Nt1310 Unit 4 Battery Current Lab

Table 3.1, located below, shows the battery voltage at the beginning of the lab.

Table 3.1: Battery Pack Functional Test

Measured (V) Expected

Initial Battery Voltage 9.540 9-10 VDC

The initial battery voltage was recorded as 9.540 volts, a number greater than 9.00 volts, indicating that the battery was almost fully charged.

Table 3.2, located below, shows the battery pack characterization. The table shows the voltage of the battery and the current through the battery as a function of time.

Table 3.2: Battery Pack Characterization

Minutes under charge Battery Voltage (V) Battery Current (A)

0 9.540 0.120

1 9.548 0.114

2 9.586 0.107

3 9.605 0.100

4 9.624 0.095

5 9.642 0.091

The above table shows that the current through the battery decreases

as a function of time, and the voltage across the battery increases as a function of time. The current decreasing as a function of time is expected because as the battery approaches the 10 volts that the DC power supply was set to, the voltage difference between the DC power supply and the battery decreases. Furthermore, the voltage increasing in the battery as a function of time is expected because the battery is charging.

Table 3.3, located below, shows the initial measurement of the thermistor and solar panel voltage.

Table 3.3: Solar Array Functional Test
Measured Expected
Thermistor resistance (cold) 12.118 k ~10 k
Solar panel voltage 10.500 V 1-10 VDC

The measured values in the above table are near the expected values, and therefore, the solar panel was functioning properly according to this test. It should be noted that the satellite used during this lab had only one solar panel, so there is no row indicating the voltage of the second solar panel. In addition, the absence of a second solar panel indicates why the solar panel voltage is slightly higher than the expected value. The expected value for table 3.3 was created expecting two solar panels providing voltage to two different spots. The satellite used to create this lab report had two solar panels providing voltage to the same spot. Therefore, the spot measured in this lab should have had a voltage between 2 – 20 volts rather than 1 – 10 volts—provided that the voltages from the two solar panels add linearly. Thus, the solar panel voltage measurement is acceptable despite the fact that it is slightly higher than the expected value.

Table 3.4, located below, shows the solar panel characterization. The voltage across and current through the load resistor were measured as a function of the load resistance placed in series with the solar panel. The bottom row of table 3.4 shows the resistance of the thermistor when the solar panels were heated up.

Table 3.4: Solar Array Characterization
Voltage (V)
Current (mA) Resistance ()
0 Isc = 5.00 mA n/a
Voc = 15.560 0 n/a
0.650 5.21 120
1.180 5.20 220
2.500 5.15 470
3.650 5.07 680
7.700 4.88 1500
15.14 0.15 100000
Thermistor resistance (hot) 9.060 k

The values in table 3.4, with the exception of the thermistor measurement, were used to create figure 3.1 and figure 3.2 in section 3.2 Plotted Data. The expectations for the data in table 3.4 are that the current will decrease as the load resistance increases and the voltage will increase as load resistance increases. The data trends displayed in table 3.4 follows the expected trends for current and voltage as the load resistance increases with the exception of the first value in the table. It is expected that the current would have its maximum value when the load resistance is zero ohms; however, the recorded value for the current when the resistance is zero is lower than two of the other data points. The unexpected value is most likely due to a bad measurement taken by the multimeter, or the actual value on the multimeter was recorded incorrectly during the lab.

Table 3.5, located below, shows the measured and expected values for various test points on the EPS module.

Table 3.5: EPS Module Functional Test
Measured (V) Expected
5 VCC test point voltage 4.96 4.9-5 VDC
3.3 VCC test point voltage 3.28 3.2-3.3 VDC
5 VCC bus voltage 4.96 4.9-5 VDC
3.3 VCC bus voltage 3.28 3.2-3.3 VDC

Comparing the measured values to the expected values in table 3.5 indicates that the EPS was functioning properly. All of the measured test points were within their expected values.

After collecting the data form table 3.5, the EPS module underwent the software functional test and passed.

Table 3.6, located below, shows the result of the EyasSAT GUI for different solar panel inputs. The board voltage (BV), board current (BI), solar panel voltage (SPV), and solar panel current (SPI), were recorded as a function of the solar panel input (SP Input). The first seven data points were gathered to characterize the BV, BI, SPV, and SPI as a function of the SP Input. The following six data points were gathered to characterize the BV, BI, SPV, and SPI as a function of time for a constant solar panel input. The first of these six data points was taken right as the DC power supply was increased to 10.2 volts, and the following five data points were taken at one minute intervals. The final data point was gathered at the voltage when BI became negative, and was used to characterize the BV, BI, SPV, and SPI values right as an eclipse was reached in the satellites orbit.

Table 3.6: Solar Panel Input Test
SP Input (VDC)
BV (VDC) BI (mA) SPV (VDC) SPI (mA)
4.99 9.0 -29.6 4.8 0
6.02 9.1 -29.6 5.8 0
7.01 9.1 -28.6 6.8 0
8.09 9.0 -29.6 7.9 0
9.08 9.0 -29.6 8.9 0
10.0 9.3 52.8 9.8 94.8
10.2 9.5 101.2 10.0 142.9
10.2 9.5 90.5 10.0 132.3
10.2 9.5 80.9 10.0 122.7
10.2 9.5 75.0 10.0 116.9
10.2 9.5 71.2 10.0 113.1
10.2 9.5 66.3 10.0 108.3
9.8 9.2 -20.9 9.6 4.4

The expected trends for the data in table 3.6 are as follows: as the SP Input increases the BV and the SPV will increase as well; as the SP Input increases above a certain point the BI will become positive, if the SP Input is kept at a voltage where the BI is initially positive for some time, the BI will stay positive but its magnitude will decrease with time; as the SP Input increases above a certain point the SPI will have a magnitude greater than zero; if the SP Input is kept at a voltage where the magnitude of the SPI input is greater than zero, the SPI will stay positive but its magnitude will decrease with time.

The data in table 3.6 follows these trends; therefore, the EPS board was functioning as

expected.

Table 3.7, located below, shows the BV, BI, SPV, and SPI as a function of the angle the solar panels made with the halogen lamp. The final data points shows the BV, BI, SPV, and SPI values when the lamp was turned off.

Table 3.7: Electrical Power Subsystem Integration Test
Angle
BV (V) BI (mA) SPV (VDC) SPI (mA)
45 deg 9.1 -26.7 9.5 0.6
Normal to one side 9.1 -29.6 9.4 0
Lamp off 9.1 -29.6 8.7 0

The expected trends for the data in table 3.7 are that the SPV and SPI will decrease when the EyasSAT module is turned from a 45 degree angle to an angle normal to one of the solar panels.

The SPV and SPI will further decrease when the lamp is turned off. The reasoning behind this trend is an angle of 45 degrees lets both solar panels receive light from the halogen lamp, so this data point will have the largest SPV and SPI measurement. Turning the EyasSAT module normal to one solar panel means that only one solar panel is receiving light so the SPV and SPI decrease. Turning off the halogen lamp means neither of the solar panels are receiving light so the SPV and SPI values decrease even further. The data in table 3.7 follow this expected trend, so the solar panels functioned as

expected.

Table 3.8, located below, shows the power budget of the EPS module calculated using the lamp off data point in table 3.7.

Table 3.8: EPS Power Budget
Module
BV
(VDC) BI
(mA)
(ignore - sign) Power (BIxBV)
(mW) Expected
(mW @ 10 VDC)
EPS 9.1 29.6 269 250-300

The data in table 3.8 shows that the EPS uses 269mW. 269mW is within the expected value of 250 – 300 mW; therefore, the EPS module is using an expected amount of power.