ELECTRIC SCOOTER 101

ELECTRIC SCOOTER 101

Posted by Milosh Chorbikj on on 2019 Feb 8th

For many of us, the labels in the specifications of electric scooter, such as Voltage, Wats or Ah don’t mean anything. A large number of people only compare them by their quantity and compare it with the price. However, that's not always right. Scooter with the highest figures in the graphs of volts, watt, or ah does not mean that it will have the best performance. This article can serve as a quick beginner’s guide to determine the basics of a standard electrical system on a electric scooter. I am confident it will help you a great deal.

Voltage
What is voltage? You hear this term in everyday conversation, but do you actually know what it is? Well, let's put it simply. Voltage is the pressure from an electrical circuit’s power source. This pressure is used to push the charged electrons through the circuit — the guided movement of these electrons forms the electrical current. This current carries a power that can be used to perform any specific mechanical function, in this case, moving the wheels of the electric scooter. The pressure generated by the power source is measured in volts (V).

Excellent analogy for explaining the voltage is if we compare it to water. Electricity flowing through the wires is same as water flowing through a pipe. Higher voltage means higher pressure, and with higher pressure, the water moves faster through the pipe. The pressure goes down depending on the source; hence voltage goes down when the battery is used and loses its charge. In short, when an electrical device extracts power from the battery, the voltage goes down.

Three types of batteries mainly power electric scooters and here are the acronyms that usually accompany them:

Nickel Metal Hydride Battery (NiMH) - are explicitly created for the electric scooters. Their name explains their chemical composition. They are thirty percent lighter than sealed lead acid batteries, and therefore they are pretty expensive.

Sealed Lead Acid Battery (SLA) - is the standard type of battery because they can generate a very high current required for starting the scooter. They are the oldest type of batteries and were the first to be used in electric scooters, and even today, they are the most used batteries in many electric scooters. The main drawback is their weight and large size.

Lithium-ion battery (Li-ion, LFP, LiPo) - are a relatively recent development in the tech industry and therefore they are most expensive. They are the lightest type of batteries on the market today, and they last about three times longer than a regular Sealed Lead Acid (SLA) battery. Also, they require less maintenance and do not suffer from the "battery memory" problem like the NiMH batteries. The Lithium-ion batteries are divided into two sub-types of Li-ion batteries:

  • Lithium FerroPhosphate (LFP) - have a longer life than standard Li-on's and are generally regarded as significantly safer.
  • Lithium Polymer (LiPo) - usually manufactured in a pouch format as opposed to the traditional cell format. Their small and flat shape makes them very valuable in electric scooters.

Wattage
To understand wattage, we first must know that a joule is a unit of energy. Therefore wattage is one joule consumed per second (1 W = 1 J/s). In simple terms, a wattage is a unit of power, the rate at which energy is consumed. For instance, if a 70W rated light bulb runs for 5 hours, it will consume 70 W x 5 hours = 350 Watt-hours = 0.35 kW-hour of energy. KW-hour is also the unit used for power consumption in our house bills.

Let's make some real examples using electric scooters.

  • Scooter #1 has a 24 Volts and a 20 AH battery = 480 watt-hours
  • Scooter #2 has a 12 Volts and a 40 AH battery = 480 watt-hours
  • Scooter #3 has a 24 Volts and a 10 AH battery = 240 watt-hours.

The first and the second scooter, even thou have a different power source and different battery, they have similar energy on board, and they will probably perform in a very similar fashion. The difference is that the one with the higher voltage (#1) will accelerate faster and climb better – at the cost of some of that energy. The third scooter, I think it's obvious now, that is not going to go nearly as far as the other two.

Amp-hour
Amp-hour is a term related to the battery, i.e., a rating that describes how long a battery will last discharging at a fixed rate. For example, a 24 Amp-Hour battery can discharge 2.4-ampere current for 10 hours. If you cut down the current discharge by half to 1.2 amperes, the battery will discharge in 20 hours, and so on. Can you imagine? The more amp-hours the scooter has the more range you will get. This is very important for you to know when deciding what electric scooter is best for you.

However, the range of electric scooters is influenced by more outside factors than any other performance feature. Usually, the manufacturers use the symbol "~" that means approximately, "The range of this scooter is ~70Km." This range can be achieved under ideal conditions, for example; while riding at an average speed of 20 km/h, under full power, with 80 kg load, at a temperature of 23 °C and on smooth pavement. So, this leads us to our next question; what is the proper way to calculate the range of electric scooter?

Range calculus
Using the specifications of the battery and the electrical motor we can we can calculate the theoretical range, just with applying some basic arithmetic and high school physics. We will explain this using a simple example. We will try to calculate the range of a medium-sized electric scooter with these specifications:

Battery 24 Volts (V) and 20 amp-hour (Ah), and motor power 300 Watts (W).

The basic formula for calculating the speed is something we all know:
DISTANCE (Km) = SPEED (Km/hr) x TIME (hr)

This formula states that if we ride at a consistent speed until the battery runs out, we get the distance we can cover.

For the speed, we will apply the highest achievable rate for the scooter, for example, 25 km/h.

For the time, we will calculate it form the rated motor power and battery capacity. First, we must calculate the battery capacity using the formula:
Watt-hour (Wh) = Ampere-Hour (Ah) x Voltage (V) or 20Ah x 24V = 480Wh

The battery capacity is 480 watts per hour. Now, because we know the amount of energy in the battery and the power of the motor, i.e., the consumption of the motor, we can calculate how long it will take for this motor to use all of the battery energy:

TIME (hr) = Battery capacity / Power consumption or 480Wh / 300W = 1.6 hr

So now we have the speed and the time so we can use it in the first formula:

DISTANCE = SPEED x TIME or 25 Km/hr x 1.6hr = 40 km.

However, this range is achieved in ideal conditions, and it won't be right. The calculation only considered the characteristics of the battery and motor. We have to include the rider, the riding conditions, and other external factors into the calculations. The biggest electric scooter range killers are: overload, tire-pressure and riding uphill or aggressively.

Overload
I think it's obvious that an electric scooter will have problems with a larger driver compared to a lighter one. All electric scooters have a maximum permissible payload, which is usually 100 kg. Some larger models carry as much as 150 kg. However, we must know that the maximum permissible load is not the same as the optimal load. Electric scooters that are now available on the market are making their performance tests and calculations for determining the distance with a load of 75 kg because it is the average weight of a healthy adult male. Therefore, every driver weighing more than 75 kg can expect a lower range than the published figure. They need to choose scooters with a stronger engine, between 350 W and 500 W, so that when driving, the scooter will not struggle.

Tire Pressure
In the automotive industry, it is common practice, that a car with under-inflated tires spends more fuel. The same analogy applies to electric scooters. Without complicated mathematical calculations, the physics is obvious, under-pressurized tires deform the wheel and increase surface contact between the wheel and the ground. A higher surface contact means higher friction; higher friction means higher resistance.

For less resistance, we should aim to hold the tire pressure of the electric scooter to be close to the pressure indicated by the manufacturer. Reinforced tires, tires with higher pressure from the indicated one, also have its own set of problems. The ideal pressure for the electric scooter is usually shown in the user manual, and the pressure indicated on the tires themselves most often is the maximum allowable pressure for those wheels.

Driving Aggressively
In order to move a stationary object; to increase its speed or to slow it down, you need energy. This comes from the simple physics rule that an object at rest tends to stay at rest and an object in motion tends to stay in motion. According to this law of the physic, the distance is reduced with each pulling, increasing the speed or braking, i.e., aggressive driving.

Electric scooters spend most energy on their departure, then during acceleration, and on third place while breaking. This applies only to models that have electric breaking which loads the engine even more. Finally, the scooter consumes the least energy when running at a constant speed. The more we accelerate or decelerate during our driving; the distance spent with one charge of the battery will decrease.

In order to achieve greater distances, we need to reach our cruising speed by accelerating without haste and keep this speed as long as possible. If we drive a scooter with electric brakes, it's also helpful to coast to a stop rather than braking hard. In this way, we will be able to go more kilometers, and our tires and brake pads will also have a longer lifespan.