Fuse help on small solar setup.

kcarr2010 Registered Users Posts: 1
I know this has to been asked 100 times but I want to make sure I got it right.
2 - 100w panels wired parallel.
1 -2000w inverter
1 -12v 100ah battery
1 - 20a charge controller
So from what I gather I need a 30 amp fuse between the panels and the charge controller. I need a 20a fuse between controller and battery and last I need a 200a fuse between battery and inverter. Is this correct. Sorry I am new so if i left something out in the description please let me know.
I appreciate your help!!
Thank  you


  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    Welcome to the forum Kyle2st, your 100 AH battery (assuming a flooded cell Lead Acid) can, at best, supply about 20% of its AH capacity for any length of time. I.e.:
    • 100 AH * 0.20 (C/5 rate of discharge) = 20 Amps continuous max suggested
    • 20 amps * 12 volts = 240 Watts
    Or, only about 10% of your 2,000 Watts AC inverter's capacity:
    • 2,000 Watts * 1/0.85 AC inverter eff * 1/10.5 battery cutoff = 224 Amps
    Or if the battery were capable of such high current (Some AGM and Li Ion batteries may be able--But not many), would take the battery bank dead in less than 30 minutes:
    • 100 AH / 224 amps * 60 min/Hr = 26 minutes (an in reality, at high discharge rates AH apparent capacity goes down)
    And a 200 Watt solar array, would take days to recharge a 100 AH battery bank from "dead" to full (and you should never take a lead acid battery to "dead"):
    • 200 Watt array / Vmp~18 volts = 11.1 amps in full sun
    • 100 AH / 11.1 amps = 9 hours of full sun
    Most places get between 3-5+ hours of sun per day--So you are looking at 2-4+ days to fully recharge.

    I suggest that a 2,000 Watt 12 VDC AC inverter would need an ~800+ AH Lead Acid battery bank @ 12 volts minimum to run somewhat reasonably, and a 1,200 to 2,400+ Watt solar array...

    Regarding fuses/circuit breakers, I would suggest that you take the planned maximum current, and use the NEC derating factor of 1/0.80 or 1.25x against fuse/breaker ratings to prevent false trips (generally a breaker/fuse will not trip at 80% of rating, and should trip at 100%+ of rating).

    Your thoughts?

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    WRT to fuse/breaker sizing, note that these should be sized to protect the smallest connected wiring.  For example, you could (but shouldn't) wire the inverter to the battery with some small gauge wire, for which a 200a fuse would be far too big.  
    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