advice on fuse or breaker for my 24 volt syltem

wastwast Posts: 41Registered Users ✭✭
I am looking for a configuration plan for hooking my 2 24 volt 170 ah batteries for running my refrigerator.. 2 190 solar panels in series for charging .. what size breakers will I need.. I will probably add more solar panels for charging later on...

Comments

  • mcgivormcgivor Posts: 2,205Solar Expert ✭✭✭✭✭
    edited June 9 #2
    The purpose of overcurrent devices, be it a fuse or circuit breaker, is to protect the conductors, therefore whatever the smallest conductor is, within a circuit, the overcurrent device must be sized accordingly. Rationale, say for instance heavy gauge conductors are used to minimize voltage drop between the array and controller, but the conductors of the panels themselves are rated for 15A, as an example, then the maximum over current protection would be 15A. Likewise between controller/battery/inverter, all sized according to conductors. It's a common misconception that the overcurrent device is to protect the components, it's actually to protect the conductors.
    So without knowing the conductor sizes all suggestions would be null and void. Therefore if expansion is proposed in the future, selecting larger conductors and overcurrent devices may be prudent. Additionally overload devices are to protect the the components, such as motors, but for the purpose of a solar installation the concern is primarily for the protection of the conductors. Please understand I'm not attempting to be condescending in any way, just attempting to provide some insight.
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery bank 

  • wastwast Posts: 41Registered Users ✭✭
    mcgivor said:
    The purpose of overcurrent devices, be it a fuse or circuit breaker, is to protect the conductors, therefore whatever the smallest conductor is, within a circuit, the overcurrent device must be sized accordingly. Rationale, say for instance heavy gauge conductors are used to minimize voltage drop between the array and controller, but the conductors of the panels themselves are rated for 15A, as an example, then the maximum over current protection would be 15A. Likewise between controller/battery/inverter, all sized according to conductors. It's a common misconception that the overcurrent device is to protect the components, it's actually to protect the conductors.
    So without knowing the conductor sizes all suggestions would be null and void. Therefore if expansion is proposed in the future, selecting larger conductors and overcurrent devices may be prudent. Additionally overload devices are to protect the the components, such as motors, but for the purpose of a solar installation the concern is primarily for the protection of the conductors. Please understand I'm not attempting to be condescending in any way, just attempting to provide some insight.

    thank you and I am on this forum to try and get a better understanding of how this solar and wind off grid system works and with anything electrical not being my strong suit I welcome info from people with knowledge in this field.. so from my panels to charge controller I was planning on using 6awg multistrand wire and 8 awg to the batteries... would this be adequate and what size breaker would I need.. on my primary system I have 3 12 volt panels with 10 awg and midnight solar combiner box with 3 15 amp breakers( one for each panel)
  • littleharbor2littleharbor2 Posts: 1,027Solar Expert ✭✭✭✭
    edited June 9 #4
    Not knowing the type of controller you are using makes output wire sizing impossible. That being said you wouldn't ever use smaller output wiring than input wiring. With a PWM controller the wire sizing would normally be equal for input and output. With an MPPT controller you would usually need larger output wiring due to the increased current output heading to your batteries.

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric, 700 ah @24 volt AGM battery bank. Plenty of Baja Sea of Cortez sunshine.

  • EstragonEstragon Posts: 2,838Registered Users ✭✭✭✭✭
    I suggest you check the manual for the inverter you plan to use to run the fridge. It should spec minimum wire size (I generally suggest using the largest wire that physically fits on the inverter terminals, and shortest practical length to minimize voltage drop), and recommended fuse/breaker size. 8ga sounds a bit light to me for a 24v inverter big enough to run a fridge, but the manual should have this info.

    6ga is likely more than adequate for pv to controller unless you need to go a long distance. If adding panels later though, it might make sense to use 6ga. depending on how many and how far.
    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
  • wastwast Posts: 41Registered Users ✭✭
    Not knowing the type of controller you are using makes output wire sizing impossible. That being said you wouldn't ever use smaller output wiring than input wiring. With a PWM controller the wire sizing would normally be equal for input and output. With an MPPT controller you would usually need larger output wiring due to the increased current output heading to your batteries.

    charge controller is a 40 amp mttp.. so is 10 awg big enough from panels to controller and what size breaker is good for the the required conductor...

  • wastwast Posts: 41Registered Users ✭✭
    wast said:
    Not knowing the type of controller you are using makes output wire sizing impossible. That being said you wouldn't ever use smaller output wiring than input wiring. With a PWM controller the wire sizing would normally be equal for input and output. With an MPPT controller you would usually need larger output wiring due to the increased current output heading to your batteries.

    charge controller is a 40 amp mttp.. so is 10 awg big enough from panels to controller and what size breaker is good for the the required conductor...


    also planned on using 4 awg from inverter to batteries...
  • mcgivormcgivor Posts: 2,205Solar Expert ✭✭✭✭✭
    edited June 10 #8
    Reading between the lines, it would appear to me at least, that the planned installation is not based on calculation of load demands. Understandably with a first time endeavor mistakes will be made. In order to build a balanced system the starting point would be loads,then  Since the original question was in reference to over-current protection, which is a legitimate question, it's relevance would come later in the process. My suggestion would be to start a new thread with a discussion title "System design", or something along those lines, the rational behind my comment is a refrigerator is an often underestimated load. Just a thought 
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery bank 

Sign In or Register to comment.