Can you do 2 battery banks with one acting as a "backup"?

TucsonAZ
TucsonAZ Solar Expert Posts: 139 ✭✭
I'm doing a build (some of you may have read my other post) and ended up with an odd number (5) of AGM 125ah batteries. Since I'm doing a 24v system I will only be using 4 of those which leaves the 5th unused and at home. I called the person I got them from today to see if he still had another of the 125ah batteries floating around and he didn't. He did however have somebody that needed a 125ah battery like I had and offered to swap me 2 of the same batteries [only in the 100ah version] for the spare I have. If I did that could I have 2 battery banks at 24v and use a switch between the banks that would allow me to top off one bank on sunny days then switch over to the other bank and fill that bank in case I need it?

I may also be able to get him to swap me 8 of the 100ah batteries for 5 of the 125ah batteries if that would be advantageous but wiring 8 12v batteries for 24v may be an issue I'm not sure on that.

Thanks a lot for the input on this, my 250ah bank is on the smaller side for 1,680 watts of solar so I figured I would look into how I could maximize the size of my bank.

Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Can you do 2 battery banks with one acting as a "backup"?

    There are ways to do this.

    You could use a dual battery charge controller.

    You could charge the small bank from the inverter 'as needed' and keep it maintained and in reserve.

    You could use the AUX port on one of the better controllers to switch its output to the other bank when Float is reached (sacrificing float stage for charging a bank that's not really used would probably not be economical).

    You could use the 100 Amp hour units alongside the 125 Amp hour ones and sacrifice some battery life.


    I actually tried a dual bank system once. Found it was a pain in the anatomy.
  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Can you do 2 battery banks with one acting as a "backup"?


    I actually tried a dual bank system once. Found it was a pain in the anatomy.

    This is exactly what I was thinking. To properly look after them is going to be a real pain. Better to have everything as one bank, let the controller do the work and all you'd have to do is check on things once in a while instead of ending up married to a dual battery system.
  • TucsonAZ
    TucsonAZ Solar Expert Posts: 139 ✭✭
    Re: Can you do 2 battery banks with one acting as a "backup"?

    Okay, thanks for the help and info, I will yield to your advice on this one!
  • jonr
    jonr Solar Expert Posts: 1,386 ✭✭✭✭
    Re: Can you do 2 battery banks with one acting as a "backup"?

    I'd only deal with splitting off 1/2 a bank if you were unable to get to a full charge (say due to lack of sun hours). Then you have a problem and charging one bank with the other is one solution.

    I am available for custom hardware/firmware development