PWM or MPPT

I have a 175 watt solar panel with 36.5V and 4.80A, from which I have to charge a 12V battery through a PWM charge controller, means 14V x 4.80A = 67W , so the panel works on 67watts? If I use a MPPT charge controller will it makes any difference?

Comments

  • mike95490mike95490 Posts: 7,642Solar Expert ✭✭✭✭
    A MPPT controller would deliver 95% of the panel harvest, which is over 2x what the PWM controller delivers.

    Generally, the tipping point cost wise, is 300w of panel, but you can see,
    67w via PWM
     compare to
    165w MPPT 
    (actually, the panel will seldom produce more than 80% of Pmax =140w, regardless of controller)

    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 ,

  • MastermindMastermind Posts: 2Registered Users
    But when I connect the panel direct with the battery with out pwm controller, panel draws the same amps I.e 4.8, why is that ?
  • mcgivormcgivor Posts: 1,747Registered Users ✭✭✭✭
    edited April 14 #4
    But when I connect the panel direct with the battery with out pwm controller, panel draws the same amps I.e 4.8, why is that ?
    The battery will pull down the voltage of the panel supplying all current possible, a PWM controller allows the same direct connection, but when the voltage of the battery increases as it's  approaching full charge it will begin to regulate the voltage with a series of PULSES  of varying WIDTH,  which in turn MODULATES the input to the battery to meet its requirements.

    If the panel were connected directly to the battery for an extended period  time, the voltage would continue to rise above the safe limits which would generate heat and ultimately damage the battery, hense the need to control. 
      1500W, 6× Schutten 250W Poly panels , Schneider 150 60 CC, Schneider SW 2524 inverter, 8×T105 GC 24V nominal 

  • mike95490mike95490 Posts: 7,642Solar Expert ✭✭✭✭
    But when I connect the panel direct with the battery with out pwm controller, panel draws the same amps I.e 4.8, why is that ?
    Panels are a current source.  Till now, you have only dealt with Voltage Sources.  Your panel puts out 4.8A at 14V = 67.2 w

    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 ,

  • BB.BB. Posts: 27,432Super Moderators admin
    A PWM controller is simply an On/Off switch... The higher percent of time the switch is on, the more "average" charging current (PWM is pulse width modulation... Say you have a 1 second cycle--if the switch is on 10%, it is on for 0.1 second out of 1.0 second. If it is on 100% of the time, the switch is on for ~1.0 second out of every 1.0 second).

    Solar panels output current in proportion to the amount of sun. Full noon time sun, panel pointed at sun, you will get ~Imp (current maximum power) from zero volts to Vmp, then current will fall to zero amps at Voc (Voltage open circuit). Note--This is an approximation, but works good enough for this explanation. If you have 50% sun, then you get 0.50 * Imp worth of current).

    Power is = Voltage * Current... If you have 4.8 Amps from the solar panel, the power "into the battery" depends on the battery voltage:
    • PWM charging a 12 volt battery with a "24 volt" solar panel:
    • Pbatt ~ Vbatt*Ibatt = 10.5 volts battery * 4.8 amps (near dead battery) = 50.4 Watts
    • Pbatt = 12.8 volts * 4.8 amps (charging battery) = 61.44 Watts
    • Pbatt = 14.75 volts * 4.8 amps (~80-90% state of charge) = 70.8 watts
    • PWM charging a 24 volt battery with "24 volt" panel:
    • Pbatt = 29.5 Volts * 4.8 amps (80-90% SoC battery) = 141.6 Watts
    An MPPT (Maximum Power Point Tracking) controller "matches" the high(er) voltage / low(er) current from the solar panel to the battery's low(er) voltage / high(er) current requirements.

    Think of the PWM controller like a 1 speed transmission.

    Think of the MPPT controller like an automatic transmission that matches the "optimum" panel voltage+current input (i.e., RPM and Torque from engine) to that of the battery bank (i.e., RPM and Torque at wheels).

    -Bill

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