Monday, June 6, 2016

Solar water heater dashboard upgrade

 When I installed solar collectors for heating the hot water in my house back in 2006, I decided to add a small "dashboard" in the kitchen to monitor the temperatures.  Since I am an electrical engineer, I was able to cobble together a device that displays collector temperature, storage tank temperature, and a green light to indicate when the circulation pump is running.  A red LED indicates low antifreeze fluid in the collector overflow  tank.
Original solar dashboard

 There is more detailed information about the construction of this dashboard on this page of my website:
Basically, it uses digital volt meters with LM34 temperature probes that produce a voltage that directly correlates with temperature so that 78.1° is represented by .781 V.

 Over the years I have grown accustomed to looking at this dashboard to confirm that the system is working, and also to decide when to take a shower, run the dishwasher or clothes washing loads by looking at the storage tank temperature and seeing when it has peaked during the day.  The only drawback is the displays did not include a back light and sometimes were hard to read in the evening and nighttime.

I recently came across a new temperature meter designed for monitoring heat exchangers in high-end gaming computers. They are much more attractive, include a back light and use standard 10K thermistors as temperature sensors so I ordered a few to see if I could adapt them.
Temperature meter for heat exchangers
 These meters are available from MPJA (click the image above for details) and also on eBay for under five dollars.

When I received them, the first thing I did was cut off the computer power connectors and connected 5 VDC from a wall power supply to the red and black wires.
Removed computer power connector

 Then I cut off the temperature sensor and replaced it with a standard 10K thermistor that I sell as an accessory for the solar temperature controller products I manufacture (ART TEC Solar).
Original sensor above and standard 10K thermistor below
 I used an 8 conductor CAT-5 computer cable for the wire run down to my solar heating equipment in the basement.  I used two wires each for the sensors, and two wires each for the LED status monitors.

 I mounted the 2 meters in a standard plastic box and mounted it to the window frame above my kitchen sink in place of the original dashboard.  I find these meters much more attractive and they are easier to read day and night.
Updated solar dashboard
 Here is a larger view of the meter next to my kitchen window, right above the sink:
 I am quite pleased with the more contemporary styling of this new dashboard.