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Fan confusion

Posted by gonadgranny 
Fan confusion
April 28, 2016 01:27PM
Hello all.
I have a Prusa I3. Currently as per the instructions, the one and only fan is pointed at what I presume to be the extruder radiator and is connected to a 12v supply which is always on. What is the purpose of this fan? Should it always be on or connected to the variable output?
I have seen that some people use cooling ducts. are these to be used in conjunction with the extruder fan? Should this fan be connected to the variable fan output?
Re: Fan confusion
April 28, 2016 01:41PM
Hi Dan,

Welcome to the forum. Interesting choice of user name.

The fan on the extruder removes heat that conducts back up the throat from the hotend. It should always be running when the hotend is hot. Without it there is a tendency for the rising heat to soften the filament at points where it's more likely to cause a jam, particularly with pla.

MK8 style extruders that often ship with Prusa I3 kits have a fan and heatsink that looks like it's cooling the extruder, but in fact it's pulling heat out of the thick aluminium block that the hotend throat screws into.

Some hotends use a heatsink and fan just above the heater block to dissipate heat more effectively and make the transition zone between molten and fully solid filament shorter. The e3d V6 is a prime example. Again, the fan should be running all the time the hotend is hot.

The variable fan output is for cooling the print, to make sure that the previous layer is sufficiently solid to support the next layer of printed plastic. This needs to be under software control because the amount of cooling varies depending on the shape and size of the model, as well as the type of filament. A lot of kit printers are supplied without a print cooling fan, and particularly if you're printing pla it's a very useful addition.
Re: Fan confusion
April 28, 2016 01:52PM
Thanks for the very swift and informative reply, exactly what I wanted to know!
I'm in the process of printing a cooling duct for my printer now which will hopefully make the prints with steeper angles come out better because it struggles currently.
As for the name, its an anagram of my actual name "Danny Grogan". I use it because its never taken but might give across the wrong impression I guess!
Thanks again.
Re: Fan confusion
May 17, 2016 10:39AM

The single fan that acts as a radiator should always be on. You can run lines from the main supply to this fan so anytime the power is on it is running. On Ramps you can also locate the 12V Aux power (2 pins you must solder in). As far as the print cooling fans ( usually 2 on each side) these are not always running and should receive information from the board as when to be activated. Use the appropriate output on the board for these.
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