I am new to houseboating.  We have a 1976 Kayot.  The boat is on the ball year round, therefore, no shore power.  Electrical system is very simple.  I have a 12V starting battery, and just  2 - 6 volt batteries for house power.  Charging comes from 2 solar panels. Everything used on the house system is 12 volt; IE., no inverter.  When I do need 120V, we use a portabale genset.   Usage/consumption is limited to interior/exterior lights (mix of flour & incendecent), water pumps, Ref. - controls only, stereo w/ amp, 12V receptacles for phone charges, portable DVD player, etc.  I have read many of the posts regarding battery / power set ups and am looking for some basis info.  and understanding on battery systems, though I am somewhat embarrassed to ask.

Excluding cost differences, what is the main advantage / disadvantage to using 6V batteries in series, as opposed to a single 12 volt batteries?  The reason I ask is that I currently have limited battery storage space.  So, if I want to get more power capacity out of my batteries without making a larger battery storage area, assuming I can only fit two batteries in my storage area in addition to the one 12V starting battery, if  I swap out my 2 - 6V batteries in series and changing to 2 - 12v batteries in parallel will I be better off?  If I did go to 12V batteries, I am assuming keeping wet cell type.  I don't know how the solar charging system will be effected.  I have no data on my panels except that they each measure approx. 12" x 48" and have 30 cells each.  One looks like it has a lable that may read:  Arco M61, but it is very difficult to say for sure.  We typically houseboat for a "weekend" 2-3 days during the summer, then the boat sits all week and recharges.  Our boat is located in the central valley of northern CA, so we get plenty of sun during the summer months.

2-12 volt batteries in parallel will give you just about the same as 2-6 volts in series, depending on the batteries. If space is a problem look into a TALLER battery; such as the Trojan T-145 (260 amps) or the Trojan L-16 (420 amps). Usually height is not that much of an issue. http://www.trojan-battery.com/

You don't have to get Trojans, there are other makes as well.

Solar charging shouldn't be an issue as long as you stay with 12 volts. It's more a matter of how much you actually use. The bigger batteries with more capacity will allow you to use more; if the panels can keep up you're good. You'll find out soon enough. If not, add another panel.

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Willie
She's a tired old barge but she's paid for! http://s71.photobucket.com/alb...p;current=ef324993.pbw

Fact:  6 volt batteries (ie: golf cart batteries) have a much longer run down time. measured in amp/hr rating.

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Boatless at the moment
www.spboatsales.com

So is it all about amp hrs and capacity per batt? If so, then do the golf cart batts have an edge over 12 v batts?

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Riverliver

If the batteries are high quality and the installation done properly it really doesn't matter if you have two 12 volts in parallel or two 6 volts in series.

The catch words are "quality" and "properly"

My experience with the majority of the marine deep cycle batteries is that they are really rather poor quality. Since they often need to be capable of "starter duty" they tend to be built more as a general purpose battery than a dedicated deep cycle battery. I have never obtained the advertised performance in amp-hours and the charge/discharge cycle life (number of times you can do that) has been really bad.

Golf cart batteries, on the other hand, are built for golf cart duty. Golf courses all over the world buy these batteries to keep a fleet of golf carts running. These carts get used every day and the batteries get a lot of charge/discharge cycles. The person who's job it is to keep the golf carts running knows how the batteries perform and if he is getting the approrpriate bang for the buck. A battery that is sold to golf courses for golf carts is going to provide the advertised amp-hours and do it for a reasonable number of cycles.

The proper installation with two batteries in series is also easier. With two 12 volt batteries you will need four battery cables: Positive, Negative, and then two jumper cables to connect in the second battery. This results in two of the battery posts having a minimum of two cables, which is actually frowned upon some boat building standards. Another problem is that the typical parallel installation ends up with a shorter cable run to one of the batteries so in heavy current situations the closest battery bears the brunt of the load. This uneven load can make the one battery fail early, but the bank lives and dies together so it results in shorter battery life.

With 6 volts in series you have three cables: Positive, Negative and one jumper cable. All posts have just one cable on them. The current through both batteries is always the same.

Before making a change in batteries measure your battery box carefully. A golf cart battery is somewhat more "square" on the footprint and a bit taller than a typical 12 volt battery. Two 12 volts may not fit in the space two golf carts would. Like stmbtwle said, if you have lots of space above the batteries you can go to an L16 size, which has about the same footprint but is twice as tall. Be prepared for the sticker shock, however. Golf cart batteries are fairly cheap due to the large volume of them that are sold. L16s lose the economy of bulk.

Rod

Welcome aboard potis.

Let's start at the beginning, or what should have been the beginning. You first need to know what your need is. What your total usage will be (watts). Get this by adding the wattage of all your appliances, lights, and other goodies that use electricity, then convert into amps. Your storage will need to be twice your usage, (we used 3X on our boat), to be effective for solar. ie: if your maximum electrical demand in amp hours (ah) is 180ah, you will need a minimum of 360ah in battery storage. Note: If you're a weekender, you can calculate your usage for a 3-day weekend and double that.

Now that we know the demand and the recommended storage, we can buy batteries. The 6v golf cart batteries are probably standard for our usage ONLY because they are best suited for a 'complete discharge to fully recharged' situation. I would only suggest using the 12v batteries if room is a major issue.

Also consider your solar controller/charger. This needs to be adjusted properly so you get maximum output, and it's very important that it is a 3-stage charger.

Lastly, irregardless of which battery type you decide on, the one single most important word you must remember is maintenance. Water level is crucial to battery life.

If you moved you new boat from another body of water, you may also want to check the angle of your solar collectors (panels). Remember that the reflective angle of the sun changes dramatically twice yearly.

I would also suggest that you browse the other threads on 'solar' within this forum.

Good luck,
Skally

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Chance Favors The Prepared Mind!

Edited: 01/29/2008 at 02:44:36 PM by Skallywag

Thanks for all the terrific feedback.  I do understand the importance of determining my real load and requirements as Skallywag noted.  I will be working on that study as as a first step when I try to sketch up some wiring diagrams for each of my systems. I should have noted, that with my existing set up (as I purchased the boat last summer) so far everything works fine.  I have never drained batteries, or had any problems. But, we do try to conserve quite a bit when on the boat.  Another reason I have brought this up now is that I noticed that dates on my current 6v golf cart batteries is  2002.  I don't know what the typical life expectancy is, but 5 years seems pretty darn good!  Anyway, I'm thinking it is time for a change out and that is what prompted my thinking on the subject of 6v vs 12v batteries.     I do understand the importance of battery maintenance.  I check the water in the batteries on every visit, and top off as needed.  As far as the charger goes, I will need to pull it out to see what type it truly is.  It looks very simple.  It is about 2-1/2" x 4".  It has busses on it, one side labeled "battery" with a  pos & neg. buss, and the other side is labeled "array" and has a pos & negative buss.   No "working" or adjustable parts.  Just a small red indicator light showing all circuits are complete.  Each solar panel has a single pos & neg lead that are landed on the charger and each battery has the same.  It does not appear to be three stage, maybe just a straight  trickle chrage.(?)  You guys have given me the info. I was hoping for and a good place to start my work.       Thanks!!

Note that the house batteries don't HAVE to be located in the engine room. You may have room for a couple more golf batteries somewhere else, and just tie them in. Do your house batteries serve as a starting backup? If so, just make sure the cables are big enough to carry that load.

I'm going to guess from their physical size that your panels are in the range of 50 watts each, and together are probably good for 30-40 amp hrs or more a sunny day.

I think your "charger" is actually a controller to prevent the solar panels from overcharging the battery. Solar panel output fluctuates all over the place according to light input and temperature; on a bright, cool spring day you can get as much as 20 volts at the panel. Without the controller you could fry your batteries. You can get more modern, three stage, power-point tracking controllers but they're NOT cheap. With the array you're using now I'd stick with the controller you have. It probably came with them, and it sure doesn't look like it's damaging your batteries. It may be better not to try to "fix" it. However in the event you find you're not getting "quite" enough charge after installing more batteries, you could look into a new controller; it'll be more efficient than the old one and it'll cost less than adding another panel.

Interesting reading on the subject:
http://learn.altenergystore.com/
http://www.solar-electric.com/...ar_electric_basics.htm

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Willie
She's a tired old barge but she's paid for! http://s71.photobucket.com/alb...p;current=ef324993.pbw

Edited: 01/29/2008 at 06:56:40 PM by stmbtwle

A great place to shop solar prices, (panels and all accessories) is at this place here.

Skally

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Chance Favors The Prepared Mind!

That's another good site!

My recommendation would be to sort out your batteries first and THEN worry about the solar. You may not have to change anything. A bigger battery doesn't necessarily mean you need more solar; it depends more on how much you actually USE.

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Willie
She's a tired old barge but she's paid for! http://s71.photobucket.com/alb...p;current=ef324993.pbw

You guys really nailed it.  Everything you point out is what I was thinking about, but needed "reassurance" from people that know what there talking about, so thank you very much.  And to answer you question, no, my house batteries are not a back up to my starting battery.  If I were to lose my starting battery, I have a few options.  I carry a generator and battery charger on board, I have a portable back up type "jumper" battery on my ski boat, which is always with our houseboat, and I have dual batteries in my ski boat.  So, my starting batteries are not a concern.  And I think you a right, if I wanted to add another bank of 2 more 6 volts, I'd probably just add another battery box in addition to the one I have, and not try to enlarge the one I have.  

This is a subject that has been much discussed (and cussed) not just on this forum but on the 6 or 7 other boating forums I belong to and on several RV forums as well. 6 volt or 12V? Well what really matters is what you have at the end, 12V and how many amp hours. Amp hours determines how long the batteries will last with a constant drain.

The other issue is construction. Golf cart batteries are true deep cycle batteries. Most (not all) Marine deep cycle batteries are not "true" deep cycle batteries. However there are Marine 12V batteries available that are true deep cycle batteries. But most are combo batteries that can be used as house batteries, and to start your engine.

But, what counts here is amp hours. a set of quality 12v marine deep cycle batteries, when properly charged and maintained will give just as long and faithful a service as 6V golf cart batteries. So it amounts to "you pays your money and you takes your choice" Both will do the job equally well.

Here's your reading assignment on batteries. http://newboatbuilders.com/pages/electricity3.html

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Ike
"Don't tell me I can't. Tell me how I can!"
New Boat Builders Home Page
My Boating Safety Blog
My Boat Building News Blog

Uh oh.... more homework

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Willie
She's a tired old barge but she's paid for! http://s71.photobucket.com/alb...p;current=ef324993.pbw

A good read, thanks Ike

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Riverliver

The link and it's related links had great info. - thank you.