Aug 162022

TL;DR I recently acquired a very rare Coleman Free Piston Sterling Cooler that I’ve been looking for since hurricane Katrina.

For some reason I’m too lazy to take pictures and it is just a greyish rectangle so here’s a link to a more interesting teardown

So this quest began when I experienced a month without electricity in the deep south after hurricane Katrina. I was spared any property damage because I didn’t own any but ever since then I’ve thought a lot about what you can provide for yourself when access to normal distribution chains is limited.

I learned I don’t really need much in terms of power. At the time a 1st gen iPod was my only entertainment and I had plenty of books on tape. I didn’t actually miss hot showers as much as I’d have expected and there are a thousand ways to boil water for cooking. But my key takeaway from that time was how much a bag of ice can make you feel like a civilized human being for a few hours, so that became a bit of a mission- to figure out the simplest, most efficient and reliable method of making ‘offgrid’ ice.

That mission led me to ‘study’ compression, evaporative, vortex tubes, peltier, sterling, ad\absorption, and magnetic refrigeration. I think I’m at least aware of every cooling technology humans have documented, though only conceptually- I’ve never had to test my understanding by designing or calculating anything so I’m a dilettante of refrigeration technology at best.

When it came to finding something I could actually buy and use I had trouble matching my spending power to the capabilities I wanted. There were RV (absorption refrigerators) that seemed a possible solution, but they were way out of my price range and I don’t like that they contain ammonia. I actually bought a used vortex tube and tried it on a compressor at work but it was too loud and pretty inefficient considering powering a compressor. Though I have wondered if I ever lived by a little waterfall if I could use a trompe for unlimited cooling. Thermoelectric is kind of a joke in terms of performance. Evaporative coolers don’t really work in the humidity I live in and direct evaporation can’t make ice. They did have compression cycle camping coolers at the time but they were pretty expensive too and had mixed reviews on reliability. I will say since then compression mini-coolers have gotten way more reliable and cheaper and I did buy one and was relatively satisfied, but lets get back to the grail quest.

The consumer product that stood out to me was the Coleman Free Piston Sterling Cooler. I won’t gush over it here because if you know you know and if you don’t I don’t want to make you sad you can’t have one. Unfortunately by the time I learned they existed they weren’t produced anymore and nobody was selling their for anything near my price range.

I looked into other FPS coolers and found some that looked suspiciously like the Coleman, but were sold as medical freezers starting at a few thousand dollars. I haven’t really researched this but I imagine what happened is Coleman realized they couldn’t maximize profits by selling a consumer device that you could realistically expect to pass onto your grandkids. So the technology went to medical freezers where they could charge more per unit and the units would be beat up and need replacing more often. That’s just my theory.

Any case I couldn’t afford the medical ones and as time passed the few used ones I found were either for parts or too expensive. I’d pretty much given up by 2012 and semi-forgot about the whole thing, but something possessed me to make a post in Reddit’s /r/offgrid sub just taking a pulse on who was even aware of them. I think I got 4 replies at the time and then the post disappeared into obscurity.

Almost a full decade later some keen fellow in California was going through some cast-off gear and stumbled on a big camping cooler. To most people it would look like any other camping cooler from walmart, maybe ~$100 resale if it works. But it didn’t have a power cable so no way to test. In 99.9% of people’s hands it would have ended recycled or more likely a dumpster. But this keen fellow’s keen senses told him this was a rare item and deserved more attention so he took to the internet.

Somehow through he convolutions of Google search this keen fellow stumbled on my decade old post and made a comment on it. Still not sure how the post wasn’t archived, but I got the reply. We exchanged phone numbers and worked out the details. About a week later a big honking UPS package arrived containing a superficially worn, but seemingly perfectly functional Coleman FPSC. The exterior does look like it’s had a year or two in the sun and got scratched up a bit, but the filter looked so pristine I wonder if this thing was ever actually powered on.

I had to splice a power cable together but I had the connector nub so that was pretty easy. It started cooling immediately. I put a meter to it and it spikes to 60W on startup, then it settles in to between 10-40W depending on setting. The insulation is pretty hardcore and the exterior doesn’t even get cool on the lowest setting, unlike my compression cooler, which was so poorly insulated I build a secondary.

And that’s pretty much the story. I wanted one and somehow the universe put one in my path, thanks universe! And extra thanks to that keen fellow and all the keen fellows in the world that go the extra mile to keep useful stuff out of landfills.

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