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AGM battery charging question

Discussion in 'Beginner Electronics' started by Damian, Oct 29, 2012.

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  1. Damian

    Damian Guest

    Hi guys,
    I would appreciate if I could get some advice on below question.
    I have two AGM deep cycle batteries(identical). Thye 6V batteries about
    300ah each. I am hoping to connect they on series to get 12V.
    My question is that,
    Is it safe to charge the batteries connected as above with a single 12V
    charger without any damage to the batteries or the charger?!
    I am hoping the charger simply treat the two 6V batteries as a single 12V
    battery and charge they equally without any issues.
    Thank you for any advice.
  2. ummm. AGM Batteries have slightly different characteristics to the
    batteries the charger you're considering will work well with insofar as
    charging requirements.
    I'm guessing here, but IF the batteries are basically equal in their
    resistance etc, then 12 Volt chargers might work well enough - depends
    on just what actual voltage the charger belts out in response to the
    internal resistance of the victim batteries - in other words how well
    the charger is 'regulated'. All bets are off with the exceedingly cheap,
    brightly coloured and nasty devices laughingly called chargers, commonly
    found in the local accessories store right beside the plastic wheel
    trims and furry steering wheel covers:)

    We have a few battery experts about this group , hang on, THESE groups.
    Will be interesting to see their response.
    Natch, my suggestion is that if you actually shelled out 'ard earned
    for the batteries, you'd be treating them to a real live computer
    controlled tricked up charger.
    What do you intend to use this massive power source for, may I ask?

  3. Damian

    Damian Guest

    Hi Toby,
    I am planning to use the two batteries(yes they are massive) on my small
    caravan for camping, etc.

    I do have a charger which I paid around $50 and which is advertised as a
    good maintenance charger for AGM batteries
    Here is the link for the charger.

    I also have a good regulated power supply(1V to 24V) which I built years ago
    and use as a battery charger as well. By manually manipulating the volatage
    and current with control knobs, I have been using it as a maintenance
    Only thing I don't know much about is whether connecting two batteries in
    series to gain voltage is good or not. I read that unless the two batteries
    are identical in size, condition, etc it's bad news for both batteries. But,
    are they really 'identical' even when they are brand new?! That I am not
    sure. So, I need some real help.
  4. PeterD

    PeterD Guest

    If the batteries are the same yes, series will be fine. Most
    applications (UPSs etc.) they are series and charged as a bank. Before
    charging in series you must, however, ensure that each is identical in
    capabilities (as well as specifications) and that each has an identical
    level of charge.

    Any charger to charge an AGM battery must be designed to charge those
    types of batteries. You cannot use a generic charger, you need one with
    an AGM setting.
  5. terryc

    terryc Guest

    Yes and No.
    Yes, it works fine, as long as you have an appropriate charger.
    No, you need to make sure they stay as close as possible in voltage.
    That said, you should source a 6v charger to sync them from time to time.
  6. terryc

    terryc Guest

    Erk. Rubbish. My rule of thumb is that you'll pay a similar amout for
    the battery charger as you do for the battery.

    You really need a charger that performes the appropriate stages for your
    type of battery.
    Do regular voltage checks and work them monthly or quarterly.
  7. Ok - thought so re the Van - or perhaps a trailable boat.
    The trick there is to use one of the new 'innovations' while on the
    You don't need monster cables to get sufficient Voltage to the caravan
    any more.
    There a device on the market which via trickery (OK, an invertor+ a few
    bits) which supplies 'correct' voltage to the batteries in the van/boat.
    Actually it does heaps more than that. Maybe there's one in the range
    that doesn't run a few power sources. Have a dig about on and near this
    The important thing is the ability of the thing to FULLY charge your

    < >
    Richie would say bloody maarvelos. Really.
  8. Damian

    Damian Guest

    Hi Neil,
    Thanks for the information.
    Dont they(AGM batteries) suppose to last for 5-10 years without needing any
    maintenance(privided it's kept charged properly)?
    I thought we pay extra money to get sealed AGM deep cycle batteries because
    they suppose to last lot longer than wet cell batteries.
    You don't think that's the case?!
  9. Damian

    Damian Guest


  10. Damian

    Damian Guest

    Thanks. That link was very helpful.
  11. Damian

    Damian Guest

    Thank you. I think this is a great product even though it's bit pricy. I
    think I'm going get a one.
  12. Them's the goods - there may be others out there, as I'm sure there will
    be others attempting to compete with the function, which is essentially
    a better way to charge remote batteries than previouly existed outside
    of uber epensive commercial stuff.
    The people who've installed the stuff I linked to are mightly pleased
    with it.
    Only downside I can see so far is that the device should be in a well
    ventilated location. Goes without saying that given what it does,
    there'll be a little heat to dispose of.
    Additionally the solar cell charging function ain't so redundant soon
    given the prive of the PV arrays falling day by day.
  13. Damian

    Damian Guest

    Hi Neil,
    I got little confused here.
    I would like to follow your advice and purchase a battery.
    I personally like the idea of maintaining the battery myself exactly the way
    you mentioned.
    I thought batteries with screw caps on the top are usualy automotive
    starting batteries. And the sealed batteries are the ones usually used for
    solar, caravan, UPS, etc. I thought AGM(and deep cycle) batteries are
    usually sealed.
    Do the semi traction batteries give out Hidrogen gas when it's been charged?
    If so, do I need to install in outside the caravan or uder the bonnet like
    starting batteries?
    How is this semi traction battery different from typical vehicle starting
    Can you please send me a link to purchase a semi traction battery like
    I'm in Melbourne, Australia.
  14. terryc

    terryc Guest

    125Ah are the largest common Deep discharge wet cells in Aust. Rather
    than put tweo in parallel to get larger capacity. I preferred to buy two
    6Volt 225 Amphour batteries. that was to prevent the problem of one
    failing and pulling down and maybe destroying the other.

    Another factor is my ability to lift individual batteries in and out of
    locations. I remember that the 12V 125AmpHr batteries weighed 35kg each
    Can not remember the figure for each 6V 225Amphour battery.

    My rule of thumb is that if the battery is rated in amphours, then it is
    designed for "deep discharge" use. If it is rated in CCA, then it is a
    ICE starter battery.

    This is why cheap battery chargers are a bad idea. They do not limit the
    final trickle voltage and can run wet cells dry.
    I actually go to a battery specialist who originally had traction as
    well as alarm batteries but a seems to have moved more to alarm and
    specilist motor starters(changing market in the area). Look in yellow
    pages, etc for battery supliers in industrial areas and avoid main
    street battery shops.
  15. Damian

    Damian Guest

    Thanks mate.
    The two massive 6V batteries that I mentioned aren't in my hands yet. I have
    been considering getting them to maintain a good long lasting power source
    for the van. But, now I think it may be an overkill and a pretty heavy job
    as well.
    I think I am better off with a 125Ah sealed deep cycle battery and may be a
    backup one. I reckon it's better to rely on a small generator rather than
    carrying massive heavy batteries like I was planning to do.
    What do you think about that?
  16. Damian

    Damian Guest

    Hi Neil,
    Thanks for clarifying that for me. I now know lot more about batteries than
    I did before. I think I will get a sealed maintenance free battery as it's
    bit challenging for me to install the battery outside the van and installing
    it under the bonnet is not a choice either as there's no room.
    So, I won't be able to get a battery with the ability to maintain like
    I am thinking a maintenance free AGM deep cycle battery(or two). Does that
    sounds like a good idea for my application?
  17. terryc

    terryc Guest

    You need to look at your power requirements and work them out.
    The dooles like mobile phones, torches, the radio(s)(AM/FM/UHF, etc)
    (Where did they all come from)
    The laptop
    The 12 volt TV.
    Medical machines.

    Even stuff like fans on diesel/gas space heater and/or 12V electric
    blanket. Sigh, there is even 12v hair dryers.

    When it comes to stuff like aircon, then you need to run a generator of
    sufficent size to run it. Add in the microwave to that as well.

    Over here, camp sites can be divided into those that allow generators,
    where mos caavans go and thse that don't, where most campers go. man
    people don't like one destroying the peace and quiet.
    Batteries and a solar panels are a basic way to go here if you have
    light demands like a refridgerator, lighting amd the doodles.. Most
    times you will have no problems if you have adequately specced the
    batteries to give you a couple of day's requirements.

    It is when you are camped for the week, then you can run into problems
    from it being heavily overcast all week. I have something like the honda
    generator on my plans as a emergency back up.

    I have also gone for four days capacity, so that effectively means that
    at worst case I only loose the peace and quiet for one day in four.

    If you are travelling every day/few days, like doing the big loop, that
    C-tek D250S that was linked is the way to go as it tops up your caravan
    battery from the solar panels when you're stopped or from the car
    alternator when you are travelling. you need an auto isolator that
    switches the car feed in after the car alternator has recharged your
    starter battery.

    OTOH, some places here, it just means that instead of stopping in the
    bush camps, you pay for a powered site overnight and charge your
    batteries up then.

    I'll point out that I'm talking from the Australian perspective where we
    have 30 million population spread over an area the size of
    Europe/Mainland USA, but mostly in a few big cities and little facilties
    in between.
  18. Damian

    Damian Guest

    Hi Neil,
    If I understood you correctly, you meant a mechanical unit similar to the
    built in alternator, right?!
    I couldn't find any on ebay using the keyword 'supercharger' or 'super
    charger'. It shows all the turbo stuff.
    Can you please post me a link to that?
  19. Damian

    Damian Guest

    Hi Neil,
    By the looks of it, this is an idependent unit. Basically it is a smart
    charger generator, am I right?
    I am amazed to see that its available on LPG as well.
    I wonder how they manage to compact all that stuff into a small unit. Must
    be an ingenious design.
    I definitely want to get hold of one.
    Only thing I am wondering right now is that where to install this unit.
    It's not cheap, but for obvious reasons.
    I am sure Chinese clone makers are dismantlng it right now to find out how
    to copy it. :))
  20. Damian

    Damian Guest

    Hi Neil.
    I haven't been aware these units are available here.
    I'm looking into it right now to find it.
    It should be cheaper for locals. I wonder why the Aussie one is more
    Caravans are expensive here too. UK built ones are usually better quality
    and not as expensive as the ones in here. I don't know the reason.
    Everything seems to be expensive in Oz right now. :)
    Perhaps that's how they kept the economy going witout going into a
    recession. :))
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