Mixing panel voltages

System
System Posts: 2,511 admin
in General Solar Power Topics #1
I am very new to solar. I recently decided to start experimenting so I did a little reading and then bought a 120watt / 12V Mono panel, and a 25amp Mppt controller. I already have (4) one year old Continental Golf Cart batteries to start with.

Once my 120watt panel arrived, I liked the quality so I contacted the company and purchased a second one ( exactly the same ). When it arrived, I discovered they sent a 200watt / 24V panel.

Should I keep this panel or send it back and request the one I ordered so they are both the same? I would like to keep it but not sure what is the proper way to wire it ( parallel or series ).

I plan to use the equipment to run a DC submersible well pump for my pond, and also power a Cobra 2500 watt inverter ( just to play with )

I know you are probably wanting brand names and spec's of the panels but I am currently at work and do not have it with me. I just thought I would get the ball rolling and ask if I should use the 200watt panel, and if so, what wiring configuration to use.

Thanks for any advise.

Brian
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Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: Mixing panel voltages

    Welcome to the forum.

    There's two ways of connecting panels: parallel or serial. In the case of a parallel connection the Vmp's of the two panels needs to be nearly the same. In this case we can surmise that they aren't, so parallel connection is out. You would lose too much power this way.

    It is possible, albeit unlikely, that the Imp's of the two panels are close enough to allow a serial connection since you have an MPPT charge controller. The controller's maximum input Voltage will also be important here.

    Personally I'd ignore the 120 Watt panel and get another 200 if you're trying to charge golf cart batteries. Around 400 Watts would be a good array size for two of them, and somewhat small for four.

    As always, the devil is in the details.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #3
    Re: Mixing panel voltages

    did you get charged for a 200w pv or a 120w pv?

    what are the vmp and imp specs of both pvs.
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  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    #4
    Re: Mixing panel voltages
    brianb236 wrote: »
    I am very new to solar. I recently decided to start experimenting so I did a little reading and then bought a 120watt / 12V Mono panel, and a 25amp Mppt controller. I already have (4) one year old Continental Golf Cart batteries to start with.

    Once my 120watt panel arrived, I liked the quality so I contacted the company and purchased a second one ( exactly the same ). When it arrived, I discovered they sent a 200watt / 24V panel.

    Should I keep this panel or send it back and request the one I ordered so they are both the same? I would like to keep it but not sure what is the proper way to wire it ( parallel or series ).

    I plan to use the equipment to run a DC submersible well pump for my pond, and also power a Cobra 2500 watt inverter ( just to play with )

    I know you are probably wanting brand names and spec's of the panels but I am currently at work and do not have it with me. I just thought I would get the ball rolling and ask if I should use the 200watt panel, and if so, what wiring configuration to use.

    Thanks for any advise.

    Brian
    The voltages are very different, so you cannot connect them in parallel. If you connect them in series, the current will be restricted to that of the lower current module. If they only charged you for the 120W module, then it might be worth keeping it and taking a bit of a hit on the current capability of the array. If they charged you for the 200W module, send it back. Hopefully they would pay for all the shipping since it was their error, but that will probably be more than the difference in selling price of the modules.
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  • System2
    System2 Posts: 6,290 admin
    #5
    Re: Mixing panel voltages

    I was charged for the 120W panel. I will get the spec's tonight. I think the amps were pretty close to the same. The volts were double on the 200W from the 120W.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #6
    Re: Mixing panel voltages

    Another option would be to connect the 200 watt 24 volt panel to your MPPT controller (assuming within specifications) and get a second, less expensive, PWM type charge controller and connect the "12 volt" panel (should be Vmp~17.5 volts) in parallel to the battery bank.

    It is usually OK to parallel charge controllers/charging sources to one battery bank.

    As always, keep battery to charge controller wires short and heavy for low voltage drop. And use a separate wiring run from battery to each controller (avoid sharing one cable run with two charge controllers).

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