Connecting up 2 Solar Panels at the Panel end

Have 2 x 80watt solar panels to install on the van roof. I realise that when connecting to dual batteries, the positive lead from the panels goes to one battery positive terminal and the negative lead from the panels goes to the other battery, then the batteries are parallel up. Similar setup for the load ie off the battery terminals from the panels.This provides equal charge and load to both batteries.

It is easier to just parallel the panels up on the roof, ie positive to positive etc then connect the panels to the terminal block on the roof and the cable to the batteries. However one panel (the furtherest away from the roof connection box will have and extra 1.5 m of cable(3m total) which will mean the one panel not only is driving the batteries its trying to charge the other panel by say .5v because of the 3m cable loss. (resistance.)

Should I be connecting the cable from the batteries to the positive of one panel and the negative of the other and then parallel them up, so will have 3 cables connecting the panels.

Or is the small loss not worth the effort of the 3 cable setup.

Comments appreciated.

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Reply By: ctaplin - Friday, Apr 17, 2009 at 15:27

Friday, Apr 17, 2009 at 15:27
You really need to use a solar regulator between the panels and the battery or you will boil of the electrolyte and damage the plates.
AnswerID: 360001

Follow Up By: PeterInSa - Friday, Apr 17, 2009 at 15:32

Friday, Apr 17, 2009 at 15:32
Thanks, will use a BP Solar regulator, should have included that in the write up.

FollowupID: 627914

Reply By: Member - John and Val W (ACT) - Friday, Apr 17, 2009 at 16:51

Friday, Apr 17, 2009 at 16:51

From you description, I'm not too sure just what you are aiming at.

First - to connect two batteries in parallel, you would connect the two positive terminals together, and also the two negative terminals together - no negative is ever connected to a positive.

The panels - These should be connected together in parallel, ie the two positives together, and the two negatives together. They will then function as a single big panel. It's good practice to use heavy cable for all these connections, though as the current will be less than 10 amps, it needn't be huge. There will be no significant voltage loss in the cable. In any case, unless the battery is fully charged, the voltage delivered to the battery will be dictated by the battery, not the panel or wiring. The controller is there to disconnect the panels from the battery when the battery if fully charged.

In the setup you describe, with panel A feeding to panel B then on to the battery ( through the controller), neither panel charges the other, they both send current to the battery.

Hope that helps


J and V
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AnswerID: 360023

Reply By: Member - Mike DID - Friday, Apr 17, 2009 at 17:50

Friday, Apr 17, 2009 at 17:50
There is no point in connecting the solar panel to the + of one battery and the negative of the other because the current is so low.

There is no problem connecting the two panels together at one of the panels, because solar panels are constant-current sources. Even if you had a 100 watt panel and a 5 watt panel, there would be no problem wiring them together.
AnswerID: 360032

Reply By: Member - dieseltojo K (VIC) - Friday, Apr 17, 2009 at 23:14

Friday, Apr 17, 2009 at 23:14
Hi Peter,
Some good reply's here already,and there are a few options as well.On my set up I joined the panels pos to pos and neg to neg,with heavy B&s size cable .These combine into one cable and go down into the van to a Morningstar regulator.
From separate terminals on the regulator a pos wire and a neg wire come from the regulator to the battery Via a 30amp self regulating fuse(,Costs about $6-00).
From a separate terminal on the regulator a pos wire comes from the regulator to the ( load) which is all your lights fans etc.Via a fuse box to a buzz bar then to pos on the battery.
From a separate terminal on the regulator a neg wire comes from the regulator to a neg buzz bar near the battery then to the neg on the battery.
Unless you deliberately wont 24 volts just connect the batteries pos to pos and neg to neg
The pos from the pos buzz bar goes to the pos on one battery and the neg from the neg buzz bar goes to the neg of the second battery.

While it looks complex in writing it is simply a case of following directions to the letter for your chosen regulator and charger etc.the BP regulator may have a simpler connection system.With a good regulator there is usually no need for blocking diodes within the solar panels,and the regulator will prevent current going backwards from the batteries.
Hope this helps but others are welcome to put alternatives.
Regards Paul

AnswerID: 360080

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