Today I tested the power supply section of the AirMobile board.
As you can read in this post, the feature of this board is that it is powered up by a Peltier cell, thus harvesting the wasted heat of a car radiator.
First of all, a note about the The step-up transformer turns ratio will determine how low the input voltage can be for the converter to start. Using a 1:100 ratio can yield start-up voltages as low as 20mV.
To make the test, I placed the hot face Peltier cell on a house radiator. I simulated the car movement by means of a fan that cools down the cool face of the cell itself.
Because the header pins is connected to the commanded 5V output, I pulled up the "5V-Enable" input pin of the LTC3108 circuit.
In video below the board being powered by the radiator heat can be seen.
During these first experiments, there are some aspects that needs further investigation:
- where is the high-frequency ripple on the Peltier cell's output from? It is present also when the cell has no load connected so it should not be due to an error in the board...
- when connected to the LTC3108 the cell's output voltage is constantly around 50 mV. Is it the LTC3108 that varies its input impedance to make the cell work with that specific output voltage? When tested with no load, the output of the Peltier cell is much higher than that..
- it would be very interesting to monitor the difference of temperature between the two surfaces of the Peltier cell
- It would be very interesting the measure the current that flows, but I don't have a multimeter that is enough precise
- It would be very interesting (may be later during this challenge) to compare the efficiency of different step-up transformers