devonsc

I've already obtained a set of readings of voltage and current by using different value resistors to plot the IV characteristic graph. The readings are as shown in the following:

V (open circuit) = 20.3V and I (short circuit) = 80mA

Using 51ohm: 0.63V, 14.54mA
Using 220ohm: 2.82V, 14.10mA
Using 330ohm: 4.25V, 13.65mA
Using 560ohm: 7.04V, 12.59mA
Using 680ohm: 7.98V, 11.98mA
Using 1kohm: 11.32V, 11.53mA
Using 2.2kohm: 17.20V, 7.79mA
Using 4.7kohm: 18.70V, 4.01mA

I don't quite understand what you mean by the optimum value of resistance that gives a maximum output power. Through the P=IV, I obtain the power of only 133mW using the 2.2kohm. Does this mean that this is the maximum output power? ops: Then, what does the 1.6W mean? ops:

I get what you mean, I'll perform this test as soon as the sun rise [/quote]

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devonsc

Just to make sure that I will be doing the right thng when the sun rise later.

Is this how I'm suppose to connnect it?

=> Solar panel (positive) to the diode (positive) to avoid reverse current?
=> Diode (negative) to the battery (positive)
=> Battery (negative) to the solar panel (negative)

Sorry to put this in point form as I do not know how to come out with a diagram which can be viewed directly without downloading. ops:

ops: Hopefully this is right.

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williB

good graphing program..

http://nces.ed.gov/nceskids/graphing/line.asp

Nigel Goodwin

That's exactly what I wanted you to do and it's something you can use in the write up of your project - good marks for things like that!.

It looks like the maximum power is about 133mW into a 2K2 load, using it to charge a 12V battery should be pretty close to optimum, and give about 10mA charging current.

The 1.6W I mentioned was just multiplying the open circuit voltage and short circuit current, the reason being that the maximum power was going to be less than that - considerably so.

You notice how puny the power output is?, that's why I've been going on at you all this time - no point messing about with DC/DC converters if you don't have enough power to start with!.

BTW, I've never played with solar panels, but I've always fancied getting one to experiment with - but I've always been aware of how large a panel you need for any reasonable output.

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Nigel Goodwin

Wrong way! - at least as I understand positive and negative of a diode!.

Positive of solar panel to anode of diode, cathode of diode to positive of battery - the cathode is the end with the stripe.

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

devonsc

Thanks for a quick reply

Real sorry for my nonsense about the connection ops:

As attached is a simple diagram, just to reconfirm. Is the diagram what you mean? Does it mean that I leave both cathode of the battery and cathode of the solar panel hanging? Need not connect to anything? ops:

Errr... ops: Got the feeling that I'm going to get scolding from u for asking this....sorry

Attached Files

anode.doc (19.5 KB, 15 views)

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Nigel Goodwin

Oops! - no diagram!.

I think you already know the answer! - the negatives of the battery and panel obviously need connecting together :lol:

And I don't 'scold' people! - I might break an occasional arm or leg, but never 'scold'!.

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

williB

there is an annoying problem with the graphing site..
once you put all your data in and create the graph..
thats it..
a BACK click on your broser wipes out your data..

devonsc

Hi there, whaow! you were fast in checking my replies, sorry about that diagram, I forgotten and posted one later on. But I guess thats a wrong one..heres another to reconfirm the connection. ops:

Thanks

Attached Files

corrected_diagram.doc (19.5 KB, 32 views)

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williB

deavon ... i am not seeing your diagram..

devonsc

The diagram is there now...the latest diagram is the one entitled : corrected diagram

Do you manage to download it? Need advice, any problem again with the connection?

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williB

all i see is text

..

devonsc

Wilib? It's suppose to be a simple block diagram that shows the connection on how am i suppose to check out the charging current.

Is the block diagram right?

Well, I will post the result in here right after I managed to find out the answer later. Thanks again.

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williB

if you do this it should work ...
have your graph on the screen..
do a ctrl print screen..
go to MS paint
select your picture with the dotted box just below edit..
then go to edit select cut..
go to file select new.. then ' NO'
back to edit select paste
back to file select save as...
select Jpg and add a file name..
now you have your file saved..be sure you know where you saved it to or else you'll never find it again..
go back to the electo tech forums click add attachment
click browse.. click on your file click preview
click submit..

Attached Images

untitled_967.jpg (26.0 KB, 377 views)

devonsc

The simple block diagram, showing the connection to check the charging current

Thanks...

Attached Images

untitled_645.jpg (17.6 KB, 363 views)

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