Solar panel battery charger.. any favorites

[westcoaster1358]

Going to be leaving the boat on a can a lot this summer and always worried about batteries, anybody have any experience with the small 6 watt battery chargers, they sell at West Marine? I would hook up directly to batteries.  I have four battries all wired together, so how do I hook up charger wire from solar panel (positive on one battery and negative on other)?  Do I have to leave battries on?  Any advice would be appreciated.  Thanks,  John

[Stephen Butler]

We purchased the 6W panel at WM, 2 years ago.  We use it to "trickle charge" our batteries while we are away from the boat...4 to 6 months at a time.  It works extremely well at this maintenance task, and we would recommend it.  As for using it while afloat, our electrical consumption is just too high, to rely much on a 6W panel...which is why we finally went with a 1000W Honda gen set.  We did look at adding some large solar panels, but the cost and mounting challenges, versus the Honda, came down on the side of the Honda. 

[Stu Jackson]

John (It'd help if we knew your hull #, thanks, because access to the electrical panel seems to me to be much easier on a Mark I boat. Please see: http://c34.org/bbs/index.php?topic=1506.0)

A few items that will affect your decision:

1.  How big a battery bank do you have?  (You did say they're wired together, see below)  A 6 watt would barely keep up with just the self discharge of a 400 amp hour house bank, and that's about all, whereas a 6 watt would keep up a 200 ah house bank quite well.  This is for when you're away for the week, to come back to a house bank that's pretty well cared for.  I'd use an 11 watt unit on the larger house bank (what we've got -- we have 360 ah in three batteries, plus a separate 60 ah start battery; I rarely plug in).  Sounds like your house bank is probably around 400 ah. 

2.  Controllers - if you use an 11 watt charger on a small or "split" house bank (say if you only have two 130 ah Group 31 for each half of your house bank) make sure you don't exceed about 1 1/2% of the amps output of the solar panel to the bank without a controller.  If you do an 11 or 6 watt on a 400 ah house bank, no problem, no controller required.  You'll need to do the math, WM shows the amps for different wattage solar output, I just don't have it in front of me.

3.  Panels -- We've had good experience with an 11 watt Unisolar flexible panel laid out on the top of our dodger, held on with shock cord, faces southeast based on the orientation of our slip, gets good sun most of the day.  Using a solid panel will get you into supports, etc.

4.  Rest of the electrical system -- not the ? you asked, so we won't go there... (i.e., 1-2-B switch and charging the start battery, combiner, echo charge, alternator, generator, etc.)  Steve's explanation is correct about what you will expect from the panel.

5.  Wiring -- if you're doing it to keep up, as we suspect, then all you need to do is to wire it as you note, right to the batteries.  An alternative would be to wire it into the 1-2-B switch, but based on our boats, it might be easier to wire directly to the bank(s) because of where the switch is located.  {We have the wire running down the companionway and under a rug at its base and through a notch I cut into the bottom frame of the door to the hot water heater.}  However (you had to know that was coming! ) I have a project waiting to be done:  our panel is on the port side of the dodger -- put a simple plug through the cabintop over the head, run the wiring behind the "medicine cabinet" to the switch, rather than all the way to the bank.  I assume you leave the 1-2-B switch OFF when you leave the boat, so just wire the panel to whatever posts on the switch connect to your batteries (i.e., NOT the C post).  Your question didn't seem to explain whether or not all of your batteries are in one bank or more.  It's unusual to put "all your eggs in one basket," unless you're talking about your house bank only and you have a separate start battery.  If all one big bank, it's  no brainer, if split, you'll either have to charge one one week and the other the next and find some way to switch the panel output.  The start bank can usually be left alone, unless you already have a combiner, echo charge or relay to connect when input voltage is being sensed, since it uses only a bit of power to start the engine and then gets recharged from the alternator once you're underway.   We'll need to get more info to help you out there, and maybe a whole separate subject that is covered in #4 above.     In either case, always leave your switch in the OFF position when you're away from the boat.  Connecting directly to the batteries, or to the 1 or 2 posts of the switch is electrically the same thing.  The C post of the switch simply determines which of the 2 other positions of the switch get the power from the batteries to serve whatever the C post is connected to (i.e., starter if so wired and the DC panel).  Don't wire to the C post, becaus you want to keep the switch OFF when you're away from the boat.

[Ron Hill]

John : I'd try the 6W solar charger and as you mentioned wire the panel directly to the batteries. Leave your battery selector OFF. 
Here's how I'd wire the panel to the batteries.  Connect the + to the positive terminal on battery #1 and the - to the negative on battery #4. 
You should get enough dribble charge to keep them up if you're only away for a week or two.  If you plan on staying away much longer then follow Stu's advice with an 11W panel.   

[Stephen Butler]

For what it's worth, we have no difficulty keeping 2 group 27's fully charged, for up to 6 months at a time, with the 6W panel.  Giving this some more thought, our boat is in Florida, with lots of sunny days and the panel positioned for maximum exposure to sunlight.  Haven't done the math, but I suppose that if the boat was further north, and weather conditions were not as good, and the position of the panel not optimized, then a larger panel would be the "ticket."  As for wiring the panel to the batteries, Ron's suggestion is exactly how we have it, and it works wonderfully.  Hope this is of help.