Download Power Source Testing

La ACES Student Ballooning Course
Electronics Unit
Activity E5. Power Source Testing
Summary:
Students will investigate the performance of various battery chemistries at low temperature.
Materials:
This activity will be done by the team as a whole. The team should have available the following
materials, equipment, and supplies (*indicates supplied by LaACES):
1. HOBO data logger*
2. Two-cell battery holder* and selection of AA batteries - NiMH, alkaline, lithium
3. Components for resistive voltage divider*
4. Components for voltage input cable for HOBO*
5. 27 ohm load resistor*
6. Small insulated ice chest
7. About 10 ponds of dry ice
8. Small hookup wire and soldering tools
9. Multimeter
The laboratory should also be equipped with the following:
1. Flat work tables sufficient to seat all students with plenty of work space
2. Computer (PC) with BoxCar software installed (software supplied by La ACES)
Procedure:
1. A cable will have to be prepared to connect the battery pack to the HOBO data logger. In
addition, the battery pack voltage is too high to connect directly to the HOBO, so a resistive
voltage divider will have to be employed. Refer to the circuit diagram below. You could use
a small piece of perfboard to hold the parts, or just connect them with "flying leads." Use a
short (10 or 15 cm) piece of small diameter shielded cable to connect to the stereo plug that
will attach to the HOBO.
2. Prepare a "low temperature environmental chamber" by putting a few pounds of dry ice into
an ice chest. Be careful handling the dry ice. Gloves are a good idea. You can get frostbitten.
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Electronics Unit - Activity 5
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La ACES Student Ballooning Course
Electronics Unit
Activity E5. Power Source Testing
3. Program your HOBO to sample internal temperature and one channel of external voltage
input. Sampling every 5 or 10 seconds will be appropriate. Launch the HOBO data collection
process
4. Insert two AA cells (same type) into the battery holder and place the whole assembly of
batteries, resistors, and HOBO into a sealed container such as a Tupperware® or ZipLock®
freezer container.
5. Put the container in the ice chest with the dry ice and leave it for a half hour or so.
6. Remove the container and retrieve and save the recorded data from the HOBO.
7. Repeat the test process for other types of batteries.
8. Transfer HOBO data into Excel and plot graphs.
Expected Outcomes:
Students should discover which battery type is best able to maintain terminal voltage at low
temperatures. In addition, they will gain experience in programming and using the HOBO data
loggers.
Issues:
While just about any scheme can be used to build the test circuit, be sure that exposed
connections can't short circuit when stuffed into the freezer container. Plastic electrical tape can
help.
Before connecting the test circuit to the HOBO it would be a good idea to verify that the voltage
being presented to the HOBO doesn't exceed about 2.5 V. Before plugging the cable into the
HOBO, measure the voltage across R2 with a multimeter and verify that it's under 2.5 V.
References:
HOBO User's Manual (supplied with HOBO data logger)
Box Car User's Manual (supplied with HOBO data logger)
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