Tips for Extending Battery Life for Multiple Chamber Measurements

Researchers often want to set up the LI-8100 Analyzer and LI-8150 Multiplexer to collect Soil CO₂ Flux measurements over an extended period of time. When the LI-8100 Soil CO₂ Flux Analyzer is used in conjunction with the LI-8150 Multiplexer, several Long Term Chambers are in operation. While this system is designed to be used with AC Power, LI-COR realizes this is not always an available power source. To solve this problem, many researchers utilize a combination of Solar Panels and DC Batteries.

If the Power for the LI-8100/8150 system is already configured and there is an issue with instrument start up or battery life, then the following tips may be useful in determining a solution that might better suit the set-up of the System. These tips and solutions may help resolve power issues, extend the life of the batteries, and even allow collection of additional measurements.

If the issue is a start-up problem

This may include when the LI-8100 System operates normally most of the time, but has trouble re-starting. This may also include circumstances when the LI-8100 System indicates it is receiving Power (some LEDs illuminate, begins to start, etc), but then the System shuts down. For example, this may also occur after the System has been modified by the attachment of additional chambers.

When the System is initially powered, the LI-8100 and LI-8150 open up all the connected Soil Chambers in groups of four. First, Chambers connected to Ports 1-4 are opened, then Chambers connected to Ports 5-8 are opened, until all Chambers are open. If four Soil Chambers are connected to Ports 1-4, opening these will draw about 60 Amps from the battery. In comparison, if only two Soil Chambers are opened, this will draw about 47.5 Amps. It is also important that the incoming voltage level is at least 12 volts of DC power during this start-up period. This requirement is needed to open the Chambers, power the Heaters, and boot up the software. Power consumption is highest when all these operations are beginning. (Once the system has warmed-up, there is a significant decrease in power draw to maintain operations).

To help troubleshoot this issue, confirm the Input Voltage reaching the Multiplexer. A voltmeter can be used to do this. First, disconnect the 8150-706 DC Power Supply Cable from the LI-8150 Multiplexer. Measure the voltage from two of the pin-holes. This will indicate the power that is being received at the LI-8150 Multiplexer. There needs to be 12 volts DC available to start the System.

There are some power-saving techniques that can be used to help reduce the initial power draw during start-up. As mentioned above, the Soil Chambers are opened four at a time. The LI-8150 Multiplexer has four banks of chamber controllers inside it, each bank having the ability to control four ports (or Chambers). If the Soil Chambers can be spread out between banks, there will not be as much of a power draw during initial start-up.

Assume that there are four Chambers available. Connect two of the Chambers into the first bank (Ports 1-4). Connect the second two Chambers into the second bank (Ports 5-8). This way, only two of the four Chambers will initially be opened at the same time, rather than four. The LI-8100 software can be programmed to only monitor the Ports that are actually connected to Chambers.

If there is not enough voltage (from the readings described above) or the LI-8100 System still won't initialize after re-configuring the Chambers into different ports, then the solution might be to add an additional battery to provide the Amperage and Voltage to get the initial power going.

Here are some suggestions to extend the useful life of the battery to obtain more measurements

Consider adding an additional Solar panel or an additional battery. LI-COR recommends deep-cycle marine batteries which usually have large Amp-Hour ratings for longer measurement periods.

When using the LI-8100/8150 System with multiple long-term chambers, the System is programmed to cycle through the attached Chambers and then to repeat this measurement cycle after a specified length of time (for example, once an hour). In between measurement cycles, the pump may be continually running. Make sure the Turn off flow pump(s) between repeats box is checked in the LI-8100 Windows Interface Software or using the PDA. This can be found under the Chamber Configuration category, Repeat. This will program the LI-8100 System to shut down the pump in between measurement cycles and save battery power. It will also help eliminate the possibility of something being pulled into the Analyzer during periods of non-measurement.

Other Battery Tips for Multiple-Chamber Long-Term Measurements:

1. Recharge the batteries only once they are fully drained (or are below the required level to operate the LI-8100 System). This will help them reach their full capacity when they are recharged.
2. Shorten the duration of the measurement. Measurements typically shouldn't be longer than 2 or 2-1/2 minutes and setting the 'Observation Length' to a shorter time frame would preserve some battery power. However, make sure that measurements are not jeopardized by making them too short. This can be checked with a couple different methods. Use the LI-8100 File Viewer software to examine some previously collected data sets. On the “Regression Analysis” tab, the 'Stop' times can be changed by entering new times or by sliding the red “stop” bar to the left. There is also a “Guidance” tab that indicates how the timing of samples affects the measurement outcome. Examine how changing the time affects the Flux values (which are automatically re-calculated). The Flux values may stay the same up to a certain observation length. Experimentally, this could also be checked by simply shortening the measurements and observing whether the values are in the same range as when the duration is longer.
3. The Heater in the LI-8100 requires battery power. The Heater tries to maintain the Optical Bench Temperature at 51 degrees C (or 122 degrees F). If it is cool, the Heater is powered more frequently to maintain temperature. This may be more evident at night when ambient temperatures are cooler. The LI-8100 Analyzer Box can be further insulated so there is less heat loss to help minimize Heater use. However, users need to ensure that they do not over-insulate the LI-8100 by blocking ventilation, which may cause the Optical Path Temperature to rise over 50 C and thus overheat the Analyzer. This can be avoided by placing the LI-8100 in a shaded area to avoid direct sunlight or a reflective cover or sheeting can be placed over the LI-8100 to reduce direct sunlight during the day, yet hold in warmer air on clear, cool nights.