06/09/2016
For those of you interested in how the electrical and data systems on the Lightning Probe are managed, we have prepared a schematic diagram showing how the different modules are connected to one another:
Lightning Schematic
As you can see, the power required by the circuit boards and sensors varies depending on whether a particular sensor is on, off or in standby mode. Most of the sensors and the Arduino microprocessor boards consume small amounts of power, but there are a couple of greedy components that really ramp up the power demands. The MQ2 gas sensor, for example, uses 400mW of power to warm up the heater element that takes readings.
Providing this power is only half the battle. As you know from your science lessons, energy cannot be created or destroyed – it just moves around or changes form. In this case, the 400mW of electrical energy being used by the MQ2 sensor is turned into heat. At ground level, air currents take this heat away and move it around the atmosphere. Way up in the stratosphere, there is very little air so these convection currents are very weak. This means that components that are usually cooled by air may overheat unless we can move the heat energy away from them.
The other thing to consider is that at low temperatures, battery performance suffers drastically. Our power supply calculations are based on having a bank of 4 D Cell batteries connected in series to provide 11,000mWh of power capacity at 21C. At -20C the capacity of our battery bank may be half of what it is at room temperature – i.e. 5500mWh. With a peak power demand of 1100mW, this drop in capacity is significant – we may lose 5 hours of flight time if the batteries get to that temperature. Any lower and the batteries would stop working completely.
Ideally, we’d use the waste heat generated by the sensors and circuits to warm the battery, but with no air to move the heat around, we’re just left with conduction and radiation as ways to transfer heat to our batteries. We’re looking at using radiation from the sun to warm the batteries, using mineral oil as a convection medium, creating heating loops out of wire and using different materials to insulate the battery banks to keep them warm. It may also be possible to use the structure of the Lightning probe to transfer heat to the batteries. These are the problems we’re wrestling with at the moment.
