Automatic battery bank switching

Discussion in 'General Open Forum' started by fish brain, Jan 28, 2018.

  1. fish brain

    fish brain Active Member

    I am looking for help with switching battery banks on a solar system.
    I currently have a cabin with a solar charger that will charge two battery banks. I have only had one bank up till now, but on really cloudy days the batteries can get low enough that it could affect their life expectancy. I would like to add a second bank and have the system automatically switch to the second bank when the power in the first bank reaches 50-60 % .
    I have been trying to find something, but have had no luck so far. I'm hoping someone on the forum might have an idea
     
  2. bigbruce

    bigbruce Crew Member

    Have you thought about wiring all of the batteries in parallel as one big bank. Should double your amp hours and give you the same result as having two banks (I think)
     
    ChilliSpoons likes this.
  3. CIVANO

    CIVANO Well-Known Member

  4. CIVANO

    CIVANO Well-Known Member

  5. Wild Bill

    Wild Bill Active Member

    What kind of charge controller do you have? Anyway I would just parallel the battery's.
    Batterys will last longer if they are cycled shallower.
     
  6. fish brain

    fish brain Active Member

    That works in theory, but you need to upgrade your solar panels and charge controller. plus the battery people tell you never to mix batteries of different ages. so if I am adding new batteries I should have them separated
    Thanks CIVANO both your posts seem to allow combining the battery banks while allowing them to charge on separate circuits. I need to check with someone smarter than me to see if I can do this, but it seems like it might work.
     
  7. fish brain

    fish brain Active Member

    Thanks Bill,
    As I replied to bigbruce, it means a new controller and more panels.
     
  8. Wild Bill

    Wild Bill Active Member

    I have to disagree, your panels and controller will still only have their rated maximum output and it doesn't matter if you hook it up to one or a hundred battery's.
    It will take longer to charge 8 battery's than 2 without a doubt but once charged take longer to discharge.
    If your small bank is fully charged by 2:00 in the afternoon the rest of your production is wasted.
    I don't believe the load connections on your controller were intended for battery charging.
    How old are the original battery's? Agree paralleling new with 6 year old battery's is a waste.
    The battery combiners will work however both sets will discharge at the same time. It's actually just two diodes
    I would talk to a solar equipment establishment.
     
  9. bones

    bones Well-Known Member

    Check with 2015 code book first. Probably be able to use a transfer switch with loss of voltage transfer
     
  10. Wild Bill

    Wild Bill Active Member

    So tell us a little bit about your system.
    Number of solar panels and watts
    Charge controller make and model
    Battery bank specifics, number of, battery type, age.
     
  11. Wild Bill

    Wild Bill Active Member

    I assume he is running 12 or 24 Volt banks
     
  12. bones

    bones Well-Known Member

    Should be a combination series parallel, more than likely it just 12V. The big question is how many amps are calculated?
    This will determine whether you can just use an ACR from blue seas. The acr will allow for amp meter and 12V switch over after charge. Trouble being the rated current. Without checking, I believe you need 150%. The automatic transfer switch being the best option. But budget will limit the options
     
  13. fish brain

    fish brain Active Member

    I have the Go Power Solar Extreme system http://gpelectric.com/products/solar-extreme
    It has:
    Three 160 watt solar panels for a combined 380 watts
    30 amp pulse width modulated digital solar controller
    Two Interstate 385 ah 6 v batteries about 6 months old
    I initially thought about just adding the extra batteries like you mentioned Wild Bill and bigbruce, but I worry about an imbalance, so thought the second bank would be better because I didnt want to ruin the ones I have as they are about $450 each. I think the panels work well on the sunny days, and even most moderately cloudy days, It just seems to be extra dark days that I am having the issue.
    I guess no matter if I create two small banks or just one large one it will take as long as it takes to charge them, If I need them to charge faster, then I would add more panels and do the controller upgrade.
     
  14. Wild Bill

    Wild Bill Active Member

    Well dual battery bank charging is a neat feature, looks like it's optimized for rv use as it charges bank one (house battery) fully before it charges bank two (vehicle battery) .
    Adding battery's to a six month old bank, I would talk to battery guys considering it's a $1000 investment. Probably not cycled that many times. Easiest and best way. MIGHT be just fine lol!
    You could do a Costco golf cart battery bank, that's what I need to buy this year.
    All you would need to combine them is one $6.00 diode tying the two banks together. If bank two doesn't get charged up it won't contribute until battery voltage equalizes. Anode to bank two, cathode to bank one, diode rated to maximum expected load.

    I have two 260 watt panels and had two old 8D batterys, ran a house fridge, lights etc. Going to do a bank of golf cart battery's this spring.
    I think I'm going to add a windcharger as well, https://mwands.com/store/
    I have a clear shot at the wind so with a 1700 watt charger you can pretty much expect 100 to 200 watts.
    Still need another charge controller and a dump load so about $800 all together.

    Hey just want to add that we had cells replaced on forklift battery's all the time.
     
    Last edited: Jan 30, 2018
    fish brain likes this.
  15. charlie415

    charlie415 Well-Known Member

    Adding another bank identical to what you already have should not be a problem as you batteries are only 6 months old.
     
  16. charlie415

    charlie415 Well-Known Member

    The biggest concern if you double your capacity is charging it back up. With 770AH if you deplete 40% you need to replace 308AH. Your 380w charging is probably only 60% efficient on average so that's about 19AH. So roughly 15 hours to replenish. That's why a lot of cabins have generator back up to pick up the slack. Having more capacity is great but you need the capability of keeping the charge up or you risk damaging your battery bank.
     
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