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Old 30-09-2007, 11:34   #1
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6 volt vs 12 volt?

Mt boat came with two banks of batteries. One with two 12 volt batteries for starting the engine and a second bank of eight 6 volt gel cell batteries that are made for golf carts for general use.
Would I be better to change out the eight 6 volt batteries for four 12 volt batteries? Or add four more batteries for extra power?
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Old 30-09-2007, 11:55   #2
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Not exactly sure what you are asking. I think you will find your bank is wired in series/parrelell, giving you a 12V system, if voltage is what you are refering to. Or are you wanting to increase capacity?? If it is capacity, then what Ahr rating do you currently have??
Depending on age of the bank, it is difficult to add new to anything over ruffly 12months of age. The new will not charge the same as the old and the system will end up out of balance and not charge safely. So if your bank is older, which I assume it is, you need to change out the entire bank and increase it to the capacity you want.
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Old 30-09-2007, 12:02   #3
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Probably it would work out about the same. Check how many amp/hours the batteries are. ie. You might have 8 x 200A/h 6 volt batteries = 800A/h at 12 volts. 12 volt batteries the same physical size would likely be around 100A/h, so 8 of them would still be 800A/h at 12 volts .
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Old 30-09-2007, 13:42   #4
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Assuming that your batteries have been wired up into 12-volt banks, it doesn't matter what voltage each is. Lead acid batteries are built from individual cells, and each cell has a voltage around 2.2 volts. In order to get more capacity (amp-hours) you need to make each cell bigger, and that means heavier, and eventually you can't lift or drag the battery because it is now too big and heavy. Industrial batteries (like those used to power electric fork lifts) may be made from six 2.2 volt cells, each one the size of a car battery and designed to be replaced individually--because the completed battery would be too large and heavy for one or two men to lift.

The odds are that either the previous owner got a great deal on 6V batteries (golf courses use lots of them for golf carts, so they get a volume discount) or there is some other simple physical reason (too tall, too wide, too heavy) why they bolted together more 6v batteries instead of using 12v batteries.

If you look into what is available, and the dimensions and weight of them, it may become more obvious why the PO did things the way they were done.

In theory, it would be more reliable to use fewer batteries, as you will have fewer cables and fewer terminals to tighten and clean, etc. In practice--the job can be done either way.
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Old 30-09-2007, 14:04   #5
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Battery use and theory can be a bit complicated and confusing to many of us. Some people feel the six volt batteries can take more abuse than some twelve volt systems and the charging controls do not have to be so precise. Sometimes as has been mentioned size and price and it seems to be a personal choice.
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Old 30-09-2007, 14:37   #6
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I've had both. I switched the last boat from 6 - 6 colt golf carts to to one 12 volt starting battery and 2 12 volt AGMs The current boat is back to 4 golf carts and a starting battery. There really isn't any reason that the voltage of the batteries matters. The technologies do have differences and costs.

Flood batteries can develop a bad cell and when a one cell goes bad it tricks the regulator into overcharging all the cells and eventually trashes them all from too much voltage. More wet cells means the posibility could be higher. If you are using 8 deep cycle high amp hour golf carts I think you need to examine the whole system. It seems doubtful you could properly manage and charge that many batteries. Not fully recharging them can lead to a lot of problems assuming you have proper voltage regualtion and watched all the cells on a regular basis.

Batteries really are a big picture evaluation. It's not just what kind of batteries you have, it is the whole system and the whole scheme of how much power you use and how you get it all fully charged again. The details of how it is put together and if you have all the regualtion properly adjusted matter more than the type of battery you use.

You'll find a wealth of battery discussions here with some really well verssed experts. It takes only a few readings to pick out the people that really do know this material well. It does however demand you map out your entrie electrical system and come up with amp hour useage patterns and charging requirements. When you do the math it works itself out and then you'll know for sure. Not doing this can waste a whole lot of money. With 8 batteries you have a serious investment at stake and it could all be trashed with a poor design.
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Old 30-09-2007, 14:46   #7
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More info

We just bought the boat so still learning about it. It's in Newport, OR and I'm in Denver, CO. Won't be back till Christmas.
I checked the batteries before we left and found them in boxes set up as pairs. They appear to be just as big as regular car batteries or maybe a bit larger. I'm just trying to get the most amount of storage out of the space available on my boat. Plan on doing some extensive cruising next few years.

The batteries date back to 2005 and appear to be in great shape. The entire system is monitored by a Xantrex control board and gets charged at the dock as well as when the engine is running--two alternators on the engine. The system is connected to a Heart Interface Freedom Inverter/charger with a Link 2000 integrated battery monitor and inverter control unit.

I'm not sure as to more information than that. I just want to get the biggest bang for my space.
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Old 30-09-2007, 16:06   #8
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It really sounds to me (based on the quality of the components you have mentioned) that you have a very well thought out DC system.

I wouldn't change a thing yet - until you know you need that extra space or something goes wrong. This is even more true since you mention you won't be back to the boat for months.
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Old 30-09-2007, 16:58   #9
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Two issues. You cannot mix gel cell and standard lead-acid batteries together as far as charging is concerned. A charger meant for lead-acid batteries charges at a higher charge voltage than does a charger meant for a gel cell battery. A lead acid charger can damage a gel cell battery. Get rid of the gel cell or have nothing but gel cells with the charger set to the correct type of battery.

The other issue is ampacity of a 6 volt golf cart battery vs that of a standard 12 volt battery. You can get more amp-hours out of two 6 volt deep cycle batteries put in series than one 12 volt deep cycle battery. Golf cart batteries have more plates and more capacity than a comparable 12 volt battery. I'm not saying that they are the equivalent, I am saying that TWO 6 volt batteries have more amp hours than one 12 volt marine grade deep cycle battery. Check the West Marine catalog and you will see.
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Old 30-09-2007, 17:07   #10
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"I am saying that TWO 6 volt batteries have more amp hours than one 12 volt marine grade deep cycle battery. "
David, something is lost in translation. Two six volt batteries bolted up make one twelve volt battery. Volts and amps have nothing to do with each other, if you lash up two 100-AH 6V batteries you'll simply get one 100-AH 12V battery.

But if you buy one 12V battery instead of two 6V batteries, you'll have one less set of cables and terminals, and less space and weight wasted by the physical cases. All else being equal, IF you can find the 12V battery in a physical form factor that fits the boat (and you can lift) it should be cheaper and higher capacity than two 6V batteries. If only because it is one product instead of two, and one set of case walls instead of two.

West Marine is convenient but hardly the best place to go for batteries, there are all sorts of physical standards for size and capacity and some manufacturers offer a far larger choice than others. West only carries the most popular conventional sizes.
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Old 30-09-2007, 17:53   #11
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I also have 8 six volt golf cart batteries for my house batteries. I like that even with no wind or sun for charging The fridge and rest of usage only runs them down around to 12.5 volts after 24 hrs. Then Im forced to run genset for an hour to bring them back up to gravity. Trying to keep in ninety percent range as I hear I will get better battery life that wayl
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Old 30-09-2007, 17:59   #12
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6v golf cart batteries will hold up better to the demands of cruising than 12v.
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Old 01-10-2007, 00:26   #13
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Then Im forced to run genset for an hour to bring them back up to gravity.
Mate, either that is one huge mother Genset, or you are not bringing the bank up to charge. I suspect the later, because even if it was a big mother Genny, you can only recharge approx 25% of the total bank size. So if you had a bank of 800Ahr and have taken 400Ahr out over the 24hr period, then you can only charge at a rate of 100Ahr. Which means you need to be running the genny for four hrs to get back to full charge. But even then, that doesn't work, because the batteries are not 100% efficient, so you need more to top off. Then seeing as most chargers drop off the current supply as the battery increases, chances of 100A for four hrs is also rather remote. So when all tallyed up, you could be needing the genny to run for more like 5-6hrs to top off so you can get another 24hr day again.
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Old 01-10-2007, 01:17   #14
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Wheels - Are you getting the 400ah above based on the voltage drop?

A fridge and some lights shouldn't take 400Ah in 24 hours? +16 amps continuous draw?

My fridge is 3a and some lights - 24 hrs <100ah...
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Old 01-10-2007, 02:40   #15
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Nah mate. It is assumption really. The original poster has not stated actuall Ahr capacity. I am just assuming he has 800Ahr, as 6V 200Ahr batts are not uncommon and not at all large. So if he is dropping to 50% over 24hrs, I am just using 400Ahr as a figure to make an example. What ever the actual actually is, the main concern I am trying to show is that 24hrs of discharge can not be rectified by one hr of charge, or...400Ahr or even significantly less, can not be replenished in 1 hr.
I do however, have one fridge/freezer that consumes a total of 17A @ 12V continuosely. It does not cycle. As a result, I run it mostly on gas and at any other time, 230V. One day I am going to rip the cooling gear out of it and replace with an economical compressor type arrangement.
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