Hall or temperature sensor defective?

General

Motor damage on newer Stromerbikes is rather rare. With the old motors (ST1 V1 / V1.1) and integrated electronics, there were still many problems and failures due to overheating or water ingress.

With increasing mileage, the engine mounts can become a problem. This is usually caused by water ingress

In rare cases, a Hall sensor or the thermistor may fail. The 3 Hall sensors report the current motor position and speed to the Omni, the thermistor reports the motor temperature.

Faults can be detected by measuring the motor plug.

> See also here in the chapter: Motor - 'Motor overheated'

Components used

• Hall sensor: Honeywell SS461R
• Thermistor: NTC, 10 kΩ (25 °C and Beta value ~3500) - 15 kΩ

Measure and repair Hall sensors

Hall sensors can be tested with a multimeter. To do this, switch it to diode measurement mode. With the Higo L1019 motor plug (used, for example, on the ST5 2021 ABS | ST5 2018 | ST3 2022 Pinion | ST3 2018 | ST2 2020 Belt | ST1 2021 LCI | ST1 2019), connect the red measuring tip to ground and use the black measuring tip to measure the reverse voltage of Hall: Green / Blue / Yellow. The measured voltage should be around 0.6 V for all sensors.

> See also PROBLEMS - Motor - 'Repairs'
> See also a well illustrated work instruction from 'GRIN Technologies' - 'Hall sensor testing'
> See also in the electricbike.com forum a very good guide from 'Tommycat' for measuring the Hall sensors and a BLDC motor without internal controller - 'Testing BLDC motor's Phase Wiring - Hall Sensors and Wiring'
> See also the video tutorial of 'High Tech // Low life'

Measure thermistor, repair

The Stromer hub motor has a temperature monitoring system to prevent overheating. If the motor gets too hot (from approx. 135 °C), a yellow warning triangle is first displayed in the Omni and assistance is reduced. If you continue riding, the assistance is stopped and you must pause the ride. If a red warning triangle is displayed and the engine temperature in the Omni is constantly above 150 °C, there is probably a problem with the temperature sensor.

The NTC thermistor can be measured with the multimeter in resistance mode. A resistance of ~10 kΩ should be measured between violet and black (ground) at an ambient temperature of 20 °C. If you measure a resistance that is infinite or far below 1 kΩ, the thermistor is defective.

Repair or replacement is only possible by opening the motor.

> See also here in the chapter: Motor - 'Repairs'

A somewhat more convenient variant is available for electricity traders to test.

Thermistor workaround

The user jitensha and supplementary svenkuehn' has published a workaround in Stromerforum.ch that bypasses a motor opening. Using a 10 kΩ resistor, the Omni is tricked into believing that the NTC is working, thus achieving a motor temperature display of approx. 21 °C.

At the Higo L1019 motor plug At the top, disconnect the violet cable from the motor plug or socket. Solder an ohmic resistor of 10 kΩ to the cable. Connect the other end of the resistance to earth (black).

This workaround overrides the heat motor protection. If the motor enters the danger zone of 135 - 140 °C (ST3), the power is no longer reduced and the Stromer does not stop operating at approx. 150 °C. This can result in the motor overheating, which can lead to motor failure!

FW SUI 4.5.0.3 - Update March 8, 2025

Stromer writes: "The permitted engine temperature in Sport mode has been slightly increased so that it can be used for longer. (Administrator's note: Probably applies to the ST5 / ST7 models). As the possible recuperation current has been increased at the same time for the ST7, the two measures can also cancel each other out when recuperation is used."