"Convert" Always-On Fan To PWM



  • I have a Duet Wifi and as assumably everybody knows this has two always-on fan connectors and three PWM fan connectors. Now I do need actually four PWM controllable fan ports.

    I have multiple options here:

    1. Buy a DueX board - I think this is overkill for just one fan
    2. Select and move one of the current PWM'd fans to always-on and free one PWM port this way
    3. Wire two fans in parallel where it makes sense

    What I mean by 3 is: if I would have two fans that should run under the same conditions (whatever they may be) I could one of these directly connect to the PWM port and the other one I could use V+ from any applicable source e.g. the V_FAN pin of one of the always-on ports and wire the GND in parallel with the other fan that occupies the PWM port.

    I know that this would basically be possible both electrically and logically because PWM is switched on GND pin.
    What I do not know are the exact constrains. I guess the 1.5A limit applies also in this case, right? That means both fans must not draw more than 1.5A together. And I assume it will simply be added or do I need any obscure other math in this case?

    Did I miss anything here?



  • Not sure I understand because your description of "3" sounds awfully complicated. I have two fans cooling the boards. One cools the Duet and the other cools the Duex5. I just connected both positive wires together, both negative wires together and connected the combined connections to the fan header.



  • @deckingman said in "Convert" Always-On Fan To PWM:

    Not sure I understand because your description of "3" sounds awfully complicated. I have two fans cooling the boards. One cools the Duet and the other cools the Duex5. I just connected both positive wires together, both negative wires together and connected the combined connections to the fan header.

    You are right. 🤦 That is a lot easier. 😂

    Out of some reason I thought that one V+ pin would not be able to supply the required amount of power - while at the same time asking if one GND pin would be able to take it... Sometimes my brain is strange. 😀


 

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