FIGURE OUT MAX
CURRENT COMING FROM YOUR SOLAR PANEL:
Buy a 12 Volt DC
Solar Panel that comes
with a cigarette lighter plug that will plug into your
Powerpack. If your
12 Volt DC
Solar Panel has a Wattage
rating of 30 Watts, then you would use the power equation
Amps = Watts / Volts
to solve for the maximum amount of current you will expect
to see coming from your solar panel. For a 30 Watt 12V solar panel,
you would get Amps = 30W / 12V = 2.5 A
Read & understand the
manufacture's instructions for the solar panel regarding operating, installing,
Setup the the solar panel
outside in full day light adjusted so that it is facing the sun. Set the
Powerpack next to it.
If the power pack is too far away to reach the DVD and TV then run a 25' to 100'
extension cord from the battery
Powerpack to the
STUDENTS CALCULATE NET CURRENT DRAW FROM
BATTERY: Explain to the students that they must now subtract the Max Solar
panel current from the calculated current delivered by the 12V lead Acid battery
power pack from
lab 1 to get
the new current delivered by the 12Volt battery pack.
Using the example parameters explained
lab 1 we
assumed that DVD and TV will be drawing about 6.7 Amps of current from the 12
battery. Now assuming that you are using a 30W 12V
Solar Panel that can
deliver approx. 2.5A into the cigarette lighter plug of the powerpack, the
net current delivered by the battery will now be :
6.7 Amps -
2.5A = 4.2 Amps
students can recalculate battery duration to 50% depth of discharge looking at
the discharge characteristics graph below (Explained in
Using the example of needing 4.2Amps, we can assume that this falls just to the
left of the 3.6 mark shown below on the curve. That would correspond to a
100% discharge time of approximately 3 hours. Since we have agreed to only
go to 50% depth of discharge (Explained in
lab 1), the
final approximated discharge time is about 1.5 hours.
READ & UNDERSTAND THE SAFETY
INSTRUCTIONS FOR YOUR BATTERY POWERPACK.
Now get some good popcorn &
pizza and sit down to watch the movie while it is plugged into the
and solar panel.
GRAPH SOC ON THE WHITE BOARD: Stop the movie periodically to plot
depth of discharge versus Time on the white board.
Assuming your students have calculated it will take 1.5 hours to get to 50% depth
of discharge, then stop the movie at 30 minute intervals.
TO CALCULATE DEPTH OF DISCHARGE:
Do this by shutting down the TV and DVD and un plug the power cords from the
This is done on the
by first waiting 3 to 5 minutes for the battery to settle. Then
push the red button labeled "display function" and reading the charge status
that pops up telling you a percentage between 0% and 100%
which is what you call the S.O.C.
(State of charge). The depth of discharge is calculated by
subtracting the SOC from 100. So if you read a state of charge of 75%,
then your depth of discharge is 25%.
Have the students compare their graph data to that shown on the discharge
STUDENTS CALCULATE HOW MANY WATTS ARE NEEDED TO POWER THE TV AND DVD MOVIE
PLAYER WITH 100% 12V SOLAR ENERGY: Total power required to run
the DVD and TV was calculated in the first step of
So if 70 Watts is needed to run the TV and DVD player you solve for required
solar panel as follows:
1.15 (inverter efficiency factor) = 80.5 Watts total solar power
students would have to hook up 3 30W
Solar Panels to
produce enough power to run a TV & DVD movie player that runs off of 70 Watts of
There are three possible outcomes to this power energy
classroom student-run lab experiment:
The calculations made by the students where
accurate in predicting the amount of time it would take for the lead acid
Powerpack to reach a
50% depth of discharge. In this scenario students should celebrate!
It took longer for the
Powerpack to get to a
50% depth of discharge than the students predicted. In this case you
could explain that maybe the AC inverter used inside of the
Powerpack is more
efficient than first thought. Or that variability in the sealed lead
acid battery manufacturing process may have caused the 18 Amp Hour battery
to have a little more capacity than the manufacture's specifications.
Like 20 Amp Hours instead of 18 Amp Hours.
The calculations fell
short and the battery
it's 50% state of charge much earlier then predicted. If this happens
then bring up the fact that the sealed lead acid battery inside of the
possibly seen too many charge / discharge cycles which corresponds to the
life cycle characteristics
above. Or show them the Sealed Lead Acid Battery Shelf Life & Storage
chart below and explain that maybe the
Powerpack sat on the
shelf too long without float charged or cycled. long.
In order to show the students actual power
delivered by the solar panel, you can do some additional wiring and use the RS232 Serial Com Port
Pedal Power DC power monitor Watt Meter
with a computer to show students how many Volts, Amps, Watts, and Watt-Hours is