Questions about 12v fans on 24v system

  • I did see an older thread, I thought rather than bring it back to life, I'd ask my questions in a new.

    I have a couple of questions relating to 12v fans on a 24v system. I'm planning on using all 12v fans so I'd like to go with option 2 as outlined below.

    My questions are:

    1. Does anyone have a buck converter, hopefully available on Amazon that they can recommend.

    2. From what I understand V-FAN jumpered between VIN and center pin just passes through whatever the supply voltage is, in my case 24v. If I remove that jumper and connect it as descriped in option 2, 12v will be passed from my buck converter to that center pin and to all the fans, including the always on fans?

    3. If I choose option 2, and choose to connect the ground to somewhere other than the ground of an always on fan, I should still be able to use the always on fans correct?

    @dc42 said in 12V 2A fans on 24V Duet Wifi 1.04:

    You are absolutely right. Here are some ways of wiring it that will work:

    1. Wire the buck regulator input directly to the VIN terminals, and the output to the centre pin of V_FAN.

    2. Wire the buck regulator positive input to the VIN end of VFAN, the output to the centre pin of V_FAN, and ground to any power ground connection (possibly the ground side of an always-on fan output).

    3. Put a jumper on V_FAN at the VIN end. Wire the buck regulator input to an always-on fan output. Wire the positive wires of 12V fans directly to the buck regulator output, and the negative wires to the FAN- pins of the controlled fan outputs as usual.

    With #1, all the fans must be 12V and there is no fuse protection.

    With #2, all the fans must be 12V and the input of the buck regulator is protected by the 1A fuse.

    With #3, the connection of a 12V fan is more complicated, but you can use 24V fans as well. The buck regulator input is fuse protected.

  • Moderator

    1. How bout this:

    2. Correct. All fans will get whatever you pass into the V_fan pin, including always on.

    3. The Duet switches the fans on the ground side, so you'll need to connect the fans ground wire to the ground pin of whatever fan port you want to use.

  • Thanks, I had actually ordered that SainSmart Buck Converter right before you posted. I got it wired up as Option 2 above. Instead of using the Ground from one of the Always On Fan Connectors, I used a ground from the Expansion Header which I currently don't plan to use. Works perfectly.

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