TM Racing 300 EN Fi (MY2021) Fan Driver

Overview

This project describes an electronics scheme for a custom low-side switch to run an arbitrary 12 V fan on a TM Racing 300 EN Fi MY2021 enduro motorcycle, using the bike's original fan connector.

Project file:

• TM_fan_driver.eprj (open with EasyEDA Pro)

The bike fan connector provides:

• +12V
• GND
• Switching signal

Signal behavior:

• 2.4 V = fan OFF
• 0 V = fan ON

Circuit Schematic

Purpose

The circuit lets you:

• Keep compatibility with the stock bike control logic
• Drive a non-stock (arbitrary) 12 V fan
• Use a robust low-side switching stage suitable for automotive/electrical noise conditions

Functional Principle

A low-side switch controls the fan by switching the fan negative terminal to ground:

1. Fan positive is connected to bike +12V.
2. Fan negative is connected to the output of the low-side switch.
3. The low-side switch references bike GND.
4. The bike control signal (2.4 V OFF, 0 V ON) is conditioned/inverted as needed to drive the low-side transistor/MOSFET correctly.

Wiring Summary

• Bike +12V -> Fan +
• Bike GND -> Driver GND (and common ground)
• Bike Switching signal -> Driver Signal input
• Driver Switched output -> Fan -

Design Notes

• Ensure all grounds are common.
• Use components rated for automotive transients and fan startup current.
• Add flyback/transient protection for inductive load behavior and wiring harness noise.
• Validate thermal performance of the switching device at maximum fan current.

Validation Checklist

• Confirm connector pinout on the motorcycle harness.
• Measure control signal: around 2.4 V when OFF, 0 V when ON.
• Verify fan turns on only when signal is ON (0 V).
• Check voltage drop and switch temperature under continuous operation.

Disclaimer

Use at your own risk. Verify wiring and electrical ratings before connecting to the motorcycle harness.