As a few of you are aware I have been working on a “green” satnogs station. By green I mean self-sustaining for energy. (Solar / Wind)
So far I have decided to think about this as sort of like a cubesat. As it has a power budget, max size (I am not making a huge thing), and thermal budget (Based on Battery thermal limits).
Firstly I looked at the current draw of my Raspberry Pi during observations and while idle. I found that it draws almost a full amp during observations sometimes more. I also found that just sitting doing nothing but checking in with the network it uses between 200mA and 400 mA. Based off these numbers I decided the based course of action would be to make a system to turn off the Pi when not needed. To keep track of observations and to show the Pi as online an ESP32 was programmed to check the job api and decide if the Pi needed to run.
Secondly I needed to find some form of energy storage. For this I looked online a different battery options. I found that LiFePO batteries were one of the more forgiving types of Lithium batteries. I selected 2 Headway 38120 batteries for my power storage. By connecting them in series with and using a 2S BMS board I will have a voltage supply that varies from 4.0v to about 7.2v with a capacity of 8Ah These batteries have a charging temperature range of -10C to 45C meaning during winter I will have to run a heater for them. It also has a dis-charge temperature of -20C to 65C.
Lastly I decided that I will have a separate arduino (ATmega328 chip on a custom board) running as my power management system. It will watch battery voltage and decide when to cut off the rest of the system and when to run the heaters / charge the battery. For example during winter it will disable charging if the temperature is to low but attempt to run the heater until some low voltage point were the whole system will just shutdown to protect itself with the power management system only waking up now and then to check if it can begin charging.
So far I have the ESP32 code finished and working. I also purchased the batteries and BMS board and also the arduino for the power management board.
I still have to figure out my power generation system and also the heaters. Additionally I still have to decide on the RF side of the whole system.
For power generation I was thinking of using a solar panel facing south and maybe using a vertical wind turbine under the system as part of its support structure.
Anyways I am open to suggestions and criticism.