24v battery bank to 12v load?

litninrod
litninrod Registered Users Posts: 12 ✭✭
in Off Grid Solar & Battery Systems #1
Something I didn't notice (or maybe didn't understand) when getting my components is the wattage input limit of my charge controller. It can take up to 100v and up to 40a, so maxed out it would handle 4000w or panels...or so I thought. In actuality, it only accepts up to 520w. 
I have 2 - 235w panels, so 470w total. Adding a third one would put me over the 520w limit. BUT, that's at 12v. The CC says it can handle 1040w if I had a 24v battery bank. I was going to add 2 more Duracell 6v 230 AH batteries to the first 2, intending to double my amp hours, but I could run them all in series and make it a 24v battery bank. So that should allow more input capability. 

Now here's what I don't know. The "load" leads on the CC are hooked to a small blade fuse panel, which have a couple 12v dc lights running off of it. If the battery bank is changed to 24V, does the controller load also increase to 24v dc, or does it step down automatically to a 12v dc load? 
Question 2 - the inverter runs directly off the batteries, but isn't it designed to turn 12v dc into 110v AC? Or is it capable of turning 24v dc into 110v AC also?
2 - Trina 235 w panels
2 - Duracell Ultra 230AH 6v golf cart batteries connected in series to make a 12v 230 AH system
HQST 40A MPPT Solar Charge Controller
Mighty Max 12 Volt 1000 Watt Pure sine wave inverter
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Comments

  • Dcmike
    Dcmike Registered Users Posts: 21 ✭✭
    #2
    if your controller is programmable you can make it put out 12 volts on the load side and unless the inverter is one of those 12/24 volt inverters the answer is no you will need a 24 volt inverter
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  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    #3
    The capacity of the batteries will not change wether arranged as 12 or 24V nominal, 2 strings of 2, or 1 string of 4, 
    460 Ah × 12V = 5,5Kw , 230 Ah × 24V = 5.5 Kw, what will change by going 24V is the current the inverter requires, it will be halved, so smaller conductors fuses could be utilized. Because the effective charging current is halved, allows for a larger array, with the same controller, current is inversely proportional to voltage. 

    The load terminals of the CC will be whatever the nominal voltage chosen is, so in order to use 12V loads a DC - DC buck converter, would be required, personally I've not seen a controller that can be programmed to reduce the voltage for the load terminals, not claiming they don't exist, just speaking in general terms. Similarly DC - AC inverters use a nominal input voltage, so a 12V inverter would not accept a 24V input and could  damage the unit, 

    So basically if you go 24V to increase array capacity, you will need a new inverter, plus a means to reduce 24V to 12V. Remaining at 12V and wanting to increase array capacity, only a second controller would be required, each on its own array but connected parallel across the battery. Since your loads are not large 12V is fine, if planning larger loads in the future, a voltage change to 24V would be a good idea. 
    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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  • litninrod
    litninrod Registered Users Posts: 12 ✭✭
    #4
    OK, thanks for the information guys.
    2 - Trina 235 w panels
    2 - Duracell Ultra 230AH 6v golf cart batteries connected in series to make a 12v 230 AH system
    HQST 40A MPPT Solar Charge Controller
    Mighty Max 12 Volt 1000 Watt Pure sine wave inverter
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  • mryimmers
    mryimmers Solar Expert Posts: 117 ✭✭✭
    #5
    I changed my system from 12 volt to 24 and got one of these little guys cheap on eBay  

    http://www.translectricinc.com/catalog/partdetail.aspx?partno=SM2412-5
    it powers a small 12volt load (electric fencer)

    As for inverters I got on eBay too, cheap too if you are patient, I got Exeltech, very happy with them
    510 watt pv, TS-MPPT 60, Exeltech XP1100, XP600 & XP250 @ 24V, 4x Trojan 105RE, Trimetric 2030, Yamaha EF2400i gen.
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  • Horsefly
    Horsefly Registered Users Posts: 476 ✭✭✭✭
    #6
    For our 24VDC system we powered our 12VDC loads with one of these:
    https://www.amazon.com/Pyle-PSWNV720-Power-Converter-Technology/dp/B003P17X8I

    It's only about $40, and is supposed to handle up to 360W at 12VDC (that would be 30A, which is quite a bit). It's worked great for us but our loads are pretty small (car stereo for tunes in the cabin, plugs for phone chargers, and some night lights that are supposed to be for boats).
    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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