48V Battery bank charging

tr0ytr0y Solar Expert Posts: 99 ✭✭✭
in Caravan, Recreational Vehicle, and Marine Power Systems #1
Mods - If you think this is the wrong place please move

I have just come into a good deal on a 48v inverter and [email protected] 48v  of lithium battery bank and would like to install this in my RV. I would be removing my 12V inverter charger and my 12V battery bank 600Ah of AGM battery ( 3 200Ah 12V ). 

To service my existing 12V needs I would install a DC to DC converter and leave one small 12V starting battery connected for my generator start. 

Now with the back story in place, I have approximately 1800 watts of PV flat mounted on the roof (best I have seen is 1400w), in series / parallel ( 3 sets of 2 )  running open circuit is about 63v, into a Midnight Classic 150 and that to the battery bank. 

I am wondering what the hive mind here would be on charging ? Do I have enough PV ? I am confident on the Charge Controller. What am I missing ? What have I not thought of ?

Thanks  
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Comments

  • BB.BB. Super Moderators, Administrators Posts: 32,999 admin
    #2
    Troy,

    I moved your post to the RV section...

    Will there be an issue with battery bank temperature (falling below freezing) in the RV (heated/insulated)?

    Regarding how large of solar array--In general, 10%-13% rate of charge is usually a goodly amount of charging for the battery bank:
    • 200 AH * 58 volts (actual LiIon charging voltage) * 1/0.77 panel+controller derating * 0.10 rate of charge = 1,506 Watt array
    Seems reasonable for your RV... Flat roof (no tilt)--Suggests summer and/or southern US for dry camping. If you go "north" in winter, more genset usage...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • bill von novakbill von novak Solar Expert Posts: 891 ✭✭✭✭
    #3
    tr0y said:
    Mods - If you think this is the wrong place please move

    I have just come into a good deal on a 48v inverter and [email protected] 48v  of lithium battery bank and would like to install this in my RV. I would be removing my 12V inverter charger and my 12V battery bank 600Ah of AGM battery ( 3 200Ah 12V ). 

    To service my existing 12V needs I would install a DC to DC converter and leave one small 12V starting battery connected for my generator start. 

    Now with the back story in place, I have approximately 1800 watts of PV flat mounted on the roof (best I have seen is 1400w), in series / parallel ( 3 sets of 2 )  running open circuit is about 63v, into a Midnight Classic 150 and that to the battery bank. 

    I am wondering what the hive mind here would be on charging ? Do I have enough PV ? I am confident on the Charge Controller. What am I missing ? What have I not thought of ?

    Thanks  
    Li-ion has very different charge requirements than lead acid.  One big difference is you do NOT need to make sure you charge at least at C/10 or C/13 or whatever - you don't need any minimum charge rate.  Max charge rate is per the mfr.

    37 amps at 48 volts seems like it should certainly be OK for a 200 amp hour li battery.
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  • BB.BB. Super Moderators, Administrators Posts: 32,999 admin
    #4
    The 10% was just the rule of thumb for a "full time off grid" 10% rate of charge for a system that does need any daily management for loads/hours of sun. I was not trying to imply what the minimum/maximum rates of charge were for that bank (as always, check the mfg. documentation).

    Ideally, yes, need to know what the loads are (AH @ volts ,  WH, etc.) and location+seasons of usage (hours of sun). Harvest needs to match (somewhat exceed) daily loads.

    Li Ion batteries are a much nicer cell that take/supply current in a much more "sane" manner vs Lead Acid (bulk/absorb/float).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • tr0ytr0y Solar Expert Posts: 99 ✭✭✭
    #5
    Thanks All -

    This being an RV the use and requirements vary as I live in it full time for a couple of weeks then it sits. 

    I have been somewhat lazy on a real audit of the energy need as I based it on what I could do with getting PV on the roof. That ended up being about 1800 watts, knowing they would derate and some shading would happen. 

    My reasoning to a lifepo4 and 48v set up, is really dumping a couple hundred pounds of batteries and fixing the mistake of going 12v originally, and a good deal on inverter and battery.

    So I feel confident I can make enough amperage to charge efficiently and I have two generators on-board, 4000 Onan and a 2000 Honda Inverter. Pretty sure with that I can meet all of my needs. 

    Thanks  
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  • wankel7wankel7 Registered Users Posts: 18 ✭✭
    #6
    Is it an inverter and charger? Do you plan on using shore power?
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  • BB.BB. Super Moderators, Administrators Posts: 32,999 admin
    #7
    The 48 volt battery bus may actually be an issue... Check the maximum size of AC inverter you need (don't over size wattage, they can have high "tare" losses--just consuming 20-40+ watts even if zero AC load).

    48 VDC inverters tend to be higher wattage rating vs 12 or 24 volt systems.

    Do the entire "paper design" first before you purchase your hardware... Paper is cheap if you need to "fix" something.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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