It started with a trip to Good Will, its basically where people donate things, and the store puts a usually fairly low price on them, so that they can cover operating costs, and still provide products to people who need them. While I was there, I found a little cooler that is meant to plug into a lighter socket in a car. I found this one for $3, and its basically a cooler with a Peltier cell, a heat sink, and a fan. If you arent familiar with Peltier cells, when you apply a voltage, one side gets hot and one side gets cold. As long as your pulling the heat away, the cold side will continue to get colder until around 40 degrees Fahrenheit below the ambient temperature. I figured this would be a great start. The issue with these, is they dont have any thermal control, therefore they run pretty much nonstop.
It was in perfect shape when I got it, minus the fan being seemingly underpowered. So I took the front off and replaced the weak 60mm fan with an 80mm computer fan. It seems to be helping quite a bit.
36 degrees Fahrenheit after running for about 20 minutes in about a 68 degree Fahrenheit room. Not bad, however it will continue to get colder, to the point that it would easily freeze liquids. This is also wasted power. So I had the idea to order one of these thermostat modules, it reads in Celsius, which to me is a bit of an inconvenience, but it was cheap! 7 dollars, shipped and all. In this picture I have it hooked up to my larger 12v Peltier fridge that is hooked up to my large battery bank.
I also apologize for the mess of hot glue
It makes mounting these kinds of things where you dont want to drill holes, very quick and easy.So, lets check price so far,
Small 12v Peltier fridge bought second-hand $3
80mm computer fan, Free, salvaged
Thermostat module $7
So far so good!
Now one issue with these fridges, is the insulation. So I've been testing some radiant heat shielding, which is basically bubble wrap with a thing mylar foil on either side. This will add some extra insulation, and more important, reflect sunlight away which would heat the surface of the cooler and cause it to warm up.
The top of the cooler/fridge also seemed to have fairly poor insulation, so I added some more radiant shielding on the inside
Just from the time I started writing this, its already gone down in temperature another 4f!
Now we want this to be super portable. I'm working on a Lithium Ion battery pack for this, but for the time being, I've got a 12ah SLA battery hooked up. This peltier cell draws about 3 amps. Thats 4 hours of run time off this battery, if it was running nonstop. With the improved insulation, and added thermostat, its only running at about 30% duty cycle. So the run time isnt the greatest, but can be easily increased by adding a bigger battery, or more in parallel.
Now I said something about solar didnt I? With a 3a peltier cell, we are only drawing about 36 watts. Thats not bad. A 50 watt solar panel can be had for about $80, and a 10 amp charge controller (excessive) can be had for 7-10. So we are already putting more power into the battery, than the fridge is using, so the only time the battery will be drained, is in cloudy conditions, or at night.
Lets run through costs one more time:
$3 for the fridge (Secondhand)
$7 for the thermostat
$0 for the fan (salvaged)
$0 for the radiant shielding (salvaged)
$10 for a 10a charge controller
$80 for a 50w solar panel
$30 for a 12ah battery
So right at $120 for a vaccine cooler, that is capable of being charged by solar, EASILY maintain a 60f temperature in up to 100f ambient, and is highly portable, not to mention it was made with mostly salvaged materials! If this doesnt fit the Without Borders Project, I dont know what does
