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Any 12v experts out there ??

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  • Any 12v experts out there ??

    Hi All

    Still learning about all things 12V so looking for a bit of advice. I have spoken to a number of different sources, ARB, Battery World, Baintech etc and I am getting different responses. Thought I would throw it out to the forum.

    I have a Baintech Powertop 100AH battery box connected to an Anderson plug. ARB47L fridge.

    I am getting mixed responses on whether I need a DC to DC charger to go with it. The powertop itself does NOT have a DC to DC charger. It has a 20amp battery charger built in however which charges when getting greater than 13.2V. My understanding is that the Temperature Compensating Alternator in the Fortuner/Hilux always provides at least 13.2V (could be wrong but see link

    The powertop also has a mains power charger at 6amps (obviously much slower but designed to be left on on charge at home overnight before a trip). After leaving on mains charger for nearly 24 hours I would assume the battery is fully charged and it provides 13.2V at this point.

    I took it away for a week over the break using fridge the whole time. Based on advice that I needed a DC to DC charger to get a full charge I was assuming I would have to plug in at some point (I had occasional access to mains power).

    I was actually quite amazed at how little driving it needed to top it back up all the way to 13.2V. It regularly got back up to 13.2V just after some small trips to get supplies or to the next beach. The success of the charging makes me think that I definitely don't need the DC to DC charger after all (despite advice of experts.. who of course are trying to sell the DC to DC chargers). It was no worries running the fridge for a week. Not sure how may hours per day driving on average but probably only 30-40 mins per day.

    Let me know if I am missing something.. otherwise for those contemplating a similar setup - it works fine without the additional DC DC Charger.


    Crusade, Summit Bar, Dobinsons Monotube, BFG AT.

  • #2
    im not familiar with the Baintech Powertop but since you say it only charges itself above 13.2 V you would think it did have a DCDC charger built in. My research showed me it all depends on the battery type being charged whether you use a DCDC or not. Some batteries can handle a lower charge voltage , many do not. If you are only running a fridge you can get away without a DCDC but if you have a winch they are required.
    there is more to this i'm sure , but i ended up with an Ironman 40A DCDC and havent looked back. the Ironman unit also provides for auto jump starting , which for me was a mandatory requirement. I'm happy to learn more on this subject all the time.
    2016 GX , in White


    • #3
      thanks for the response.. it definitely does not have a "DC DC" charger - just the standard alternator charger. I believe it is a Gel battery.

      the more I look into it all this 12V stuff ii is a real "dark art" .. everyone seems to have a different view !

      anyway it seems to work.. just trying to work out if there is anything I have missed in preparation for a longer trip without the option to plug in (which I didn't need anyway). I guess a solar panel of some kind will be the next addition. Those solar blankets look like they dont' take up too much space
      Crusade, Summit Bar, Dobinsons Monotube, BFG AT.


      • #4
        Hey 4Tuner,

        I am no expert but how i understand batteries is AGM and sealed deep cycle batteries prefer to have a current controlled charger. Speaking very generally they like to charge at 10% of their total current rating. 100Ah battery likes to charge at 10A. Your alternator pumpes out alot of juice and can cause some sealed batteries to bulge, boil and explode. So a charger whether it's dcdc or just a current limiter should be used with these batteries.

        lead acid batteries dont mind a bulk charge and they are used as starter batteries in cars. They can be hooked up to your alternator.

        But this is where i believe the dcdc sales pitch comes into it. A lead acid battery (note figures depend on your battery) needs to be charged around 14.4v to reach 100% charge. So if you have 100Ah battery it needs to be charged at 14.4v to get 100Ah. I have noticed my fortuner alternator sits around 13.6v. This isnt enough to get my battery to 100% it could be (please read you battery spec sheet) around 80% meaning you only have an 80Ah battery. This will effect your run time of accessories.

        So dcdc chargers give your battery 100% state of charge and can safely charge most types of batteries. Depending on brand they can do other maintenance functions on the battery such as equalization. The idea is they will increase the life of your battery. And safely charge AGM and other types of batteries you might run in a caravan or boat.

        Dcdc chargers do charge slower than an alternator and can need to drive for an hour or two after a deep discharge to bring them back up. I have a 25A dcdc charger and it takes about that long.

        The interesting thing to note is i run an Intervolt charger and the boost voltage for SLA batteries is 14.4v but the float voltage is only 13.2v which is less than the alternator. So it really depends what type of second battery you want to run and whether you are depending on your battery operating at 100% or whether 80% covers your needs as to whether you need a dcdc charger.

        I went for one (i have no affiliation with the manufacturer) because i liked the screen i got with the Intervolt it tells me state of charge, both battery voltages and i liked that it has a built in solar regulator.

        Hope that i havent lead you up the garden path thats just what i learnt when i was looking into it for mine...


        • #5
          I may be wrong but I always think of it this way... 13.2V is only the "intensity" of electricity charge flowing through the battery. It is not the measurement of how much energy being stored in the battery. So over the short duration of driving time, a charger may have managed to boost voltage up to 13.2V, but it doesn't mean the battey is completely charged. Charge capacity is measured with time of consumption, as in amp-hour, not voltage.

          Quantity of charge flowing through the battery is measured in amps, but this is not to be confused with volts. The energy resulting from the flowing of electricity from the battery is measured in watts.

          So i am in the impression that a DC-DC charger would boost the amp, to increase the amount charge flowing into the battery.


          • #6
            Here is a link that explains the voltages required to charge different types of batteries to 100%. I run a N70t deep cycle lead acid battery personally so i chose to paste a link because im familiar with it.



            • #7
              Thanks for the comments..good to hear other views.

              I now understand the dc to dc charger is important for conditioning thr battery which is probably more crucial for a permanent install.. considering mine only goes in for trip and then stays on the shelf fully charged from mains power.. i will put the money a dc dc charger would cost toward a good quality solar panel blanket instead.

              Happy with the powertop so far.. attractively priced for sure and can buy through arb
              Crusade, Summit Bar, Dobinsons Monotube, BFG AT.