Herb and Barbara - our interests and family

Micro Energy System Upgrades—Rev 2.1

The current system is at revision level two (2.0) and with the addition of the temperature sensor, is now at 2.1.

Using  the Arduino micro-computer as the brains of the monitoring and charging system affords me the ability to easily upgrade the system and add new features without the need for tedious circuit board wiring. The addition of a temperature sensor took about 45 minutes to install (no I did not include the time to write the software) and now gives Marie the ability to check and record the temperature about two inches off the ground.

The sensor is an LM-35 from National Semiconductor and is a less than $2.00 part. It has a  linear output scale which makes it very easy to calibrate. (Linear + 10.0 mV/°C scale factor ) .


Translated—to calibrate the unit is software requires that you measure the output, using a DVM with a 300 millivolt scale, divide that number by 10 and you have the temperature in Celsius.


I mounted the sensor in a piece of PVC and connected it to the Arduino using shielded, twisted pair wire. This is very important as the a wire run of more then a few inches will generate noise that the A to D converter on the Arduino will interpret as a temperature swing.


I put a .01 uF cap across the output to ground on the sensor and an additional 25Mf cap as the connecting cable entered the box where the Arduino is located.

The turbine is again flying with a new prop mounting plate from Wind Stuff Now. The new mast is 1 inch pipe and will have the guy ropes replaced with cable as soon as we get the new anchors in place.


The garden is also growing nicely. The photograph to the left shows Swiss Chard and the irrigation tape.


Pumping water through this irrigation tape is what the Micro Renewable Energy System was designed to do. I installed radio telemetry and the Arduino micro-computer to collect information on wind and solar system performance in real world applications. With this system I am able to document how well improvements perform and demonstrate that it is not always necessary to spend a great deal of money to have a small working system.


One of the goals of the farm is help others who want to start small CSA farms. The renewable energy system is one of the ways to cut start up costs.

Update 5/28/09


We have added a third battery to the system as we expect to use the irrigation system more during the summer. The present battery capacity is 255 amp-hours. The pump draws about 4 amps and we, on a good day with wind, put between 5 and 7 amp-hours back into the batteries. With the additional capacity we can run the pump for 4 hours a day. This will give us about the equivalent of 2 inches of rain at the end of the row. We run the pump for about 30 to 40 minutes for every 4 or 5 rows of vegetables. This gives us the water we need to grow the plants with and does not run down the battery bank. For this summer we have about 1.5 acres under irrigation.




Update July, 19, 2009


The decision to add the third battery has proven to be a good one. Texas is famous for the hot summers and this one is no exception. We have had several weeks of 95 degree to 110 degree weather and the garden is suffering. Marie has had to run the pump much more then anticipated and consequently a battery problem has come to the forefront.


The batteries were recovered from oil field use and consequently never had a really good life. I use a PWM charger on them to bring them back to life but I always knew that some day the problem would reoccur unless I continued with PWM charging.


It is back and we have had to replace the original batteries with three new ones from my garage. The original batteries are now in the work shed being charged by my PWM charger. It has taken three days for the first one to recover so I suspect it will be a multi-day process to bring them back.


I have added a volt meter to keep track of the wind turbine output (this is a $4.99 car volt meter from Harbor Freight) but in truth it is just there to tell me that there is not enough wind to charge anything. During our summers it is often difficult to get enough wind to make use of the wind turbine. While the turbine does turn, the output is frequently far under the battery voltage so no charging happens.


In checking the current in from the solar panels, I showed Marie how important it was to clean the panels. The initial measurement of the panels showed about .5 to .6 amps from each of the three panels. After cleaning, we got 1.5 to 1.6 amps from each of them. This is a real life lesson in maintenance of a solar system and how even a light coating of dust can reduce the output.