Undersize charge controllers?

schmekschmek Posts: 34Registered Users ✭✭
Hi,

Can charge controllers be undersized regarding wattage, similar to the way inverters can be undersized? By undersized, I of course mean compared to the rated PV capacity.

Comments

  • EstragonEstragon Posts: 2,219Registered Users ✭✭✭✭
    Depending on location and controller, reasonable overpanelling (~20%) is okay IMHO. Most decent controllers should protect themselves, and having extra pv makes for better charging on hazy / light overcast days.

    That said, running controllers constantly at rated capacity will make them run hotter than otherwise, and may shorten their lifetime.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • mcgivormcgivor Posts: 1,642Registered Users ✭✭✭✭
    edited May 6 #3
    Q. Can a pickup truck rated to carry a load of 3/4 ton actually carry a load of 1 ton?
    A. Probably but the added stresses imposed will dramatically shorten the expected life expectancy  of the components over the long term
    An analogy, yes, but relevant.

    Q. Can a 3 ton truck carry a load of 1 ton
    A. Yes, every day, without fatigue of its components.

    It's the same with electronic components, lower stress leads to longer life.
      1500W, 6× Schutten 250W Poly panels , Schneider 150 60 CC, Schneider SW 2524 inverter, 8×T105 GC 24V nominal 

  • EstragonEstragon Posts: 2,219Registered Users ✭✭✭✭
    Carrying on with the truck load analogy, we have to consider that gravity(ie insolation and actual pv potential) is not a constant.  In a hazy coastal environment, the "1 ton load" might only rarely actually weigh more than the 3/4 ton rating.  In a clear alpine environment, it might actually be more than a ton.  There's also the size and type of battery to consider.  Sort of like considering whether the load is going over bumpy, hilly roads with lots of sharp curves and a live load rolling around in the bed, or flat blacktop with a stable load.

      
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • schmekschmek Posts: 34Registered Users ✭✭
    Noted, thanks guys. I find lots of information about how inverters are undersized, but nothing of charge controllers being undersized. 
  • BB.BB. Posts: 27,351Super Moderators admin
    edited May 7 #6
    Note that there are two major types of solar charge controllers:

    PWM: Pulse Width Modulation--More or less a transistor that turns ON/OFF between solar array and battery bank. This type of controller, you cannot over panel without causing them to shutdown/overheat/damage.

    MPPT: Maximum Power Point Tracking--These are use a "DC to DC" Converter internally (tech talk--typically a "buck mode" DC to DC converter). These controllers can safely and reliably "throttle their maximum output current to "rated value" without damage. We typically suggest a maximum over paneling of ~ 1/0.77 (1.3x MPPT's rated power) for a cost effective installation. Hot solar panels tend to have less than rated output Wattage (actually Vmp falls as solar cells/panels get hot---Pmp=Vmp*Imp).

    But, as always, heat (and thermal cycling) is the enemy of all things electronic (virtually anything "ages" faster when hot). If you run a controller at 100% of rated power all day long--It probably will not run for as many years as a controller that runs at 50% rated output.

    The technical side--For every 10C (18F) increase in temperature, the "thing" will last 1/2 as long (70F = 100% life, 106F = 1/2*1/2=1/4 as long as life). Also, thermal cycling is a huge factor in failures (simply going from cold to hot back to cold every day).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • fratermusfratermus Posts: 20Registered Users ✭✭
    > I find lots of information about how inverters are undersized, but nothing of charge controllers being undersized

    Try googling "overpaneling" instead of "undersized";  should be more info. 
    2017 Promaster 159" DIY camper
    570W mono / 220AH GC
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