I'm wanting to monitor the power consumption of my Fridge (and Freezer) on a boat where the voltage runs from 12-15.6vDC
The Thermostat is an Inkbird(from Amazon) that closes a relay when the compressor needs to come on. This alerts the Compressor controller to turn on the compressor. This controller also activates a small computer type fan to blow air over the coils. I'm wanting to capture the time period the unit is running so I can track the power consumption. There are several factors that can cause the consumption to go up.
- Door gets left slightly ajar
- Frost builds up over time
- Compressor leaks Freon
- Exterior Temperature changes.
Rather than rely on a meat computer (me) to track these things I want to post them to a raspberry pi which will track them over time and alert me when things go off the rails. To do that I need to know when the unit is running and I need to do it with very low power consumption (because I'm living on batteries and sunlight).
There is a single Voltage ADC on the Arduino that will measure the voltage between 0 and the supply voltage. I could do some type of voltage divider and look for something there using the fan connections which are only powered when the compressor is on, but that means I need 2 Arduinos. Is there some simpler mechanism for detecting the thermostat has closed the relay? Maybe something that does i2c so I can deal with everything in a single unit. Would be even better if I could feed that back directly to the raspberry pi, relying on the fan voltage to activate the device so it is only consuming power while the compressor is running.
The things I want to do is have the rPI watch the runtimes and alert me if the consumption rises over several days, or if the unit is on continuously for longer than expected; I also want to be able to send alarms onto the navigation bus, and an audible alarm when there is something I need to look at. But that is just software. I need the sensing to drive that. What is a super simple, low power way to deal with that?
The rPi is already being used for other things (navigation, wifi, media player, etc....)