"Convert" Always-On Fan To PWM

wilriker

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:

Buy a DueX board - I think this is overkill for just one fan
Select and move one of the current PWM'd fans to always-on and free one PWM port this way
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?

deckingman

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.

wilriker

@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.