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uvukee
(@uvukee)
New Member
Adding extra fan

Hello everyone,

I have just bought MK2S.
I would like to add an extra fan to improve cooling for printing.
I realised that there are only 2 pins for fans.

My question is what is max current for fan pin? And if I can connect 2 fans (or even 3?) to one fan pin?

Posted : 15/10/2017 8:08 pm
uvukee
(@uvukee)
New Member
Topic starter answered:
Re: Adding extra fan

I do not want to risk without knowledge.

For now I designed myself and printed new part for cooling. I'm so suprised. It incredibly improved print quality.

Maybe in future I will attach additional fan with external supply. I will see if I still need it.

Posted : 18/10/2017 10:38 am
PJR
 PJR
(@pjr)
Antient Member Moderator
Re: Adding extra fan

Fan Outputs (both are the same):

There should be no issue connecting a second fan.

Peter

Please note: I do not have any affiliation with Prusa Research. Any advices given are offered in good faith. It is your responsibility to ensure that by following my advice you do not suffer or cause injury, damage…

Posted : 18/10/2017 12:35 pm
uvukee
(@uvukee)
New Member
Topic starter answered:
Re: Adding extra fan

Thank you for your reply and time.

But unfortunately, It doesn't say to me too much about what is max current allowed.

Posted : 18/10/2017 2:36 pm
Knickohr
(@knickohr)
Member Moderator
Re: Adding extra fan

https://www.infineon.com/dgdl/irlml6346pbf.pdf?fileId=5546d462533600a401535668a336262e

2 fans or 3 parallel should be no problem.

Thpmas

Posted : 18/10/2017 3:30 pm
david.w8
(@david-w8)
Eminent Member
Re: Adding extra fan

The 12V supply going into the Mini Rambo 1.3a (what came in my MK2) is split into multiple 12V rails after the various fuses. On the 1.3a the fans are fed by the 12V4 rail. The 12V4 rail is limited by a 0.75A PTC (resettable) fuse F5. It also shares the 5A blade style fuse with the extruder heater. So your fans + extruder heater current can't exceed 5A.

The real limiting factor here is the 0.75A PTC fuse. The part cooling blower has a startup current of ~0.15A, the hotend fan will be a little lower, but still pretty close. Lets assume that both draw 0.15A continuous, just to be safe. Since the 2 stock fans use up to 0.3A total, you have 0.45A available. That will be plenty for 1 or 2 more fans, likely even more. My suggestion is to add up the rated current of all the fans you want to add (not including the stock fans) and keep that number below 0.45A.

As a side note, most fans will not draw their rated current for longer than a few seconds at startup, and even if you started all the fans simultaneously, the PTC fuse will easily tolerate a small overcurrent for a few seconds. I added a rambo cooling fan to my printer as it's in a heated enclosure and I just made a splitter to run it off the same circuit as the hotend cooling fan.

Posted : 01/11/2017 9:27 pm
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