Battery charger to top off/maintain battery bank

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  • Switchback
    Junior Member
    • Jan 2016
    • 28
    #1

    Battery charger to top off/maintain battery bank

    I have a solar panel setup on my ice house. 240 watts from the panels into a 12v battery bank run in parallel. I know parallel isn't the correct way of doing things, but the batteries were pretty much free and everything in my house (lights, fans, tv etc) are 12v. The current batteries are 7-10 years old...I'll be replacing them with 2 Trojan 105's next year.

    For the first time I will be using my shack in the summer. Unfortunately it will be placed in a heavily shaded spot so I'm worried about keeping my batteries happy. I have 110 power on shore, so I'll be running a charger.

    My question is whether it's a good idea to use my ctek 7002 (7amp smart charger) in this application or if I need to get a different one? Do the smart chargers get pissed off/confused if you are pulling current out of the batteries while it's trying to charge?
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    • Sunking
      Solar Fanatic
      • Feb 2010
      • 23301
      #2
      Originally posted by Switchback
      IMy question is whether it's a good idea to use my ctek 7002 (7amp smart charger) in this application or if I need to get a different one? Do the smart chargers get pissed off/confused if you are pulling current out of the batteries while it's trying to charge?
      No, they are made to do that. They do not care where the current goes. With shade and shore power you have no need for solar, nor will solar work.

      Your challenge is a 7 amp charger is not enough to charge any battery larger than 70 AH. A pair of trojan T-105's need 20 to 30 amps to charge properly. If you had sun from sunrise to sunset using MPPT requires 250 to 400 watts of panels. Shade, not possible.

      MSEE, PE

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        • Switchback
          Junior Member
          • Jan 2016
          • 28
          #3
          Thanks. I didn't think it would work but I thought I'd ask guys who know more then I do.

          Anyone have any recommendations for a charger to use in the summer? I've heard xantrex has good chargers but from reading reviews it seems they're having some problems these days.

          As far as my new batteries for next year, I knew my panels were going to be under sized for 105's. I think I want a 150ah bank because I think that's the proper size for my panels but it seems like kinda an odd ball size (unless I go with parallel 12v batteries which I don't want to do). Lots of options around 100ah and 200 ah but not much in between. I use the house for 2 days and then it sits and charges peacefully for 5 days.

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            • Switchback
              Junior Member
              • Jan 2016
              • 28
              #4
              I've looked into bigger battery chargers, but most of them bulk charge at 14.4. Trojan batteries, as well as some other batteries I've seen want 14.8 on a bulk charge. Most chargers I've seen are also .2-.4 volts below Trojans recommended absorption and float levels.

              In a practical application, does that voltage discrepancy really matter? Solar CC charge at highly varied rates, depending on sun and stuff so my guy says it's just fine.

              Here is one I've been looking at. This is a 55amp model, I'd drop down to the 35amp model

              PowerMax PM3-55 110 V to 12 V DC Power Supply Converter Charger for Rv Pm3-55, 55Amp https://www.amazon.com/dp/B00F8MC440..._LLzTybRBF0WVK

                Comment

                • SunEagle
                  Super Moderator
                  • Oct 2012
                  • 15151
                  #5
                  Originally posted by Switchback
                  I've looked into bigger battery chargers, but most of them bulk charge at 14.4. Trojan batteries, as well as some other batteries I've seen want 14.8 on a bulk charge. Most chargers I've seen are also .2-.4 volts below Trojans recommended absorption and float levels.

                  In a practical application, does that voltage discrepancy really matter? Solar CC charge at highly varied rates, depending on sun and stuff so my guy says it's just fine.

                  Here is one I've been looking at. This is a 55amp model, I'd drop down to the 35amp model

                  PowerMax PM3-55 110 V to 12 V DC Power Supply Converter Charger for Rv Pm3-55, 55Amp https://www.amazon.com/dp/B00F8MC440..._LLzTybRBF0WVK
                  That powermax is the one I use in my RV for 2 x 6v 232 Ah interstate coach batteries. It works just fine for them but they are really not what I would call deep cycle solar batteries.

                    Comment

                    • Switchback
                      Junior Member
                      • Jan 2016
                      • 28
                      #6
                      Originally posted by SunEagle

                      That powermax is the one I use in my RV for 2 x 6v 232 Ah interstate coach batteries. It works just fine for them but they are really not what I would call deep cycle solar batteries.
                      Ok. I'll keep shopping around and see what I can come with

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