The parts I ordered online have started arriving. The first to show up were the small DC solenoid valves I plan to use for airflow control. These tiny valves cost around ￥8 RMB each (including shipping) – which is just a bit over €1 Euro. They’re incredibly cheap, so I ordered a bunch—different versions ranging from 12V to 3V to experiment with.
After receiving the valves, I did a quick test— and the result wasn’t quite what I expected. When powered, I could clearly hear the magnetic “click” as the solenoid engaged. So I tried blowing air through it manually to check whether the valve actually opened – and it did. But here’s the catch: you have to blow hard. This means it doesn’t open easily under low airflow or passive ventilation.
I contacted the seller, and they explained that this valve is designed for water systems – it requires some pressure to work properly. They mentioned it would work fine for controlling gas from a high-pressure tank, but not for gentle airflow. So I’ve decided to drop the idea of using these valves for airflow. Instead, I’ve ordered a few larger solenoid valves that are specifically labeled as “zero pressure” or “low pressure activated”. Hopefully they’ll allow airflow without needing force—just natural ventilation. Once they arrive, I’ll test them and see how they perform.
Next, I started receiving the heating components I ordered – including various PTC modules and ceramic heating plates with aluminum housings. I plan to install and test them one by one to see how each performs in terms of heat-up speed and stability.
For testing, I repurposed a 5L sealed container. I placed the temperature sensor, PTC heating element, and a small fan inside. After sealing the container, I used the SONOFF TH Elite (THR316D) to control the PTC and monitor the internal temperature and humidity in real time. To verify the accuracy of the readings, I also placed a SNZB-02D temperature and humidity sensor inside as a reference.
I started with a 220V 200W PTC heating module, which conveniently came with a built-in fan. The fan also runs directly on 220V, so wiring was very straightforward. To install the THS01 temperature sensor, I first cut its wire so I could thread it through a waterproof cable gland I had pre-installed on the sealed container wall. After pulling it through, I tightened the gland to ensure the seal, then soldered the wire back together and insulated it with heat-shrink tubing. I did the same for the power line: the 220V output from the TH Ehite controller was routed through another waterproof gland into the sealed box to keep everything airtight. Inside, I simply connected the power input of both the PTC and the fan to the incoming 220V line.
Once the TH output is enabled, the PTC and fan both start running, and the connected sensor feeds back real-time temperature and humidity data from inside the sealed box to the TH Elite controller. I quickly discovered that the 200W PTC heater was incredibly powerful. In less than a minute, it raised the temperature inside the sealed container from 30°C to 70°C. But then, a couple of issues came up. The SNZB-02D Zigbee sensor I placed inside was still showing only 60°C, while the sensor of TH Elite was already reading 70°C. It took me a moment to realize the reason: the SNZB-02D’s operating range only goes up to 60°C. So in this setup, it’s completely unreliable for high-temperature readings. Another thing I noticed—condensation. As the temperature ramped up rapidly, droplets started forming on the inner walls of the container. I’m guessing this was caused by hot air hitting the still-cool surfaces of the plastic walls, leading to moisture condensing.
At that point, I stopped the test immediately. It became clear that 200W is a bit too much for a 5L sealed box. If the temperature kept rising to 80°C or 90°C, I might’ve ended up damaging the SNZB-02D or worse.
Next, I swapped in a lower power 100W PTC module for testing. Unlike the previous one, this unit didn’t come with a built-in fan, so I had to add a DC fan powered by a small AC-DC module to help circulate the heat inside the container. The test went pretty much as expected. The temperature rose more slowly this time, and after reaching about 75°C, it began to plateau. It took roughly 30 minutes to climb from 75°C to 79°C, and after that, the temperature held steady around 79°C for over an hour. It seems like 79°C is roughly the thermal limit for this 100W PTC module in a 5L sealed space.
Then I moved on to test a 50W PTC module. From 25°C to 55°C, the temperature ramp-up was still reasonably quick, but after that, things slowed down significantly. Once it passed 60°C, the temperature barely changed. After nearly 2 hours of operation, the highest temperature I recorded was only about 63°C, with the system mostly hovering around 60°C. That’s just not enough for drying PC or ABS filaments, and even for PETG, it’s borderline. Realistically, it would only be usable for PLA—which, ironically, doesn’t usually require drying in the first place.
Lastly, I tested a ceramic heating plate with an aluminum housing. Its spec was marked as 220V / 70°C, and according to the product description, it includes a self-regulating thermal protection that kicks in around 70°C to prevent overheating. In theory, if a fan constantly blows the heat away, the plate should stay under 70°C and continue running steadily. But in practice, things didn’t go quite as planned. The heating speed was extremely slow— it took nearly 30 minutes just to raise the internal temperature from 25°C to 30°C, and after two more hours of operation, the max temperature only reached around 35°C. Clearly, the power output is far too low for this application. It hit its thermal limit pretty quickly, and that’s about all it could manage.
I’ve also ordered a larger sealed container – about 30x40cm in size with a height of 25cm, which can hold up to four spools of filament at once. I think this one might be more suitable for testing the 200W PTC module, as the extra volume could better absorb and distribute the heat without overshooting too fast. Once it arrives, I’ll run some tests to see how the 200W heater performs in a space this size.
Meanwhile, for single-spool drying in the 5L container, I plan to try a 150W PTC – as the 100W unit only managed to reach around 80°C, which isn’t quite enough for drying many high-temperature filaments.
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