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  • Small 40w just to charge a RV battery

    Newbie here, so hope there's no such thing as a stupid question.
    I currently have a 45w Harbor Freight 45w panel going to a cheap 20a Chinese CC to a 101ah battery that is solely used to only charge the battery no inverter or radio. Only Have the RV pos and neg leads connected to battery........................ Just got new nature power 40w panel today. It says 12v and voc is 21.3 . It came with a set of battery clamps. If I only want to solely charge the RV battery can I connect it straight to my battery OR should I connect it in parallel with the harbor freight panel "voc is like 21.6 or 23."and through the Pwm CC to the battery???

  • #2
    Sadly, what most folks don't know about the HF panels, is that the cardboard box is more useful then the panels are. The type of panel (amorphous) degrades rapidly in sunlight, and HF is not known for quality parts.
    But, you have a 45W and a 40w panel. Yes, you can connect them both to the battery at the same time.
    HF via the 20A controller.
    Can you discover if anywhere on the packaging, anything that says the 40W panel has a "Blocking Diode" anywhere ? even the cheapest of the cheap (HF) controllers have the blocking diode, and when you don't have one, at night, the battery can possibly discharge through the idle PV panel.
    It may be possible/preferable to parallel both panels at the 10A charge controller input, and let it manage everything.
    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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    • #3
      Yep, parallel the HF and Nature power panels to the charge controller.

      Unfortunately, that is still not enough to do a proper charge. An FLA battery needs about C/12 charge current *minimum* to avoid electrolyte stratification, so 101ah / 12 = 8.4A charge current. (Note C/8 would be the MAX current for FLA). With both of your panels, you are only supplying half of the minimum. Your battery will not like that.

      Unless you are using this solely as a maintainer, and not charging to any significant depth, you might do ok. But if you are discharging from full beyond about 10%, you'd be wise to start over with a panel of at LEAST 80w to service that battery properly.

      So bad news kind of - either pay up front for more panel power, or pay on the back end when the battery dies sooner than expected.
      Last edited by PNjunction; 09-05-2016, 05:35 PM.

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      • #4
        Thanks guys! Yes the HF is the basic of the basics. But I picked it up at an auction new in box for $20.00 and picked up the monocrystalline NP for $40.00 off of craigslist. Had to turn the NP away from the sun yesterday cause by 10:00 the battery was showing 14.5v. I will say that if I were going to get a small panel that the Nature power is really nice but not for $210-299 that I saw on Internet , thank God for craigslist!

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        • #5
          Originally posted by Jnj6370 View Post
          Had to turn the NP away from the sun yesterday cause by 10:00 the battery was showing 14.5v. I will say that if I were going to get a small panel that the Nature power is really nice but not for $210-299 that I saw on Internet , thank God for craigslist!
          Well, if your charge controller is set to absorb at 14.5v, this would be totally normal. Let it try to finish, don't turn away. Eventually it will either time-out (say if the controller is programmed to do only one hour of "absorb") and fall back to 13.8v float, or it will just stay that way until sunset trying to reach a minimal charge current level which it may not be able to do in a day with such a large battery if it was deeply discharged.

          A super fast rise to the absorb voltage from a deeply discharged and neglected battery is an indicator of heavy sulfation too. Don't know if you are having problems with the battery already.

          Check out the manual for your charge controller. I think you didn't need to turn your NP away at all, unless the battery is just totally thrashed in the first place.

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          • #6
            I was going to make a similar comment regarding 14.5V, it sounds totally normal to me. It is the controller's job to manage the battery voltage by dialing back the current when necessary. I'd let the controller do its job. Many of us bulk/absorption charge at 14.8V on deep cycle batteries.
            I'm an RV camper with 470 watts of solar

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            • #7
              I believe the key words that the OP mentioned are "cheap 20A Chinese CC".

              While most CC's would stop charging the battery when is it full and go to float charge some of the cheap ones may cook them till they are dry.

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