Connecting up Solar panels

[barbados]

Hi All,

I have just acquired a homemade solar panel from a friend and require some assistance in its setup.

It is build using 3V 0.750A solar panels which have been connected up in groups of 5 to produce 15V 0.750A mini panels.

I have three of these mini panels which i would like to connect up in parallel to produce a larger 15V 2.25A panel.

My question is do i have to put a diode on each of the three mini panels before connecting them up or can i connect the three panels and the connect a single diode to it.

Your advise is much appreciated.

Many thanks

Andre

[ghurd]

One diode is enough.

The 15V is open circuit voltage?

There are 6 cells in each 3V panel?

If so, it would be a good idea to use a Schottky diode.

G-

[barbados]

Hi Ghrud,

Yes six cells were used in each of the panels, with five of these panels making up a sub panel ( 15v 0.75A) and  three sub-panels in parallel being used to make the final panel( 15v 2.25) .

My concern is that if each panel is not pushing out the same exact current that one panel producing more current could possibly damage one of the other panels.

Your thoughts are appreciated.

Thanks

Andre

[kurt]

they will be fine with just 1 diode but you are very low on open volts for 12v charging commercial panels have an open voltage around 21 volts at room temperature in full sun for 12v charging that is why ghurd suggested a Schottky diode because they have a low voltage drop so you will have more voltage to charge your batteries    

[hansmaas]

I have a diode at each panel, just in case one panel is giving out less than the others due to shade, damage, etc.

This to make sure that the less performing panel is not taking the energy from the other panels.

http://hansmaas.come2me.nl/

[ghurd]

Kurt is correct about the Schottky diode.

I figure the panels working voltage at about 14V, without a diode.  The diode voltage drop will make the panel barely able to charge a battery.

A Schottky diodes voltage drop is only a little bit less, but that little bit can make quite a difference when operating at the edge of works or does not work.

The concern about a higher operating current in one panel damaging another is unfounded.

Each sub-panel will supply what it can.  Even if one panel can not make any current at the time, nothing will go backwards through it.

For output, make sure no cell is shaded.  Shading one cell will drop the output of that sub-panel to near 0ma.  The shaded cells voltage is lost, and it uses voltage from other cells which are trying to force current through the shaded cell.

It will not cause damage, and current from the other 2 will not go backwards through it, but the output of that sub-panel goes to 0ma.

If this panel is for camping, I would be very tempted to not use a diode at all.

Connect the battery in the morning, disconnect the battery in the evening.

G-

[TomW]

G;

Good point on the diode not needed between individual arrays. It is a myth that seems to be encased in concrete. Although a myth the diode sellers would like to see continue, I suspect.

I ran my 300 watt, 12 volt array with no diode at all for years with no perceptible back flow at night from the batteries. I use one now to ensure the turbines I added do not put a high voltage into them in reverse. Beyond that I do not think it is necessary. Others likely disagree.

Tom

[ghurd]

TomW;

I can sell you some 1N4004s for a good price.

G-

[TomW]

Nyuck Nyuck.

I got a strip of them here but thanks anyway.

Tom

[barbados]

Hi Guys,

Thanks for your very informative comments, the panel is not for camping but rather for powering  small water pumps used in my ponds.

These pumps were originally rated at  12V 1.6 AMPOS but i have seen then work with as little as 3V 0.30 AMPS, my hope  is to provide a system to power them using solar energy.

I have some 6 V batteries and am thinking of using them as my battery source.

Thanks again for your kind assistance.

Andre

[ghurd]

Hi Andre,

A brushed pump will continue to use power after it has stopped turning.

Consider operating the pump with no battery or diode.

The solar panels directly to the pump.  Try it and see.

G-

[barbados]

Ghurd,

I see what you are saying but i would like to have a 24 hour system running especially at night when oxygen levels drop .

With the info i have gotten so far I will see now my 6v batteries run and  let you know.

I have also built a very interesting solar panel from old garden light I will post a pic tomorrow you may find it interesting.

Thanks again.

Andre