Introduction: Quad Heat Pump Peltier Cooler!
This diy electric cooler originally used a single 60watt, 12volt Peltier. It was very convenient for storing cold groceries and vegetables until I reached home. I however wanted a more efficient version. I achieved this by undervolting the Peltiers to 3v each to reduce waste heat.
Read on for how I made an improved Peltier cooler using 4 Peltiers wired in series. This new version has a higher coefficient of performance and uses only 15watts!
Step 1: The Multi Heat Pump Modules.
I have two heat pumps each having 2 Peltiers. I tested each Peltier at 1volt to ensure they were good. These pull 0.5amp at that test voltage. Only one Peltier from the box pulled less than that value so I couldn't use it in this project.
It is very important to test the Peltier prior to installing.
Step 2: Mounting the Heat Pumps.
Using the existing opening on the lid of my electric cooler, I fitted the two heat pumps and secured them. On the inside of the lid are the cold side heatsinks.
Step 3: Agitator Fan.
This tiny low powered fan is used to stir up the air inside the cooler to accelerate cooling. It uses less than 1 watt which is good since any higher will introduce too much waste heat.
Step 4: Cooling Fan.
I used an axial fan to blow ambient air over the hot side heatsinks.
Step 5: Insulation.
I used strips of foam to insulate the cold side heatsinks. I wanted no voids between those heatsinks and the lid.
Step 6: Temperature Sensor.
The digital thermometer on the lid takes measurements via this sensor I secured under the lid. Mind you, the temperature that will be read will be a worst case since warmer air stays near the top.
Step 7: Performance.
At 12 volts, the consumption is approximately 15watts. The lowest temperature achievable is 21C which is very good at an ambient of 29C. Peltier coolers cannot freeze such an empty void but if previously chilled food is placed in it, it will keep the food cold in hot weather.
As a little safety feature, I powered the cooler via 20 second delay ON timer relay so the car won't power this while it is trying to start.