Was there ever a resolution to the part cooling fan PWM issue?

Discussion in 'Tool heads & ToolChanger' started by John Meacham, Jul 9, 2021.

  1. John Meacham

    John Meacham Well-Known Member

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    My toolchanger is working great except still has that one major issue. The stock fans only worked at 100% and the differently labeled ones I was sent as a replacement barely work with PWM either and are a fraction of the strength.

    Has anyone found fans that work, or have any other workarounds?
     
  2. German

    German Member

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  3. John Meacham

    John Meacham Well-Known Member

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    Hmmm... I have been considering that. I already tried a simple passive low pass filter but it didn't help. (It was a sloppy dead bug wired thing with what i had on hand, so perhaps there is a way to do it.).

    At this point if I'm going to be making a board, I might as well go a bit further adding a couple more components and have it be a generic hot end board, not a CAN bus thing or something that deals with extrusion or time critical stuff at all, just something that will handle translating the pwm for the part cooling fan (and maybe reading feedback from a 3 or 4 wire fan locally so the firmware doesn't need to), and watching the temp and turning the heatsink fan on and off at a set threshold to just remove that critical safety responsibility from the firmware completely. buffering a PT100 signal could also be done there too.

    Does that sound useful to anyone? it would still just accept PWM signals and give analog feedback so the firmware need not change at all, it just no longer has to send heatsink fan signals or keep track of exactly which thermistor is used as the analog feedback will be normalized and buffered on the board.
     
  4. German

    German Member

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    You could try setting the fastest PWM frequency you can and use a LC lowpass filter. I couldn't go this route because I use a Duex5 which has a fixed PWM low frequency rate.
     
  5. John Meacham

    John Meacham Well-Known Member

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    I am also on the Duex5 so suffering the same issue. Have you tried the original fans that came with the toolchanger (blue and grey) along with the replacements they sent out (blue and white?) I have both and neither works that well.
     
  6. German

    German Member

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    I got some Aliexpress fans that worked ok, but they work even better with the PWM boards (they no longer whine now, and having a silent non-whinning 15% PWM fan is posible)
     
  7. John Meacham

    John Meacham Well-Known Member

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    I'm now wondering if just taking a uC and reading the PWM and re-emitting it at a much higher rate to the point a RC passive filter can be used would be a suitable solution. The 25khz from the duet main board wasn't a lot better than the 500hz of the duex, but i didn't try a filter on the main board ones (and there are not enough 25khz capable fan outputs anyway)
     
  8. German

    German Member

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    25KHz would be enough for a well calculated LC filter. In fact, it can be done with 500Hz, but the inductor size would be huge and expensive.
     
  9. German

    German Member

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    I was told so when I was designing the PWM board, but I wanted to stay the simpler the better, and went the analog way.
     
  10. German

    German Member

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    And you'd also watch for resonances...
     

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