thisucks1: Help with battery charging for off grid system

This discussion was created from comments split from: help!....pwm charger not charging?.....


  • thisucks1thisucks1 Registered Users Posts: 3
    i have an issue thats driving me nuts . the charge controller wont charge above 13.5 and reads full, as soon as i disconnect the array or tthe sun goes down reads 12.3-12.4 , last night was 12.1
    i tried four different controllers , all do the same . then i checked the batteries, did all the tests , even charge each by itsels and let them set for two hours, all hold a charge of 12.97 - 12.88
    but if i connect one battery to the charge controller , the charge junps to 14.4 , as soon as i connect another battery, the charge drops to 12.3-12.5 , but i narrowed it down and i can now connect three batteries in series and it charges at 14.2-14.4 and 14.5 , 
    all batteries test good. but im assuming its the batteries , i ordered another charge controller maybe a fith will do something. seem like somethings shorting out. when the refrigerator kicks on the charge drops to 13.5-13.9 then starts back up to is that normal? 
    my inverter is large for my system 7000watt pure sign wave.  i wonder if that could be an issue with my three 100 watt panels and only run a fridge w freezer and laptop and light
  • BB.BB. Super Moderators, Administrators Posts: 29,993 admin
    Welcome to forum ThisS*1,

    I am going to move your post to its own thread... Makes it easier to Q&A your specific issues.

    Can you tell us a bit more about your system? Size/configuration of your solar array, the type/size/configuration of your battery bank, and roughly near what major city the system is installed. This allows us to check your present system configuration and better understand what may be happening.

    In general, a 300 Watt solar array and 7,000 Watt AC inverter--This is not what, I like to call, a balanced system design.

    Folks generally expect a lot of energy from an off grid power system... In reality, it takes a lot of solar panels+sun+a good size battery bank to generate a lot of energy. Large AC inverters are relatively cheap--And most folks do not have the rest of the system needed to support a large AC inverter...

    For your size system, 300 Watt watts of solar panels would support (in a typical off grid home/RV) a 150 to 300 Watt AC inverter (and 2-4 "golf cart" sized batteries minimum). Add a full size refrigerator, and you are looking at closer to a 1,200 Watt array and something like 12 golf cart batteries connected in series parallel for 24 volt @ ~650 AH battery bank. And a 1,200 to 1,500 Watt AC inverter nominal.

    Ideally, I/we like you to describe your loads/energy needs (like AH @ xx volts or Watt*Hours per day), then we look at a system that can support those needs. 

    And you need to conserve as best you can (most efficient loads, turns stuff off when not needed, etc.)--Generating solar power is usually much more expensive vs conserving power.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BB.BB. Super Moderators, Administrators Posts: 29,993 admin
    I will also add that, my guess, is that your solar chargers are working more or less correctly. When you have a large battery bank and "small" charging source, the battery bank will sit at low voltages for hours, or even days, until the batteries are brought up to 14.75 volts and held there for 2-6 hours or so...

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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