Recuperation and recuperation

What is recuperation?

Braking energy is recovered during so-called recuperation. This occurs during braking by converting the energy released in the generator (in Stromer S-Pedelecs the hub motor) into electrical energy. This energy is fed back into the battery and can be reused for assistance when riding. The principle is familiar from old bicycles where the dynamo supplied the bicycle lamp with electricity, then more recently with electric cars where braking energy is also fed back into the battery and for a very long time with trains.

• Kinetic energy: When you brake or drive downhill, the vehicle has kinetic energy (kinetic energy).

• Hub motor as generator: The hub motor, which is located in the wheel hub, is driven by the movement of the wheel. Instead of driving the wheel, it is now driven itself and acts as a generator.

• Conversion into electrical energy: The hub motor converts the mechanical kinetic energy into electrical energy. This is done by induction, a physical principle in which the movement of magnets in a coil generates electrical voltage.

• Feeding energy back into the battery: The electrical energy generated is fed back into the vehicle's battery. This recharges the battery and increases the vehicle's range.

How Stromer works

The advantage of a hub motor is the possibility of recuperation. The TDCM hub motor used by Stromer acts like a dynamo. It converts the rotational movement of the rear wheel into electricity, which recharges the battery. This is particularly interesting when riding downhill, where the recuperation is used as a motor brake.

The system had one level for the 36 V models (ST1, V1, V1.1 with external display) and two levels for models with the Omni display:

Display on the handlebars

Recuperation is activated with a reed contact on the right-hand brake lever. It only becomes active from 50% battery charge and below and must also be activated in the menu beforehand (Code 1009 = 1). The strength of the motor brake can be set with code 1011 (goes up to 99). There is Rekup 1 (easier downhill driving) and Rekup 2 (steeper downhill driving).

Omni Dipslay

1st level: Recuperation via the brake levers

In the first third of the brake lever travel, electrical recuperation is activated via a reed contact in the brake lever. If the lever is pulled further, the mechanical/hydraulic brake system is activated. The recuperation force in the left brake lever is about 1/3 to 1/2 of that in the right brake lever. 

With the firmware update SUI FW 4.5.0.3 from 05.03.2025, recuperation is additionally boosted when both brake levers are actuated. This allows recuperation to be controlled even better.

The bar above the battery charge level shows the current energy flow. If the bar builds up from left to right, the bike is in recuperation mode. Power is flowing back into the battery. The longer the bar, the greater the energy flow. The maximum deflection is approx. 2/3 of the display width.

To set the recuperation intensity, press MENU > BIKE > BRAKES > in the Omni Display. 'Strength' and sets this using the plus and minus buttons. In the OMNI APP, the setting is located under CONFIGURATION - SENSORS > 'Brake sensor'. The setting is effective across all support levels but is independent of the recuperation levels in the control ring.

2nd level: Recuperation via the control ring with the [-] and [+] button

The second level is activated by pressing the [-] button on the control ring for 2 seconds and can be varied in 5 steps by repeatedly pressing [+] and [-]. It is deactivated by pressing and holding [+] and [-]. The latter also happens automatically when the speed falls below approx. 10 km/h.

The effect of recuperation is speed-dependent. If you are already traveling fast on a steeper descent and switch on the RECUP, it will not have as strong an effect as if you switch on the RECUP at the start of the descent when you are still traveling at a moderate speed.

It switches off on a steep descent at high speed (at approx. 55-60 km/h) because the maximum battery charging current of 15 A would be exceeded, but is reactivated automatically if the speed falls below this limit again.

Cruise control (cruise control)

With the function Cruise Control (from Stromer firmware version 4.4.3.3. - 20.11.2023), the previous recuperation mode is supplemented with a downhill assistant.

The Cruise Control function automatically adjusts the motor resistance (recuperation) to maintain speed even on changing gradients. An attempt is made to maintain the speed from the moment of activation (long press on the minus button). The cruise control speed can be adjusted upwards or downwards in predefined speed increments using the plus or minus button on the button ring.

In OMNI under Menu > Bike > Recup Mod... settings can be made for the recuperation mode. Here you can use MODUS to switch between Cruise Control (standard function) or the previous Recup mode can be selected. You can also use SPEED to set the speed increments (default: 5 km/h) and PEDALING to set the pedal force for automatic deactivation of recuperation.

> Go to the complete OMNI flow chart here.

Tip: Activate Cruise Control or Recup at the start of the descent to maintain your speed better. If you are already traveling fast, both modes can no longer maintain the speed and you will speed up.

Gain in range

Stromer speaks of a range gain of up to 20 % when using recuperation.

Practical test

Route length: 3.8 km Gradient: 10-18% | Ø = 11.6%
Motor starting temperature: 77 °C
Ambient temperature: 28 °C
System weight: 130 kg
Recuperation strength: Maximum= red bar
SoC start: 66%
SoC end: 73%
Recuperation gain = 7%

Problem: Engine temperature warning after 3 km: 145° C (warning triangle in the Omni)
> See also main menu: PROBLEMS - ENGINE - 'Motor overheated'

Summary

Energy recovery actually works well. However, there are limitations:

• A relevant gain in charge or range requires a longer descent with a greater gradient (> 8%) so that the full energy recovery can be used (red bar in the Omni).
• The battery must not be full.
• The motor produces waste heat when recuperation is used. At level 5 (100% recuperation) and on long, steep descents, the motor runs into the overheating protection (yellow warning triangle). If you reduce the recuperation, the 'charge gain' of the battery suffers, but you can recuperate for longer.
• Recuperation in stages 4 and 5 'pushes' too much current into the cells and exceeds their maximum charging current, which is not conducive to the service life of the battery. See box below.
• To get into the double-digit % profit zone would certainly require 2 longer descents or several short ones on the tour. However, before you can ride down, you usually have to ride up, which puts things into perspective.
• On gentle downhill gradients, the recuperation gain 'sinks' into the background noise of consumption and cannot be read, at least visually, from the capacity display in %.

Good to know

The "Cruise Control" and "Recup" mode cannot be activated if the battery is charged to 100% or the battery temperature is 50 ºC.

A system error E210105 (battery overheating alarm) can occur if the battery is very hot > 50 ºC (e.g. after a long climb or descent with recuperation, as well as outside temperatures > 30 ºC). As a rule, you will notice a reduction in assistance or the failure of recuperation before this happens. As the OMNI also freezes, the error can only be resolved by resetting the OMNI (long press on the on/off button).
Stromer strongly recommends taking a break to allow the battery to cool down. Only then is recuperation available again.

The maximum recuperation current is 15 amperes, with the old ST1, depending on the firmware, 4.5 to 6 A. To protect the battery, this is reduced as the battery charge level increases. As a result, recuperation is only weak or no longer noticeable when the battery is almost fully charged.

Recuperation stage 4 & 5 "pushes" approx. 2.5 A of current into each cell string of a 13S/6P batteries. This value is around 0.8 A, or 50 %, above the recommended charging current of 1.7 A for a Panasonic NCR 18650 GA (used in the BQ983, among others) and can reduce its service life. Levels 4 & 5 should therefore be used with caution.