DIY thermal differential controller (solar hot water pump controller)

[Daox]

In anticipation of using a solar hot water system, I am working to design a DIY thermal differential controller. The main reason behind this is that it is a simple device that costs $130+ for a commercial controller. I know I can make one for less than half that price. Plus, if I put together good documentation others should be able to easily construct them as well.

So, what is a thermal differential controller anyway? A thermal differential controller is what is used to control the pump between the solar panel and hot water tank. It senses when the solar panel is hotter than the tank and starts up the pump so that the water can go get warmed up. When the panel cools off, the controller then turns the pump back off so it doesn't cool down the tank. Sounds pretty simple doesn't it? Well, it is and thats why I don't want to pay $130 for one!

The setup is pretty simple. You have a micro controller and two sensors. One sensor goes in the panel and ones goes in the tank. You also need a relay of some sort to switch your pump on and off.


For the micro controller, I am going to use an arduino. It is very popular micro controller and is more than capable of handling this small task. I'm also some what familiar with using it.

The sensors will be 10k thermistors. These are what are commonly used on the commercial controllers. This makes for quick and easy replacement should the user choose to go that way. The other option is making your own sensors which will save a fair bit of money. This is the route I will pursue.