The electronic insulin pen cooler
The electronic insulin pen cooler
If you are diabetic, you know how stressful it is to carry insulin pens in a hot summer day: You permanently worry about the pens getting too warm and the precious, life-saving insulin going bad.
The idea of a small refrigerator that would fit in a purse, or a small backpack, sounds quite obvious until you try shopping for one. You quickly find that you can get small thermal bags that rely on ice packs (that are never icy when you need them), or expensive, heavy and fragile toaster-size electric coolers.
This project is about a portable, compact, lightweight, robust, efficient, inexpensive and always-ready-when-you-need-it electric cooler for two insulin pens.
We call it Cool-ins
Size, Design & Construction
Cool-ins is composed of a high-insulation Styrofoam core inside a neoprene rubber sleeve. These two part combine form an impact-resistant, light-weight, rubbery case. The two thermally insulating materials minimize the amount of electrical energy needed to cool down the pens and keep them cool, resulting in long battery life.
The cooler has room for two pens. The inside dimensions are compatible with all popular insulin pens. A zipper at the end of the cooler, opens up, allowing the user to flip the cover and access the pens.
The neoprene fabric and plastic are of light grey color to helps overall efficiency. The lighter color reflects away as much of the external heat as much as possible.
Cool-ins weighs only 214 grams (7.55 oz) - excluding power source. It can follow you everywhere.
Thermoelectric Controller Circuit
Cool-ins works using Thermoelectric cooling technology. It is a "real" refrigerator in the sense that it uses electricity to create cooling (i.e. no ice packs). The electronic cooling element is very small, resulting in a very compact design. See this wikipedia article for more about thermoelectric cooling.
Controlling the cooling element efficiently is a fairly complex process and requires a TEC (thermoelectric controller). Cool-ins is equipped with an electronic board containing a microcomputer, three temperature sensors (measuring the internal, fan, and external air temperature), a variable speed fan, and an adjustable current source for the thermoelectric cell.
An algorithm running on the microcomputer balances the power to the cell and fan speed depending of the cooler's internal and external ambient temperature, in order to achieve the optimal cooling and maximizing battery utilization.
Cool-ins does not have built-in batteries. Instead, it has a USB connector for plugging into an external battery pack (not included) of the kind made for smartphones. These packs are now very commonly available and very inexpensive. Using these packs greatly lowers the overall cost of the cooler, makes it lighter, and allows more room for heat-insulating material.
When at home or hotel, the cooler can be powered from your phone's regular plug-in charger. When in the car, it can be plugged into a cigarette lighter adapter.
Electric consumption is between 0.2Amps up to 1.0Amps. This means at 5 to 20 hours using a 5000mAh battery. For longer journeys, use a 20000mAh battery and get 20 to 80 hours of cooling. Cool-ins' low consumption also means that it is compatible with practically all smartphone chargers.
The cooler is extremely simple to operate: just plug the power and it will then work to reach and maintain a safe 22 degrees Celsius inside (72 Fahrenheit). Unplug it and it stops. That's all!
A LED flashes at different rate depending how hard the Thermoelectric cell is working - and therefore how much power it is using. Typically, the LED will be fully on when the power is first applied. Once the target temperature is reached, depending how warm the outside temperature is, the flashing will slow down as less energy is required to only keep it cool.
A button makes it possible to select different cooling settings.
The cooler is capable of reaching an internal temperature up to 15 oC (project's target) colder than the ambient air temperature. If the ambient air temperature is above 37 oC (99 Fahrenheit), the cooling element will not be able to keep the interior at 22 oC. Internal temperature will be allowed to rise by one degree for every extra degree outside.
Ready for Production
After many months of development and tests, Cool-ins is fully functional and ready for production.
First article has been fabricated using black plastic and neoprene. White/light-grey will be used for production.
The Styrofoam core's shape and dimension has been optimized to maximize insulation. Its insulation characteristics have been verified using actual Styrofoam material.
Neoprene sleeve with zipper has been designed, fabricated and verified to fit. When in production, the color will be changed to light gray to reflect heat and improve thermal characteristics.
A plastic holder for the fan and thermoelectric controller has been verified to fit the core.
The thermoelectric electronics controller has been designed, assembled and verified to work. Temperature is measured with 0.1 degrees resolution. Fan speed and Cell power can be adjusted with precision.
The microcomputer's software effectively controls the cooling element and fan in order to cool and maintain a desired temperature.
All these elements have been assembled into a working cooler that was put to test.
Tests of the final assembly have shown that the internal temperature can be nearly 14 degrees colder than the ambient temperature. This number is expected to be improved in the production version as the various component will be built with higher quality and tighter dimensional tolerances. The project's objective is to achieve 15 oC - or better - difference with the ambient temperature.
The above video shows the coller prototype in operation.
Production Plan & Schedule
The cooler design is final and it is ready for production. Going into production requires significant investment in tooling.
- A mold must be fabricated for the 3 parts making the Styrofoam core
- A mold must be fabricated for the 2 parts forming the plastic fan/TEC holder
Funding objectives have been determined primarily to cover these tooling costs, plus the procurement costs for the electronics components for the Thermoelectric Controller, the neoprene sleeve and other miscellaneous parts.
Project is scheduled to take 10 weeks from successful funding to shipping. Deliveries may be expected the first week of July 2019. We will do our best to meet or beat this schedule
Risks and challenges
Molded parts fabrication are the highest risk components as molds rarely get perfectly right the first time around. We expect a couple of iterations to be needed, so we have scheduled 8 weeks for mold fabrication, and another 3 weeks for parts delivery.
Thanks to 3D CAD and 3D printing verification, all Styrofoam and plastic parts dimensions have been verified to fit perfectly together. The Thermoelectric Controller is functional and PCB is ready for volume production. Delays or complications are possible but considered very unlikelyLearn about accountability on Kickstarter
- (45 days)