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In this video I'll show how I built a miniature battery-powered (and portable) air conditioner. This uses an actual vapor-compression cycle and *not* a solid-state thermoelectric (peltier) cooler. You could do this with a sine wave inverter and a battery connected to a regular A/C unit, but this one actually uses a compressor with a brushless motor that's designed for use in a DC circuit with battery/solar power.
The refrigerant loop is brazed together with 1/4" (6.35mm) copper tubing, and the condenser and evaporator coils are sourced from tabletop icemakers (which I have a bunch of that I got for cheap from a surplus sale). The box enclosure consists of 3d-printed ABS plates that screw together at right-angles with tab blocks threaded for #6-32 machine screws.
The power supply is a pair of 4-cell LiPo batteries in series, providing a nominal voltage of 32V. The compressor is usable for up to 48V, but the brushless motor speed controller (ESC) was limited to 36V. The top face has a power meter that shows battery voltage / current draw so you can turn off the unit when the battery voltage goes too low, and unlike an induction motor based compressor, this one is variable speed, which allows the refrigerant flow rate to be changed without the use of an expansion valve.
The compressor is designed to use R134A as refrigerant (6.7 bar B/P @ 25C), but I was planning to use Butane (R600, 2.5 bar B/P @ 25C) as a refrigerant since i figured it would be running below the rated power. But due to a problem with my Butane order, I ended up just using Propane (R290, 9.5 bar B/P @ 25C) as the refrigerant instead, as I've done in many of my other cooling projects. I was worried that this might overload the compressor, but it managed to run just fine, even at 32V.
The best use of this A/C unit is to point it directly at your face, since it's not likely to be able to have much effect on the temperature of a large room. It feels pretty similar to a car's air conditioning with the fan running on a low-medium setting. Despite the relatively small power, I was happy enough with the results that I want to do another micro DC-power cooling project, and I think I'll do the next one with solar power for chilling water.
A few stats on the machine:
Operating Voltage: 32V
Battery Capacity: 70.4 W-hr
Typical Power Draw: 42W
Coefficient Of Performance (COP): ~1.0
Refrigerant: Propane (R290)
Refrigerant Mass: ~10g
Lowest Evaporator Temperature (Unloaded): -6.7C
Evaporator Temperature (Fan Running): -12.6C (23.8C ambient)
Condenser Temperature: 38.8C (23.8C ambient)
Total Weight: 3.15 kg
Music Used:
Kevin MacLeod - Groove Groove