I’ve been testing this automatic fan upgrade for my Duplicator 4 and WOW what an improvement in the quality of life around here. Finally I can just start a print on my Dup 4 and walk away knowing the active cooling fan will start on its own. No more being a slave to the printer. It goes in series with my existing fan circuit and bolts on using hardware already there. It is micro adjustable so you can set it to turn on after a set distance into the print, up to about 5mm or even more if you use a longer M3 bolt in the adjustment mechanism. The fan always turns on at exactly the same distance into the print, not like when I had to do it by hand. I’ve been giving the printer a real workout lately printing inventory for my web store. I think my prints are coming out better than ever, with consistent results. There’s a manual override switch just in case I do need to go back to full manual control.

I always wanted to control my active cooling fan from gcode, but that requires soldering a surface mount MosFET (Q6) on to the Duplicator 4’s MightyBoard. I’m pretty good at soldering, but Q6 is a surface mount part and without the proper equipment I wouldn’t take the chance or damaging my MightyBoard and voiding my warranty. That would suck to put it mildly. These boards are in short supply and I can't risk being down. Plus I almost always just turn my active cooling on full after the first layer. I have gcode control on my i3 but never do more than 100% fan after the first layer. That could be done with a micro switch and 3D printed mount. I could use an external wall wart power supply and be totally isolated from my printer’s electrical system. Complete assembly instructions: https://ricswika.wordpress.com/2016/01/24/automatic-cooling-for-wanhoe-duplicator-4/

Hardware Parts (Buy parts kit here) Sub-miniature Micro Switch With Lever Roller (Uxcell PN:s14073100am0209 ) SPDT On/Off/On 3 Position Mini Toggle Switch (Amico PN:s12101100am0009 ) Hex Nut Fastener, M3 Female Coarse Thread Hex Drive Cap Screw, M3x10mm or M3x15mm 3 ½” of heat shrink tubing 3 feet two conductor hook up wire (old speaker wire works fine)