how would I determine the power output of an unknown solar panel ? if i just measure the voltage its going to be higher than normal but when measuring current the voltage will drop to nout !

so what do I do ?

one clue may be that I can count the number of "junctions" in the panel or cells

__________________
I AM the exeption that disproves the rule in many ways but the rules still apply (unfortunately)

my site:www.simons-photography.com
http://rushdenrotaract.org.uk

 

hi,
If its a 12V panel, do you have a 120R 2Watt resistor [ thats 100mA]

or a 12V cycle lamp, say 3Watt, thats about 250mA.

Problem today is the lack of Sun.

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

 

yes on this particular day sun is hard to come by well i have many resistors I'm assuming I'm dealing with 6 V panels

__________________
I AM the exeption that disproves the rule in many ways but the rules still apply (unfortunately)

my site:www.simons-photography.com
http://rushdenrotaract.org.uk

 

hi,
It should be easy to see if its a 6V or 12V nominal panel.

Choose a resistor that will pass about 100mA for starters and measure the output voltage at the same time.

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

 

ok I'll do that I have 2 panels with 15 strips/junctions rated at 7 volts and these have 10 junctions so i presume I'm looking at about 5 volts and I think the output is approximately 100 mA I'll give them all a go when the sun comes out

__________________
I AM the exeption that disproves the rule in many ways but the rules still apply (unfortunately)

my site:www.simons-photography.com
http://rushdenrotaract.org.uk

 

A quick test would be a tungsten table lamp, you might wait a long time for some Sun today.

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

 

Corrected.

__________________
I also post at the following sites:
http://www.stop-microsoft.org http://www.heated-debates.com
Screen name: Aloone_Jonez
And http://www.silicontronics.com, same screen name as here.

 

But bear in mind the output from a solar panel under those circumstances is only a tiny fraction of what you get from the sun.

Do you remember the robot school olympics programme that used to be on TV?, and how massive the lights were for the solar car event.

__________________
PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk

 

hi,
I was suggesting a way on how to determine if they are 6V or 12V panels, the OP isnt sure.
Of course I agree, ref the high intensity of artificial light versus current output.

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

 

well eric its more of a case that they are "custom" panels they come from equipment like i said one is probably 6 volts but the other compared to that must be 5 ! :-(

__________________
I AM the exeption that disproves the rule in many ways but the rules still apply (unfortunately)

my site:www.simons-photography.com
http://rushdenrotaract.org.uk

 

corrected again we are having some sun here (just a bit don't blink or you will miss it)

__________________
I AM the exeption that disproves the rule in many ways but the rules still apply (unfortunately)

my site:www.simons-photography.com
http://rushdenrotaract.org.uk

 

". . . determine the power output. . ."

You measure the open circuit panel voltage and call it Voc.
You put a load resistor, Rload, onto the panel with a resistance low enough to drop the voltage 10% to 50%, and you measure the voltage, Vload, across the resistor.

Then, Iload = Vload/Rload.
Then, the internal cell resistance, Rint, = (Voc-Vload)/Iload.
Then, the maximum power obtainable from the cell is achieved when it is loaded down by a load resistor of value equal to Rint.

(Voc and Rint equals the Thevenin equivalent voltage & Thevenin equivalent resistance).

If the panel doesn't mind being shorted, just measure the Voc and short circuit current Isc, then Rint = Voc/Isc.

Rint will probably vary with incident sunlight intensity; for sure Voc will.

 

well then Rint is 87.5 ohms for the smaller panels and 115 for the slightly bigger ones but I'm not sure i can calculate Rint as Voc/Isc I think I'd best go the longer way round

thanks for the calculations

__________________
I AM the exeption that disproves the rule in many ways but the rules still apply (unfortunately)

my site:www.simons-photography.com
http://rushdenrotaract.org.uk

 

So with Voc = 6v and a 100 Ω load resistor you'd get (3^2)/100 = 90 mW, enough to power an LED.

 

well at least I can its accomplishing something

__________________
I AM the exeption that disproves the rule in many ways but the rules still apply (unfortunately)

my site:www.simons-photography.com
http://rushdenrotaract.org.uk