Need help with fuse sizes for 24v off grid

St8koutSt8kout Registered Users Posts: 33 ✭✭
in Off Grid Solar & Battery Systems #1

For the fuse between a 40A Tracer 4215BN charge controller and a 24v battery bank, I know it's supposed to be around 62A for 12V, but what about 24V? The manual does not say either way.

The manual is a bit confusing as it only says "Rated battery current 40A"  "Rated load current 20A" "12/24V Auto work."

http://www.epever.com/en/uploads/news/201512/1449124059577504.pdf

As it is I ended up buying the wrong size fuse (200A) for between the battery and a 1500W inverter because I forgot it was 24V ( I need a 110A fuse for 24V according to the inverter manual). (Those freakin' T fuses are expensive.)

Thanks in advance.

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  • mcgivormcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    #2
    40 A is 40 A regardless of the voltage, at 24V the amount of power will double what it would be at 12 V. The inverter fuse should be sized according to the conductors feeding it, typically a 200 A fuse is used with #4/0 conductors, and a125A fuse for #1/0. (110A is not common) Usually the recommended fuse size is the minimum to prevent the fuse burning prematurely, dose the inverter manual list conductor size along with the fuse size? 
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.  
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  • HorseflyHorsefly Registered Users Posts: 451 ✭✭✭✭
    #3
    I'm guessing he's not talking about the fuse between the batteries and the inverter, since he specifically said between the charge controller and the battery. 

    @St8kout, I think with a 40A charge controller you probably want a 50A breaker / fuse.
    Off-grid cabin: 6 x Canadian Solar CSK-280M PV panels, Schneider XW-MPPT60-150 Charge Controller, Schneider CSW4024 Inverter/Charger, Schneider SCP, 8S (25.6V), 230Ah Eve LiFePO4 battery in a custom insulated and heated case.
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  • PhotowhitPhotowhit Solar Expert Posts: 5,987 ✭✭✭✭✭
    #4
    Did you check your manual?

    I went to look, I thought Midnite had a page on breaker(fuse?) sizing but couldn't find it. They are responsible for many/most of the smaller DC breakers.

    In my charge controller manual (Midnite classis) they provide this information;

     Breaker sizing can be confusing
        •PV input needs to be 1.25% larger than SOC
        •Output sized for max output current (no derating)

    And remind you;
        •Breakers are there to protect wiring, not electronics
    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).
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  • St8koutSt8kout Registered Users Posts: 33 ✭✭
    edited December 2016 #5
    mcgivor said:
    40 A is 40 A regardless of the voltage, at 24V the amount of power will double what it would be at 12 V. The inverter fuse should be sized according to the conductors feeding it, typically a 200 A fuse is used with #4/0 conductors, and a125A fuse for #1/0. (110A is not common) Usually the recommended fuse size is the minimum to prevent the fuse burning prematurely, dose the inverter manual list conductor size along with the fuse size? 

    Somehow I forgot the fuses were to protect the wires, not the components. I was looking at it from the point of view of the max current the Controller can produce, and set the fuse rating a bit higher. With the oversize cabling I'll be using it would take a direct short to cause any risk of fire.

    ---------------------------------------------------------------------------------------

    As far as the Inverter fuse:

    what's throwing me off is Go Power says for their 24V 1500W inverter, to use GP-DC-KIT2 DC Installation Kit, which comes with a 110A fuse/block and #4 AWG cables.

    For their 12V 1500W inverter, to use GP-DC-KIT3, with comes with a 200A fuse/block and #2 AWG cables.

    I guess I didn't notice that they use two different cable sizes. I was assuming that the fuse size was because the 24V version was drawing half the amps of the 12V version.

    I'll actually be using my own 1/0 AWG cables. The max amps the inverter can draw around 83 amps, (2000W/24V). So I suppose it doesn't really matter if it's 110A or 200A.

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