Ever wondered how to keep a crucial car system running even when the primary power source fluctuates? Or perhaps you’re designing a custom automotive project and need to ensure a component stays active? This often involves understanding how to keep a control board relay closed in a car. It can be tricky navigating voltage drops, unexpected power interruptions, and the intricacies of relay types.
To keep a control board relay consistently closed in a car, connect its coil to a reliable, continuous power source – this is often the car’s ignition system, or a dedicated auxiliary switch, or a timer circuit – ensuring a stable voltage and proper grounding.
This guide dives deep into the mechanics of automotive relays, offering practical solutions, expert tips, and troubleshooting techniques. You’ll discover not only how to keep a relay closed, but also why certain methods work, empowering you to tackle a wide range of automotive electrical challenges. We’ll cover everything from basic relay operation and wiring diagrams to advanced techniques like using capacitors and flyback diodes. Plus, we’ll debunk common myths and address frequently asked questions about relay malfunctions. Get ready to master the art of relay control!
- Key Facts:
- Relay Usage: Automotive relays are crucial for managing high-current circuits, enabling low-current switches to control powerful components like headlights, fuel pumps, and cooling fans.
- Voltage Sensitivity: Most automotive relays operate on a 12V DC system, but their “pull-in” voltage (to close) and “drop-out” voltage (to open) can vary, impacting their responsiveness to voltage fluctuations.
- Current Consumption: A typical automotive relay coil draws between 150mA and 200mA when energized, a factor to consider for continuous operation. (Source: Electro-Tech-Online Forums)
- Latching Relays: Latching relays offer an alternative to continuous power, maintaining their state (open or closed) with only a momentary pulse, significantly reducing power consumption. (Source: DigiKey)
- Flyback Diode Importance: A flyback diode is essential when controlling inductive loads (like relays) to prevent voltage spikes that can damage sensitive electronic components. (Source: Reddit)
What is a Control Board Relay and How Does it Work in a Car?
A control board relay in a car is an electrically operated switch that uses an electromagnet to control a larger current. When energized, the electromagnet pulls a switch, completing the circuit; when de-energized, the circuit breaks. Think of it like a remotely controlled light switch, but instead of controlling a light bulb, it controls a high-power component in your car.
Relays allow low-power circuits (like a switch on your dashboard) to safely control high-power circuits (like your headlights). This is crucial because sending high current directly through delicate switches could damage them or even cause a fire. The relay acts as a gatekeeper, using a small control signal to manage a much larger flow of electricity.
Types of Relays Used in Cars
Car relays come in three main types: Normally Open (NO), which closes the circuit when energized; Normally Closed (NC), which opens when energized; and Latching, which maintains its state until a pulse changes it. Understanding these differences is key to choosing the right relay for your application.
| Relay Type | Description | When to Use |
|---|---|---|
| Normally Open (NO) | The circuit is open (off) by default. When power is applied to the coil, the relay closes the circuit (on). | Most common type; used for circuits that are usually off, like headlights or a starter motor. |
| Normally Closed (NC) | The circuit is closed (on) by default. When power is applied to the coil, the relay opens the circuit (off). | Less common; used for circuits that are usually on, like a security system alarm. |
| Latching | The relay stays in its last position (either open or closed) even after power to the coil is removed. It requires a pulse of current to change its state. | Ideal for applications where continuous power to the coil is undesirable, like battery disconnect systems. |
Basic Components of a Relay System
A relay system consists of an electromagnet (coil), a switch (contacts), terminals for connection, a power source, and a ground connection. These components work together to control electrical flow. The diagram below illustrates a typical relay setup.
- Coil: The electromagnet that creates the magnetic field to move the switch.
- Contacts: The switch that opens or closes the circuit being controlled.
- Terminals: Connection points for wiring the relay into the circuit (typically labeled 85, 86, 30, 87, and sometimes 87a).
- Power Source: Provides the electricity to energize the coil (usually 12V in a car).
- Ground: A return path for the electrical current.
How Can You Keep a Control Board Relay Closed in a Car?
To keep a control board relay closed in a car, you must ensure continuous power to its coil. This can be achieved by connecting it to a stable power source, like the car’s ignition, or using an auxiliary switch. It’s like keeping a light switch flipped “on” – the light (or in this case, the relay) stays on as long as it receives power.
There are several ways to provide this continuous power, each with its own advantages and disadvantages. Let’s explore some of the most common methods:
Providing Continuous Power from the Ignition
Connecting the relay coil’s positive terminal (e.g., 85) to a 12V source from the car’s ignition and the negative terminal (e.g., 86) to ground ensures the relay stays closed when the ignition is on. This is a convenient method for circuits you want to activate only when the car is running.
- Wiring Steps:
- Identify a 12V ignition-switched power source in your car’s fuse box. (Consult your car’s wiring diagram).
- Connect a wire from this power source to terminal 85 of the relay.
- Connect a wire from terminal 86 of the relay to a good chassis ground point.
- Connect the device you want to control to terminals 30 and 87 (or 87a if using a normally closed relay).
- Key Takeaway: Using the ignition power ensures the relay only activates when the vehicle is running.
Using an Auxiliary Switch for Relay Control
An auxiliary switch installed between the power source and the relay coil allows manual control. When the switch is on, it provides continuous power, keeping the relay closed until the switch is turned off. This method gives you direct control over when the relay is energized.
- Step-by-Step Instructions:
- Choose a suitable switch (toggle, rocker, etc.) that can handle the relay coil’s current.
- Connect a wire from a 12V power source (e.g., battery or fuse box) to one terminal of the switch.
- Connect a wire from the other terminal of the switch to terminal 85 of the relay.
- Connect terminal 86 of the relay to a good chassis ground.
- Connect the load (device you want to control) to relay terminals 30 & 87.
- Tip: Use a switch with an indicator light to easily see if the relay is energized.
Implementing a Timer Circuit for Relay Control
A timer module or delay-off timer circuit, added between the power source and coil, offers control over how long the relay stays closed. It provides continuous power for a preset duration. This is useful for applications where you want a device to run for a specific time after a trigger event.
For example, you might want interior lights to stay on for a minute after you close the car door. A timer circuit connected to the relay controlling the lights can achieve this. You would set the timer to one minute. When the door closes (triggering the circuit), the timer provides power to the relay coil for that minute, keeping the lights on.
Using Capacitors to Prevent Voltage Drops
Placing an electrolytic capacitor across the coil terminals (85 and 86) stores charge and provides temporary power during brief voltage drops, ensuring the relay remains closed without interruption. This is like a mini-battery backup for the relay.
- How it Works: The capacitor charges when power is applied to the coil. If the voltage dips momentarily, the capacitor discharges, supplying the necessary power to keep the relay energized.
- Choosing a Capacitor: The size of the capacitor depends on the relay’s coil resistance and the desired hold-up time. Experimentation may be required. As a starting point, try a capacitor with a value of several thousand microfarads (µF) and a voltage rating of at least 25V. (Source: Electrical Engineering Stack Exchange)
- Important: Connect the capacitor with the correct polarity. The positive (+) side goes to terminal 85, and the negative (-) side goes to terminal 86.
Tip: A larger capacitor will provide a longer hold-up time, but it will also take longer to charge initially.
Importance of Proper Grounding
A solid ground connection for terminal 86 is crucial. Poor grounding can cause intermittent operation, potentially causing the relay to open and close unexpectedly. The ground provides the return path for the current, and any resistance in this path can reduce the voltage reaching the coil.
- Troubleshooting: If your relay is behaving erratically, check the ground connection. Make sure it’s clean, tight, and connected to bare metal on the chassis. Avoid using painted or rusty surfaces.
What Can Cause a Relay to Malfunction or Open Unexpectedly?
A relay can burn out due to excessive current, voltage spikes, overheating, or physical damage. These factors can cause the internal components to fail, preventing the relay from staying closed. Understanding these causes can help you prevent relay failures and troubleshoot problems.
Preventing Voltage Spikes with Flyback Diodes
A flyback diode across terminals 85 and 86 protects against voltage spikes from inductive loads when turning off. The diode’s cathode connects to terminal 85 (+12V) and anode to terminal 86 (ground). When you turn off power to an inductive load (like a relay coil), the collapsing magnetic field generates a voltage spike. This spike can be many times higher than the supply voltage and can damage the relay or other connected components.
- How it Works: The flyback diode provides a path for the current to flow when the power is switched off, safely dissipating the energy stored in the magnetic field.
Overcurrent and Relay Damage
Exceeding the relay’s rated current capacity can cause overheating and damage, preventing it from staying closed. Always ensure the load doesn’t exceed the relay’s specifications. Each relay has a maximum current rating for both the coil and the contacts.
- Prevention: Check the relay’s datasheet for its current ratings. Use a relay with a rating that exceeds the maximum current the load will draw.
Heat and Relay Performance
Excessive heat can damage a relay’s internal components, leading to malfunction. Ensuring proper ventilation and using heat insulation where necessary can help maintain optimal relay performance. Relays generate heat when energized, and high ambient temperatures can exacerbate this.
- Problem: If a relay is mounted in a confined space with poor airflow, it can overheat and fail.
- Solution: Mount the relay in a well-ventilated area. If necessary, use a heatsink or add insulation to protect it from external heat sources.
Latching vs. Non-Latching Relays: Which is Right for Keeping a Relay Closed?
For keeping a relay closed without constant power, a latching relay is ideal as it holds its state after being energized. A non-latching relay requires constant power to remain closed. This is the fundamental difference between these two types of relays.
- Latching Relay: Requires only a momentary pulse of current to switch states (open or closed) and then remains in that state until another pulse is received.
- Non-Latching Relay: Requires continuous power to the coil to maintain its state. If the power is removed, it returns to its default state (normally open or normally closed).
If your goal is to keep a circuit closed indefinitely without drawing continuous power, a latching relay is the best choice. However, if you need the circuit to open automatically when power is removed, a non-latching relay is appropriate.
Below is a video about choosing the right relay for your project:
FAQs About How to Keep a Control Board Relay Closed in Car
Can a relay stay closed?
Yes, a relay can stay closed. A non-latching relay will stay closed as long as power is continuously supplied to its coil. A latching relay will stay closed after a pulse of power, until it receives another pulse to open.
What would cause a relay to burn out?
Excessive current, voltage spikes, overheating, and physical damage can all cause a relay to burn out.
Can a relay work on and off?
Yes, a relay is designed to switch on and off. A non-latching relay will switch on when power is applied to the coil and off when power is removed. A latching relay will switch on or off with a pulse of current and stay in that state. Intermittent operation, however, can indicate a problem like poor grounding.
What ruins a relay?
Overcurrent, voltage spikes, excessive heat, and physical damage are the primary culprits that ruin relays.
How do I wire a relay to control a car system?
Connect the relay coil (terminals 85 and 86) to a power source and ground. Connect the device you want to control to the relay contacts (terminals 30 and 87 or 87a). Use the car’s ignition or an auxiliary switch to control power to the coil.
How can I prevent relay interference?
Use a flyback diode across the coil terminals to suppress voltage spikes. Ensure proper grounding and shielding of wiring to minimize electromagnetic interference.
What type of relay should I use for my project?
Choose a relay based on the voltage and current requirements of the load, the desired control method (continuous or momentary), and whether you need it to stay closed without constant power (latching).
How do I troubleshoot a malfunctioning relay?
Check the power supply, ground connection, and wiring. Test the relay coil with a multimeter. Inspect for signs of physical damage or overheating.
Do relays fail open or closed?
Relays can fail in either the open or closed position, depending on the nature of the failure. A burned-out coil will typically result in a relay failing open, while welded contacts can cause it to fail closed.
What does a control relay do?
A control relay uses a small electrical signal to control a larger electrical current, acting as a remotely operated switch.
Summary:
To keep a control board relay closed in a car, ensure continuous power to the coil, manage voltage drops, and use appropriate components like diodes and capacitors. Choose between ignition power, auxiliary switches, or timer circuits based on your specific needs. Consider using a latching relay if you want to maintain the closed state without constant power consumption. Remember to protect your relay from overcurrent, voltage spikes, and excessive heat to ensure reliable operation. By understanding these principles, you’ll be well-equipped to tackle a variety of automotive electrical projects and troubleshoot any relay-related issues that arise. What challenges have you faced with automotive relays? Share your experiences in the comments below!
