No Voltage when plugging in part cooling fan. Did I break it?



  • Accidentally blew the 1A fuse rewiring my x carriage part cooling fans. Swapped it with a 3A fuse (in retrospect i should've just waited for the 1A to come in but it would've taken weeks i don't have). But i googled a little bit and a 3A fuse should be okay (I hope 😞 )
    When i set the fan to full speed, i get 12 volts where the fan would plug in at testing it with a multi-meter. As soon as i plug the fan it, it drops to 0 volts. Did I break something?



  • If you made no changes to the config then I'd say, yes, you broke something.

    The interesting thing is however that normally the outputs fail in a always-on manor, but nothing is impossible. It could be the fan failed as well. If you have another working 12v fan I'd try that on the output in question. (as to avoid using a damaged fan to cause more damage on another output)



  • @bearer
    i just checked for current when turned on all the way. does 7milliamps sound right?
    This happens for the fan0 and fan1 port, but not fan2.
    Edit: 170 milliamps on fan2. i think i broke it. is there a way to fix it?



  • Current?

    An, see the edit; you're saying the fan that was on fan1 draws 170mA on fan2 output, and spins normally? I'd say that suggests the fan is good.



  • Fix it, sure; lets just agree on whats wrong first. Fixing fans is a pain.

    Fixing the fan output is "just" a matter of replacing a mosfet most likely. The two little buggers circled in yellow if both fan0 and fan1 was broken. Suitable replacements are AO3400A / PMV40UN2.
    bb9b8e12-c720-4f87-8c4a-0afea43ea6f3-image.png

    Due to the heavy nature of the 4 layer board with 2oz copper it can be a bit tricky to solder without pre-heating the board (That the mosfests are right up close to the headers doesn't make it easier either unfortunately)



  • I definitely dont have the tools to do that. is there a way i can check the mosfet using a multimeter to confirm/deny its demise without power on?



  • You can use the diode test to test the mosfets I guess.

    Doing in circut testing might not give a conclusive answer if they didn't fail always on though
    https://www.google.com/search?q=test+mosfet+diode+mode

    edit:

    I definitely dont have the tools to do that.

    You'd be surprised at what you can do MacGyver style if you have a relatively high power (60-100w) soldering iron with a suitable tip and a frying pan (ideally some sand i the pan to get the heat evenly up into the board); but it is a bit tricky.



  • @bearer
    Let me rephrase that. I dont have the confidence to do that to an almost $200 board when the rest of it works lol. After a little digging apparently I'm not the only dummy that has done this, and he describes exactly my case, except the fan doesnt work at all.

    https://forum.duet3d.com/topic/1152/pwm-fan-controller-possibly-destroyed-advise-requested/4?_=1585291986545

    Thank you for pointing me in the right direction.



  • @Turbo said in No Voltage when plugging in part cooling fan. Did I break it?:

    Let me rephrase that. I dont have the confidence to do that to an almost $200 board when the rest of it works lol.

    Fair enough; although in that area its a tricky to damage unrelated functions unless you take a blowtorch to it or something. On the other hand you can pull a pad or knock off one of the nearby resistors which will further complicate a repair down the road (but unlikely to affect the rest of the board)



  • @bearer
    Fair enough. What I'll probably do is get a proper 1A fuse (amazon prime is back to one day for those somehow with all this panic going on), and then use the fan2 header since it still works, and sometime this autumn ill either take it to someone who knows what they're doing if I really feel the need to repair it, or upgrade to duet 3 (or maybe even 4?), hopefully by then they'll be shipping again and will have more stupid proofing on it 🙂
    Thanks again



  • Afaik there isn't any adittional protection for the fans on the Duet3, problem is the fet breaks befor the fuse. Adding something like an automotive smart switch instead of a fuse might be able to act fast enough to save the fets; recall having seen some IR3315 being used to protect a group of fets in an prehistoric design. I'll see if I can find a current part and put it on the hardware wish-list, but doubt it adds cost and complexity (and still is only 99%) so who knows.



  • @Turbo said in No Voltage when plugging in part cooling fan. Did I break it?:

    @bearer
    Fair enough. What I'll probably do is get a proper 1A fuse (amazon prime is back to one day for those somehow with all this panic going on), and then use the fan2 header since it still works, and sometime this autumn ill either take it to someone who knows what they're doing if I really feel the need to repair it, or upgrade to duet 3 (or maybe even 4?), hopefully by then they'll be shipping again and will have more stupid proofing on it 🙂
    Thanks again

    That's the nice thing about having a spare fan output .... and exactly what I have done ....
    I am not going to rip my whole setup apart when everything can be made to work by moving a connector and re writing a line in confg.g.

    BTW I don't know how most of the FET failures manifest themselves but in my case there is a tiny crater in the middle of the FET 🙂 Look at the two FET's that bearer indicated and see if you can find any abnormality on the surface.


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