fans on different voltages



  • Hello,

    I'm building a new printer around a Duet3D and have some questions regarding fans with differing voltages. On the wikipedia page for 4 wire fans it says:

    "4-wire fans have a separate PWM input wire. The recommended connections are:
    Red (or yellow, if there is no red wire) and black wires: connect them to the + and - pins respectively of an always-on fan connector.
    Blue wire (PWM control): connect it to the FAN- pin of your chosen controlled fan connector."

    So my questions:

    If I have a 24V system with a 24V fan on heatsink, and want to connect a 12V fan, does this mean I can connect its red and black wire to a 12V power source, the blue wire to the FAN- pin of the fan header, and use it like that? Or should the red and black always have the same voltage as the system?

    I would get the 12V using a DC-DC buck converter connected to the same PSU.

    If the above approach is not suitable, can the fan be controlled using a DC-DC SSR? (with the 12V line coming from a DC-DC buck converter)

    I still have to get the fans, but as I prefer one specific brand, I'm limited to 5V or 12V models. Is any of either easier to integrate in 24V system?
    I don't want to solder, which is why I'm not considering the Zener diode-approach and looking at components that allow me to do it without soldering.

    Thanks!


  • administrators

    #1 will work provided that the 12V supply has a common ground with Vin. Alternatively, if all the fans will be 12V, remove the jumper from the V_FAN jumper block and feed +12V to the centre pin.



  • Thanks! Not all fans will be 12V... (at least in the beginning)
    But getting the 12V from a buck converter that converts the the 24V output of the power supply to which the Duet is connected would guarantee the common ground. Yes?

    Is it possible to use a DC-DC SSR to drive a fan? If it is possible, it probably is overkill, but at least there would be no ground issues or so I think?

    As another alternative, it work if I connect a 12V fan using a buck converter to the fan header?

    (just trying to get all my options)



  • You could also get a duex2 or duex5 board and set the fan headers there to 5v or 12v with the same 24v power supply.



  • @mikebridge Interesting idea, although getting a Duex2 or5 may be a bit of overkill to drive some fans... 🙂

    Easy would be the solution @dc42 confirmed, especially when a buck converter can be used to get the 12V from the same 24V PSU that powers the duet (of maybe better: from an always on fan header?). I can get 4 wire models of the fans. Just still looking for confirmation that there would be no ground issues then.

    Also, still curious if positioning one buck converter for each fan, between the fan header (24V) and the fan (12V) is an option. But I don't know if the PWM signal into a buck converter correctly translates to the output...?

    As a last resort, and perhaps most isolated from the Duet board is the use of DC-DC SSR's, but can they be used for fans?


  • administrators

    @vj said in fans on different voltages:

    Also, still curious if positioning one buck converter for each fan, between the fan header (24V) and the fan (12V) is an option. But I don't know if the PWM signal into a buck converter correctly translates to the output...?

    Do not do that with controlled fan outputs, because you may damage the fan mosfet. It's ok for always-on fan outputs.

    A DC-DC SSR would work.



  • @vj said in fans on different voltages:

    Thanks! Not all fans will be 12V... (at least in the beginning)
    But getting the 12V from a buck converter that converts the the 24V output of the power supply to which the Duet is connected would guarantee the common ground. Yes?

    As @dc42 said, using the buck converter on the fan pins is a really bad idea. Buck converters basically have an internal switching mechanism, which will compete with the PWM on the input, and the result will be at best unpredictable, and at worst it will destroy stuff.

    I have a 12V buck converter, which I'm feeding to a positive rail for my 12V fans, with the negavive going to the negative fan terminal on the Duet. I bought a couple of 24V fans which I'm still using, but I plan on moving them all over to 12V at some point, since they're a third of the cost and seem to last twice as long. I have a bunch of fan headers soldered onto breadboard so that I can jumper the negative wires wherever I want, or use the tach wires if I so choose.



  • Thanks for the replies!
    Basically, PWM-ing a buck converter is a bad idea. 🙂

    @SupraGuy
    I read on the wiki about the option of feeding fans with a positive power from another source and connect the negative on the negative of the Duet for control. But somehow I would prefer more separation: most likely this comes from the fact that I'm no electrical engineer and would like to keep a situation where I understand the way it all works. 🙂

    So my options are:

    1. 24V-12V buck converter on the same 24V supply as the Duet3D (or powered from an always on fan connector), pwm cable of fan to FAN-
    2. A 12V source to power the fans (could be the same as above, or its own supply), one DC-DC SSR per fan to connect it to the fan header.

    If I use the always on fan connector to provide 12V power (via the buck converter), is there no issue with current/power? Let's say to power 1-3 fans?



  • @VJ I don't think that the DC SSR is needed. It adds complexity and possible points of failure needlessly.

    My buck converter is powered from the main 24V supply. I have a supply that has multiple connections, so I'm using one set to go to the Duet, and another to go to the converter, via a 3A fuse. My 12V converter is supposed to be able to supply 5A, so this should be a more than adequate supply fuse. The advantage of using the always-on fan connector would be that it's already fused.

    The arrangement that I'm using is effectively the same as your first situation, but since I have some 24V fans still in use, I can't just feed the 12V to the V_FAN pin. I'll probably do that at some point when I get around to swapping out the 2 24V fans that are in use.



  • @supraguy said in fans on different voltages:

    @VJ I don't think that the DC SSR is needed. It adds complexity and possible points of failure needlessly.

    True... I know it is overkill (negative lead or pwm cable could connect to the Duet), but it is private situation (not a professional use) so an extra point of failure is not so critical and it would make the wiring more understandable to me. 🙂

    My buck converter is powered from the main 24V supply. I have a supply that has multiple connections, so I'm using one set to go to the Duet, and another to go to the converter, via a 3A fuse. My 12V converter is supposed to be able to supply 5A, so this should be a more than adequate supply fuse. The advantage of using the always-on fan connector would be that it's already fused.

    True on the fuse, hadn't thought of that.

    The arrangement that I'm using is effectively the same as your first situation, but since I have some 24V fans still in use, I can't just feed the 12V to the V_FAN pin. I'll probably do that at some point when I get around to swapping out the 2 24V fans that are in use.

    For sure at the start I will have a 24V fan, but that may change in the future. There is still a difference in the wiring: you wrote that you put the negative lead of the fan to the negative of the Duet; I would connect the PWM cable (requires a 4 wire fan though) as dc42 confirmed would work (taking into account ground issues). 🙂

    Regarding what dc42 mentioned earlier in his first post

    #1 will work provided that the 12V supply has a common ground with Vin

    If you use different outputs on the same powersupply, does it give the 12V supply a common ground with Vin?



  • @vj said in fans on different voltages:

    If you use different outputs on the same powersupply, does it give the 12V supply a common ground with Vin?

    Yes, I will have a common ground point, since the converter doesn't isolate its output ground.



  • @supraguy said in fans on different voltages:

    @vj said in fans on different voltages:

    If you use different outputs on the same powersupply, does it give the 12V supply a common ground with Vin?

    Yes, I will have a common ground point, since the converter doesn't isolate its output ground.

    Good to know! Euhm... out of curiosity... the powersupply also does not isolate its different outputs?

    (the more I learn, the more I think I will go with the option of a DC-DC converter connected to the fan output, and PWM fans with the PWM control cable connected to FAN- of the desired fan output; no using an SSR)



  • @vj said in fans on different voltages:

    @supraguy said in fans on different voltages:

    @vj said in fans on different voltages:

    If you use different outputs on the same powersupply, does it give the 12V supply a common ground with Vin?

    Yes, I will have a common ground point, since the converter doesn't isolate its output ground.

    Good to know! Euhm... out of curiosity... the powersupply also does not isolate its different outputs?

    (the more I learn, the more I think I will go with the option of a DC-DC converter connected to the fan output, and PWM fans with the PWM control cable connected to FAN- of the desired fan output; no using an SSR)

    Been searching this fan stuff and just wondering if this turned out as planned?


 

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