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  • Charge Controllers - PWM or MPPT

    PWM Controllers:
    a FET switch is used, under control of some algorithm, to
    rapidly connect a power source, to a battery. The switch "makes" and "breaks"
    many times a second, to control the charge. (Pulse Width Modulation)
    When the battery is quite low, the FET switch is ON, and the
    panels are connected directly to the battery, and since PC panels are a
    "current source" their voltage drops (or is pulled low to the battery
    voltage) and some power is lost, depending on the difference of the Vpmax
    of the solar, and the present voltage of the batteries.
    PV voltage - Battery voltage = Difference x Amps = Lost wattage

    Note if the array was a 200W array, amps would be 11.11Aa
    18V @ 11.11A = 200watts
    18V PV - 12.2V battery = 5.8V @ 11.11amps = 64.438 w lost



    MPPT Controllers: [Maximum power point tracking]
    a more sophisticated circuit is used, much like a "DC
    Transformer" to dynamically convert the power source (water, wind generator
    or PV panels) via an efficient DC-DC conversion process. This can also
    down convert high voltage DC, to suitable charging voltage for the battery,
    with very low losses, about 95% efficient. This is a good thing if you
    have a remote array - you can run high voltage DC to the controller and avoid
    expensive high amp wire, and incur lower losses.
    The MPPT advantage vanishes when the controller switches
    from the BULK charging mode, to ABSORB, and does not need the extra power
    recovered from the conversion process, and falls back to PWM for ABSORB and
    FLOAT stages. This can be managed in different ways for individual
    systems, as many MPPT controllers have user programmable settings.

    this is the simple gist of it, the actual workings are much deeper than
    I can go into here.

    As the system gets larger, the cost trade off between the
    simple PWM controller and the expensive MPPT (with possibly shorter
    lifetime with more complex innards) and PV panel & rack costs, shifts, and
    it's left to each user to decide which controller is most appropriate for
    their situation. The tipping point is around 600 - 1,000 watts

    old post might be here:
    webcache.googleusercontent.com/search?q=cache:www.solarpaneltal
    k.com/showthread.php%3F4109-Oh-the-Mystery-of-PWM-vs-MPPT-Controllers&hl=en&
    client=firefox-a&hs=ko4&gl=us&strip=1
    Powerfab top of pole PV mount (2) | 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
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