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Author Topic:   Solar Powered Battery Chargers
flyfisherman posted 02-18-2007 05:03 PM ET (US)   Profile for flyfisherman   Send Email to flyfisherman  
[This article has been moved to the SMALL BOAT ELECTRICAL discussion from another topic area. Please use SMALL BOAT ELETRICAL to discuss this topic--jimh]

[The author initiated a survey, but this has been deleted. CONTINUOUSWAVE discourages the use of surveys to gather information. If you wish to conduct a survey please contact me via email to discuss the survey questions and how the survey results will be presented. Thanks--jimh.]

I have to keep my boat in storage and it seems like I never think to go pick it up the day before a trip and charge the batteries. I was reading about [solar powered battery chargers] and I wondered how effective they are. I saw [a solar powered battery charger] that was advertised as "weather proof," so I was thinking I could just leave it on the boat when I put it up after a trip and it would keep the batteries charged between trips.

Any thoughts?

Shrdlu posted 02-18-2007 05:15 PM ET (US)     Profile for Shrdlu  Send Email to Shrdlu     
Check out

They offer several solar panels for marine applications, including one capable of maintaining two batteries. Separately, they offer a mounting bracket and a variety of connection accessories including a cigarette lighter plug.

I bought this system for my 210 Outrage, which will sit on its trailer in a power-less boatyard much of this summer. I ordered mine direct from ICP, but West Marine also carries it.

I have not hooked up the panel yet, so I can't speak from experience.

flyfisherman posted 02-18-2007 05:30 PM ET (US)     Profile for flyfisherman  Send Email to flyfisherman     
Thanks for that. I think I've got a West Marine catalog around here somewhere. From what you're saying, they must be pretty weatherproof, huh? What I'm thinking of is one that could just lay up in the bow area and keep the batteries charged and then just take it off and stick it in the truck before I launch. Nothing installed permanently or anything. Does that sound reasonable?
where2 posted 02-18-2007 08:35 PM ET (US)     Profile for where2  Send Email to where2     
Thanks for the reminder, I need to move the solar charger on the Whaler at work to the 4th battery... We are using the 15 watt version on our 25' Whaler Frontier. We have it attached to an ICP charge controller and cycle it around to the various batteries (4 total). I usually hook it up to one for a week, then move it to the next one the following week, and so on. (we have 4 batteries because we are running a 24V setup in addition to a redundant 12V setup).

The unit we are using came from West marine, as did the charge controller. As you are describing, we chose not to permanently mount the unit. It simply lays in the sunshine on the rear hatch.

We're happy with the one we use.

flyfisherman posted 02-18-2007 10:47 PM ET (US)     Profile for flyfisherman  Send Email to flyfisherman     
Thanks for your feedback. You've obviously found that it stands up to the weather well, huh?
jimh posted 02-19-2007 09:22 AM ET (US)     Profile for jimh  Send Email to jimh     
A "15-watt" solar panel implies that the current will be around one-ampere, and that is probably at optimum conditions when the sunlight is strong and the sun angle favorable. One might estimate those conditions occur perhaps 4-hours per day. If you account for the taper in the charging current as the battery terminal voltage rises, it may be reasonable to de-rate the charging current by half. The aggregate sounds like you could expect about 0.5-amperes for 4-hours each day, or about 2-Ampere-Hours (A-H) of charging.

With a typical boat battery of 50-A-H capacity, it sounds like it will take a month of sunshine to charge it.

I'd call the device a solar powered battery maintainer.

scalez posted 02-20-2007 11:50 AM ET (US)     Profile for scalez  Send Email to scalez     
ditto on jimh's post! This is dead-on.

See my research and the great responces in this forum under 'PV battery charging at dock w/o 120V' or something to that effect. Good links for a short course. I've learned that PV charging doesn't come cheap in spite of all the marketing lingo and promotionals. Time is money, only in this case, in reverse.

It sounds like you have the time and therefore could save the money but you need to realize that properly charging a battery requires a staged process: bulk, absorption & float. Each battery type(flooded, gel, or AGM) has it's own charging voltage profile dealt with by a quality charge controller. For any absorption you are needing @ 14+ V for absorption, for bulk @15+V. Remember: Volts x Amps = Watts. PV panels are rated in Watts, therefore on a 'typical' PV for charging(not maintaining/floating) you'll see @17v X 5Amps reduced by the controller to 14.2-4V X 5+Amps. Depending upon where you are located(eradiation index) and the size of your panel, this may require numerous days to bring a AGM(the best marine battery for this) back from 50% drawdown.


scalez posted 02-20-2007 11:55 AM ET (US)     Profile for scalez  Send Email to scalez     
also see :
ratherwhalering posted 02-20-2007 12:48 PM ET (US)     Profile for ratherwhalering  Send Email to ratherwhalering     
Do these units have voltage sensitive charging? By this I mean will they shut off when the battery is fully charged, or is there a chance of over-charging?
where2 posted 02-20-2007 11:41 PM ET (US)     Profile for where2  Send Email to where2     
Weatherproof: Yes, we stow it for hurricanes, and leave it out for most everything else. We get no snow, and have had no hail.

The extra "Charge Controller" handles the issue of over charging. It's a brain that mounts between the solar panel and the battery. It is not included with the 15W panel.

Call it a maintainer, a trickle charger, your choice. It was my interpretation reading the original post that the question was: Can you use a solar panel to keep the batteries healthy when you use the boat infrequently, but store it outdoors? My answer was "YES, but you need more than a 2W panel, here is what is working for me, and how I use it".

It was not my interpretation that we were starting with batteries with defective cells, and a poor charge. Nor were we starting with a depleted set of deep cycle batteries used as a power source for a trolling motor.

jimh posted 02-21-2007 11:00 PM ET (US)     Profile for jimh  Send Email to jimh     
If you have a boat left in the water and there is a sump pump running on automatic, having a solar powered battery maintainer would be an asset as it would tend to help maintain the battery charge against the on-going pump drain.

A battery in good condition, if there is no other current drain, should not experience any self-discharge over a period of a 30 days.

Larger boat batteries have capacities more like 80-Ampere-Hours, so you would need about two months of sunshine to re-charge one of them with a "15-watt" solar cell.

In my own case, I try to keep my boat out of the sun as much as possible. It is stored indoors and under a cover about 99-percent of the time. The sun may be a good source to generate electricity on a very modest scale, but it is also causes a lot of damage to the boat from ultraviolet radiation. The hull and deck surfaces, the canvas, the wood, the vinyl, the plastics--all are affected by sunlight. I try to keep the boat in the dark as much as possible.

crabby posted 02-28-2007 08:33 PM ET (US)     Profile for crabby  Send Email to crabby     
I used to run a camp in the far North and I swung the whole place over to solar, but we used much bigger panels than have been discussed here (65 to 80 watt panels, sometimes several in parallel). We could run all of our comm gear, lights, entertainment, water pumps, battery chargers for handheld radios, even charge laptop computers. But we had great capacity and large battery banks.

Last winter I used a little 15 watt panel to keep a standard 80 amphour starting battery charged while hooked to a bilge pump in a slightly leaky old Uniflyte I had stashed behind a friend's home and never once did the setup fail me. I would not expect that it could have recharged a battery that was run down on a weekly basis but it certainly helped keep the Uni afloat.

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