Automatic Cooling for Wanhoe Duplicator 4


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.

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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.

Active Cooling

This project assumes you already have installed active cooling. You’ll need active cooling to get a good 3d print of the parts you’ll need for this project, so if you haven’t got active cooling installed, get going and do that first. You’ll see a big improvement in print quality. You can choose a fan duct from here: If you are only running one side, pick a duct that only cools that side. I use this one, but pick the one that’s best for you.

 Theory of Operation


Drawing 1

The automatic fan circuit installs in series between your active cooling fan and whatever you are using as a power source. I use an external 12 volt wall wart power supply since I have a lot of them laying around unused and everything is totally isolated from my printer’s electrical system.. Some people draw power from the printer power supply and still others steal it from one of the extruder fans. However you do it, the fan circuit will work because it is just a passive switch that interrupts power from getting to your fan. So polarity doesn’t even matter in the hook up. As you can see, the upgrade shown in green in  Drawing 1, boils down to a switch either open or closed, with one wire going in and one wire going out.

For automatic operation, power is routed through the normally closed micro-switch . When the print bed is high enough, the micro-switch opens and shuts off the fan. You adjust the Z position of the microswitch to control the point where the fan turns on.

In override mode, you manually turn the fan ON or OFF. The toggle switch routes power directly to the fan when ON and opens the circuit when OFF.


Hardware Parts

Gather these parts (order parts kit here):

  1. Sub-miniature Micro Switch With Lever Roller (Uxcell PN:s14073100am0209 )
  2. SPDT On/Off/On 3 Position Mini Toggle Switch (Amico PN:s12101100am0009 )
  3. Hex Nut Fastener, M3 Female Coarse Thread
  4. Hex Drive Cap Screw, M3x10mm or M3x15mm_MG_4174
  5. 3 ½” of heat shrink tubing
  6. 3 feet two conductor hook up wire (old speaker wire works fine)


You’ll also need some tools:

  1. 2.5 mm hex driver
  2. needle nose pliers
  3. wire cutters
  4. soldering iron and solder
  5. heat gun or cigarette lighter for heatshrink

I tried to design the project to work with a range of parts that you probably already have. You don’t need to use these exact parts. The position is adjustable so you can use a micro-switch without the lever roller for example. You can use any head for the adjustment bolt and various lengths and it will still work.

Step 1) Raised Lettering

Recommended Supplies:

  1. Large Chisel tip Permanent Sharpie Marker
  2. Clear Acrylic Sealer that bonds to plastic

_MG_4103Use a permanent sharpie marker to color the raised lettering. The large sharpies with the chisel tip work great for this. Seal the surface first with clear a few coats of acrylic otherwise the sharpie will not stick properly and will wick into the gaps between layers resulting in a fugly part as you an see in some of the photos where I didn’t seal. Trace over the lettering with the sharpie following the path you would take if you were to write it out. Make sure to hit the little points on the ends. Seal again with clear acrylic made for plastic. Use a few light coats.

Step 2) Toggle Switch

Remove the mounting hardware from the toggle switch and screw the inside nut all the way in on the threaded mounting shaft or remove it completely. Use needle nose pliers to hold the switch while you carefully screw the switch all the way in. The slot on the switch threads goes towards the little hole. Make sure the tabs on the 12mm washer go in the slot on the switch and into the little hole on the mount. This is the end of the switch that gets two wires in the next step. Install the lock washer and outside nut. DO NOT TIGHTEN because you’ll need to turn the switch later when we solder the wires._MG_4124

_MG_4125Step 3) Wiring

Cut the heatshrink into 7 pieces of about 1/2″ each. Cut a 3” piece and a 3′ piece of two conductor wire. The small piece goes inside the switch. The long piece hooks the switches to your existing cooling circuit. Split the conductors for about 1” on each end and strip about 1/4” of insulation from all of the ends.

  1. Slide a piece of heatshrink on to the 3” wire and solder it to an end tab on the micro-switch as shown. It doesn’t matter which end. Slide the heatshrink over the tab and shrink it.
  2. Slide a piece of heatshrink over the opposite conductor and solder it to the tab on the other end of the micro-switch. Slide the heatshrink over the tab and shrink it._MG_4076
  3. Twist together one free end from the 3” wire with an end from the 3′ wire. Slide heat shrink over the union as shown. Solder the twisted wires to the end tab CLOSEST TO THE LITTLE HOLE and SLOT from step 2. You will need to turn the toggle switch slightly to solder the connection. Move it back later. Slide the heatshrink over the tab and shrink it._MG_4077
  4. Slide a piece of heatshrink over the free end of the 3” wire. Solder the wire to free end tab of the toggle switch. Make sure this is the tab on the end opposite to the little hole and slot from step 2. Slide the heatshrink over the tab and shrink it.
  5. Slide a piece of heatshrink over the remaining end of the 3′ wire. Solder the wire to the CENTER tab of the toggle switch. Slide the heatshrink over the tab and shrink it._MG_4082

Step 4) Fasten Micro-switch

The micro-switch is fastened using two small pieces of 1.75mm printer filament.

  1. Cut two pieces of filament about 1” each.
  2. Carefully test fit the carriage onto the mount and make sure it slides up and down.
  3. Slide the carriage down off the track and slide the micro-switch into the rear of the carriage as shown. Make sure the roller is up like in the photos! Route wiring as shown._MG_4087
  4. Put the carriage back on the track with the micro-switch loose inside. Slide it up a little.
  5. Use a tool to center the the micro-switch and push it forward into position so the holes line up. Make sure the little roller is towards the end like in the photos. Insert the small pieces of filament. Cut so both end are flush with the surface. Made sure the carriage still slides up. If not you may have some filament in the way and need to trim a bit more._MG_4085_MG_4083

Step 5) Install Adjuster

The adjuster sets the point where your fan turns on during a print. If you don’t have the hardware to fit, don’t worry it’s optional. You can make the adjustment by hand, it just isn’t as precious or convenient.

  1. Carefully push a M3 nut into the receptor. Put one finger inside the track directly behind the M3 nut and push from the other side with a hex wrench. It goes in tight with the edges parallel to the housing. It should snap in. If the nut won’t go in, DO NOT FORCE IT, file out the sides of the receptor SLIGHTLY until the nut slides in.
  2. With the carriage all the way down, snap the M3 cap head bolt into place. Support the socket from behind with a small tool to avoid breaking it and roll the bolt in. The bolt should snap in tightly. Push on the head with a tool to make sure it is in all the way._MG_4129
  3. Push the carriage up until the M3 bolt mates with the M3 nut. Turn the M3 bolt using a 2.5 mm ball driver or hex wrench until the carriage moves all the way up. DO NOT OVERTIGHTEN. The carriage should slide all the way up without binding. Adjust wiring routing if necessary. Turn the M3 bolt and make sure the carriage moves. One turn of the bolt moves the set point by 0.5 mm._MG_4132_MG_4138

Assembly is complete! The automatic fan switch is now ready to be installed on your Duplicator 4.



  1. Use a 2.5mm hex driver to remove the M3 nuts from the left side of the left Z axis mount on your Duplicator 4._MG_4157
  2. Press the M3 nuts into the mounting bracket. Seat them all the way in by using a small tool.
  3. Fasten the mounting bracket to the bolts you unfastened on the left side of the Z axis mount. Make sure the flange faces forward and up as shown in the photos. Do not tighten._MG_4158
  4. Home your printer bed from the printer menu: Main Menu|Utilities|Home Axes
  5. Adjust the micro-switch position down about 2mm below the top position._MG_4159
  6. Slide the fan switch assembly into position from left to right so the mounting bracket slides under the ledge on the assembly and the micro-switch hits the bed frame and closes firmly without up using all of the travel.

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  7. Tighten the bolts snugly. Do not over tighten.

Hook Up

  1. Route the hook wires out the back of your printer. They can be routed right towards the center and out a small hole already in the back panel, or left and down out the lower left corner._MG_4169_MG_4167
  2. Locate the wires supplying power to your active cooling fan. You may need to follow the wires back from the fan to find a good location. It is ok to run the hookup wires up to umbilical cord go to the hot end if necessary.
  3. Cut the positive supply wire going to the fan.
  4. Strip about 1/4″ of insulation from the ends of the wire you just cut.
  5. Slide the remaining two pieces of 1/2″ heatshrink over each lead of the hookup wires and solder.
  6. Solder the hookup wires from the fan circuit to the wires you cut, so the fan switch circuit is in series with the fan power supply. Polarity is not important._MG_4042

Testing and Adjustment

  1. Move the toggle switch to the OFF position.
  2. Energize the active fan circuit. If you are drawing power from the extruder fan, you’ll need to heat up your printer until the extruder fan turns on. The active cooling fan should not run.
  3. Move the toggle switch to the ON position. The active cooling fan should run.
  4. Move the toggle switch to the AUTO position and home the printer bed. The active cooling fan should be off.
  5. Turn the adjustment bolt to raise the micro-switch until the the switch opens and the fan turns on, then back off until the fan turn off. This is the zero position. If you can’t move it far enough to turn the fan on, that is ok.
  6. From the printer menu, go to utilities, jog mode, z axis.
  7. Blip the z axis down. The fan should turn ON after one blip.
  8. Blip the z axis up. Then should turn OFF.
  9. This is the default adjustment where the fan turns on after the first layer. You can lower the position of the micro-switch to make the fan turn on farther into the print.

Installation is complete.

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