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Bcbickford35's avatar
Bcbickford35
Explorer
Jun 16, 2014

6 volt versus 12 volt HELP

I have 2005 keystone TT I currently have 2 12 volt batteries that are shot. I have enough space for 3 batteries. About half our camping is boondocking. Am I better off replacing with 2 6 volt batteries, or 2 6 volt and 1 12 volt, or just replacing the 2 12 volt. Your advice is much appreciated

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  • BFL13's avatar
    BFL13
    Explorer II
    Jun 23, 2014
    Ok so what about a 6 in series with another 6 that has lower capacity?

    A guy in our campground has this with six-year old 6s that came with his new- to- him trailer. One has three cells just in the green and the other has the middle cell in the green and the outer two are in the red. (when "full"--I have helped him with the charging, Vector and solar both)

    The pair still acts "normally" for voltages, discharging and recharging. He can even use his microwave and toaster, drawing over 100 amps for a few minutes with no problems seen.

    His plan is to keep using the pair until something bad happens, then get new batteries. However, I am surprised the combo works so well as it does.

    Anything in that applicable to the three-6s combo?
  • RJsfishin's avatar
    RJsfishin
    Explorer
    Jun 23, 2014
    Well what happens when I start my MH w/ 1/2 dead house batts, and the chassis batt is full charged ?? Most all the amps go into the house batts, that's what happens ! And I have the amp and volt meters everywhere to prove that.

    I'm not saying 3 6'er will work correctly, but you guys are sure doing a poor job of explaining why not.

    wwest wrote:
    RJsfishin wrote:
    I never could see why the 3 6'ers wouldn't work, but the hi tech'ers on this forum wouldn't have no part of it.

    Maybe look at it in a reverse flow fashion,......if you were charging the 3 6'ers, dare tell me they wouldn't charge equally. So if they'd charge equally, they'd discharge equally !


    Simple, when the single 6 volt battery reaches a state of full charge the 2 6 volt parallel batteries have each only reached 1/2 of the charge "power" that the single battery received.

    50 amp charge current, only 25 amps for each of the parallel batteries.

    Worse yet, in order for the total fully charged level terminal voltage to reach the nominal 12.8 volts the single battery will be being overcharged and seriously outgassing.
  • wwest's avatar
    wwest
    Explorer
    Jun 23, 2014
    RJsfishin wrote:
    I never could see why the 3 6'ers wouldn't work, but the hi tech'ers on this forum wouldn't have no part of it.

    Maybe look at it in a reverse flow fashion,......if you were charging the 3 6'ers, dare tell me they wouldn't charge equally. So if they'd charge equally, they'd discharge equally !


    Simple, when the single 6 volt battery reaches a state of full charge the 2 6 volt parallel batteries have each only reached 1/2 of the charge "power" that the single battery received.

    50 amp charge current, only 25 amps for each of the parallel batteries.

    Worse yet, in order for the total fully charged level terminal voltage to reach the nominal 12.8 volts the single battery will be being overcharged and seriously outgassing.
  • wa8yxm's avatar
    wa8yxm
    Explorer III
    Jun 23, 2014
    Can you "3 sixes" guys not see that you'd have one of 3 states
    Six volt battery bank
    Eighteen volt battery bank
    (Note that neither of these meet the 12 volt need of the RV)
    Or a battery bank that would think it had two batteries in parallel one with 3 shorted cells (Good way to kill batteries)

    Or a battery bank where you had one BIG and one Small battery in SERIES (Again will not work).

    You need two sixes and a 12.

    And teh concerns about "It will not accept charge at the same rate" are groundless, True, but groundless. I've proven it over and over. (By testing)

    There are two ways to calculate charge rate, Amps and %charge

    If you have a 200 amp battery and a 100 amp battery in parallel, and you charge at 30 amps (just to make it easy) then the big one gets 20 amps and the small one 10.. If you draw 30 amps, the big one supplies 20 and the small one 10,

    But the state of charge on the two.. LOCK STEP, absolutely the same at all times. For if by some means one is higher than the other. Well then the other takes more of the charge till it catches up (or gives less on discharge).

    YOu can not use 3 sixes, 3 pair yes, 3 no, Sixes must be even numbered, but you can use 2 six + one 12.
  • Huntindog's avatar
    Huntindog
    Explorer
    Jun 23, 2014
    RJsfishin wrote:
    I never could see why the 3 6'ers wouldn't work, but the hi tech'ers on this forum wouldn't have no part of it.

    Maybe look at it in a reverse flow fashion,......if you were charging the 3 6'ers, dare tell me they wouldn't charge equally. So if they'd charge equally, they'd discharge equally !
    They won't accept a charge at the same rate. The two sixes would be able to accept a higher charge rate, but they can't because the lone six will be the bottleneck. So yes they will charge equally, but at the slower rate. They will all end up at a full charge.
    When discharging, the lone six will again be the limiting factor. When it is discharged, the two sixes will still have plenty left.... I suppose by rewiring them as normal, that you could then have a few more amps available. But then would need to rewire them again to charge. Sounds like a hassle for little gain.
  • wa8yxm's avatar
    wa8yxm
    Explorer III
    Jun 23, 2014
    Let me put it this way.. Six volt batteries are always installed in RV's in PAIRS. 3 sixers will not work 3 PAIR, will...

    Each PAIR, is the equal of an 8D 12 volt battery.. (There are no six volt batteries in RV, they are only six volt batteries while you are transporting TO the RV, Each pair of sixes becomes one big 12 volt battery)

    So when the poster said 3 sixes, I assume he meant 3 pair.

    The O/P has room for 3 batteries.. Thus he can put in 2 sixes and ONE 12, but he can not use 3 sixes.
  • tenbear's avatar
    tenbear
    Explorer
    Jun 23, 2014
    It seems to me that if you take the 3 batteries down to 50%, the single 6v battery will be down to about 33% while each of the 2 6v batteries in parallel will be down to 66%. Doesn't seem like a good plan.

    But what do I know.
  • MEXICOWANDERER's avatar
    MEXICOWANDERER
    Explorer
    Jun 23, 2014
    3 3-cell batteries...

    Connected in series 18 volts

    Connected for 12 volts, one left over, doing nothing.

    Refer to batteries by CELL COUNT per string.

    Then how many strings *parallel* you have

    "I HAVE 2 STRINGS OF SIX CELLS EACH"
  • BFL13's avatar
    BFL13
    Explorer II
    Jun 23, 2014
    Have to run a capacity test on them each way, but how do you know the 20hr rate to use for the ten hour run down to 50% if you don't already have an idea what the capacity is? You know you are at 50 by SG and voltage (after voltage bounce back for an hour)

    BTW Phil, it says in that Trojan guide mena linked that using a resistance test method for measuring capacity on a deep cycle batt is bad for it.
  • RJsfishin's avatar
    RJsfishin
    Explorer
    Jun 23, 2014
    I never could see why the 3 6'ers wouldn't work, but the hi tech'ers on this forum wouldn't have no part of it.

    Maybe look at it in a reverse flow fashion,......if you were charging the 3 6'ers, dare tell me they wouldn't charge equally. So if they'd charge equally, they'd discharge equally !

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