voltage to run mptt?

Discussion in 'Solar Power' started by mick noe, Sep 15, 2016.

  1. mick noe

    mick noe Funster

    Joined:
    Apr 14, 2009
    Messages:
    610
    Likes Received:
    508
    Location:
    near Boston Lincolnshire
    bought a shiny new mppt a victron75 15 but read in the instructions that it needs 5v above battery voltage to start charging, should I now rewire my two 100w panels in series to make this work correctly?
     
  2. tonyidle

    tonyidle Funster

    Joined:
    Aug 6, 2013
    Messages:
    2,878
    Likes Received:
    2,699
    Location:
    Kendal, Cumbria
    Look at the panel nominal output voltage - it's likely to be 20v or more.
     
    • Like Like x 1
    • Useful Useful x 1
  3. bubble63

    bubble63 Funster

    Joined:
    Aug 10, 2012
    Messages:
    497
    Likes Received:
    446
    Location:
    cambridge
    That wasn't my understanding of mppt
    See this https://en.m.wikipedia.org/wiki/Maximum_power_point_tracking

    I 'think' the maximum power point tracking controller steps up the voltage as required
    As you can't push voltage up hill i.e. 12 v won't go in to a 12.5 v batt.
    So it inverts it to AC and steps it up , enabling it to put the current in at a 'synthetically ' higher voltage
     
    • Thanks Thanks x 1
  4. Derbyshire wanderer

    Derbyshire wanderer Funster Life Member

    Joined:
    Mar 30, 2014
    Messages:
    412
    Likes Received:
    676
    Location:
    Derbyshire
    It will work just fine with the panels in parallel. As the day starts it needs the extra 5v to start its cycle but as said above the single panel voltage will be a little over 20v at peak output.
    Mine is wired this way and it works perfectly.
    The extra voltage is converted into extra watts by transforming the available input in the most effect way it can.
    BTW, it is best to remove the jumper plug and let it charge your battery bank with the algorithm that uses the clever voltage cut off to enable complete charging every few days. Not so useful in summer but in winter it will make a big difference to maximising you battery life and output.
     
    • Thanks Thanks x 1
    • Useful Useful x 1
  5. WillH

    WillH Funster

    Joined:
    Feb 9, 2008
    Messages:
    1,618
    Likes Received:
    1,291
    Location:
    SW Scotland
    Peak output on a panel can be as high as 30v or more.
     
    • Thanks Thanks x 1
  6. TheCaller

    TheCaller Funster

    Joined:
    Sep 23, 2013
    Messages:
    1,819
    Likes Received:
    2,158
    Location:
    Lincs
    It will work fine either way. There is a theoretical advantage to wiring the panels in series, because the panel output voltage is then doubled & so the controller will switch on slightly earlier in the morning & will keep producing a small amount of power on an overcast January day when parallel connected panels may never reach the 17 - 18v required to start the controller's charging process.

    This advantage is cancelled out if you get partial shading of a panel. On a parallel circuit, you will lose most of the output of the shaded panel, but the one in full sun will continue unaffected. In series, the partial shading of one panel drastically reduces the output from the pair.

    Which is best for you will depend on when & where you use the van & whether you have access to EHU while it is not being used.
     
    Last edited: Sep 15, 2016
    • Like Like x 2
    • Thanks Thanks x 1
  7. tonyidle

    tonyidle Funster

    Joined:
    Aug 6, 2013
    Messages:
    2,878
    Likes Received:
    2,699
    Location:
    Kendal, Cumbria
    Bypass diodes should prevent that although I agree there's not much if any advantage anyway in series connection.
     
    • Thanks Thanks x 1
Loading...

Share This Page