Wiring Configurable Outputs: Why & When You Need Relays
FuelTech ECUs are designed for versatility, giving you the ability to control various components through configurable outputs. However, knowing when to use relays becomes crucial to ensure both optimal performance and to protect your ECU.
Output Specifications
FuelTech ECUs feature outputs categorized by color, each with specific current ratings:
- Blue Outputs: 5A per output
- Grey Outputs: 1A per output
- Yellow Outputs: 5A per output
These outputs enable precise control over a wide range of devices such as solenoids, pumps, and shifters. Yet, it’s essential to respect these current limits to prevent overloading, which could cause damage to the ECU.
Note: Total combined current load with ground activated outputs: FT450-10A, FT550/600-30A continuous
Total combined current load with 12V activated outputs: FT600-20A, FT550-10A continuous
When to Use Relays
Certain components, like fuel pumps or larger solenoids used in transbrake and nitrous systems, often draw currents exceeding 5A. Extended operation can further increase amperage draw due to heating. To prevent excessive current draw and protect your ECU, relay utilization is recommended.
- Relay Utilization: Employ relays controlled by the ECU to manage high-current devices. Relays act as robust switches, handling heavy loads safely while minimizing the direct load on the ECU outputs.
Determining Current Draw
If unsure of a solenoid or component’s current draw, you can measure it using a multimeter and Ohm’s law:
- Measure Resistance: Determine the resistance of the solenoid or component.
- Calculate Current: Divide the vehicle's operating voltage (e.g., 14V) by the resistance to obtain the current draw. If this value exceeds the output rating (e.g., 5A for Blue or Yellow outputs), a relay is necessary.
Example: Solenoid resistance = 2 Ohms
Vehicle operating voltage = 14V
Total current draw of solenoid = 7A
NEEDS RELAY TO AVOID DAMAGING ECU
Wiring Guidelines
Blue/Grey Outputs
- Ground-Activated: Blue and Grey outputs are ground-activated. Connect these to the relay’s ground post to switch the high-current load safely.
Wiring Diagram for Blue/Grey Output Control:
Yellow Outputs
- Versatile Control: Yellow outputs can switch between 12V activation or ground. Proper wiring ensures correct operation without backfeeding to the ECU.
Wiring Diagram for Yellow Output Control:
Configuring in the FT Manager Software
Ensure the relay is configured correctly in FTManager:
- Navigate to the desired function in FTManager.
- Locate the “Output Signal” option menu.
- Select “Activated at 12V (Only w/ Yellow Outputs)” to match your wiring setup.
When properly configured, it should look like this example:
Conclusion
Using relays effectively with FuelTech ECUs not only protects your engine management system but also enhances performance by protecting against overloaded circuits during competition. By understanding the current limits of ECU outputs and employing relays where necessary, you ensure that your vehicle’s critical systems operate safely and efficiently. This approach not only protects your investment but also optimizes performance, allowing you to make the most out of FuelTech’s advanced control capabilities on the racetrack.
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