Experiment 1

DC-DC converter experiment

To know the work of a DC-DC converter and batteries, a experiment like following is taken place.

• DC-DC converter spec on catalogue
  • input 4.5-16V
  • output 5V
  • efficiency 74%
• Resistance 1000 ohm(fixed) to consume 25mW
• Batteries 5 AAA cell prime batteries in series, which are 7.5V output.

fig1 batteries , DC-DC converter and resister

Put the voltage across the load to a pen plotter, and recorded it.

fig2 Experiment appearance
 

fig3 plotter record

Fig3 is the last part of the record. Vertical axis is the voltage across the load ,the scale is 2V/cm Horizontal axis is time ,the scale is 1mm/min

• The time at point A is 1507min
• B is 1524min
• C is 1715min

The time in which batteries correctly worked is 1507min (25hr 7min). So the energy provided by batteries is calculated.

    5 mA x 25.1 hr = 125.5 mA hr 

                or

    5 mW x 25.1 hr = 625.5 mW hr 

Due to the information from Panasonic , the AAA alkali primary cell's spec is

• When current is 2-3 mA , then AH rating is 1200 mAHr (Until voltage drops to 0.9V)
• When current is 500 mA , then AH rating is 600 mAHr

From the result of the experiment, the resistance consume only 10% of the battery electrical capacity. Then see the behavior of the graph of the fig3. Between point A and B, the voltage alternates 5V and 0V in every minutes. The cause is guessed as

• When batteries goes below certain voltage
• The DC-DC converter stops providing power and batteries take a rest.
• Soon batteries recover enough then plotter shows 5V.
• Between B and C batteries can not recover to ,because lack of energy, enough level so they soon drop to 0V.
• After C, batteries can't recover to the level which the DCDC converter can work.

So to see weather the reason why the resistance consumes only 10% of energy is due to drop of batteries voltage, we made another test. This time we also measured batteries' voltage. The results are shown in figure4.

fig4 second DCDC exp.

Point A is the time when one cell's voltage became 0.9V, and the time is 22.1hr(1325min)
Point B is the time when output is the beginning of output became unstable, and the time is 25.2hr(1510min)
So the DCDC converter can be regarded as it ran out of the batteries and stopped. Its efficiency can be calculated as 9.2%.

Solar cell experiments

In our CanSat, solar cells has an important meaning. So we checked solar cells' character. At this time we checked whether a solar cell is charged with electricity when it is not generating power. Following is the experiment We have 2 solar cells. No1 cell is one cell. NO2 cell consists of 3 cells in series. First we cheked measured basic status.

fig5 Solar cell experiments 1-3

All the resistances are 50 ohm and light conditions are all the same.

The results are

fig6 Solar cell experiments 4,5

This time one cell is not lit up.All the resistances are 50 ohm and light conditions are the same when cell is lit. The results are

From the results of these experiments, it can be found out that solar cells does not generate electricity when some cells which are conneted in series are not lit.

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