voltage booster charge controller


i have a system (battery) voltage of 48V

my panels have a Vmp of 35 V

can you guys suggest a charge controller that can boost voltage.


  • BB.BB. Super Moderators, Administrators Posts: 28,315 admin
    Re: voltage booster charge controller

    None of the "standard" off-the-shelf solar charge controllers that I am aware of can "boost" the output voltage...

    Vmp must always be higher (by at least 1-2 volts) than the battery bank's charging voltage (or equalization voltage--if flooded cell) under all conditions (high solar panel temperature drops Vmp, long wire runs also drop Vmp of system).

    The normal solution would be to get another 35 volt Vmp panel and wire it in series with the first panel to get ~70 volts. Then to use a MPPT (Maximum Power Point Tracking--usually prefered for larger systems) or a PWM (Pulse Width Modulation--usually used for smaller systems) solar charge controller to ensure the batteries are properly charged.

    There may be DC voltage converters you can use to double the panel voltage--but this usually wastes some power, and can add complexity and extra costs to running the system (unless this is some special application, I would not recommend following this option).

    For a good range of solar charge controllers... You can look through our Host's site (NAWS).

    Outback and Xantrex for the larger controllers (typically 400 watts or more of solar panels). BlueSky and MorningStar for smaller systems (they also have some larger controllers too).

    You have to look closely at all of the specifications. It is not easy to find the optimum mate of Solar Panel + Charge Controller + Battery Bank for a new user (and I have made more than my share of goofs here too--I just help here keeping spam down and answering questions when I can--I am not connected with NAWS or the solar industry).

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: voltage booster charge controller

    what you need to do is to put your pvs in series strings of 2 (or possibly 3 depending on the ocv, controller max v, and the local average high/low temps usually encountered) and get a good mppt controller that can downconvert it to your required voltage of your 48v battery bank. this higher voltage will also save a bit on resistive losses. for more on that and proper wire gauges see the sticky on it in general solar topics. http://forum.solar-electric.com/showthread.php?t=29
  • mike95490mike95490 Solar Expert Posts: 8,067 ✭✭✭✭✭
    Re: voltage booster charge controller
    altercreed wrote: »

    i have a system (battery) voltage of 48V

    my panels have a Vmp of 35 V

    How many panels?
    How many watts each?
    Have you already bought a charge controller ?
    ready, fire, aim !
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • crewzercrewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    Re: voltage booster charge controller


    PV modules with a Vmp of 35 V are often called "24 V" modules. You may have unwittingly stepped into the dreaded "charging a 48 V battery from 24 V modules" quandry.

    Depending on the battery type (flooded-cell or VRLA), your battery bank will need between ~56 V and ~59 V or more to charge, and up to ~62 V to EQ, all ref 77 F (25 C) battery temperature.

    PV module specs are based on optimistic "STC" (lab) conditions. PV module voltage varies inversely with temperature. The "24 V" modules with a Vmp of 35 V will rarely deliver 35 V while the charge controller is operating in the bulk stage. Allowing for voltage drop in the wiring and the controller, two of these modules wired in series may deliver ~55V in the summer. This may be too low to fully charge the battery bank.

    On the other hand, the winter Voc of three of these modules wired in series may exceed the charge controller's max DC input voltage spec.

    If there's a solution, it's a delicate balancing act. We need to know more about your planned system:

    1) Location (i.e., city and state)
    2) PV module mfr and model #
    3) Battery mfr and model

    Thos recent discussion contains related details: http://forum.solar-electric.com/showthread.php?t=4312

    More later,
    Jim / crewzer
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