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Old 30-05-2011, 15:16   #1
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Solar panel

Well, I think I've been given a great gift. A friend works offshore and gave me a new, surplus, bp solar model SX320J solar panel. It's a 20W unit. I have no experience with solar and don't really know what to do. I have a small (26') boat with a single 12V deep cell. I have a 12V charger/maintainer while in the marina. How do I hook this sucker up and is it good for my system? Thanks
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Old 30-05-2011, 17:14   #2
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Re: Solar panel

Wire it straight to the battery.



Its easy and will give you a little bit each day. But its only 20 watts so it will keep the battery charged while you are at work for the week.
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Old 30-05-2011, 18:56   #3
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Do I need to install something inline to make sure it doesn't overcharge the battery?

Can I leave it hooked up when I plug in the battery charger/maintainer?

Thanks again
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Old 30-05-2011, 19:07   #4
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Re: Solar panel

Yes, you'll need a regulator. This will stop over charging and also prevent the panel from actualy draining the battery when it's dark. These are pretty cheap and can be found on most marine suppliers listings, or even on Ebay.
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Old 30-05-2011, 19:18   #5
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Re: Solar panel

Quote:
Originally Posted by simonmd View Post
Yes, you'll need a regulator. This will stop over charging and also prevent the panel from actualy draining the battery when it's dark. These are pretty cheap and can be found on most marine suppliers listings, or even on Ebay.
Whether you need a regulator depends on the open circuit voltage of the solar panel. Solar panels are current limited devices, so even if they have an excessively high voltage they won't pump more amps through the circuit than their specs say they will produce. But if the panel's voltage is too high some energy will be wasted that could be recovered by trading voltage for amps with a switching power supply. More important than a voltage regulator for such a small panel is a blocking diode that will prevent the battery from discharging through the panel when there isn't enough light to make the panel work.

Fabbian
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Old 30-05-2011, 19:21   #6
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Re: Solar panel

You are on the border line in needing a regulator. You didn't mention how big your battery bank is. You'd best disconnect the shore power charger as this panel should keep the batteries charged and recharged with the intermittant drain you'll probably have on the battery. Leaving the shore charger hooked up will surely overcharge the batteries in conjunction with the panel. Might think about adding a second battery if your current one is a standard Group 27 12volt battery. YOu'll get more benefit from the extra battery than from a charge controller.

Monitor the battery fluid levels. If that is going down appreciably over a 3 month period, then add a charge regulator as you are sending too much juice to the batteries and risk damaging them.
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Old 30-05-2011, 19:30   #7
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Re: Solar panel

One big advantage to using the solar panel is that unless you are living aboard you should be able to disconnect the shore-power connection. This will very likely reduce the rate that your zincs are being dissolved by electrolysis. So it's worth figuring this out...
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Old 30-05-2011, 19:42   #8
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Re: Solar panel

With a 20W panel you should be o.k. without a controller but as mentioned you need to make sure that the panel doesn't discharge the battery at night. Some panels have a built in diode that only allows for current to flow to the batteries. You can look your panel up online to find out if it has a diode, if it doesn't I'd get a small/simple controller mostly for this functionality. If you want to save a few $$ you can just add a diode in between the panel and battery which will only allow the flow of current to the batteries, and not back to the panel.

20 Watts will do a good job of trickle charging the batter and keeping it up but won't keep up with much usage on the water.

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