Benefits of 48v over 24v battery system?

backroad
backroad Solar Expert Posts: 185 ✭✭
in Advanced Solar Electric Technical Forum #1
Being the old fart truck driver that I am, sometimes (:) I'm a little dense in understanding things.

My old system that went up in flames was 24 volt and I'm stying to undertand why I'm probably going to build the new system in a 48 volt configuration. I understand that the wire sizing can be consideraby smaller but my cunfusion comes in to battery storage capacity.

The old system had a battery rating of 1185 amps with 3 strings of 4 L16's (12 total). The way i'm understanding this, is that a 48v system with 2 strings of 8 L16's (16 total) would only be a 790 amp system. I know my thinking is messed up. My ADD has kicked in big time.

BTW.....the new shed, just for the electrical panels and solar electrical is up. The wire for the outside panel to the house was donated by an electrical supplier that my son's employer deals with. People are awesome........
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  • Ecnerwal
    Ecnerwal Solar Expert Posts: 101 ✭✭
    #2
    Re: Benefits of 48v over 24v battery system?

    It's the voltage you're missing.

    790 amp hours * 48V = 37.9 KWh, or about 19 usable at 50% Depth Of Discharge.

    1185 amp hours * 24V = 28.4 KWh, or about 14 usable at 50% DOD.

    So you get to store an additional 5 KWH (usable) in the new bank, as well as being able to use smaller wire and smaller breakers for the same power (at higher voltage, but lower current).
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #3
    Re: Benefits of 48v over 24v battery system?

    actually, what you are missing is the watts which considers both the voltage and the current. what ecnerwal was trying to say was you left out the voltage in addition to recognizing the current for watts is the voltage x the current(amps).
    to visualize this is to place 2 100ah 12v batteries in parallel. this is 200ah at 12v because the currents add in parallel while the voltage stays the same. the wattage is 200 x 12 = 2400w. now take those same 2 batteries and place them in series and you get 24v at 100ah because now the current stays the same, but the voltages add. the wattage is 24 x 100 = 2400w. you didn't lose or gain any battery power as it is the same power and wattage is electrical power.
    the twist comes when that power must deal with external forces such as resistance. the wires have a finite resistance and the power delivered is influenced differently with each battery bank example. the reason is by ohm's law which is amps = volts / ohms(resistance).
    the bottom line is don't be confused about the smaller currents that are appearing with higher voltages and know that the loads are usually represented by wattage as well.
    the following part can be confusing to you so disregard this if it does confuse you and that 1st sentence means that a light designed for 12v that is 1w will draw the same power as a 24v light designed to be 1w. these are both resistive loads though and is why you can't use a 12v light with 24v applied to it because ohm's law states that the current will double with 24v applied instead of the 12v to the same 12v light causing the overall power to be 4x as much and the light destroys itself. that means the 24v light is designed with double the resistance as compared to the 12v light to keep the wattages the same.
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  • n3qik
    n3qik Solar Expert Posts: 741 ✭✭
    #4
    Re: Benefits of 48v over 24v battery system?

    One other thing to weigh in on, Unlike 12/24 volt systems, 48 volt systems will see about 60 volts, this can/will be lethal.
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  • jacobs
    jacobs Solar Expert Posts: 72 ✭✭
    #5
    Re: Benefits of 48v over 24v battery system?
    n3qik wrote: »
    One other thing to weigh in on, Unlike 12/24 volt systems, 48 volt systems will see about 60 volts, this can/will be lethal.

    If 60 volts scares you, don't EVER connect to the grid or use an inverter to produces that horribly dangerous 120/240 volts ac.

    I'm still alive after using a 144 vdc system for almost 30 years now. Yes I've been shocked numerous times by it but it's nothing worse than getting shocked by 120 vac.
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  • n3qik
    n3qik Solar Expert Posts: 741 ✭✭
    #6
    Re: Benefits of 48v over 24v battery system?

    The main difference between a DC and AC shock, is and AC shock you have a chance to let go between cycles. With DC, if your muscles contract, there is no letting go.

    Also its not the voltage that kills you, it's the current across the heart, 150 MA if I remember correctly.
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  • jacobs
    jacobs Solar Expert Posts: 72 ✭✭
    #7
    Re: Benefits of 48v over 24v battery system?
    n3qik wrote: »
    The main difference between a DC and AC shock, is and AC shock you have a chance to let go between cycles. With DC, if your muscles contract, there is no letting go.

    Also its not the voltage that kills you, it's the current across the heart, 150 MA if I remember correctly.

    I let go REALLY quick!!! I've never had any problems with muscles contracting and my heart is still beating......I think. Battery bank is 440ah. Maybe I have dry skin?

    Edit:
    I won't even mention what the open circuit voltage is on my PV's (it would really scare you).....But I've been shocked by it at 9 amps. My wind generator....20 amps.
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  • backroad
    backroad Solar Expert Posts: 185 ✭✭
    #8
    Re: Benefits of 48v over 24v battery system?

    Now you're reminding me of the times that I've tested a 9v transistor radio battery by touching it to my tongue. I think my taste buds are still not working well. :):):):)

    I new that there were numerous reasons that I was going to a 48v system and now me thinks that i might understand it a smidgen better. Thanx a bunch kids....
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #9
    Re: Benefits of 48v over 24v battery system?
    n3qik wrote: »
    The main difference between a DC and AC shock, is and AC shock you have a chance to let go between cycles. With DC, if your muscles contract, there is no letting go.

    Also its not the voltage that kills you, it's the current across the heart, 150 MA if I remember correctly.

    AC 60 mA. With DC, 300 to 500 mA is required.
    http://en.wikipedia.org/wiki/Electric_shock#Ventricular_fibrillation

    But it's the high resistance of dry skin that usually saves us. In general, dry skin is a poor conductor that may have a resistance of around 100,000 Ω, while broken or wet skin may have a resistance of around 1,000 Ω
    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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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #10
    Re: Benefits of 48v over 24v battery system?

    gee, i seem to remember reading years ago that it was like 30 or 35ma. anybody care to disprove it?:cry::p
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  • n3qik
    n3qik Solar Expert Posts: 741 ✭✭
    #11
    Re: Benefits of 48v over 24v battery system?
    jacobs wrote: »
    I won't even mention what the open circuit voltage is on my PV's (it would really scare you).....But I've been shocked by it at 9 amps. My wind generator....20 amps.

    Yes they can get up to 150V for off-grid and 600V for grid tied. The point is the array is not worked on as offen as a battery bank. So the battery voltage is mine point of concern.
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