Summary
This is a modular demand response controller for household or commercial appliances that tend to consume a lot of power. The original goal was to intelligently control water heaters.
Water heaters tax the power grid heavily during peek times (morning and afternoon), when people are using the most hot water. These spikes in power consumption require power providers to plan ahead and preemptively start up temporary power plant that may not meet the typical efficiency and cleanliness standards.
Fortunately, water heaters store enough hot water for most normal household tasks, including taking a shower. Whether they turn on during your morning shower or not, makes no noticeable difference. Unfortunately, hot water heaters are controlled by mechanical switches that activate the water heaters when the internal water temperature drops below a certain point. This causes the heaters to activate during events like your shower in the morning, when it might not be necessary. If the water heater was to delay it’s activation to some random time during the middle of the day, we could alleviate this peak demand issue. This controller is designed to monitor the water heater vitals, observe it’s usage patterns, and intelligently control it’s activation.
Schematic and Board
The Controller
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The CTA2045 Adapter
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Simulation
This board required some custom analog design. I simulated some of the more complex circuits in LTspice. The circuits and simulation are shown on the GitHub Simulations Page.