Max volts for battery charging.

Submitted: Friday, Jul 11, 2014 at 09:53
ThreadID: 108687 Views:1252 Replies:3 FollowUps:1
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Hi all,

I have a 12 volt deep cycle 120 Amp Battery. I connected my 2X 60 Watt solar panels with a built in controller directly to the battery terminal. The voltage to the battery had a 17.5V readout. My questions are? Is this the correct way to connect the solar panels to the battery and is 17.5 volts too high for the battery.
Any help would be appreciated .
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Reply By: Green Rv - Friday, Jul 11, 2014 at 10:40

Friday, Jul 11, 2014 at 10:40
the max input from solar reg should be 14.4 volts
17.5v will fry the battery
are you sure the part you are looking at is a built in reg it could be just a junction box
i ask this as a 60w solar will be making 17v without a reg
AnswerID: 535866

Reply By: Nomadic Navara - Friday, Jul 11, 2014 at 12:07

Friday, Jul 11, 2014 at 12:07
As above, is the box a junction box or a regulator? If it's a regulator it's buggered or you have bypassed it.

The voltage from a panel in good sunlight should be around 22 V open circuit (ie nothing connected.) The 17 V is its operating voltage when delivering maximum power. If you put a heavier load on it than the one that will work at maximum power the voltage will drop significantly and the current will increase slightly. If you short out the panel with an ammeter the current will be more than the peak power point current, we often do this to test how the panel is working.

The regulators stuck to the backs of panels are generally simple devices. You can get better regulation with a good one purchased separately. For best charging mount them as close to the battery as you can, not on the back of the panel.
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Follow Up By: Nomadic Navara - Friday, Jul 11, 2014 at 12:12

Friday, Jul 11, 2014 at 12:12
In addition, you did not specify the battery you have. Different batteries require different charging voltages. Get hold of the specification sheet for your battery. Select a controller that is capable of being set the required charge voltages.
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Reply By: Tony H15 - Saturday, Jul 12, 2014 at 16:33

Saturday, Jul 12, 2014 at 16:33
I have a solar panel does the same thing. When connecting it requires battery connection first, if you connect solar first it will go way past the 14.4 volts.
Flip the panel over, so out of the sun, connect to battery and flip back over again. Cheap regulators!

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