Otis Singleton
Electric fans are a great way to keep your car cool, but wiring them up can be a challenge. While there are many ways to wire dual fans, it's important to select the right method for your needs. In this guide, we'll explore the different options available and provide step-by-step instructions on how to hook up two electric fans, covering everything from choosing the right wire gauge to controlling fan speed and preventing common issues. So whether you're looking to wire dual fans to a single switch or want to control them individually, we've got you covered!
Characteristics and Values Table for Hooking Up 2 Electric Fans
| Characteristics | Values |
|---|---|
| Number of Relays | 1 or 2, depending on fan size and current draw |
| Relay Type | High-current relay rated for combined fan output |
| Relay Function | Isolates high amp load of fan circuit from switching circuit |
| Fan Control | Individually or together, based on engine temperature or air conditioning load |
| Fan Output | Cooling fan outputs on aftermarket fuel injection systems |
| Fan Mounting | Direct mounting to core or using an aluminum fan shroud |
| Relay Kit | Standard 40-amp relay or dual 30-amp relays for larger fans |
| Wiring | Color-coded to correspond with relay kit wires |
| Fuse | 30-amp fuse for each fan or both fans, depending on setup |
| Switch | Optional, but not recommended due to high current draw |
| Fan Size | 8, 10, 12, 14, or 16-inch diameters |
| Fan Type | Electric or mechanical |
| Fan Performance | Electric fans draw more current and may overheat without proper shroud |
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What You'll Learn
Using a relay kit for dual fans
The Painless Performance electric fan relay kit from Speedway Motors is an example of a kit that can be used to wire an electric fan with a relay. This kit includes a circuit breaker to safely get power directly from the battery. When mounting the relay, it is best to find an area that will be largely free of significant moisture within the engine bay or within the inner fender well if you want to hide the wiring.
The wiring process for a relay kit with dual fans is as follows:
- Take both positive wires from the fans and connect them to the yellow wires on each relay.
- Run switched power (usually from the ignition switch) to the blue wires on the relays.
- Splice both black wires from the relays together and connect them to the thermostatic switch.
- Connect a fused constant power to both red wires on the relays (load side of the relay). Use a minimum of 14-gauge wire here.
- Connect a 12-volt power wire to the starter solenoid main post and run the wire to relay terminal 30. Use a 10-12 gauge wire and add a fuse if desired (30 amps should work for 2 fans).
- Disconnect the black/green wire feeding the fans from the connector below the thermostatic switch and connect it to relay terminal 87.
- Make a B/G wire and connect one end to relay terminal 86. Connect the other end to the connector where the fan feed was removed.
- Double-check your wiring, attach the relay, and tie loose wiring with tape or ties.
This setup uses the switched thermostat to trigger the relay, and relay contacts 30/87 will supply power to the fans. It is important to ensure that the wires to term 30 and term 87 can handle the max current for your fans, and that the wire to term 30 is fused at the starter.
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Selecting the right battery cable wire size
Current and Distance:
The correct wire gauge for your battery cable is determined by two main factors: current and distance. First, calculate the total power requirements in watts of all the appliances connected to your electric fans. Then, divide the watt rating by the input battery voltage to find the current draw. For example, if you have a 3000-watt inverter and a 12-volt battery, your maximum current draw would be 250 amps. Shorter cable distances are generally preferable as they minimize voltage drops.
Wire Gauge Recommendations:
The wire gauge you need will depend on the current rating of your electric fans. For applications requiring 250-300 amps, it is recommended to use 1/0 AWG wire for distances less than 5 feet. For longer distances, you can use 2/0 AWG, 3/0 AWG, or 4/0 AWG wires to ensure efficient power transmission. Additionally, consider using a 2 Gauge Welding Cable for battery cables in normal stock applications. Higher output alternators will require a larger diameter cable.
Type of Wire:
It is recommended to use oxygen-free fine copper strand (OFC) wire for your battery cables. Copper provides better conductivity than other materials such as copper-clad aluminum (CCA). For automotive applications, choose SAE-rated SGT or SGX battery cable insulation for its high temperature rating and flexibility. Avoid using welding cable, OFC, or CCA wire for underhood applications.
Existing Cabling:
If you are using existing cabling, thoroughly inspect the cables for any signs of damage, dry rot, or chemical damage. Damaged cables can contribute to electrical issues and voltage drops. When in doubt, it is advisable to replace the battery cables with new ones to ensure optimal performance and safety.
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Wiring fans to a switch
If your home isn’t already wired to support a two-switch system, the task becomes more complicated. You may need to hire a certified electrician to set it up for you, as building codes in some areas require this to be done by an expert.
Once you have confirmed that your wiring supports a two-switch system, you can begin wiring your fan to the switch. The specific steps will depend on the make and model of your fan, so be sure to consult the instructions included with your fan. Here are some general guidelines:
First, identify the wires coming from your fan unit and the wires coming from the junction box in the ceiling. The wires you’ll likely see on your fan unit are:
- Black: the ‘hot’ wire, which connects to your home’s power.
- White: the neutral wire needed to complete the circuit.
- Bare Copper or Green: the ground wire, which protects your fan from power surges.
- Blue: attaches to the light unit on your fan (may be red, not blue).
- Red: sometimes included as a conductor wire (may be blue, not red).
Next, using your wire strippers, strip the coating on the ends of the wires to expose the copper end. Then, connect the corresponding wires from the fan to the junction box using wire nuts and push connectors. For example, connect the black wire from your fan unit to the black wire in the junction box. Repeat this process for the white, green/copper, and blue/red wires, if applicable.
Finally, turn the power back on and test your fan to ensure it is functioning properly.
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Using a controller for electric fans
Another option is to use dual thermostatic switches that control each fan individually. This method requires a second temperature switch, additional wiring, and dual relays. Some people prefer to have the second fan on a manual switch for additional "emergency" cooling, while others will wire their second fan to use the air conditioning compressor signal to engage the second fan.
There are also fancy controllers and in-dash temperature gauges with fan outputs, as well as cooling fan outputs on most aftermarket fuel injection systems, to control one or both fans.
When selecting a controller, it is important to consider the power requirements of the fans. Most fan control is about power to the fan, so you need to be able to send more power when you want the fans to run faster and less power when you want them to run slower. This means that you either need a device that can control two channels in parallel or something inline to distribute the power evenly. Wiring the fans in parallel will help, but there is no guarantee that the fan speeds will match.
Additionally, if you are connecting the fans in parallel, they will draw twice as much current. As such, it is important to consider the total power of the fans and the capacity of the controller. If the total power of the fans exceeds the capacity of the controller, it may fry the controller.
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Connecting fans to a single relay
Firstly, you'll need to remove your car's mechanical fan and mount the dual electric fans onto your radiator. Then, install the activation fan relay kit in a location that is free from heat and moisture. It's important to ensure the relay is easily accessible for future maintenance.
For the wiring, you'll need to identify the correct wires and their corresponding terminals. The wiring setup may vary depending on the specific relay and fan setup, but here's a general guide:
- Connect the wire from terminal 30 to the battery or ignition. This wire should be fused at the starter.
- Terminal 85 (COIL POSITIVE) connects to the ignition positive.
- Terminal 86 (COIL TRIGGER) connects to the fan thermostat negative.
- Terminal 87 (LOAD) connects to the fan positive.
- Terminal 87a is typically not used.
It's important to note that some fans draw more power than the ignition circuit can supply. In such cases, it's recommended to wire the relay to the battery to eliminate this issue and ensure sufficient power supply to the fans.
Additionally, consider soldering the connections and using a high-quality fuse to ensure a reliable and safe setup. You can also add a circuit breaker to the setup to prevent short circuits.
While connecting fans to a single relay is possible, some prefer to use dual relays to control each fan separately, allowing for more precise control based on engine temperature or other factors. Ultimately, the chosen setup depends on your specific requirements and preferences.
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Frequently asked questions
A basic inexpensive controller wired to a relay will do the trick. You'll also need to send a trigger signal through a diode to the same relay when the AC is on.
Using a quality relay, even with a mechanical controller, will result in a more reliable and longer-lasting system. You can use dual relays to control each fan separately, or a single high-current relay to control both fans.
Selecting the right battery cable wire size is crucial for optimal electrical performance and preventing potential issues. Speedway Motors offers a guide to help you choose the right wire gauge for any length of wire run.
Unlike the switch-under-the-dash method, a relay setup ensures that you won't forget to turn the fans on. It's also important to never run a mechanical fan with an electric fan on the same side of the radiator.
