Newbie need help

SystemSystem Posts: 2,511 admin
Hi guys I am new to this great forum. I am going to put together some solar panels but not sure which to do. I just bought 50 3x6 cells to make a solar panel 36 cells in series would be 18 volts,63 watts and 3.5 amps. I plan on using two 12 volt deep cycle batteries that are 900 cranking amps in parallel. I have another configuration I thought about 32 cells in series would be 16 volts,56 watts and 3.5 amps. I am not sure which configuration to use. All help will be greatly appreciated thanks a lot.
also can I just use a charge controller if I use the 18 volt configuration or do I need a regulator cause the batteries are 12 volts?


  • DapdanDapdan Solar Expert Posts: 313 ✭✭
    Re: Newbie need help

    Hey there,

    I am new to this great place too. I would advise you to go with the 36 cell arrangement at 18v inorder to charge a 12v battery. wrt the battery make sure you are using a deep cycle battery since you quoted cranking amp, you should be quoting amp hours or reserve capacity. it will not work well with a starting battery and the battery will die in short order.

    you would not need a regulator. the CC will regulate the voltage and current according to it charging cycle (bulk, absorption & float). it seem as though you have enough cells to make one panel and not enough to make two:D

  • BB.BB. Super Moderators, Administrators Posts: 32,088 admin
    Re: Newbie need help

    We really try to dissuade people from building their own panels... It is difficult to make them, does not save much money now-a-days, and they probably will not last the 20-25+ years a factory built glass/sealed panel will.

    If you do build a large panel--make sure you install it where it does not matter if it catches fire (especially if you build it out of plastic and/or wood).

    Panel Fire Question

    The panel's Vmp (Voltage, maximum power), must be higher than Vbatt+2 volts... Flooded cell batteries are typically equalized around 15-15.5 volts--so your panel should be at least 16.5-17 volts minimum.

    If your panel is much more than 1 amp per 100 amp*hours (20 hour rate), then you should have a solar charge controller to prevent battery overcharging.

    Also, if you don't use a controller (say just for trickle charging), you need a blocking diode (so the panel does not discharge the battery at night), and a fuse to help reduce the chance a short circuit will cause a fire (perhaps ~2x the Imp/Isc of the panel).

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2System2 Posts: 6,290 admin
    Re: Newbie need help

    Hi thanks for the info guys. I have 50 cells right now to make a panel but will be buying more soon but needed to know which arrangement would be better. Constructing the panels are pretty simple just sodering them together. The batteries are from a heavy duty truck(Semi)commercial so I will have to check them out. I have found three all together would it be better to use all them in parallel?
    Thanks Again Dave
  • BB.BB. Super Moderators, Administrators Posts: 32,088 admin
    Re: Newbie need help

    Since it sounds like you are building a "large" panel(s)--Then you will be looking at an MPPT (Maximum Power Point Tracking) controller (MorningStar for the smaller sizes; Outback, Xantrex, others for the larger sizes)... ("Large" is >~200-400 watts of solar panels--you can use PWM controllers too--less expensive, need to match panel Vmp to Vbatt+2v much more closely for best efficiency).

    With MPPT, pretty much all you have to worry about is Vmp (>~17 VDC for a 12 volt battery bank) and Voc (<~150 VDC)--anything inbetween will work just fine. And, of course, Imp/Isc and Pmax are within controller limits.

    Series/parallel connections of panels based on your needs (longer distance, tend towards series--high voltage--connections. shorter distances, tend a bit towards parallel--lower voltage--connections. copper wire expensive, tend towards series--high voltage--connections).

    The MPPT charge controllers pretty much work on Vmp*Imp*(controller-efficiency)=Vbatt*Ibat as long as you are withing the controller's limits.

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