Dual Charging System

Help! I have an 80 Watt panel w/7 amp charge controller charging a single battery that we use to power DC lights/outlets. I also have a generator that we use to power Air Conditioners/etc. Can I connect a marine style trickle charger w/built in controller to the same battery that the solar panel is connected for a "dual charge system" whenever we are running our generator? Will this harm the battery or wiring in any way? Is this overkill?


  • icarusicarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Dual Charging System

    The short answer is Yes, you can without any trouble. The question I would ask however, is, Is this a UPS system, or are you charging during the day and running the lights at night? If the former, there would be little reason to add the charger (although I don't know how big your battery is) If the latter, what are you doing to monitor the battery condition.

    As has been said before "do the math". Figure out what your battery capacity is, what your average loading is, and how much charge capacity you need.


    PS Without knowing for sure, but your 80 watt panel (assuming 12volts) could exceed the amperage capacity of your controller depending on temperature. Panels can exceed their specs as the temperature drops.
  • System2System2 Posts: 6,290 admin
    Re: Dual Charging System

    I am not clear what a UPS system is - the battery that we have is an Interstate 8D-XHD. We have DC lights/plugs and a 900 Watt inverter connected to it at this time that will be on mostly at night.
  • icarusicarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Dual Charging System

    Sorry, UPS = Uninterruptable Power Supply.

    A couple of things. I don't know the amp/hour capacity of your battery but here is another observation (or three!)that you may have gleaned from this site.

    Most people start out with solar with A:Not enough battery, B: Not enough recharge capacity for the battery(s)and C: Too much load.

    The first rule is that any "deep cycle" battery should (regardless of how it is hyped!) never be discharged more than 50%. (Preferably no less than 20%) Rule number two is that a battery should be FULLY charged as soon as possible after dischared, but in no case more than a day or two, or the battery life will be significantly shortened.

    There are formulae here that give a good ratio of battery capacity to solar capacity to ensure good battery life.:http://www.batteryfaq.org/ http://www.windsun.com/Batteries/Battery_FAQ.htm#Lifespan%20of%20Batteries http://www.rpc.com.au/products/batteries/car-deepcycle/carfaq4.htm#charge

    It is a pretty simple equation. For every amp/hour you draw down, you hae to put about 1.25 amp/hours back in. If for example you are routinely taking out 10 amp hours per day, at a minimum you have to put 12.5 back in. If you are only getting 6 from the sun, then the other 6.5 must come from another charging source.

    As I say, most people over estimate the capacity of their batteries and underestimate their loads. A good battery monitor is essential as well.

    Good luck,

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