Step down converter

mountainman
mountainman Registered Users Posts: 439 ✭✭
in Caravan, Recreational Vehicle, and Marine Power Systems #1
Would it be possible to temporarily  run a 12 volt inverter from a 24 volt battery with a 24-12 dc-dc converter?
2kw array 6 345 q cells  make sky blue 60 cc
 6 230ah GC @36 volts 
18 amp accusense charger. 3650 champion 
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  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    #2
    The cost of the DC-DC converter,  a high current model, would likely be more than that of an inverter designed to use 24V and would do so without the inherent losses of the converter, I would think. 
    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.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #3
    Sure, it's possible, as long as the DC-DC step-up converter can supply the surge demands the 120VAC inverter needs, without the whole system crashing.  But it's not likely going to make you happy unless you are working with less than 50 watts
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

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  • mountainman
    mountainman Registered Users Posts: 439 ✭✭
    #4
    I'm just trying to power up a 32" led TV with a
    300 watt inverter until  my new 24 volt inverter comes.
    I have a 30 amp 24-12 converter.
    2kw array 6 345 q cells  make sky blue 60 cc
     6 230ah GC @36 volts 
    18 amp accusense charger. 3650 champion 
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #5
    if you have it, sure, try it.  It either works or won't.  But spend $$ to get parts to try it, and not simply getting the right voltage inverter is wrong.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

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  • mountainman
    mountainman Registered Users Posts: 439 ✭✭
    #6
    Ok so far it is works. Thanks.


    2kw array 6 345 q cells  make sky blue 60 cc
     6 230ah GC @36 volts 
    18 amp accusense charger. 3650 champion 
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  • mountainman
    mountainman Registered Users Posts: 439 ✭✭
    edited May 2020 #7
    I wanted to double my panel watts from 500 to 1000 (4 250 grid tie) 
     To keep my existing mppt controller.
    I rewired my 4 Gc Batteries from 12 to 24 volts. 
     I Got a 24 volt 300 watt inverter for ac.
    For 12 volt rv pump and led lights I used a 20 amp  24-12 step down converter. 
     For 10 days without the converter my 12 volt usage was 880 wh. 88 wh avg.
    Using the converter for 10 days 1550 wh
    155 wh avg.   
    ~.60℅ efficiency to get 12 volts from a 24 battery.
    With this 12 volt converter led  lights are not as bright and it takes longer for the full size toilet to fill. 

    I see there are also 24-13+volt converters
    I'm sure the lights would be brighter
     but would the higher voltage converter possible be more efficient?

    2kw array 6 345 q cells  make sky blue 60 cc
     6 230ah GC @36 volts 
    18 amp accusense charger. 3650 champion 
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,626 admin
    #8
    Efficiency is a function of design, and to a degree, how you use the converter.

    If you have a 4kwatt converter, and use mostly 50 Watts 90% of the time, the 40 Watts minimum power loading of the converter becomes a major factor.

    Can you measure the current in vs current out? Measure no load current draw, measure average current loading and such.

    If you use power 4 hours per day, but run the converter 24 hours per day can also be a power suck.

    Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • jonr
    jonr Solar Expert Posts: 1,386 ✭✭✭✭
    #9
    All other things being equal, a 24V to 13V converter is just slightly more efficient than a 24V to 12V converter.    As Bill says, far more important is the design and size.

    I am available for custom hardware/firmware development

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  • mountainman
    mountainman Registered Users Posts: 439 ✭✭
    #10
    I leave the converter on 24 -7. It's main purpose is to supply the refrigerator propane solenoid.   And rv water pump.
    A couple led lights and occasionally stove vent fan.
    With everything on at once I measured 133 peak watts on 12 volts over 10 amps.
    I didn't see any 15 amp converters
    So I went with  a 20 amp.
    With double the array watts from 500 to 1000 by switching to 24 volts.
    A loss of ~3 watts per hour from the converter will hardly be noticed.


    2kw array 6 345 q cells  make sky blue 60 cc
     6 230ah GC @36 volts 
    18 amp accusense charger. 3650 champion 
    · Share on Twitter

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