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Author Topic:   Solar Panel for Battery Maintenance
editorpmm posted 12-10-2007 03:48 PM ET (US)   Profile for editorpmm   Send Email to editorpmm  
[Seeks experience in using] a small solar panel to keep a 19-foot boat's single Group 24 battery charged when the boat is not being used.

I'm curious what size solar panel, and the best way to wire it. For example, can it be wired by the 12VDC cigarette lighter on the console?

Any help would be appreciated. Thanks.

jimh posted 12-10-2007 11:50 PM ET (US)     Profile for jimh  Send Email to jimh     
If the solar panel is going to be removed when the boat is back in operation, the idea of plugging it into the boat's electrical system via a connector is a good concept. As for using the cigarette lighter, it would depend on how this is wired into the boat's electrical system. Typically you would leave a boat with the primary battery switch in the OFF position. This probably cuts off the cigarette lighter plug.

In general I think you want to leave the boat with the primary battery switch in the OFF position. That insures there won't be parasitic discharge of the battery from any of the normal loads in the boat, including things like a cabin light left on my mistake.

To connect the solar panel you ought to wire it to its own connector which then goes directly to the battery via an appropriate fuse. In this way the solar panel will be feeding the battery even when the primary distribution switch is OFF. Also, you can use a fuse of just a few amperes rating to protect the wiring from the battery to the connector.

As for the solar panel, I can't offer any advice other than to go by the recommendations of the solar panel manufacturer in terms of size, voltage, and current. My impression is that unless you go to a very large and very expensive solar panel, you will only get a very modest current output. This means you won't have to worry too much about overcharging the battery. And, of course, that is also affected by your location and climate, which influence the amount of sunshine available. The solar panel vendors usually have some maps which are useful in estimating the amount of sunshine expected.

blackdog54 posted 12-12-2007 10:54 AM ET (US)     Profile for blackdog54  Send Email to blackdog54     

The way I use my solar panel is like this:

1) Cover off starter battery
2) Sunsei SE-135 (2 watts) panel, sold at West Marine for $39.99 has 2 wired clips for the (+) and (-) battery terminals. Put clips on.
3) Power cord between battery and panel passes through a cut-out on my mooring cover and panel sits on top of the cover.

Very simple. It is rated to keep a starting battery fully charged if left connected at all times. So far, it has done just that. I don't think that there is a risk of over charging. I am in San Diego, so we get a lot of sun, but it is in my driveway, which is shaded part of the day by a large tree. It has a test light to tell you if it is charging.

There are accessoryies for this, the Solar Grip, for $54.99 if you wish to mount it somewhere. Seems like overkill. There is also a Charge Controller for $39.99 but again, I don't think it is necessary for this application. I believe it primarily there for larger wattage systems (you can combine panels as well).

The unit was given to me by a neighbor. Apparently, it comes with suction cups for mounting but I do not have those.

blackdog54 posted 12-12-2007 10:56 AM ET (US)     Profile for blackdog54  Send Email to blackdog54     
Clarification (which may be obvious)-

..."keep the starting battery fully charged if left connected at all times"...

EXCEPT when underway.

Peter posted 12-12-2007 11:02 AM ET (US)     Profile for Peter  Send Email to Peter     
My 27 Whaler WD is not a large electrical consumer (no fly-by-wire or power steering stuff requiring large battery banks, etc.). In fact, it has no shore power system at all.

I have a 6W solar panel directly connected to each of the two Group 24 batteries on my 27 Whaler WD. Typically, during the day before the boat is used, the unloaded voltage on each battery will rise up to 14+ volts as displayed on my Navman F3100. I've actually seen it as high as 15v in mid Summer. Of course there isn't much current behind this but in theory the high voltage floating on the system should and seemingly does keep the battery from self discharging. The nice thing is that electrical power for maintenance comes from a free, thermonuclear source rather than burning more petro fuels at the power plant down the road somewhere and transmitting that bit of power across miles of transmission lines.

I also use two 2W solar panels (just happened to have two) connected in parallel to the single battery on my 18 Outrage. Same result.

I would simply directly connect a 6W panel to a battery using the ring terminals supplied with the panel.

blackdog54 posted 12-13-2007 12:07 PM ET (US)     Profile for blackdog54  Send Email to blackdog54     
Peter, thanks for adding one aspect that I failed to mention. It thrills me completely that the sun, and not some other mechanism, charges my battery for free, and effortlessly.
where2 posted 12-18-2007 11:05 PM ET (US)     Profile for where2  Send Email to where2     
Another somewhat important issue is to keep track of the receipt for the solar panel. One of my co-workers has had a 6W panel commonly found at the local marine chain stores on his boat for approximately 2 years. This fall, it developed a crack in the layer that acts as a substrate for the solar panel itself. The top and bottom layers of the sandwich glass are not cracked, only the middle layer is. However, he has surely shredded the receipt as he commonly does with his credit card receipts. As a result, he has no way of getting his panel adjusted with the manufacturer under the 10 year warranty the panel comes with.

So, he bought another one, after borrowing the 15W panel we have at the office for a week.

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