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Thread: Fusing question

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    Fusing question

    Hello All. I have a 2021 Reflection 260RD. I have 400 watts of solar on the roof wired in series (approx 80 volts) and 200 watts in a suitcase solar (approx 40 volts). The roof solar comes into a circuit breaker and then goes to a 40 amp MPPT Renogy controller, and the suitcase comes into a circuit breaker and then goes to a 20 amp MPPT Renogy controller. The panels are fused coming into the controllers and the 40 amp controller has a 40 amp fuse going to a bus bar, and the 20 amp controller has a 20 amp fuse going to the same bus bar.
    My question is, do I need another fuse going from the bus bar to the battery? If so, what size fuse would I need? Is that amount of voltage coming from the panels okay? I have 2, 105 amp hour AGM batteries in parallel. Thanks for the help, John

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    Site Team Second Chance's Avatar
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    Moved to Solar Systems and Generators. Perhaps @SolarPoweredRV will jump in - very knowledgeable in this area.

    Rob
    U.S. Army Retired
    2012 F350 DRW CC LB Lariat PS 6.7
    2020 Solitude 310GK-R, MORryde IS, disc brakes,
    Sailun LRG tires, solar, DP windows, W/D
    (Previously in a Reflection 337RLS)
    Full time since 08/2015

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    Seasoned Camper
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    Hi, yes you need a fuse from the busbar positive side to the battery positive side. That fuse needs to be sized taking in consideration the sum of all the loads on the battery bank (DC appliances, inverter, generator etc)
    2021 Momentum 395MS

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    Site Sponsor SolarPoweredRV's Avatar
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    Quote Originally Posted by jdux999 View Post
    Hello All. I have a 2021 Reflection 260RD. I have 400 watts of solar on the roof wired in series (approx 80 volts) and 200 watts in a suitcase solar (approx 40 volts). The roof solar comes into a circuit breaker and then goes to a 40 amp MPPT Renogy controller, and the suitcase comes into a circuit breaker and then goes to a 20 amp MPPT Renogy controller. The panels are fused coming into the controllers and the 40 amp controller has a 40 amp fuse going to a bus bar, and the 20 amp controller has a 20 amp fuse going to the same bus bar.
    My question is, do I need another fuse going from the bus bar to the battery? If so, what size fuse would I need? Is that amount of voltage coming from the panels okay? I have 2, 105 amp hour AGM batteries in parallel. Thanks for the help, John
    First: you need to look at the specs of your Solar Charge Controller to determine if the voltages coming from your Solar panels is acceptable to the Controller. If your Controller is rated to accept that much voltage then it is ok.

    Your question about fusing the battery is a little bit more involved; The USCG requirement for boats is to have a system fuse within 6 inches of the battery, this requirement does not apply to RVs, but it is a good example to follow. With this being said, as long as all of the wires coming out of your battery are fused, then you are probably ok until you add the high current draw of an Inverter. The whole point of fusing is to protect the wire if it gets grounded out (hence the 6 inch requirement for boats).

    Consequently, if your Bus-bar is very close to your battery, then you shouldn't need a fuse at this point in time. However, once you add an inverter and/or increase the capacity of your battery bank then you should add a "Catastrophic Fuse" very close to the battery.

    As far as fuse sizing goes: unless you currently have a high draw device (Inverter), I would say that if you wanted to install a fuse to protect your whole system a 100 amp fuse placed very close to the battery would be a good safety measure. In the future, if you add an Inverter to your system, then you will want to re-visit the fuse issue and increase the fuse size appropriately, maybe a 300 or 400 amp fuse would be appropriate at that time.
    David and Peggy
    2019 Ford F350 Lariat, 6.7L Diesel, Dually, Long Bed
    Running with 20k Reese Goosebox (Love It) and Ford Factory "Puck" system.
    Stopping with 8,000 lb Disc Brakes and Titan Hydraulic over Electric Brakes system.
    Powering all this fun with 1200 Watts of Solar, two Tesla, Model S, battery modules, 24 volt Victron Inverter.
    2018 Solitude 310 GK

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