To control my domestic solar hot water system, a custom controller was built using the Arduino Duemilanove. It reads temperature inputs from the tank and roof sensors to drive a relay that turns the circulator pump on and off. Temperature readings are sent via serial port to a laptop which records and graphs the temperature data. The graphs and data are sent wirelessly to a web server, that displays the current temperatures and status using a Google Gadget.
I designed, built, and installed the controller for around $100. Here is a brief description of how to build your own DSC. This is by no means an exhaustive, step-by-step guide, and you will require knowledge of electrical wiring, soldering, programming, Linux, web servers, and more.
Hardware
Files for building the DSC controller:
Using the links above, you can order all the parts you need to build your own DSC, assuming you can read a schematic and solder (some surface mount parts). In my system, this controller runs a 120V AC Grundfos UP26-99 circulator pump. Make sure the relay can handle the current needed to run your pump. [link to datasheet required]
The PCB is my design and can be used for non-commercial purposes, with no warranty. It’s the same board design I am currently using to run my solar hot water system. BatchPCB provides low-cost, small run, well made printed circuit boards. The link above should allow you to place your own order directly without any middlemen (ie. Me). I’ve used BatchPCB for many projects and have always been happy with the results.
The parts list has Digkey part numbers to all the components I used to populate the PCB. If you notice Digikey no longer stocks a part, or you’re wondering about compatibility with other part numbers, please let me know. Digikey has a reasonable shipping and handling fee, considering that you can place an order at noon today and have the parts on your desk by noon tomorrow.
Because this circuit uses 12VDC and 120V AC, ensure you mount the controller in an appropriate enclosure and take all the usual precautions when dealing with electricity.
Temperature Sensors
A single strand of Cat5 cable forms a bus for a network of Dallas DS1820+ 1-wire temperature sensors (datasheet). The Cat5 cable is run from the controller, past the heat exchanger (for input, output, and tank sensors) and cold water inputs, then up onto the roof and into the temperature sensor well inside the solar collector. Temperature sensors can be added anywhere along the bus using telephone 3-Wire Butt Splice (blue) connectors. Be sure to crimp them tightly so that all the wires make solid contact.
- Blue = DQ (pin 2)
- Blue/White = GND (pin 1)
- Orange = +5V (pin 3)
Solder a 6″ lead of the appropriate colour to each leg of the DS1820. Wrap leg #2 in 1/8″ heat-shrink, then wrap the entire device (all three legs and part of the semiconductor) in 1/4″ heat-shrink.
The temperature sensor can be mounted to a conductive surface (pipe, side of a tank, etc.) using 3M Picture Hanging Strips, Exterior Mounting Tape, or plain old duct tape. They can also be inserted into metal knitting needles and sealed with epoxy to make probes.
Firmware
Built with the Arduino environment and the Dallas Temperature Control Library. Download the sketch.
Logging
The system can be monitored using the serial port output. I use a bash script called from a cron job to read the state and temperatures via tty and insert them into a round robin database to create useful graphs. The bash script also outputs an XML file, which is used as the data source for the Solar Hot Water Google Gadget. Get the gadget and view the system status here.
January 10th, 2010 | Tags: arduino, microcontroller, solar | Category: At Home | Comments (2)
