Charge Controllers

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A5c11
A5c11 Registered Users Posts: 11 ✭
in Solar Beginners Corner #1
Hey all,

Could somebody help me my explaining in laymans terms why I should buy an MPPT Charge Controller, and not a PWM Charge Controller?

Thanks.
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  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    edited February 2016 #2
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    MPPT Charger controls are a buck boost type of charger, they convert excess volts of the panels to the needed battery voltage and in the process they increase the amps available to the battery.  They are a bit more complex and have a transformer as part of the design.

    PWM controllers are basically a chopper circuit, that is a high speed on off switch.  They use that to control the output to the battery.  The power at the panels is lost during the off cycle of the switch.  They also require the proper input voltage from the panels as the higher the voltage is above the optimal charge voltage, the more the switch will be off and the more power is lost.
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  • A5c11
    A5c11 Registered Users Posts: 11 ✭
    #3
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    Okay - I get it now.
    Thanks.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #4
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    PWM controllers
    • are much cheaper than MPPT.
    • Also, they have lower internal losses (usually better for smaller/low power systems, typically smaller than 400 Watts).
    • You must "match" solar panel working voltage to battery bank voltage (i.e., 12 volt battery bank needs Vmp~18 volts).
    • "12 volt" panels tend to be smaller and more costly ($$$ per watt) than GT panels with Vmp~30 volts (typical).
    • Smaller panels are usually less costly to ship (140 Watts or less).
    • System may have less output power in very hot/desert climates (hot panels, suppressed Vmp voltage).

    MPPT Controllers:
    • Much more expensive (by a lot)
    • Usually for larger systems (over 800 Watt array, you probably are going MPPT)
    • >200 Watt solar panels tend to be almost 1/2 the $$$/Watt vs smaller "12/24 volt panels). But large solar panels can cost a lot to ship (if less than 1 pallet full at a time).
    • You can use a much wider Vmp-array working voltage--And can use Vmp~30 panels (>200 Watt) efficiently.
    • Much wider optimal operating range (from ~18 volt to ~100+ volt Vmp-array).
    • Higher Vmp-array voltage systems can use smaller AWG wire/have longer distances from Array to Charge Controller/Battery Shed.
    • MPPT controllers tend to have more processer power/newer software/more software functions. If you want networking/logging of output power, MPPT controllers will have these options.
    In the end, I recommend doing a paper design of both system types and see how the costs/functions will work out for you. Make sure you include shipping costs to your front door. Panels can be very expensive to ship (especially the larger panels).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • A5c11
    A5c11 Registered Users Posts: 11 ✭
    #5
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    Thanks Bill, great answer as always.
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  • oil pan 4
    oil pan 4 Solar Expert Posts: 767 ✭✭✭✭
    #6
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    MPPT controllers are also nice if you have to have max power output from limited panels that are installed in a less than ideal way.

    Solar hybrid gasoline generator, 7kw gas, 180 watts of solar, Morningstar 15 amp MPPT, group 31 AGM, 900 watt kisae inverter.

    Solar roof top GMC suburban, a normal 3/4 ton suburban with 180 watts of panels on the roof and 10 amp genasun MPPT, 2000w samlex pure sine wave inverter, 12v gast and ARB air compressors.

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  • Photowhit
    Photowhit Solar Expert Posts: 6,003 ✭✭✭✭✭
    #7
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    As panels become larger they often have 72 cell designs now that lend them selves to PWM 24 volt and 48 volt systems. So inexpensive panels are often available now for these systems again. 60 cell designed panels need MPPT type charge controller to use the available voltage they produce.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #8
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    There can also be an issue with using 72 cell (36 volt Vmp) on 48 volt battery systems and "standard" MPPT charge controllers.

    For example, if you wanted to use >72 volt Vmp-array on a 48 volt battery bank (sending voltage/current from array longer distances at higher voltages... That would be 3*36 volt Vmp = 108 Volt Vmp array... That could send the Voc (voltage open circuit) in cold weather to over 140-150 VDC--The maximum input voltage for many typical MPPT charge controllers. (typically Vmp~100 volts Vmp) is about as high as one can go in cold regions--108 volts is pretty close or over the limit).

    Do the paper designs/calculations before you open your wallet.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #9
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    Most controllers have a "sizing widget" of some sort on the Mfg's web page.  You chose your panels from a list, or type in the specs, enter your summertime highs, and winter lows and you can easily play with different configurations while the web tool calculates the Voc in the cold, and the Vmp for the summer, and if there are too many watts for the controller to handle.
    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 ,

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