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Wiring Diagram to Control Two LED Fans with a Single Switch for Beginners

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Best answers

How can I wire two LED fans to turn on from a single switch?

Wire the two fans in parallel so the switch turns both on at the same time and each fan gets the full supply voltage [#21666218][#21666220] In practice, that means connecting both fan power leads to the switch’s output side and both ground leads to ground [#21666218] If these are 12V fans, do not wire them in series, because each fan would only get about 6V and may not start [#21666221] Make sure the switch, wiring, and fuse are rated for the combined current of both fans, and increase the fuse if needed [#21666218][#21666221] This simple wiring applies to two-wire fans; 3-wire PWM-style fans need different control circuitry [#21666227]
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  • #1 21666216
    Ryan St
    Anonymous  
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  • #2 21666217
    Earl Albin
    Anonymous  
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  • #3 21666218
    Cody Tappan
    Anonymous  
  • #4 21666219
    Steve Lawson
    Anonymous  
  • #5 21666220
    Daniel Wright
    Anonymous  
  • #6 21666221
    Steve Lawson
    Anonymous  
  • #7 21666222
    Steve Lawson
    Anonymous  
  • #8 21666223
    Steve Lawson
    Anonymous  
  • #9 21666224
    Ryan St
    Anonymous  
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  • #11 21666226
    Ryan St
    Anonymous  
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  • #12 21666227
    Mark Harrington
    Anonymous  
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    Ryan St
    Anonymous  
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    Mark Harrington
    Anonymous  
  • #15 21666230
    Ryan St
    Anonymous  
  • #16 21666231
    Ryan St
    Anonymous  
  • #17 21666232
    Cody Tappan
    Anonymous  
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    Mark Harrington
    Anonymous  
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    Ryan St
    Anonymous  
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    Mark Harrington
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    Ryan St
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    Mark Harrington
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Topic summary

✨ A beginner sought guidance on wiring two LED fans to a single switch, having successfully connected one fan. Responses clarified that wiring the fans in parallel is the appropriate method to ensure each fan receives full voltage, as series wiring would halve the voltage per fan, likely preventing operation. It was advised to verify the current ratings of the fans, the fuse, and the switch to ensure safe operation and possibly increase fuse capacity when adding loads in parallel. The fans discussed are 12V LED fans, typically computer case fans with LEDs on the blades. Additional advice included using a PC power supply (PSU) with proper wiring via Molex connectors to power the fans, noting that 2-wire fans are simpler to control than 3-wire PWM fans which require more complex circuitry. Several links to wiring diagrams and PSU usage guides were shared to assist the beginner. The discussion emphasized safety, correct component ratings, and encouraged learning through experimentation.
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FAQ

TL;DR: For two 12V LED fans, wire them in parallel so each still sees 12V; series cuts them to ~6V each and can stall them. "Parallel would seem the only option." [Elektroda, Steve Lawson, post #21666221] Why it matters: This prevents slow fans, dim LEDs, blown fuses, and melted switches for beginners wiring case fans.

Quick Facts

How do I wire two 12V LED fans to one switch?

Use parallel wiring. Connect the switch between the +12V source and both fan + leads. Tie both fan grounds to the supply ground. This way, one switch feeds both fans the same voltage, and they start together. Keep leads neat and insulated. Label polarity to avoid mistakes. If your supply is a PC PSU, use its 12V line and ground. Test with one fan first, then add the second. [Elektroda, Daniel Wright, post #21666220]

Should I choose series or parallel for two 12V fans?

Choose parallel. In series, each 12V fan only sees about 6V, which can stall the motor and dim LEDs. In parallel, each fan receives the full 12V for normal speed and brightness. As one expert put it, "Parallel would seem the only option." Verify your fuse and switch current capability when adding a second fan. [Elektroda, Steve Lawson, post #21666221]

What fuse and switch rating do I need when adding a second fan?

Sum the running current of both fans and choose a fuse slightly above that total. Ensure the switch’s current rating exceeds the fuse rating and expected inrush. If you double the number of identical fans in parallel, the total current approximately doubles. Overspec the switch and wiring for safety. Provide ventilation and avoid undersized wire that heats up. [Elektroda, Earl Albin, post #21666217]

Can I power the fans with an 8×AA battery holder?

Yes. An 8×AA holder provides a convenient ~12V source to learn and test before moving to a PSU. Connect the pack’s positive through the switch to both fans’ positives, and tie negatives to battery negative. Monitor battery life, since motors and LEDs draw continuous current. Replace cells when speed or brightness drops. [Elektroda, Ryan St, post #21666224]

How do I power two fans from a PC ATX PSU using Molex?

Use the PSU’s +12V line and ground via a Molex connector. Place your switch in series with +12V feeding both fans in parallel. Confirm the PSU is properly powered on per ATX guidance before testing. Secure connections, strain‑relieve wires, and insulate any exposed metal to prevent shorts. This setup is robust for desktop builds. [Elektroda, Mark Harrington, post #21666233]

Which Molex wires do I use for 12V fans and the switch?

Connect the PSU’s +12V line through your switch to both fan positives. Connect the fans’ negatives to the PSU ground. Keep polarity correct and avoid mixing rails. After wiring, power the PSU and verify fan startup. If a fan does not spin, disconnect and recheck wiring continuity and insulation. [Elektroda, Mark Harrington, post #21666233]

Do PWM (3‑wire/4‑wire) fans change the wiring plan?

Yes. Two‑wire fans switch simply on the supply side. 3‑wire and 4‑wire PWM fans add tach and control lines that require proper controllers or motherboard headers. A plain toggle will only power them, not manage speed. For speed control, use a PWM controller or appropriate electronics. Match connectors and pinouts carefully. [Elektroda, Mark Harrington, post #21666227]

Why did my fans slow down or not light when I tried series wiring?

Series wiring splits the supply voltage across the two fans. With a 12V supply and similar fans, each sees about 6V. That reduced voltage can prevent reliable startup, cause slow speed, and dim LEDs. Parallel wiring restores full 12V to each unit and corrects the issue. [Elektroda, Steve Lawson, post #21666221]

Do fans have a startup surge I should account for?

Yes. Fan motors draw an initial surge when they start. Size your fuse, switch, and wiring to tolerate that inrush without nuisance trips or overheating. If your switch runs hot or the fuse blows on startup, it is under‑rated. Upgrade components and re‑test. [Elektroda, Steve Lawson, post #21666223]

What exactly is an "LED fan" in this context?

It’s a small DC fan with integrated LEDs for lighting or visual effects. Some models display patterns or text on spinning blades; others simply illuminate a case. Electrically, treat it as a 12V motor plus LEDs integrated by the manufacturer. You power it like a standard 12V fan. [Elektroda, Steve Lawson, post #21666223]

Any beginner safety tips to avoid shorts or damage?

Check ratings twice. Verify the fuse is appropriate, the switch and wires exceed expected current, and connections are insulated. Keep polarities consistent, avoid loose strands, and test with one fan before two. Document your wiring so future changes stay clear and safe. "In all things electrical, check your ratings at least twice." [Elektroda, Cody Tappan, post #21666218]

Quick 3‑step: How do I add a second fan to my working one‑fan switch?

  1. Split the switch’s output (accessory) to feed the second fan’s positive lead in parallel.
  2. Tie the second fan’s ground to the same ground as the first fan.
  3. Verify fuse and switch ratings, then power on and check both fans. [Elektroda, Cody Tappan, post #21666218]
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