After selecting the resistive coil as our heating method, it was time to build and test our first integrated prototype. This phase would be crucial – moving from controlled bench testing of individual components to a system that could actually demonstrate VASSR's potential in real-world conditions.
We started by "hijacking" an off-the-shelf portable kettle with a built-in resistance coil. While this might seem like a shortcut, it actually gave us several advantages. The kettle's 600mL capacity would let us test significant snow volumes, and its existing coil had a 1.4 ohm resistance – perfect for drawing reasonable current at our target voltage. We modified it by replacing the standard cigarette lighter plug with an XT-60 connector, making it compatible with our battery setup.
For power, we selected a 3s3p 18650 battery pack rated at 110 watt-hours and 10.8 volts. Based on our previous calculations, this should theoretically provide enough juice to melt about one liter of snow. The entire package – kettle, battery, and connectors – weighed in at 932 grams. Not exactly ultralight, but a reasonable starting point for proof of concept.
Our benchtop testing followed a similar protocol to our earlier experiments, using shaved ice to maintain consistency. We conducted three separate tests, carefully measuring water mass, snow mass, melting time, and battery performance metrics. The results were encouraging but also highlighted some key challenges.
In our first test, starting with 125g of water and 391g of snow, the system took just over 18 minutes to complete the melt. The battery voltage dropped from 12.12V to 11.3V during this process, delivering about 8.36 amps and using 29.5 watt-hours – roughly 27% of our battery capacity. Most importantly, we achieved 87% efficiency in converting electrical energy to snow melting.
Tests two and three showed similar patterns, though with some interesting variations. Our final test, with 409g of snow, took longer at 27 minutes but actually showed improved efficiency at 91%. Across all three tests, we managed to melt about 1.1 liters of snow on a single charge, with approximately 800mL directly attributable to battery power (the rest coming from ambient heat in our test environment).
Given the lower density of ice than water, we had to perform multiple melting cycles to achieve our total volume. We also discovered that our battery wasn't delivering its full advertised capacity. We used about 86.4 watt-hours out of the rated 110, suggesting either conservative ratings from the manufacturer or some inefficiencies in our system.
These findings led us to outline several improvements for the next iteration. We need to integrate a PCB to maintain regulated voltage throughout operation – this will help provide consistent performance regardless of battery charge state. We also need to add protection circuits to prevent battery over-discharge, currently requiring active monitoring to keep the system safe.
Perhaps most exciting were our cold-temperature test results. We had been concerned about battery performance in winter conditions, but testing in a 36°F (2°C) environment showed only a 15% reduction in capacity. Even at 14°F (-10°C), we expect to maintain about 70% capacity – more than enough to make VASSR viable in real winter conditions.
Looking at the complete system architecture that's emerging for the prototype: We're targeting a 0.5kg battery pack capable of melting 1 liter of snow (assuming you start with 200mL of liquid) in about an hour at 32°F. The vessel itself will likely weigh around 0.5kg, with the total package volume equivalent to a 1.5-liter bottle. That's because the battery pack and electronics take up about 0.5L of space, leaving 1L for water capacity. When empty, it'll weigh less than a liter of water but be capable of providing 2 liters of water when started with a full vessel.
These specifications would theoretically save about 0.5kg and 0.5 liters of space compared to carrying 2 liters of water. We could potentially reduce melting time by increasing battery voltage to 15 or 20 volts, though this requires careful consideration of the trade-offs between speed and efficiency.
With our bench testing complete, we faced a crucial decision about how to build our first field-worthy prototype. We identified two potential paths forward, each with its own advantages and challenges.
The first option was to leverage off-the-shelf components. This approach would involve using a larger-capacity portable kettle as our base, creating a 3D-printed and insulated enclosure for the battery that would attach to the bottom, forming a single cohesive unit. We'd need to add an over-discharge protection circuit and voltage regulator to ensure safe, reliable operation. The beauty of this approach lay in its simplicity and faster development timeline. By using available components, we could focus our engineering efforts on integration and safety features rather than fundamental design challenges.
The second path was more ambitious: a completely custom build. This would mean designing our own insulated vessel with an integrated heating coil and battery system. We'd have total control over every aspect of the design, allowing us to optimize the form factor and incorporate advanced features like water level detection sensors to prevent coil burn. The electronics implementation could be more sophisticated, with smoother integration of the battery, wiring, and PCBs. This approach would give us the freedom to create exactly what we envisioned, but it would require significantly more time and resources to develop.
After careful consideration of our goals and timeline, we chose to proceed with the off-the-shelf approach. This decision wasn't just about getting to market faster – it was about creating a reliable prototype that we could actually test in real winter conditions. The faster development cycle would allow us to gather real-world feedback sooner, helping inform future iterations of the product.
In the next post, I'll share how we transformed these plans into our first working prototype, complete with the challenges, surprises, and lessons learned along the way. I'll also explain how we addressed some key safety features, like preventing the heating element from operating without adequate water coverage. Stay tuned, and don't forget to drink your snow!
