Powering monitoring stations

Estimating the capacity of batteries and solar panels necessary to provide continuous power to a remote monitoring station is basically an exercise in closing a charge budget for power system. Campbell manuals provide the equations necessary for these calculations, but you will be more likely to spot mistakes if you understand the underlying concepts of electrical power systems (4:34 min).

Power systems are split into the supply and the load sides of the circuit. For a remote monitoring system, the data logger and transducers are the load and the foundation of the supply is usually a battery (9:00 min).

A dimensional analysis reveals how power delivered to the load from the supply is related to the current, or the rate of demand for electrical charge from the battery (4:04 min).

Power systems are electrical circuits that have the capacity to deliver enough energy to do harm. Here are a few notes on safety around the potential for power supplies to ignite fires or disrupt the electrical function of the human body (5:17 min).

Rechargeable batteries will draw a current to renew their electrochemical potential when a voltage higher than they supply is provided. Voltage regulators are a key to being sure a safe recharging voltage is supplied, making sure the battery does not overheat due to drawing a current the exceeds its capacity (5:19 min).

The current drawn by a data logger and associated transducers is highly variable over time. The datalogger has active and quiescent modes of operation that differ greatly in their current draw and transducers that require meaningful amounts of power can add complexity to how the overall current draw of the load will vary over time. Let's explore the basics of how to break down this variation to determine the average current draw of a load, which is the critical information necessary to determine the capacity of the battery needed to drive the system for a given period of time (17:57 min).

To run a monitoring station continuously, a battery buffering the power needs of the system will eventually need to be recharged by another power source. For remote monitoring stations, that recharging power source is typically a solar panel. Here are the basics of determining the capacity of a solar panel necessary to maintain a continuous power source to a remote monitoring station (5:53 min).

CRBasic can be used to collect data about the timing of various current draws by transducers or the data logger. If you want to follow along with the example provided, you might want to have the following program ready in CRBasic.

If using a CR310, the ports are named specifically. When using PortSet, you may need to use "SW12V" as the port identifier instead of the number 9 on a CR850. Remember that right-clicking on a function and then an argument in CRBasic will show you the valid options available for that argument if it is a limited list of options.

Don't forget to be sure the SDI-12 address for your device is set properly for this code to work.

The timer functions provided in CRBasic provide a method to understand how long the data logger is in active mode and how long individual transducers may be drawing a current. Let's work through an example of programming a data logger to collect information about various current draws (26:27 min).

The following CRBasic program is the example created in the video.

If using a CR310, the ports are named specifically. When using PortSet, you may need to use "SW12V" as the port identifier instead of the number 9 on a CR850. Remember that right-clicking on a function and then an argument in CRBasic will show you the valid options available for that argument if it is a limited list of options.

Don't forget to be sure the SDI-12 address for your device is set properly for this code to work.

Click this link to download the MS PowerPoint file

Here is the most detailed information I can find from Campbell regarding power systems. My annotations are available if you download the PDF from the following embedded document.

Download the PDF file

Campbell scientific provides a video and associated spreadsheet for power calculations. I have not reviewed the details of this spreadsheet and I generally recommend you understanding the foundation of power system concepts necessary to recognize whether this spreadsheet is providing reasonable recommendations.

Link to the Campbell web page where the spreadsheet can be downloaded