Ohms Law Load Amp Resistance Change

[John1397]

I have a solar cell that is rated 3.6 amps .5 volts 1.8 watts when you take a ammeter it does put out 3.6 amps, but this is basically a dead short reading. What I want to know is these cells put out .5 volts using ohms law how much resistance is needed to have a voltage output of .3 volts so you can then measure how many amps are flowing?

I know you could do this with a pot, ammeter, and voltmeter connected to the solar cell then as you start turning up the resistance the voltage output will drop from .5 volts to .3 volts then you can see how many amps are flowing. but it seems that you should be able to figure this out using ohms law?

This is basically a two step problem first find resistance then amps. What I am working on is a solar panel that has 39 cells and when tested it does put out 3.6 amps and has 24 volts no load and what I want to know if this is connected to a battery and the voltage output drops to 12 volts how many amps are flowing at this point?

John

http://d1dtbvo20ouog7.cloudfront.net/s/help-0003.gif

 

[nsaspook]

This might help: http://www.ni.com/white-paper/7230/en

The vi curve is not linear and each type of cell requires "Characterization".
Most commercial panels supply this data. Example:http://files.sharpusa.com/Downloads/Solar/Products/sol_dow_NE80EJE.pdf

 

[John1397]

One could use a transformer as an example instead of a solar panel.

John

 

[nsaspook]

One could use a transformer as an example instead of a solar panel.

John

One could but why?

A typical power transformer within it's normal operational specifications can be very linear to changes in load, a semiconductor P-N junction solar cell operated at it's optimum power point is not.

 

[alphysicist]

Dear John,

Thank you for reaching out with your inquiry about Ohm's Law and load amp resistance change. As a scientist, it is always exciting to see individuals exploring and experimenting with scientific principles.

To answer your first question, it is important to understand the relationship between voltage, current (amps), and resistance as described by Ohm's Law: V = IR. In this equation, V represents voltage in volts, I represents current in amperes, and R represents resistance in ohms.

Based on the information you provided, the solar cell has a voltage output of 0.5 volts and a current output of 3.6 amps. Using Ohm's Law, we can calculate the resistance of the solar cell to be approximately 0.138 ohms (R = V/I = 0.5/3.6 = 0.138). This means that at the given voltage and current, the solar cell has a very low resistance, which is why you are getting a reading of a "dead short" when using an ammeter.

Now, if you want to decrease the voltage output to 0.3 volts, you can use Ohm's Law again to calculate the resistance needed. In this case, the resistance would need to be approximately 0.083 ohms (R = V/I = 0.3/3.6 = 0.083). By increasing the resistance, you are essentially limiting the flow of current, which results in a lower voltage output.

To answer your second question, we can use the same principle of Ohm's Law to calculate the current flow when the voltage output drops to 12 volts. In this case, the resistance of the solar panel would be approximately 3.33 ohms (R = V/I = 12/3.6 = 3.33). This means that at 12 volts, the solar panel would be producing a current of 3.6 amps.

I hope this helps in your experimentation with solar cells and understanding of Ohm's Law. Keep exploring and learning!

Best,