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Thread: Seeking Low Voltage Expertice Advice

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    Default Seeking Low Voltage Expertice Advice

    Will two 6V deep-cycles rated at 220 AH wired in series give you more AH's than two 12V deep-cycles rated at 110 AH wired in parallel
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    Member Dan in Alaska's Avatar
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    No.

    Two six-volt batteries with 220AH (ea) will give you 12V and 220AH, when wired in series.

    Two 12V batteries with 110AH (ea) will give you 12V and 220AH, when wired in parallel.

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    So using 6V has an advantage over 12V is a wives tale?
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    If the application is a boat battery the two 6v 220hr will have more AH over time. In the short term there would be no difference.

    My opinion is base on the 6v battery are Golf Car batteries.

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    Basic ohms law says that, in parallel volts stay the same and current changes. In series, voltages changes and current remains constant.

    Te only advantage you MIGHT get out of rigging 2 6v batteries in series to get 12v is size and weight. Maybe. You are not going to get a doubling of amp-hour capacity.

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    Quote Originally Posted by MacGyver View Post
    If the application is a boat battery the two 6v 220hr will have more AH over time. In the short term there would be no difference.

    My opinion is base on the 6v battery are Golf Car batteries.
    How do you arrive at that conclusion, MacGyver? 220 amp hour capacity is 220 amp hour capacity regardless of what your voltage is. (Your WATTAGE will be different if you change your voltage, but in the case of parallel batteries, amp hour should be the same whether you use two 6 volt or one 12 volt battery.)

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    Quote Originally Posted by FL2AK-Old Town View Post
    How do you arrive at that conclusion, MacGyver? 220 amp hour capacity is 220 amp hour capacity regardless of what your voltage is. (Your WATTAGE will be different if you change your voltage, but in the case of parallel batteries, amp hour should be the same whether you use two 6 volt or one 12 volt battery.)
    I was told that the 6 volts are designed to bounce back better after a heavy discharge (more cycles). I suspect they have heavier plates, but have never pulled one apart. That is why they are used in golf carts.

    I have used both 12 volt deep cycle batteries and 6 volt batteries in series as my house bank, the 6 volt out perform the same AH 12 volt batteries. I currently have four 6 volt in series/parallel and am happy with the results.
    Spending my kids' inheritance with them, one adventure at a time.

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    Quote Originally Posted by FL2AK-Old Town View Post
    How do you arrive at that conclusion, MacGyver? 220 amp hour capacity is 220 amp hour capacity regardless of what your voltage is. (Your WATTAGE will be different if you change your voltage, but in the case of parallel batteries, amp hour should be the same whether you use two 6 volt or one 12 volt battery.)
    This is going to be a very simple answer to a complicated question.
    A 220AH battery is only a 220AH when new and fully charged.

    Batteries deteriorate if they are not charged properly most o/b engine can not keep a house and starter battery to full charge. Golf Car batteries are cheaper and will take more abuse there for lasting longer than other batteries in most boat application. IMP

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    Quote Originally Posted by Doug from Anchorage View Post
    Will two 6V deep-cycles rated at 220 AH wired in series give you more AH's than two 12V deep-cycles rated at 110 AH wired in parallel
    Short answer is YES, long answer is its complicated, what is the charging out put of your motors alternator?
    How far (long) do you run to "fill" the batteries back up after discharge.

    There are some high quality AGM batteries that will give you the same as (2) 6V Golf Cart batteries, but you are going to spend $ 400-600.
    Its hard to argue with 2 GC batteries for 80 bucks a pop.

    A AGM battery typically will accept a higher rate of charge, last longer and does not discharge so endures cold weather much better than a typical lead-acid battery.

    Electrical systems and particularly charging systems are the least understood system on a boat, often undersized in term of output, and AH capacity...Then things gets added, and more things get added.....add then the charging system doesnt run long enough to fully charge the batteries.

    Ideally one would make a list of what the draw current is when anchored overnight in normal conditions, then do the math, how long will the battery last? Then know what the output is of your charging system and then you will know how long you have to run to "refill". You would need to measure the actual output as often systems do not put out what they indicate on the tag.

    There are some pretty cool battery monitors available or a Volt and good AMP gauge will tell you what is going on.

    A good rule of thumb is a fully charged battery is 12.7 V and a fully discharged battery is 11.7 V, these can vary depending on type of battery...
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    stick with the 2 6v batteries in series. batteries in parallel must be connected "correctly" with balanced paths (equal resistance). if not done correctly, one battery may carry all of the charging/discharging and the others will do much less work (and one battery will probably wear out before the others). i remember there being a downside to series also (i forget) but can be easily remedied by flipping the batteries around between seasons so their + & - are connected in the opposite manner. plus, if they're flooded batteries, the 12v batteries have 6 cells to maintain fluid in (whereas the 6v's have just 3)

  11. #11

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    Thanks all for the advice. I love this forum. I'm going to go with the 6V in series for two reasons: 1. Better rebound in cycles and 2. Easier maintenance (6 cells instead of 12).

    Thanks again.
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    Quote Originally Posted by Doug from Anchorage View Post
    Thanks all for the advice. I love this forum. I'm going to go with the 6V in series for two reasons: 1. Better rebound in cycles and 2. Easier maintenance (6 cells instead of 12).

    Thanks again.
    Not knowing more about your boat and how it used, two 6v Golf Car batteries is a good choice. I should mention a 12v battery has 6 cells, a 6v battery has 3 cells and it takes 2-6v batteries in series to make a 12v batteries. You will still have the same number of cells.

    Unless you over charge a wet cell battery and boil the water out you will not need to add water. From what I know of boat charging systems that will not happen.

    Happy boating.

  13. #13

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    Probably the biggest disadvantage of using 6v batteries in a marine application is that you will have twice as many connections that will corrode and the added resistance from the corrosion adds load to the charging system.

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    Quote Originally Posted by MacGyver View Post
    Not knowing more about your boat and how it used, two 6v Golf Car batteries is a good choice. I should mention a 12v battery has 6 cells, a 6v battery has 3 cells and it takes 2-6v batteries in series to make a 12v batteries. You will still have the same number of cells.

    Unless you over charge a wet cell battery and boil the water out you will not need to add water. From what I know of boat charging systems that will not happen.

    Happy boating.
    Guess I should have been more clear. To get the same AH's as the 6V's, two 12v's are needed which gives you 12 cells to maintain. Anyway, I'm going to the 6V application. Thanks again!
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    Quote Originally Posted by Doug from Anchorage View Post
    Guess I should have been more clear. To get the same AH's as the 6V's, two 12v's are needed which gives you 12 cells to maintain. Anyway, I'm going to the 6V application. Thanks again!
    Both Trojan and Odyssey (and others) make 12V batteries that will get you in the 200+ AH range in a single battery, so only 6 cells same as 2 6V, and AGM are maintenance free. However you are looking at ~$600.00 batteries. Thats a lot of coin to lay out.

    There are advantages, lifespan of a quality battery is longer than a typical lead-acid. AGM are designed for a 12 year life (typically) and frequently will last longer. Also its a little easier to diagnose a battery failure when you have just one house battery. But thats relatively minor. I dont know what the life of GC batteries are...? I would expect 3-4 years and would be very pleased with 6 years......In the long run I expect it would be a wash and maybe the AGM would win out simply because I know I wouldn't have to think about batteries for a while.

    Also AGM batteries are more durable in applications where something is not used daily or frequently.....they simply don't lose their charge...even when left in subzero temps...... Lead acid batteries last longer when cycled more often.

    Depends on how long you plan to keep the boat...

    I am immersed in a boat rebuild project and will most likely buy some GC batteries to start with.........see how it goes and then maybe a AGM....
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    More important is, what size Honda Generator do you have on the boat to recharge the batteries after they go Kapoot?

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    Quote Originally Posted by pacific23 View Post
    More important is, what size Honda Generator do you have on the boat to recharge the batteries after they go Kapoot?
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    You need a 2000, because a 1000 will not run the coffee maker and your hair blow dryer at the same time!

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    What are you guys using as hold down trays for your golf cart batteries? I don't have the overhead room for a battery box.

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    If you don't have them in a box you have to have terminal covers, I got nicked on my CG inspection last year for that. None of my Batts have boxes, the hold downs are a frame on the floor with a strap over the battery.

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