Connect 12 volt panels to 24 volt system

MarcoMarco Registered Users Posts: 1
I have connected 6 12 volt batteries 3 by 3 in order to produce 24 volt for my power convertor. I have 8 panels. 6 of the same capacity and 2 of another. The 6 panels produce max power 48 W, max stst open CKTV 600 v, current short ckt 3.35 A, rated 3.02 A, vol open ckt 19.8 v, rated 15,9 v.
When connected in serie the system doesn't recognise the incomming current, only when I connect the batteries in serie = 12 volt sytem.
Can I connect these panels in such a way that they will load the batteries in the 24 volt setting?

Comments

  • BB.BB. Super Moderators, Administrators Posts: 32,088 admin
    Re: Connect 12 volt panels to 24 volt system

    Welcome to the forum Marco.

    I am a bit confused:
    Marco wrote: »
    I have connected 6 12 volt batteries 3 by 3 in order to produce 24 volt for my power convertor.
    Three 12 volt batteries in series would be 36 volts, not 24 volts.
    I have 8 panels. 6 of the same capacity and 2 of another. The 6 panels produce max power 48 W, max stst open CKTV 600 v, current short ckt 3.35 A, rated 3.02 A, vol open ckt 19.8 v, rated 15,9 v.

    Vmp of ~16 volts is a bit on the low side--It would have been better if the panels where in the 17.5 to 18.6 volt range for charging a 12 volt battery.

    With standard "PWM" controller (the less expensive type of solar charge controller)... You would use on panel in series to charge a 12 volt battery. Two panels in series to charge a 24 volt battery. And three panels in series to charge a 36 volt battery... And then add panel strings in parallel to get more current.

    When connected in serie the system doesn't recognize the incoming current, only when I connect the batteries in series = 12 volt system.
    Can I connect these panels in such a way that they will load the batteries in the 24 volt setting?[/QUOTE]

    Charge controllers can be made for one voltage (12 volts), two voltages (12/24 volts), etc... Some use switches to set the battery bank voltages.

    Others set the bank voltage when you first connect the controller to battery bank (if you have a "dead" 24 volt bank, it may read it as 12 volt. If you have a dead 12 volt bank, the controller may not even turn on).

    Most controllers, you should connect them to a reasonably charge battery bank first, then connect the solar array (the controllers usually pull power to run the microprocessor from the battery bank and will not function if the battery bank is dead or the wrong voltage).

    Regarding 36 volt battery systems... That is very unusual for solar power systems. And there are few (if any) controllers that will support 36 volts without programming thm with a computer (typically more expensive charge controllers).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Connect 12 volt panels to 24 volt system
    BB. wrote: »
    Welcome to the forum Marco.

    I am a bit confused:

    Three 12 volt batteries in series would be 36 volts, not 24 volts.

    How about if "six batteries connected 3 x 3" refers to 3 batteries connected in parallel, the other three also connected in parallel, and then the two groups put in series? Probably not as satisfactory as paralleling three strings each consisting of two batteries, but it would deliver the same voltage.
    SMA SB 3000, old BP panels.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Connect 12 volt panels to 24 volt system
    inetdog wrote: »
    How about if "six batteries connected 3 x 3" refers to 3 batteries connected in parallel, the other three also connected in parallel, and then the two groups put in series? Probably not as satisfactory as paralleling three strings each consisting of two batteries, but it would deliver the same voltage.

    Yes, but it also creates some undesirable alternate current paths.

    Some charge controllers (even some PWM type) can not take higher than system expected Vmp and will shut down. So if you put "36 Volts" on the input and "24 Volts" on the output you get zero current instead of whatever the panels can flow at whatever Voltage they're pulled down to.

    Three of these 16 Volt panels in series on an MPPT controller would give proper charging for a 24 Volt system, albeit comparing the number of batteries to the available panel Watts indicates the charge would be very light. 288 Watts of panel, even with an MPPT controller, would at best manage to charge 184 Amp hours @ 24 Volts. If those batteries are, say, 90 Amp hour Marine/RV units then 3 parallel would be 270 Amp hours.

    We simply need more details here to know what is actually going on here.
  • BB.BB. Super Moderators, Administrators Posts: 32,088 admin
    Re: Connect 12 volt panels to 24 volt system

    I am not sure I like the idea of a 3s wired in parallel, then 2x paralleled groups in series (I would call it a 3 parallel x 2 series installation).

    With 2 in series, then 3 in parallel you can use a DC Current Clamp meter to monitor each string for current flow, bubbling, voltages, etc... If you have a weak cell (open or closed) or bad wiring , it is pretty obvious when you do a weekly checkup of your bank (measure/log battery SG, voltages, current flow under load/charging, etc. looking for "differences").

    By placing 3 batteries in parallel, you are measuring the battery voltage of the group--and it is more difficult to find a bad cell/connection.

    Also, if you believe in fusing/breakers to protect wiring against short circuits, you would need 6 fuses to accomplish the protection that 3 fuses would in the 2s x 3p connection setup (more costs, more voltage drops, etc.).

    Any time, out of your 6 sets of batteries you find a "difference", you need to find out why and address it before it damages one or more batteries.

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