Increase reach

There are various ways to extend the range.

• Manufacturers are doing it with ever larger batteries, including Stromer with the ST7
• Additional battery solutions (extenders)
• The user has the option of reducing the assistance via the drive level or the torque sensor setting. Reducing one or both of these saves energy, but also means an increase in power output. It is said that increasing the cadence in particular 'saves' battery power. Is that true? More on this under 'Cadence' below.

Rough calculation of battery size

How do I determine which battery size I need?

In principle, the following energy consumption figures can be assumed for e-bikes/pedelecs with hub motors. The table is based on minimum pedaling effort.

Once the voltage is known, the next step is to find out how many ampere hours (capacity) are required to cover the desired daily distance without draining the battery. This depends on how much of your own power you want to use, what speed you are traveling at and what the route profile looks like.

Now multiply the desired driving distance by the corresponding watt hours/km from the table above to obtain the required minimum watt hours (energy). Divide the result in [Wh] by the system voltage (36 / 48 V...) to obtain the minimum ampere hours that the battery must provide.

Example:
Distance: 45 km
System voltage 48V
Fast from A to B, max. support: Assumption 17 Wh/km

45 km * 17 Wh/km / 48 V = 16 Ah

It must now also be taken into account that the battery is subject to an ageing process from day 1 after production. This is further accelerated by cyclical use. If you also want to drive the commute after two years and in winter, ~20% should be added. So you end up with 19.2 Ah, which corresponds exactly to the nominal capacity of the Stromer BQ983 battery.

When buying, you should always think carefully about whether to buy the largest possible battery, even if you might not use its full range. If you buy a smaller one, the price saving can be a boomerang.

Additional battery

The additional battery solution is not available from Stromer. An interface is missing.

What can you do if the battery is not sufficient for the commute and cannot be charged in the store? This is where an additional battery, also known as an extender, comes in handy. In addition to a considerable increase in range, the use of such a battery also offers other advantages.

If you would like to know more, see PIMP mySTROMER - 'Battery - Extender' and 'Battery - Second battery box' continue.

Cadence

If you don't want to invest in an additional battery, you can also work on your own performance. The more power you generate, the more the battery is conserved and the range is increased. This can be achieved by reducing the assistance level and/or by reducing the value of the torque sensor (in the Omni app = pedal sensor).

Mid-engine: For the mid-engine, there are ebikespass.de an interesting theoretical consideration of how cadence affects battery consumption.
The result: At the low cadence of 50 rpm and medium pedal assistance/speed level (power: 150 W), the current heat losses are three times greater than at 85 rpm. The efficiency of the motor at only 50 rpm is 24.5 % lower than at 85 rpm!

Can the calculation also be applied to the hub motor?

Hub motor: The calculation used here would probably have to include the gears, as these are located on the axle of the hub motor and therefore directly influence the rotational speed of the motor and thus the efficiency. The cadence is transmitted to the motor, so to speak, and does not act directly on the motor. The technical principle of the hub motor is particularly advantageous when higher speeds and therefore higher rotational speeds of the motor can be ridden.

Due to their design, Stromer hub motors are relatively "lazy" per se (max. 395 rpm) and not very efficient in the lower speed range or low speeds (< approx. 20 km/h). The efficiency decreases, the waste heat increases. As this has to be transported from the stator to the rotor via an air gap, cooling is also relatively modest, despite the large aluminum drum.

The speed/efficiency diagram of a 48 V / 500 Watt hub motor looks like this:

It is worth downshifting, especially on hills, to take power from the chain. This naturally reduces the assistance and therefore requires less energy. As the cadence increases and ideally the speed remains the same, you can avoid the motor working in the low efficiency range and thus producing heat instead of propulsion.

Side effect on the body: And there is another aspect that applies to both drive concepts. Technically, the cadence is about the torque, physically about the circulation and the joints.

At high cadences, the phases of muscle tension (contraction) are shorter. During a contraction, the blood vessels are compressed and blood circulation is impeded. However, this is important for the transportation of oxygen and nutrients. Intermediate metabolic products, such as lactate, are also better removed via good blood flow.

A higher cadence is better for the joints - because the load peaks are shorter and often lower. A cadence of > 75 revolutions per minute is recommended by sports medicine. Incidentally, as a patient in rehab, you will be trained to 75 rpm. This mark is considered the lower limit in order to keep knee strain as low as possible.