most from the mppt mstar 45

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jimbob01
jimbob01 Solar Expert Posts: 63 ✭✭
in Off Grid Solar & Battery Systems #1
hi guys,im trying to optimize my newly installed panels/ccs..
at present i have a 24v sla bank
i have 6 panels with ocv of 37.9v
ive connect them as 3 strings in parallel ... so ive tested the incoming voltage at the cc and im getting 62v at lowest in cloud.
would i be better connecting all the panels direct to the cc as surely 31v would be ideal to charge the batts at their max 28.8v eq rate?
i have 2 mstar mppt 45s with 6 235w panels
thanks for reading jim.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
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    Re: most from the mppt mstar 45

    Don't change it.

    Right now you've got an array with Vmp around 72 and Voc around 76.
    If you put all the panels in parallel on the controller two things will happen: the current on the wires to the controller will double, increasing the Voltage drop (unless you change the wire) and the array Vmp will fall to a point where the 24 Volt system may not properly charge.

    It is important to note that a rated Vmp on the array is not the same as the Voltage available to charge the batteries. Not only is the Voltage drop through the wiring, the panel Voltage goes down as they get hot. So about the time you need that maximum Voltage for Absorb (or Equalization) it si midday and the panels are at their hottest with their Voltage the lowest.

    The difference in controller efficiency between 'ideal' Vmp on the input and 2X that much is not enough to worry about, and in this case the lack of full charging Voltage in the all parallel configuration becomes a more important (crippling) issue.
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