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Charging 12 volt battery from a larger 12volt battery

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  • #31
    Thanks AZ. I think I can go ahead now and build this system. If the charge controller does not like the DC/DV charger I am happy with going straight off the big battery. Thanks to all that replied.

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    • #32
      Make sure you head back with the 'as built' specs and let us know how well it is working for you.

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      • #33
        I think your best with a small inverter set up and a battery 120v battery charger. You also want to run lights and a soldering iron.

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        • #34
          I will post results after I build it.

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          • #35
            Ray - for your application, the tecmate-optimate dc-dc charger does a great job. I use one often to keep a remote industrial vehicle topped off from a larger battery that I hump out to the field.

            https://tecmate.com/products/tm500/

            It's smart for both the target and source battery. And at only 2A, will do a great job of normal charging a 14ah agm battery. Because the absorb stage is not just pure CV, but a pulse/test type of absorb, it helps bring up lagging cells without overcharging the high ones.

            If I want to be a purist, I'll take my much larger solar charged agm out there, and let the Optimate do it's thing. Then I can claim that the tractor is being maintained by solar, without having any panels in place!

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            • #36
              New, related question - any leads on a AGM charger that can run off a vehicle alternator (while the vehicle runs its flooded battery) ?
              Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
              || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
              || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

              solar: http://tinyurl.com/LMR-Solar
              gen: http://tinyurl.com/LMR-Lister

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              • #37
                Originally posted by Mike90250 View Post
                New, related question - any leads on a AGM charger that can run off
                a vehicle alternator (while the vehicle runs its flooded battery) ?
                Your alt V is clamped by the flooded battery, but you could get one of those boost buck 12V
                converters to put the voltage where you need it. For isolation, add 3 more big diodes (half
                a bridge) from the alt winding to the new 12V circuit. Bruce Roe

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