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Constructional Project 3D Printer Filament Drying Chamber This device uses relatively simple hardware to keep 3D printer plastic filament warm, driving moisture out and keeping it out. That’s important for consistent printing results, especially with PLA or Nylon filament. Your printer can draw the filament directly out of the sealed box. Part 2 by Phil Prosser T here are two main versions of our Filament Dryer design: one that uses an off-the-shelf plastic box to store the filament, plus a custom timber box made from plywood. While making the timber box isn’t all that difficult, it is a bit involved, so we won’t go into great detail on how to build it. We think most people will prefer the convenience of simply buying and modifying a pre-made box. Both solutions perform similarly, although the timber box is, in some ways, a little bit neater. We suggest you read through most of this article before deciding which approach is best for you. Before we get to the boxes, let’s build and test the controller electronics. Controller construction The controller is built on a PCB coded 28110241 that measures 126 × 93mm. During assembly, refer to its overlay diagram, Fig.3, which shows which parts go where, as well as Photo 4 (note there are some differences between the prototype and final version of the PCB). It is not hard to put together; we have stuck to through-hole parts and easy-to-get bits. The board layout puts all the controls and adjustments along one edge, which we mounted to face the user. Start by fitting all the resistors. Make sure you use 1% tolerance 12kW and 2.7kW resistors. The others are not so 34 critical, although we tend to just use all 1% resistors these days as they don’t cost that much more than 5% resistors. Follow by mounting the diodes, ensuring that they are orientated correctly, as shown in Fig.3, and that you don’t mix up the four different diode types (again, refer to the overlay). Mount D6 on longer leads so you can bend it to sit in the fan’s airflow channel, as shown. Now install the LEDs. We bent LED7 (red, heater running) and LED12 (green, temperature achieved) over so they are visible from the control side of the PCB once it’s installed in the enclosure. LED8 doesn’t matter as it’s used for its forward voltage, not because it lights up. Next, fit the 100nF ceramic/MKT capacitors, which are not polarised, then the three electrolytic capacitors, which are. The latter must be inserted with the longer (positive) lead into the pad on the + side. The negative stripe on the can indicates the opposite, negative side. You can then solder the PIC microcontroller and LM358 operational amplifier. If you bought your PIC from the Silicon Chip store, it will already be programmed. Otherwise, you will need to install CON6 and use a PICkit or similar to program it yourself. The firmware can be downloaded from: siliconchip.au/Shop/6/484 Next, fit the five components in TO-92 packages: four transistors and the LM336BZ voltage reference. Ensure they go in the locations shown and the flat face is orientated as per Fig.3 and the PCB silkscreening. Follow with the headers and trimpots. While heatsinks are shown for transistors Q1 and Q2, they are not necessary unless you are using a Mosfet with a higher RDSon than the one we specified (for Q2) or your fan draws more current than the one suggested (for Q1). However, you need to make sure the metal tab side of each device faces to the left, as shown in Fig.3. Now is also a good time to mount REG1. Like Q1 and Q2, its metal tab must face to the left. Then you can solder the fuse clips in place; it’s easier to get them positioned correctly by inserting a fuse before soldering them, but be careful not to overheat it. On the top side of the board, that just leaves CON1, S1, S2, VR3 and F2, all of which can now be mounted, with the exception of F2. The thermal fuse warrants some care in soldering, as it will ‘blow’ at 77°C, which is not hot at all when soldering. We blew the first one we soldered, so be warned! We dealt with the thermal fuse by using quite long leads and being very fast in soldering. To draw away some of the heat, you could clamp something like pliers (with a rubber band on Practical Electronics | November | 2025 3D Printer Filament Dryer, part two Photo 4: the top side of the early prototype PCB, repeated from last month’s issue. the handle), a haemostat (self-closing pliers), or perhaps a clip-on heatsink on the lead between the fuse and pad during soldering. The fan is installed on the back of the PCB and is intended to push air into the enclosure. If you look at the side of the fan, you will typically see two arrows, one indicating the rotation direction and the other the airflow direction. If you are using a fan different from the one we got from Altronics, check that yours draws more than 50mA when running and less than 10mA when stalled. This will ensure that the protection system operates as intended. Secure the fan and its 40mm grille on the underside of the PCB using 16mmlong M3 machine screws, hex nuts and shakeproof washers. You can use a polarised header plug to connect this fan to CON4 or solder its leads directly to the PCB, as it should not usually need to be removed. At this point, the board should be fully loaded and ready to test. Testing can be done without the heater plates and before the controller is installed in the enclosure. Testing procedure Start by applying power and checking for excess heat or smoke. The fan on the PCB should be running all the time; that is normal. Check that the 5V rail is OK; there are GND and 5V test points in the lower right-hand corner of the PCB. If the voltage between those is not in the range of 4.75-5.25V, check around the LM317 regulator. Are the resistors the correct values? Is there a short on the regulator, PIC or op amp? Use a DVM to monitor the voltage on the 2.5V test point at upper right and adjust VR1 to get 2.5V on that test point. If you can’t do that, check that the LM336-2.5 is the correct part and the right way around. If the onboard fan is not running, check for about 12V on the “+” pin of CON4, the fan header. If it is present, check that the fan is plugged in the right way around and that the wiring is OK. Also verify that the BD139 transistor (Q1) and 12V zener diode are both the right way around. Now set the temperature control (VR3) fully anti-clockwise and adjust trimpot VR2 up and down. You should see the green “Set Temp Achieved” light (LED12) switch on and off. If that does not happen, check the voltage on pin 6 of IC1, the LM358. This is the forward voltage of the temperature sense diode and should be about 0.55V. Also check the voltage on pin 5 of IC1, which is adjusted by VR2. It should vary above and below 0.55V as you rotate VR2. Fig.3: use this overlay diagram to help you assemble the controller board. All parts mount on the top, except the 40mm fan, which goes on the underside. Its power wires come around to the top side of the board to plug into CON4. Watch the orientations of the ICs, Q1. Mount LED7 & LED12 on long leads bent over to face the left. Practical Electronics | November | 2025 35 Constructional Project Photo 6: this shows how the resistors & thermal cutout mount onto the heat plate shown in Fig.5, along with the wiring (with the resistors in parallel, as per Fig.4). Also note the 50mm standoffs made from pairs of 25mm male-female spacers. Check the voltage on pin 7 of the LM358. It should switch between low (0V) and high (a couple of volts below the supply) as VR2 is adjusted. If it does, but LED12 is not lighting, that points to a problem with diode D12, transistor Q3, LED12 or its series resistor. Now it’s time to use VR2 to calibrate the temperature setting. Do this at room temperature (20-25°C). Turn VR3 up a little bit. Yes, that is a technical term; aim for around 1/3 to 1/4 of its travel, which corresponds to around 10°C. Adjust VR2 until green LED12 is off, then slowly rotate it anti-clockwise until LED12 comes on. Once you’ve done that, VR3 will let you adjust the set point from room temperature to about 30°C above that. Now if you turn VR3 fully anti-­ clockwise, LED12 should come on. If it does not, repeat the prior step with the control up a ‘little bit more’ (another technical term). Turn VR3 up, and LED12 should go off. Now press the Start button, S2. The red “Heater On” LED, LED12, should light. That means the PIC and Mosfet Q3 are working, as is the thermostat. If not, check that there is about 12V on the left-hand side of the 4.7kW resistor between Q3/Q4 and Q2. This is the Mosfet gate drive. If not, verify that you have used a PNP device for Q6. The PIC output at pin 5 should start high (5V) and go low (near 0V) when you press the Start button, S2. You can check this by monitoring the upper pin of CON5, nearer Q2. If this does not go from high to low when you press S2, check the PIC. 36 With this all OK, the controller should be working and ready to test and install. The fact that the Mosfet switches the LED indicates it is working. You are ready to assemble and wire the heater plates, which we will describe in the next section. The approach to use will depend on how you are packaging the Dryer. Making the heater plates We are presenting two approaches to the heat plates. These aim to dissipate 50W in the enclosure while keeping surface temperatures to a safe level. With a 50°C enclosure temperature, these plates reach about 70°C. Any aluminium sheet more than 1.2mm thick will work, depending on what you have available. In deciding how you want to make your heater plates, here are the safety controls you need to consider: Fig.4: the wiring to the heater resistors is straightforward. If using low-value resistors, you might want to connect them in series rather than parallel. Either way, the thermal cutout must be wired to disconnect all the resistors if it gets too hot. • Do not place the heat plate in continuous contact with timber; it can auto-ignite. Use standoffs for any heater plate at the bottom of the enclosure. • Ensure that the circulation fan can circulate air throughout the enclosure. • Ensure that the air around the temperature sense diode will be representative of the overall enclosure air temperature (good circulation should provide that). • Ensure that the user can easily access the controls, especially S2. • Ensure that the 90°C thermal cutout switches are installed and located near the heating resistors. • Ensure the resistors are securely connected to the plate and will not run excessively hot. There are two primary considerations for resistor selection. Firstly, they must be able to be affixed to the heatsink securely. Secondly, you must be able to safely dissipate about 50W into your case. Our experiments showed that in a normal room, 50W is adequate to achieve 50°C. You can use resistors in series or parallel. We had a bunch of 7W 25W resistors lying around that we used in one prototype, wired in series. Do your sums and select the resistance you need, then search out the cheapest option. The resistors specified in the parts list (visible in the photos) are pretty close to optimal in terms of ratings, size and cost. Once you have made the heater plates, it is worth plugging them into the controller on the bench and checking that they work as expected. Once you set the system running, the heater plates should get hot after a few minutes. You should be able to feel that each resistor is dissipating power by touching its case while running; it will be noticeably warmer than the heatsink. If any resistors are extremely hot, check that they are correctly mounted. If they’re all reaching about the same temperature, the heater is ready to go. Wire up the plate using medium/ heavy-duty hookup wire rated to a minimum of 90°C; Altronics carries suitable wire, as stated in the parts list last month. Make the flying leads long enough that you can assemble the box easily. The required connections are shown in Fig.4. On the controller end of the wires, we recommend crimping them into Practical Electronics | November | 2025 3D Printer Filament Dryer, part two Fig.5: this plate for the plastic box holds just three power resistors and the thermal cutout. All dimensions are in millimetres. pluggable header pins and inserting them into the blocks so you can easily plug in and remove the heater boards to the controller. You can use any matching pair of 2.54mm pitch headers and plugs for this, just make sure that the connector is rated for 3A or more (the Altronics ones in the parts list are rated at 3A). We like to flow a little solder into the crimped joint to ensure it can’t come loose, but if you do that, be careful not to add excessive solder or get it on the outside of the pin, or it may no longer fit in the block. The pins often need to be straightened before they will slide into the blocks and click into place. They can be released by pressing the tab with a tiny flat-bladed jeweller’s screwdriver. We recommend against soldering the wires straight to the PCB, as this will make the whole thing very fiddly to handle and assemble. Making the enclosure As mentioned previously, you have two options: modify a plastic box or make your own timber box. We won’t go into a lot of details for the latter case; we recommend you only take that route if you are confident in sorting out the details yourself. For the simpler plastic enclosure, the secondary heat plate is just three resistors and a 90°C thermal cutout switch mounted to a 180 × 210mm sheet of 1.5mm-thick aluminium, as shown in Photo 6. The recommended drilling pattern and mounting locations are in Fig.5. We used 50mm metal threaded standoffs (two 25mm male/female spacers joined) to fix this to the end of our plastic box. The controller mounts on the primary heat plate, shown in Fig.6 and Photo 7. This uses the same size sheet, but holds the heating resistors, thermal switch and also the control board. We cut a 40mm hole in the plate and mounted the controller on 15mm standoffs so that the fan forces air through this hole. This plate also uses 50mm standoffs and mounts to the end of the plastic enclosure. In both cases, secure the resistors to the plates using 10mm-long M3 machine screws, shakeproof washers and nuts. Add a little thermal paste under each resistor for good heat transfer. Practical Electronics | November | 2025 Photo 7: this plate is similar to the one shown in Photo 6, except it’s rearranged to allow the controller board to mount on it. There’s a hole under the fan that you can’t see from this angle. 37 Constructional Project Fig.6: the second plate for the plastic box is similar to the first, except that the controller board also mounts on it, with a hole for the fan’s airflow to pass through. We use a single large heat plate measuring 330 × 225mm for the timber enclosure, as shown in Fig.7 and Photo 8. This sits in the base of the enclosure. To ensure there is good ventilation around this, we bent the outer 60mm of each side up at about 45° and screwed six 10mm standoffs on the underside of the flat part to act as feet. This creates a plenum under the entire plate and larger triangular plenums down the sides. The ends of the plenum are cut off at 45° to create openings at the opposite end to the controller. We have mounted the controller so that it draws air through this plenum. The six resistors are mounted three on each side of the plate, on the underside, so they are protected from people’s fingers and stray material. We also mount 90°C thermal switches on either side of the plate to protect against overheating. In all our testing, we did not manage to trigger these switches, but they are an important failsafe. Do not omit them. Fig.7: the heater plate for the custom box has all six power resistors mounted on it, three on each side, with each triplet having its own over-temperature cutout. The six holes in the middle are for standoffs to space it off the bottom of the box. 38 Practical Electronics | November | 2025 3D Printer Filament Dryer, part two We made a lid for the timber enclosure from two sheets of acrylic (not included in the parts list). One is cut to the full size of the box, and a second is cut so it fits neatly inside the box. By mounting these to one another with 10mm spacers (we drilled straight through both sheets, ensuring an exact alignment of holes), we achieve a poor person’s ‘double-glazed’ lid, which self-aligns itself when you put it on (see Photo 9). Photo 8: the all-in-one heater plate for the custom timber box, shown from the underside so you can see the mounting and wiring of the components, along with the feet made from tapped spacers. The box Your approach to the box will depend on how handy you are in the workshop and how much time you want to spend. We will show two examples of how it can be made, one from 12mm plywood and the other using an 18L storage box from our local hardware shop. To reduce heat loss, you need to install Correx insulation in both versions. If you chose a smaller plastic box, you would have less heat loss and be able to achieve a higher temperature and/or reduce the power consumption. We will leave this to your creativity. We certainly would not go any larger than the 18L box we used. We used some offcuts of 12mm plywood for our timber box and made a rod to hang four 200mm diameter filament reels inside. While there is no standard, most manufacturers seem to be settling on this as the size of a 1kg reel. We added a baffle inside the box that allows us to force air circulation through it. It also ensures that our controller is protected from any rough handling of the reels. Because we used timber, which is not moisture-proof, we gave the box two coats of varnish. We used polyurethane varnish, but any paint will do, so you can make it any colour you like. Check the paint you’re going to use to see if you need to seal and/or prime the timber before applying it. Our design includes provision for a rail on which you can hang up to four reels of filament. We 3D-printed the hanger hooks; the STL files for these and the other 3D-printed parts used can be downloaded from: siliconchip.au/shop/6/484 These suit 22mm diameter or smaller timber dowel; ours was pinched from an old broom handle. We also made Photo 9: we made a lid for the custom timber box from two sheets of acrylic, making it ‘double glazed’. The sheets are held together with short tapped spacers and machine screws. Note the filament exit hole in the foreground. Practical Electronics | November | 2025 39 Constructional Project Photos 10 & 11: these photos show the locations of the two heat plates and controller in the plastic case. Note how the dowel is held in place by two red 3D-printed brackets to make it easy to add and remove reels. ventilation covers, one for the exit and one for the ventilation fan (the ventilation fan should be installed in a hole in the outside of the box). Both of these allow you to close the vent. The STL files for these are in the same download package. We used long screws to secure the vent fan cover to the case; you could use superglue instead. We have included some simple drawings of our timber box in the download package, but we expect readers to have their own spin on it. Again we note that the box we built is right at the upper limit of what we would suggest you build; making it shorter would reduce heat loss. Insulation For the plastic box, we cut ‘insulation panels’ from polypropylene Correx material (fluted polypropylene board). We chose this as it is easily cut, includes air pockets for insulation and does not present a fire hazard at the temperatures we are working with. The sidewall insulation pieces are 270mm wide at the base, 290mm wide at the top and 235mm high. The end wall insulation pieces are 200mm wide at the top, 180mm wide at the base and 235mm high. The side flaps are 10mm wide at the base and 35mm wide at the top. The bottom layer insulation sheet is 280 × 170mm. Foam tape must be applied around the top lip of the box to improve the seal on this enclosure. It makes a huge difference to the system’s performance. We found it increased the temperature inside the box by 4°C for the same power input (tested at 34W). To justify the need for insulation, we tested the performance with and without insulation. With 50W continuous dissipation in the insulated box, it reached 50°C (22°C ambient), Photos 13 & 14: here you can see the finished custom timber box, with 3D-printed parts holding up the dowel from which the filament reels hang. This box can handle four 1kg reels. The Corflute insulation on the sides and the foam tape to seal the lid are essential for good performance. The controller is mounted in the section, behind the baffle panel, with a hole for the fan to push air through. 40 Practical Electronics | November | 2025 3D Printer Filament Dryer, part two NEW! 5-year collections 2019-2023 All 60 issues from Jan 2019 to Dec 2023 for just £49.95 Photo 12: the finished Filament Dryer in the custom timber case connected to a Creality 3D printer. while without insulation, it only reached 41°C at the same power level. The Correx insulation and foam seal for the lid together save around 20W during operation. You should insulate the timber box similarly, but the dimensions of the pieces will depend on the exact size of your box. Once insulated with Correx, the timber box’s performance was pretty much identical to that of the plastic one, reaching 50°C with 50W of dissipation or 41°C at 32W. Using the Dryer Using the Dryer is really simple. You thread the reels you want to dry onto the rail and hang them in the Dryer. Secure the lid and press the Start button with your selected temperature (set with VR3) and time (set with S1; up [away from the PCB] is six hours and down [towards it] is nine). We prefer to turn the temperature up to 50°C and allow the controller to take over from there, but almost all our printing is done with PLA. We hope that the discussion of safety & implementing controls in the design has led to some consideration of where and how safety in design plays a role PE in your hobby. 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