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  • Auto/ATV battery tender question

    New to this site. I recently built a nice single panel (300W?) system with a MidNight Kid controller and 3 140(?) batteries in parallel. All mounted onto a 3-car carport, very stable, good system for motion lighting and spare DC power. I also want to charge vehicle batteries, cars, ATV's, motorcycles, tractor, etc. I can run a straight line, but then I need to monitor it and disconnect, can't just leave it hooked up or I fear it will overcharge the batteries. What I have been trying to find is a battery tender that will take that 12v input source from the battery bank and maintain whatever battery is on the other end. I've tried Deltran Solar Jr and it's not suited for this, won't monitor smaller batteries and the unit seems to be pretty crappy. I'm trying to put these in 3 locations where I can just leave tractor/ATV/MC there overnight or for days if I forget it (out in the country here), but I don't think it's wise to leave it on a straight line from the solar system. Thought I'd just find the right "box" and all I find is AC-powered or tiny solar powered, nothing for straight DC 12V input from a battery bank. Anyone have experience with battery tenders used like this?

  • #2
    Your fears are unfounded. You want to set up the Kid Controller so it only is a FLOAT CHARGER. To do that you set Bulk = Absorb = Float = 13.2 to 13.6 volts. Pb batteries are best charged with a FLOAT CHARGER and can remain on FLOAT CHARGE for years. Utilities have been doing this for 100 years now. A good pure lead stationary battery can have up 40 years service life in FLOAT SERVICE.

    The only catch is you must select a voltage that wil work with mixed battery types. True Deep Cycle batteries float at 2.2 vpc while hybrids and SLI float at 2.25 vpc. So if you mix them you want to choose the lowest voltage in the mix. So if you have a true deep cycle battery in the mix, charge at 13.2 volts, otherwise 13.6 volts.

    Another option is just fully charge the batteries and keep them in a cool dry place. Top them off every month or so. If you were to go into say a Verizon, ATT, Battery Manufacture that stores batteries, they parallel them all up and FLOAT CHARGE indefinitely while in storage. Copy what the pros do, not what salesman or DIY tell you. .
    MSEE, PE

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    • #3
      I'm not using the Kid controller for load, just for balance/float on the storage battery bank. I take all power directly from the battery bank through a couple of circuit breakers. So I have no modulation of that power if I plug into a car/ATV battery. I do top them off every month or so, but I'd like to not worry if I can't get out there one night and just leave them. What I want is a float modulator that will take that 12V input FROM the battery bank and float anything I hang off it.

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      • #4
        Maybe I'm overthinking this. If the Kid controller is floating the battery bank, will it also "float" anything downstream of that battery bank? Not claiming to be an expert at any of this, just trying to learn. Thanks.

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        • #5
          Originally posted by gofish View Post
          Maybe I'm overthinking this. If the Kid controller is floating the battery bank, will it also "float" anything downstream of that battery bank? Not claiming to be an expert at any of this, just trying to learn. Thanks.
          Yes. The KID Controller is not a load, it is a charger. Yes it will charge any battery down stream.
          Last edited by Sunking; 03-08-2017, 05:29 PM.
          MSEE, PE

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          • #6
            I know it will charge a battery downstream of the battery bank, it's straight continuous DC power. Not trying to beat this to death up but my question is will it overcharge a tiny motorcycle battery downstream of the battery bank that the Kid is monitoring if I leave it on there for a couple of days (or say forever)? Do I care about having something downstream of the battery bank that will regulate the amount of charge going to that motorcycle battery?

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            • #7
              No the battery can be left connected for the rest of the battery life. That is what they are designed to do.
              MSEE, PE

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              • #8
                OK, I'll go with that and really appreciate your patience answering my question here. Longest would be 1-2 weeks when I'm on vacation and don't want to return to dead batteries so I'm comfortable with this.

                First system I've built, but won't be the last. These are fun and I'll have some "free" DC power out in my shop by next year. Thanks again.

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                • #9
                  Originally posted by gofish View Post
                  OK, I'll go with that and really appreciate your patience answering my question here. Longest would be 1-2 weeks when I'm on vacation and don't want to return to dead batteries so I'm comfortable with this.

                  First system I've built, but won't be the last. These are fun and I'll have some "free" DC power out in my shop by next year. Thanks again.
                  You are welcome.

                  Do as you wish, but there is no problem leaving a fully charged battery for a month or two as long as it is disconnected and not being drained by parasitic loads.

                  MSEE, PE

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