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Cooling Coaster: The Guts
May. 17th, 2023 04:16 pmSeveral years ago, I was looking at powered drinks coasters on Amazon to see what I might use, when I came across a rather surprising item: A USB-powered coaster that both heats and cools your cup.
Yes, 5V (turns out, at around 1.6 amps) doesn't do all that much in the grand scheme of things, but I was intrigued enough to buy one, and while I wasn't astounded by its abilities, I was impressed enough to buy a few more when the price fell back down to a reasonable level.
(after I bought mine, the price jumped up to just under $50. Later, it fell down to $15 each, so I bought a few spares)
Anyway, I took the original one apart to figure out how it works, and it's basically a Peltier device (which can be used to generate an electric current from a temperature differential, or to cause one by applying power to it) with a heat sink, a tiny fan (we'll come back to that), and a control board. The switch on the front of the unit controls which function is run, so it's pretty simple inside.
Technically, the website and box claims there's a 9V power adapter somewhere out there that's compatible with this coaster, so I rigged something up to put 9V through a USB port (as the USB cables it comes with are the only ones I have right now) and it did a far better job of cooling drinks off.
The fan is, like I said, really tiny. About 2cm across or so. So it is loud. And the one thing that makes hot days worse is really loud, tiny fans. So while it may have helped a little over the last few summers, it caused other problems too.
So I bought a couple of 5V fans that are 8cm across, and they move far more air, while being much quieter. Right now, I have the guts from the first cooling coaster on my desk, with brass standoffs in the screw holes of the fan, with the heatsink/Peltier device/drink plate stacked on top of that.
Given around a 26°C ambient temperature, the top plate manages to remain around 16°C, which is enough to slightly cool a glass of water, but not enough to do it at all quickly. I'd even left it running under a nearly full glass of water for about four hours last night, and while it was cooler, it didn't get anywhere near as cold as I would have liked.
On the other hand, I'm very close to replacing the USB power supply on my desk (that has five USB ports on it) with an old PC power supply, so I'll have all the way up to 12V to work with. In theory, I should even be able to run the Peltier device on the full 12V (given that most of the models I've seen does support up to 15V at a stretch, so 12V should be fine), while using the 5V supply for the fan itself.
I'm currently thinking about how I'd want such a thing to work, but as I don't know enough about the current-passing characteristics of any of the transistors that I have right now, so my current preference is running the entire thing off a few switches. And with the fan and the Peltier device running off different power rails, they can't exactly share the same switch. Plus, I'll want a switch to control whether the Peltier device gets 12V or just 5V, depending on how much power I want it to have. At a minimum, that's two switches. The reason I might need a third switch is to control the fan. Because right now I'm not sure how to control the 5V fan from the DPDT switch that controls which direction the Peltier device runs.
Like I said above, at just 5V, it managed to bring the metal plate that holds the glass down to 16°C, and I'm actually kind of tempted to include a temperature sensor (of some sort) leaning against the plate. Then a microcontroller (obviously) to show the temperature on an easily-viewed display, and allow you to set the target temperature for the plate to rest at. Maybe even another sensor that's spring-loaded against the glass, for a more accurate reading? But likely not, as most of that would require things I'm not prepared for just yet.
(something about MOSFETs versus regular bipolar transistors)
Yes, 5V (turns out, at around 1.6 amps) doesn't do all that much in the grand scheme of things, but I was intrigued enough to buy one, and while I wasn't astounded by its abilities, I was impressed enough to buy a few more when the price fell back down to a reasonable level.
(after I bought mine, the price jumped up to just under $50. Later, it fell down to $15 each, so I bought a few spares)
Anyway, I took the original one apart to figure out how it works, and it's basically a Peltier device (which can be used to generate an electric current from a temperature differential, or to cause one by applying power to it) with a heat sink, a tiny fan (we'll come back to that), and a control board. The switch on the front of the unit controls which function is run, so it's pretty simple inside.
Technically, the website and box claims there's a 9V power adapter somewhere out there that's compatible with this coaster, so I rigged something up to put 9V through a USB port (as the USB cables it comes with are the only ones I have right now) and it did a far better job of cooling drinks off.
The fan is, like I said, really tiny. About 2cm across or so. So it is loud. And the one thing that makes hot days worse is really loud, tiny fans. So while it may have helped a little over the last few summers, it caused other problems too.
So I bought a couple of 5V fans that are 8cm across, and they move far more air, while being much quieter. Right now, I have the guts from the first cooling coaster on my desk, with brass standoffs in the screw holes of the fan, with the heatsink/Peltier device/drink plate stacked on top of that.
Given around a 26°C ambient temperature, the top plate manages to remain around 16°C, which is enough to slightly cool a glass of water, but not enough to do it at all quickly. I'd even left it running under a nearly full glass of water for about four hours last night, and while it was cooler, it didn't get anywhere near as cold as I would have liked.
On the other hand, I'm very close to replacing the USB power supply on my desk (that has five USB ports on it) with an old PC power supply, so I'll have all the way up to 12V to work with. In theory, I should even be able to run the Peltier device on the full 12V (given that most of the models I've seen does support up to 15V at a stretch, so 12V should be fine), while using the 5V supply for the fan itself.
I'm currently thinking about how I'd want such a thing to work, but as I don't know enough about the current-passing characteristics of any of the transistors that I have right now, so my current preference is running the entire thing off a few switches. And with the fan and the Peltier device running off different power rails, they can't exactly share the same switch. Plus, I'll want a switch to control whether the Peltier device gets 12V or just 5V, depending on how much power I want it to have. At a minimum, that's two switches. The reason I might need a third switch is to control the fan. Because right now I'm not sure how to control the 5V fan from the DPDT switch that controls which direction the Peltier device runs.
Like I said above, at just 5V, it managed to bring the metal plate that holds the glass down to 16°C, and I'm actually kind of tempted to include a temperature sensor (of some sort) leaning against the plate. Then a microcontroller (obviously) to show the temperature on an easily-viewed display, and allow you to set the target temperature for the plate to rest at. Maybe even another sensor that's spring-loaded against the glass, for a more accurate reading? But likely not, as most of that would require things I'm not prepared for just yet.
(something about MOSFETs versus regular bipolar transistors)
