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UMO cooling fans only rotate at full PWM

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Posted (edited) · UMO cooling fans only rotate at full PWM


I have modified my UMOs with an E3D hotend setup with three fans. One 30x30mm fan for cooling the upper part of the hotend, and two 25x25mm fans for cooling the 3D prints, creating a crossflow.

I'm running into a weird issue from the fans that I can't seem to solve by myself. I bought a total of 4 25x25mm 12V GDT labeled cooling fans from ebay a while ago. Two are installed on one UMO (lets call it UMO A), those work great. The fans can be PWM controlled all the way down to 30.

But, two 25mm fans front the same batch, installed on the other UMO (UMO B), only work at around full PWM, about 220-255. When I try to let the fans rotate at lets say 140, the fans wiggle for a second and stall afterwards. Also when I manually give the fans a little start up push, nothing happens.

What I already tried to exclude possible causes:

• Stock 50mm fan works fine on PWM control on UMO B

• Random 40mm fan also works fine on PWM control on UMO B

• 25mm 'broken' fans from UMO B also don't work on UMO A

• 25mm 'broken' fans from UMO B do rotate at full speed when PWM is 220-255

• 25mm working fans form UMO A also work on UMO B

So this means it is not a printer issue but a fan issue. Well, since I bought them in one batch I don't understand what the cause can be. I've attached a picture of a torn apart 'broken' fan. Of course I'm not going to tear apart a working fan for comparison though. IMG_4589.thumb.JPG.be8d861ec93b3325d07939f4553ae9ba.JPG

Hopefully someone can help me in this PWM mess.


Edited by Guest
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    Posted · UMO cooling fans only rotate at full PWM

    I thought the output was 12V, because the standard fan is 12V as well..

    Is it a better idea to use 24V fans on those machines then? Or will the airflow drop significantly?

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    Posted (edited) · UMO cooling fans only rotate at full PWM

    I don't know why Ultimaker went initially for a 12V fan: it is a continuous source of problem, people replace it with a 12V fan, and guess what -- they get troubles.

    The ones from Ultimaker seem to survive 19V, but most do not.

    If you have a dual fan setup, you can either use 12V fans in series, or 24V fans in parallel. When you choose 'High Flow' fans you will have more than enough airflow.

    Edited by Guest
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    Posted · UMO cooling fans only rotate at full PWM

    @amedee Thanks for your reply.

    Today I received 24v GDT 25x25mm fans. But: these also cannot be controlled properly on the umo+ machines. They start jiggling for a second (and stall afterwards) at PWM 50~200 and rotate at full speed above that. While other 24V and 12V fans that I have, do run properly at a PWM >50. Tested on all my machines.

    The weird thing is that the two GDT 12V fans on the first upgraded machine (UMO A, as in first post) are functioning very well. They are switched in parallel. These are exactly the same GDT fans as the 'non functioning properly' ones, also from the same supplier. All the other GDT fans only rotate near full PWM.

    Also, when I search google for PWM controllable fans, they all have 4 pins. No one mentions that 2 pin fans can be controlled over PWM.

    Does anyone know a decently priced PWM controllable 25mm fan, that has two wires?

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    Posted (edited) · UMO cooling fans only rotate at full PWM

    Well, yes, that's another problem... :(

    I probably should have warned you...

    Some fans accept PWM, others do not! Votlage doesn't play a role (as long as it is not exceeded).

    If you want to know more about this, there is this video from the most boring 3D printing channel of the whole Internet (and beyond)


    Fans with 3 wires are just fans with a feedback line (like in the video), real PWM fans have 4 wires, but our printers are not designed to use that, so we have to rely on 2 (or 3) wires fans accepting PWM as input.

    I have no reference for 25mm fans, I personally rely on the 40mm PAPST 414H which are working fine...

    Edited by Guest
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    Posted · UMO cooling fans only rotate at full PWM

    Hmm that sucks. That is actually exactly what happens with the small fans, they start vibrating. But at certain 'random' PWM values they do spin though. It still doesn't explain why two out of six 25mm 12V fans from one same batch do work perfectly fine, tested on each printer.

    I pulled apart three fans. One not functioning 25mm, one properly functioning 40mm fan and one properly functioning UMO+ 50mm fan. The only potential difference I can find is the Hall sensors that have been used inside the fan's "circuit boards". The small not working fan has a 276 sensor, the 40mm has a 277 and the ultimaker has a 266 sensor.

    Maybe I should desolder the Hall sensor and replace it with one from a working fan. Because I'm not really into testing all kinds of fan brands with a price tag of >€15/fan.

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