It’s rainy season again in Shenzhen, and the humidity has climbed to around 60% every day. Looks like it’s high time I speed up my dry box project before all my filament turns into soggy noodles.
I’ve made quite a few changes to my dry box prototype lately. To better understand how the Bambu Lab AMS HT works, I connected it to an eWeLink power monitoring plug and placed a SONOFF SNZB-02WD sensor inside the chamber to compare its readings with the AMS HT’s built-in display. At the start, the AMS HT comes in hot—literally. The PTC kicks off at nearly 450W, heating up the chamber rapidly. Once it hits the target temperature, it stops heating completely, with power dropping to nearly zero. That’s when I noticed an interesting detail: there was a temperature difference of nearly 20°C between what the AMS HT showed and what the SNZB-02WD measured – especially during the early phase of heating.
Once the AMS HT’s internal temperature display drops below 65°C, it kicks the heater back on. At that moment, the power meter confirms a surge back up to around 400W. As the internal temperature climbs again, the power draw gradually decreases. When the AMS HT display reaches 68°C, it appears that the PTC heater shuts off completely – confirmed by the plug-in power meter, which now shows near-zero consumption, with only the fan still running. Here’s the interesting part: although the AMS HT display begins oscillating around 65°C, the SNZB-02WD sensor inside shows a steady, consistent temperature rise – narrowing the gap between its reading and the AMS HT’s display. This suggests that while AMS HT toggles the heater based on its own sensor, thermal energy continues to diffuse throughout the chamber, smoothing out the temperature distribution.
After about half an hour of these heating-cooling cycles, the SNZB-02WD sensor finally stabilized around 62°C—pretty close to AMS HT’s target of 65°C. Meanwhile, the AMS HT’s own display kept oscillating between 64°C and 68°C. So I decided to align my own dryer’s temperature control goals with the performance of AMS HT. My earlier dream of maintaining a ±1°C difference throughout a fully sealed box? Yeah… that turned out to be a bit too ambitious. Achieving something on par with the AMS HT is already very impressive – and honestly, it leaves that 100 RMB no-name dryer I tested earlier totally in the dust.
Inspired by the design logic of the AMS HT, I simplified my drybox’s internal structure: I switched to using a high-power PTC heater for rapid heat generation, combined with a strong AC fan to spread the heat evenly across the sealed chamber.
This approach eliminates the need for multiple small internal fans and AC-to-DC power modules, making the overall design cleaner and more focused on raw thermal performance. To ensure responsive temperature control, I placed the TH Elite’s temperature sensor right at the PTC air outlet – this way it can catch any temperature changes as quickly as possible.
After implementing the changes, I ran a validation test—and the results were great.
With the temperature range set between 45–65°C, the system reached thermal balance within about 30 minutes. The temperatures in the center and upper areas of the sealed box stayed within 5°C of the TH Elite’s outlet sensor reading.
However, when I pushed the target temperature up to 70°C, the difference began to exceed 5°C. I suspect this is due to my current PTC heater only being rated at 150W, which limits heat output. Switching to a 250W PTC – or even a 500W one like in the AMS HT – would likely enable better stability at higher temperatures, though it would require significantly more time (possibly 1–2 hours) to fully stabilize.
This drying box is intended to work with my newly purchased Bambu A1 Mini, and since I’m only printing with PLA and PETG, maintaining a stable 65°C is already sufficient for my needs. Next, I’ll focus on designing a few supporting internal structures – like the filament support axle and a container for desiccant—so this can evolve from an experimental prototype into a fully usable product.
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