Do I really need a resistor?
Im building a model house thats 1 ft high, and 1 ft. wide and 1 ft in length. Then im putting solar panels on the roof that are model size too. They are 3.6V photovoltaic solar panels.
What I was wondering was if I wanted to track how much energy the PV panels get, and I use a digital multi-meter, do I need a resistor that goes in the connection from the PV panels to the digital multimeter? I don't know if it is needed or not....
I'm an 8th grader doing a science project, so I don't really know much.. Please help =/
Thanks in advance =P
Yes. To measure the energy being collected the solar cells would have to be powering something. A resistor load is as good a choice as any.
I will assume your final voltage from the solar cells is the rated 3.6 volts. You could then connect a 10 ohm resistor across the solar cells output. But before you do that, take your multimeter and measure the actual resistance of the resistor. Lets say it measures 9.25 ohms.
Write that value down. 9,25 ohms.
Now with the resistor connected across the solar cells, switch your meter to measure DC volts. Measure the voltage across the resistor and write down the value you get. Let's say it is 3.42 volts.
Now you have enough information to calculate the energy of the solar cell.
First, from Ohm's law, we know that V = I*R, solve for I, which will give you I = V/R and for the numbers I assumed above, this would be
I = V/R = 3.42/9.25 = .37 amps
Also from Ohm's Law we know that P(power) = (I^2)*R, so for the numbers we are using that gives
P = (I^2)*R = ((.37)^2)*9.25 = (.137)*9.25 = 1.26 watts. Which is also 1.26 joules/sec
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That should do it
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Good luck. You may have to fool around a little with this. I have made several circuits and it always seems that a little changing here and there is often needed.
If you want to make the project a little more visually stimulating you can get a small motor or a small light and have the solar panels do something visual. My grandson and I built a little solar powered car and we had a lot of fun with that. The car would run when in the sun but when you made a shadow with you hand over the solar cell it would stop.
This is the one we made http://www.elexp.com/kit_cif1.htm
They have all kinds of little solar/electronic stuff
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