The eZee Bikes e-Drive System Explained

Performance

From a biological and mechanical viewpoint, using a bicycle is extraordinarily efficient. It’s simply the most efficient human-powered means of transportation in terms of energy a person must expend to travel a given distance. From a mechanical viewpoint, 85-90% of the energy delivered by the rider into the pedals is transmitted to the wheels through the gearings.

A person biking at low to medium speeds of around 10–15 mph (16–24 km/h) uses only the energy required to walk. Air drag, which is proportional to the square of speed, requires dramatically higher power outputs as speeds increase. If the rider is sitting upright, the rider’s body creates about 75% of the total drag of the bicycle/rider combination.

There are many erroneous claims in electrical bike brochures that grossly overstate their autonomy or range.

The range of the battery depends on:
a) The power delivered by the motor,  if it’s a very weak motor running with low amps, the battery pack could run for a longer time. It’s similar when the cyclist inputs a big share of the power by pedaling hard, or..

b) When riding at a very low speed, as mentioned , air drag is cube to speed.

c) energy capacity of the battery pack Wh

d) overall efficiency of the electric system and mechanical system of the bike.

The traits of an exceptional electric motor.

1. Energy efficiency
2. Performance: Power to weight/dimension ratio
3. Reliability
4. Aesthetics

Weighing at 3.78kgs, our brushless PMDC motor with inbuilt planetary reduction gears and freewheel is built in-house with exceptional technical specifications. With minimal drag, a freewheel spins freely like a normal hub when the motor is not on. Contrarily, a Direct Drive motor with similar output is heavier and has a high drag when not powered. Riding electric bikes with direct drive would be very hard without the electric power.

1. Motor efficiency loss can be attributed to:

a) Resistance in the copper wires used in the motor.
Using high grade copper, we achieve minimal winding resistance in our motors.

b) Iron loss as a result of Eddy currents.
We reduced this to the min. by using high grade silicone steel plates (for thinness)for the stator.

c) Parasitic lost from bearings and other mechanical moving parts.
We employ high quality bearings from Japan NMB and Germany FAG. Dow Corning silicone greases for the planetary gears.
eZee Gen 3 motor has an efficiency of 83 % with 250 rpm and 25 Nm of Torque. It is essential to qualify the torque output together with the speed.

2. Power / weight and dimension ratio. 

As a permanent magnet motor the obvious critical component is the magnet.
We use N35UH Neodymium magnets that retains magnetic properties up to 180°C, fitted in optimum size with min. air gap to the stator.
US / Canada nominal rated 500 watts motor delivers 30 Nm torque with 200 rpm speed at 22 amps or 800 watts.
It weighs 3.78 kgs and has a diameter 186 mm.  An ideal dimension and weight ratio for its power output. Our nominally rated 250 watts motors for EU market (EN15194), delivers that same high torque with a speed limit of 25 km/h or 200 rpm with 26” wheels.

3. Reliability

Using PWM ( Pulse Width Modulation ) technology, eZee’s motor uses state-of-the-art Honeywell SS41 Hall sensors. The planetary star gears are machined from cast Nylon 6 rods for high strength and durability. The motor hub covers are die cast and CNC machined from high grade Al alloy ADC 5, providing good corrosion resistance. Anodized black option gives provides even further corrosion resistance.

4. Aesthetics

Hub motor covers are available in gloss finish and machined surface, or also available in anodized black or silver hubs.Simple, elegant, easy to clean and maintain.

Controller

eZee’s controller is engineered with the best and most reliable electronic components in the market, delivering ultimate performance and reliability. Operating at 36V and 48V, it has an overload protection at 20amps, using IRFB 4110 mosfets that take high amps and voltage. The circuit board is sprayed with conformal coating and then a layer of silicone potting compound is applied for further corrosion resistance. Die cast Al. casing.

Battery

Lithium polymer packs refer to the way the pack is structured, using as a flat pack with multiple layers of the electrodes stacked with insulating film in between and covered in plastic foil. Cylindrical cells have a continuous foil of electrodes coiled and packed into a very thin steel casing.
18650 cells generally are rated at 3.6V and 2.2 Ah, so a pack with cells arranged 10 in series 3.6v x 10 = 36v  and 5 of these in parallel would be 2.2 Ah x 5 = 11 Ah with some losses due to impedance in a series, the true capacity of a pack would be slightly lower. Each manufacturer of such cells have their own secrets to the chemical compositions and  know-how, that’s where the differences lie.

The capacity of the battery is rated in Watts hours (Wh) which is the nominal voltage multiplied by the Amp hour (V x Ah).
(e.g. 36V x 10Ah = 360Wh). It is therefore essential to know both the V and Ah rating of a battery pack or the Wh directly.

Lithium batteries packs have a battery management system ( BMS ). It is an attached circuit board that performs the function of balancing the cells, short circuit protection, low voltage protection, over charging , limiting the maximum discharge current and  temperature control.

Battery Safety

While Li+ cells from reputable brands have managed to make cells with a very high degree of stability, a high quality BMS is just as important to prevent short circuit and provide cell management. Our packs are fully tested to comply with safety standards written in UN38.3.  Currently Li battery packs with the capacity exceeding 100 Wh is classified as Hazardous Material  – Hazmat Class 9 , and would not be allowed on aircraft  except on Cargo flights and have to be packed in carton approved with UN3841 ( Lithium battery with equipment ).  UN 3841 is a simple procedure involving a drop test from a height of 1.2 meters with no resulting damages.