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Solar Panel and 12V Deep Cycle Battery advice

john2k

Jun 13, 2012
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Jun 13, 2012
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I have a 12v 100Ah deep cycle battery which will be connected to a 10A 12V Photocell Switch that will power about 10x 1w LED lights in the garden at night. To keep the batteries topped up I have a small limited space on top of a pergola that I want to place 2x 20W monocrystalline solar panels. The reason I want to place 2x 20W instead of 1x 40W is because of space. I am thinking to get a 20W charge controller. The question is, do I link the negative cables from both panels together and the positive together and then go into the charge controller as 1 cable? or do I run cables from both panels straight to the charge controller and then join them in parallel at the solar charge controller?
 

ramussons

Jun 10, 2014
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I think it would not make any difference as long as the cables used can handle the currents.
 

Colin Mitchell

Aug 31, 2014
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You are using 80 watt-hrs per night.
One panel will produce 20 x 5 = 100 watt-hrs per day.
Just use 1 panel and connect it directly to the battery via a 3 amp diode. Nothing else is required.
 

john2k

Jun 13, 2012
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You are using 80 watt-hrs per night.
One panel will produce 20 x 5 = 100 watt-hrs per day.
Just use 1 panel and connect it directly to the battery via a 3 amp diode. Nothing else is required.

Thanks for your reply. I already have two 20w panels. And seeing as in winter months we don't get much sunshine and the nights are longer it means the led lights will run for longer. So by having 2 panels I assumed it would be a safer option. And having the panels wired to a charge controller will at least deal with any excess power. Will this be ok?

I haven't bought the cable to go from the panels to the charge controller yet. But as the two panels are next to each other I want to join the two panels together (black to black and red to red) using a weatherproof junction box and then take a single pair of black and red cable to the charge controller. Question is, Do I need to put some sort of signal diode at the end of each panel before it gets combined with the other panel to prevent each panel from sending current back to the other panel?
 

Mouthpear

Jul 20, 2020
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Thanks for your reply. I already have two 20w panels. And seeing as in winter months we don't get much sunshine and the nights are longer it means the led lights will run for longer. So by having 2 panels I assumed it would be a safer option. And having the panels wired to a charge controller will at least deal with any excess power. Will this be ok?

I haven't bought the cable to go from the panels to the charge controller yet. But as the two panels are next to each other I want to join the two panels together (black to black and red to red) using a weatherproof junction box and then take a single pair of black and red cable to the charge controller. Question is, Do I need to put some sort of signal diode at the end of each panel before it gets combined with the other panel to prevent each panel from sending current back to the other panel?
I will try and find a link to this info and post if still interested.

When combining multiple solar panels (depending on voltage required) you will run them in parallel. The way you described.

You will be smart to add diodes at each panel. When panels start to go bad or even output differs percentage wize the lower ouput/bad panel will actually start to draw power from the other panels. Then they tent to damage those good panels and even burn up catch fire.

Buy a good set of crimping solar connectors so you don't have to put in box. They sell Y connectors for splitting/combining.

For every four panels go up a gauge. If the panels have 18 AWG go to 16 AWG. DC current travels on the outside surface of conductors/strands of wire. So larger gauge more strands = more surface for current to flow easier.

Do NOT use solid core wire. Aka house wire. It is good for AC current because AC current travels through the center. Bad for DC.
 

Bluejets

Oct 5, 2014
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Do NOT use solid core wire. Aka house wire. It is good for AC current because AC current travels through the center. Bad for DC.
hehehe...yeah, right.
Back to front to begiin with but................

Think you are getting confused with the skin effect on AC at high frequencies.
@50/60hz no different.
 
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