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connecting solar charger to 2 12V

Thread starter #1
Hello all, I'm brand new here, hope I'm on the right forum, and ask for your patience as I try to wrap my brain around 12v systems.

Here's the short version:
26 foot sailboat, 2 12v in parallel, 15W solar charger, one connection supplied with charger/maintainer. I have a 1/2/all/off selector for my system.

How do I go about connecting maintaining my bank? Batteries are new. can I connect to the most "convenient" and manage both? Do i need to do anything with the 1/2/all selector?

Again, I understand that I am a preschooler on 12v and only a 2nd grader in electricity, so please bear with me.

In general I'd say you should almost always leave it in the 'all' mode.
The 1 or 2 modes would allow you to charge/discharge from a single pack but to keep the packs balanced if they're brand new you simply always use them as a pair, always. If you start to have electrical problems you can use the 1/2 switch to run your electrical system on only one pack to see if one is stronger or weaker than that other, in which case you would have the electrolyte concentration in each cell/pack checked and re-balanced, so long as the plates aren't damaged or badly sulfated, in which case you replace BOTH batteries at the same time and for the interim you use the 1/2 switch to run it off one or the other battery.

When the two packs become heavily imbalanced they don't charge at the same rate or discharge at the same rate so they end up having different voltages which means you get current going between the two packs as they struggle to try to maintain a balanced voltage, if the chemistry is off enough this can't happen and it just results in drained batteries.
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Thread starter #3
thanks for the speed!

That's what I was thinking as far as the switch goes. Does that switch "allow" current to run upstream? Can I simply connect to the battery in the galley cabinet and also maintain the one that's behind a removable wall in the back of the rear berth where there's only about 18 inches of headroom (get my picture)? that would be a fantastic thing to get an educated "yes" on!
If you're running the batteries in parallel they should be RIGHT next to each other with bus bar or super heavy duty wire connecting them and then the boat wiring heading off from there. It's not advisable to have them separated by any distance, that will cause a guaranteed imbalance over time because of the different wiring between the two charge/discharge points.
Thread starter #5
OK, maybe I need to back up. Sorry.
I ASSUME they are in parallel because otherwise I would have a 24V system? Maybe my ignorance. additionally there is a premium on balance down the center line, so one is starboard the other port. Do I need to back up further? Thank you for your patience Sceadwian. Alternately if I have a cable running from red to red (+-+) then I am parallel?
If they're just two batteries plugged into the same system they're in parallel yes. Like I said to keep the packs balanced and charged properly they need to be as CLOSE as possible to each other, physical adjacent is really the only proper way to do it, and the batteries need heavier gauge wire than the rest of the system to connect to each other. You can hook them up in different spots if you want, but without extremely detailed information about the wiring in the boat there's no way to tell how bad that's going to be for the batteries. I wouldn't even try it.
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Thread starter #7
I will continue to unveil my ignorance! I can tell you that, straight-line they are about 8 feet apart. Linear wire distance would be more like 12 feet. the wire that connects the two, from memory, is about as thick as a pencil, or maybe slightly larger. everything else is very small comparatively. I can head out there tomorrow and if you have time to do some writing, I will supply any needed info I can. I'm trying to establish a proper dependable system and would certainly appreciate any help you are willing to offer.
Why are they placed so far apart? Now you're getting into my ignorance, I don't know much about the actual details of the electrical systems of a boat =) If the batteries are connected by thick wire separate from the rest of the electrical system this at least sounds reasonable, but ideally they should be right next to each other. It may be to prevent one battery failure from water or what not from taking out the other, I'm going to guess they're fused so in a failure the other battery can take over.

The solar panels is only 15 watts so it really should not matter where you plug that into. The thicker wire between the two batteries will take care of the pack balancing.
Thread starter #9
some of the reason for the separation would be the fact that the boat is small enough to have been designed to use one battery and therefore NO locker has enough room for two side by side. It is not uncommon for people to increase their bank to support additional gizmos and to simply increase their cruising distance. Additionally, keeping the boat balanced side to side has a HUGE premium. If the boat is heavy to one side and lists, then you have a longer water line, which means you also have more hull in the water, increasing your hydrodynamic drag and decreasing your speed. We sailboaters are in a big hurry to go nowhere, fast. If you had room on one side to place two batteries, you would have to counterbalance with equal weight on the other side, again lengthening your water line, due to sitting lower in the water.

I'm heading out there today and will have some more info/description of what I have later today. Thank you for your time.

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Thread starter #10
OK folks, here's more detail

I have a red, 4 AWG 600V cable running from battery #1 to the battery selector switch, then on to battery #2. I have 2 black cables running from the negative post on #1. One goes to the starter on the motor, then on to #2, the other goes straight to #2. There are NO OTHER connections to battery #1, everything else for radios, sensors and displays comes off of #2.

#1 is the one that is easy to get to. The other one requires a belly crawl up under the cockpit and working in rather tight quarters.

so... can I maintain both w/ the solar charger by hooking to #1? If so, what do I do with the battery selector switch?

Thanks again
I still don't understand why they couldn't put an access panel to the battery, seems silly to do things like that. But I'm not an engineer =)
I think I would wire the solar charger to the battery selector switch on the #1 side, assuming the wire runs to the #1 and #2 batteries are of approximately equal length it's the best way to maintain an equal charging current to both batteries. The battery selector switch would be left in the ALL position at all times. That's the way I'd do it at least, I would follow the directions that come with the solar charger though.
Thread starter #12
That's kind of where I was leading myself, albeit reluctantly. I'll have to run the charger wire through the same through-hull as the motor controls and such, then add a quick disconnect so I can remove the charger while I'm sailing. Any thoughts on that part?
Why remove the charger when you're sailing? What's the amp hour capacity on the batteries you're using?
Thread starter #14
average minutes at 23 amp draw is 225, according to the label. That would be about 4 amp hours right? And unfortunately, until I can afford to build/buy a mount for the stern, I would have to remove it because on my size boat, deck space is very limited and there are few places it wouldn't foul lines or otherwise be in the way. Make sense? Also, my load is an am/fm/cd, a vhf radio, depth/wind/speed sensors and display, and my running lights. So I'm thinking I'm over batteried anyway for my 2-3 10 hour sails per month. Is that a fair statement?

Sceadwian, you're a blessing to me. Thanks for helping!
23 amps for 225 minutes is 23 amps for 3.75 hours. That's 87amp hours, sounds about right for two car sized batteries in parallel. I have no idea what kind of current you regularly pull from on a sailboat, but it sounds like you have plenty of overhead to me. You can use whatever you want for the quick disconnect on the solar charger, I think you said peak is 15 watts so a 2amp rated disconnect will work fine, being in a marine environment however you may want to try to find gold contacts and make sure the contacts are cleaned regularly. Even fresh water spray with ambient dirt makes for a nasty corrosion situation with electronics.
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Thread starter #16
Oh yeah, forgot to multiply the amps (duh). got it. That should get me rolling, er... sailing. Anyway, thanks for all of your help. where might I find a connector like that?
Banana jacks/plugs would work fine, should easily be able to find one's rated for 5-10+ amps, gold plated too. Shrouded would be best, helps keep accidental dead shorts from occuring when you remove them, you should be able to even find twin male jacks that prevent that completely. Radio shack will carry them if you just wanna pick a couple up quick. Radioshack chargers a premium for their parts but it's easier than finding and paying for shipping from an online source. There may be electronics suppliers in your area that would have a better selection.

The main problem with banana plugs is they're not key'd and the last thing you want to do is hook it up backwards.
A hobby store that sells radio control car/plane parts will have keyed disconnects that should work, they're not real friendly on the fingers though =)
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Oh stop it, you've padded my ego enough to last me for a month at least.
Thread starter #20
well then...

you stinkin' idiot, I went on Radioshack.com and can't find a single shrouded banana plug/jack and they all say that they're for speaker wire. I coulda gotten as much help from my wife!

How's that? back down to one month yet?

Do the speaker wire ones sound right? They run from 3.99 to 19.99. Anything else I should look for? And no I won't send you my SS# so you can claim me as a dependent!

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