes were developed to create rules for bikes that aren’t human powered but aren’t full motorcycles. For low powered e-bikes, a drivers license and insurance aren’t needed. Somewhere you start adding enough power and it’s not like a pedal bike anymore. The classifications are as follows:
- Class 1 e-bike – pedal assist only with no throttle and a top powered speed of 20mph
- Class 2 e-bike – Bike can be powered by the motor alone with a maximum powered speed of 20mph
- Class 3 e-bike – pedal assist only with no throttle and a top powered speed of 28mph
To learn more about electric bike classifications go here.
In many instances, the bike may not have enough battery voltage and motor to go above 20mph keeping it a class 1 or 2 bike. In some instances with higher powered e-bikes there may be an electronic limiter that keeps it below 20 or 28mph. This allows them to be sold as Class 1,2 or 3 bikes. On these bikes the limiter may have a way to disable it allowing it to go faster.
Electric Bike Voltage Amps and Watts FAQ
Q: How much power does an electric bike use?
250 to 750 watt e-bikes are common. Most electric bikes fall in the range from 250 to 500 watts. The Class 1-3 system limits power to 750 watts which is why there isn’t a lot that go above that. Going higher power you need a license, registration and insurance in most places.
A professional cyclist only makes around 400 watts of power from their body. 500 watts is giving you more power then you could generate if you were a professional athlete.
Q: Is 250 watts enough for ebike?
250 watts of power is enough to propel most people under 200 lbs up to 15mph on flat land. 250 watt bikes will not have enough power to climb hills without slowing down a lot and will depend on your help for pedalling. A 250 watt pedal assist will make most hills much easier to climb than without it.
Q: What voltage are e bikes?
36 volt and 48 volt batteries are the 2 most common e-bike battery voltages. Most 250-350 watt e-bikes have 36 volt batteries. Most 500-750 watt electric bikes have 48 volt batteries.
Q: How fast can a 36v electric bike go?
Most 36 volt electric bikes have a top speed between 15 to 20 mph. These all fall within the Class 1 and Class 2 bike standards which limit top speed to 20mph. Most are designed with motor and battery combinations that won’t go faster.
Q: Do electric bikes charge when you pedal?
It depends on your electric bike and it’s power system. Electric motors generate electricity when they are being turned by something else. This is how a generator works. Some electric bikes have motors and controllers that can recharge the battery. This happens when the motor isn’t powered but is spinning such as going downhills or if your pedalling with no assist. When you are pedalling with pedal assist the motor is using electricity.
All electric bikes do not have this functionality. It is uncommon on e-bikes under $500. It is sometimes found on bikes between $500-$1000 and on most of them above $1000. Check the bikes specifications and manual to find out.
Q: Is 500w enough for ebike?
500 watts is enough power for most electric bikes for general riding and hills. It is the minimum power you should get if you are a heavier rider over 250 lbs. It will give you a good amount of assist on hill climbs and will be able to go up most hills on motor alone. Professional cyclists only generate 400 watts from their bodies.
Q: How fast can a 3000w ebike go?
A 3000 watt e-bike may have enough power to go 40-50mph. This bike will not be legal to ride on roads unless it is registered as a moped or motorcycle. At that power level it is no longer an e-bike or electric bike but an electrified motorcycle.
Q: How fast is a 500w ebike?
Most 500 watt e-bikes will be limited to 20 or 28mph to be a class 1-3 bike that doesn’t need a drivers license. The bike may have a power system that can go faster under power with an electronic limiter. The limiter may be capable of being disabled. With only 500 watts of power you still won’t get much above 30mph.
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About the author
My name is Doug Ryan. I am an adventure sports fan and an avid skier, sailor, mountain biker who also enjoys paddle boarding, kayaking, wakeboarding, waterskiing, and travel. I take any chance I can get to get out in the snow or water. I actively run an adventure sports meetup where I get asked many questions. I decided to start Endless Rush Outdoors as a way to share my knowledge and enthusiasm for adventure sports their gear.