mixing batteries

Discussion in 'Motorhome Chat' started by pappajohn, Jul 7, 2009.

  1. pappajohn

    pappajohn Funster Life Member

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    about a year ago i bought two 110ah batteries to replace the 1 old one (which wasnt very old anyway).

    took the old one off and put it on charge for a few days.
    checked the voltage a few hours after taking it off charge and it was around 12.8v if i remember correct.

    checked it again today and its reading 12.3v.....been on charge once in between about 6 months ago.

    is it worth fitting it back on the M/H as it will give me a 330ah bank?

     
  2. pappajohn

    pappajohn Funster Life Member

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    everyone opinioned out???:Rofl1:
     
  3. camcondor

    camcondor Read Only Funster

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    If you have the space for a third one, and the extra payload available, then I don't see why not....I know some people advocate using same make of batteries together and changing them at the same time, but if all 3 are working and you plan on spending lots of time away from leccy hookups, then the more power the merrier:Laughing: as long as all 3 are gel / same type - I gather that gel should not be mixed with others, but not sure about this.

    I'm sure a battery boffin will be about soon; as long as they don't dispense "advice" like some of the complete nonsense on the Towing of Smart Cars thread:Rofl1::Rofl1:
     
  4. Tony Lee

    Tony Lee Read Only Funster

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    As far as self-discharge goes it is certainly OK. Since the resting voltage was 12.8V then it is likely to have reached close to 100% charge as well. A load test (not the 10-second one they do at the battery joint) would give you the best info as to the actual condition

    If the battery is the same general type as the other two then it is pretty likely that you would gain overall capacity by adding the third battery. Obviously anything like this is going to result in some sort of compromise, but it isn't likely that you would end up worse than before.

    Batteries put in parallel are never the best option because it does introduce more chance that a failure in one will severely degrade the performance of the battery as a whole, but that can be managed by use of fuses and isolating switches.
     
  5. johnsandywhite

    johnsandywhite Read Only Funster

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    :Cool: I have been using odd AH batteries for years with no problems. Some experts says that the lower AH battery will drop the available power of a higher AH battery. IMH&HO CRAP. It is surely the voltage that stabilises the batteries between themselves. ie if a 12.8 voltage battery was coupled to a battery with 12.6 volts available. What would happen? It would equalise the 2 batteries. Nothing to do with amps. IMH&HO. :RollEyes:

    HOWEVER. IF a battery was old and only holding a low voltage? Then it WOULD have an effect on the other battery.
     
    Last edited: Jul 8, 2009
  6. scotjimland

    scotjimland Funster Life Member

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    Go for it John .. :thumb:
     
  7. pappajohn

    pappajohn Funster Life Member

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    cheers Tony,

    i understand the implications of the unwriten rule about mixing old and new but as this battery is holding a good charge over an extended unused period i needed some reassurance it would/should be ok to refit it in the van.
    i'll stick a known load on it and check voltages at specific intervals and see what it says then.

    i suppose if i refit it and dont get the expected results its easy enough to remove it again:Doh:

    thanks again:thumb:
    john.
     
  8. pappajohn

    pappajohn Funster Life Member

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    hi john,

    as the old battery is only one year older than the new ones and is the same capacity (110ah) and appears to be in good condition i'll run a discharge test and see what it does then.:thumb:
     
  9. hilldweller

    hilldweller Funster Life Member

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    I can confidently predict that it will discharge.
     
  10. pappajohn

    pappajohn Funster Life Member

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    and if it doesnt i'll be touting it round all the worlds battery manufacturers.:Rofl1:

    totally self sustainable energy.....never needs charging....totally independant of anything.:thumb:

    £MILLIONS in the bank:thumb::thumb::thumb::thumb::thumb::thumb:

    ill invent the infernal confusion engine that runs without fuel next:BigGrin:
     
  11. gazznsam

    gazznsam Read Only Funster

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    the warrenty conditions with my new deep cycle batteries state not to mix new batteries with ones over 6 months old, or ones that have gone through more than 50 cycles,

    they do an exchange thing where if one battery out of a bank fails and the bank is over 6 months old, they will replace the failed battery not with a brand new one, but with one that has done roughly the same cycles as the whole bank, they dont mention how they do that.. do they take a new un and cycle it for you, or keep a stock of partialy used batteries,

    however my batteries are 6 volters, so used in series strings, where it's more importiant to have the cells matching.

    for adding another 12 volt battery in parelell to some newer 12 volt batteries, worst that should happen is the older battery will die sooner, and when it does it may draw the good batteries down, but you'll notice when the capacity drops, so can take the failing one out of the bank, if you dont leave it too long it wont harm the other batteries.

    even mixing batteries of different capacities isnt as bad as people think, different sized batteries have different internal resistances, that allows them to accept the charge they need, tho it is best if you can avoid mixing vastly different sized batteries.

    but i'd say go for it, 50% more power would be a handy thing to have, and it'll mean you wont be taking your battery bank as low as you did before,

    i.e. if you use say 40AH a day, 3 days of discharge is taking a 220 ah bank down to 55% depth of discharge (which is over the absolute most ammount you should take out of a battery)

    3 days of 40Ah discharge on a 330 ah bank is taking it down to 36% dod, a hell of a lot better,
     
  12. Tony Lee

    Tony Lee Read Only Funster

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    What I was saying was exactly the same as Jim said - "go for it" - except that I prefer to give a bit more detail about possible consequences to avoid the inevitable "that's not right" replies. Cautions such as fitting extra fuses are for you to accept or not once you are fully informed. Most don't bother with the niceties and most never have a problem.

    Have fun with your extra free-camping endurance. Certainly beats those crowded caravan parks.
     
  13. johnsandywhite

    johnsandywhite Read Only Funster

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    :thumb: Just to make a point. On our Newmar (Solar charged), I have 2 x 115AH Standard batteries that are coming up for 4 years old, plus 6 x 100AH AGM that were 4 years old when we got them and have had them fitted now for 3 years. They do everything that I ask of them. Except of course in the deeo mid winter. If it works? Why not? :thumb:
     
  14. Douglas

    Douglas Read Only Funster

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    I think what is important thing here is the "self discharge rates" a battery with a high "self discharge rate" will drag the discharge rate of any battery that is in parallel to it down to its own rate, because the good battery will constantly recharge the discharging battery.

    Of course the trick here is to decide what is the discharge rates in the first place and making the dissision of how much will be lost.

    Doug...
     
  15. johnsandywhite

    johnsandywhite Read Only Funster

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    :Smile: Quite true Doug. BTW. I notice you have a Swift 630G? I am picking up our new-to-us commuter 2004 Swift Suntor 630G on Saturday. Had any problems? :thumb:
     
  16. pappajohn

    pappajohn Funster Life Member

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    well i refitted the third battery today:thumb:

    it sits right next to the second one under the dinette seat and the connecting wires are 50amp rated and just 8" long so no volt drop there:BigGrin:

    i put the van on EHU for the night to charge and balance the bank and the last voltage check tonight was 13.8v which is the limit for the onboard charger.
    must look at a new charger sometime as this one is only 12amp max.

    i can feel a three stage 25amp charger coming on now im running a 330ah bank....i know it should be around 60/70amp but funds wont allow.

    we'll take it from there and see what happens over time.
     
  17. Tony Lee

    Tony Lee Read Only Funster

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    Your existing "float charger" is not going to get the most out of your batteries so a decent charger wouldn't be a bad idea.

    Unless you wildcamp a lot and use a generator to recharge your battery every few days and need to keep the generator run time to an absolute minimum, a 60 or 70 amp charger would be a waste of money.

    Consider your battery - 300Ah discharged to 100Ah (deeper than it should be anyway) and needing to be recharged overnight - say 10 hours (less time than you would normally have unless you are on a generator)

    A 25A charger will do the job comfortably.
     
  18. pappajohn

    pappajohn Funster Life Member

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    thanks Tony.....i was hoping someone would say that:thumb:

    reading some other posts/threads in the past it seems a few folks recommend at charger rated at 20% of total bank capacity which is why i was thinking around 70amp

    25amp, 3 stage it is then:thumb:
    another £150:cry:
     
  19. pappajohn

    pappajohn Funster Life Member

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    just found and bought one of these.....25amp, 3 stage charger.

    £104.95 + £2.95 postage


    Amperor chargers

    hope i'v done the right thing here.:Doh:
     
  20. American Dream

    American Dream Read Only Funster

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    So THAT'S why the avatar's racing away the way it is.Fit for pole at the next GP......:Eeek:
     
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