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Thread: Help Please: 12V battery and 24V panel

  1. #1
    Larry N Guest

    Default Help Please: 12V battery and 24V panel

    Greetings folks, I'm a new member and this is my first post. I'm not going to pretend I know a lot about 12V power or solar battery recharging so I'm just gona ask my questions and suffer the ridicule that comes with being a green horn, but I am a quick learner so hopefully won't ask the same question too frequently. Here goes:

    1) I have a 12 volt system (1 battery/Group 27) set up in my sailboat and want to use solar to resupply the battery bank. I have an opportunity to get an 18V or 24V 120Watt solar panel at a better than market price. Would an 18V or 24V solar panel be compatible with my 12V battery or is there a device that can be placed between the panel and battery to make them compatible?

    2) If I were to put a second 12v battery in my boat and connect them appropriately to achive a 24V battery bank, will I still be able to run my existing 12V lighting, radios, vhf, and gps, or would I risk overloading those components?

    and lastly,
    3) I may have the opportunity to buy a couple of these 120W (5) panels and may want to apply them to a home use setup. Is there common sense, easy to read manual/book that someone could reccomend that would help me to design and setup a home based solar power battery bank and then use the stored power appropriately ?

    Thanks, Larry

  2. #2

    Default Re: Help Please: 12V battery and 24V panel

    Larry,

    First, don't worry about being ridiculed. I am new here too and have received valuable help. The people here are great and very experienced and knowledgeable. Heavier on the experienced. You will get the help you need.

    Second, what I think you need is a charge controller. It is a device that, as you guessed, goes between the panel(s) and the battery (bank). It ensures that the proper volts and current are delivered to provide a proper charge profile.

    All others that respond to your post will, rightly, ask you for an understanding of your needs. That is, what are your loads and how much average usable sunlight do you expect to have available on a daily, or discharge/recharge cycle, basis.

    Craig
    Tiny mobile camper currently in use! Off grid 30 weekends/yr. 3 Kyc 85s* in series=255W , Morningstar SS-MPPT15*, four 6V East Penn 8AGC2 AGMs @ 12V=374AH, Trimetric 2020*, Prosine 2.0, Honda EU1000i. My camper.
    *Purchased at NAWS! Along with much more not listed.

    Everything has everything to do with everything else. I learn more by accident than by design.
    Kamala

  3. #3
    Join Date
    Sep 2007
    Location
    Fox, Arkansas
    Posts
    382

    Default Re: Help Please: 12V battery and 24V panel

    You don't need to justify that you are a beginner, just ask away and read the archives using the search box.

    1) I have a 12 volt system (1 battery/Group 27) set up in my sailboat and want to use solar to resupply the battery bank. I have an opportunity to get an 18V or 24V 120Watt solar panel at a better than market price. Would an 18V or 24V solar panel be compatible with my 12V battery or is there a device that can be placed between the panel and battery to make them compatible?

    Go for the 18 volt panels and you can find several economical charge controllers like the Morningstar or others rated at 15 amps or less to handle charging your batteries.

    2) If I were to put a second 12v battery in my boat and connect them appropriately to achive a 24V battery bank, will I still be able to run my existing 12V lighting, radios, vhf, and gps, or would I risk overloading those components?

    Not a good Idea due to load balancing problems. Can be done but can get costly!

    and lastly,
    3) I may have the opportunity to buy a couple of these 120W (5) panels and may want to apply them to a home use setup. Is there common sense, easy to read manual/book that someone could reccomend that would help me to design and setup a home based solar power battery bank and then use the stored power appropriately ?

    Search the archives and read about 12 volt PV systems on the web and you will garner a lot of information very quickly. There are a few books out there but I will let others comment on their value.
    15 assorted solar panels 1800 watts
    MX 60 charge controller
    940 amp hour 2 X 6-100-13 DEKA batterys
    TriMetric battery monitor
    SW4024 inverter
    Basic Stamp computer to control SW4024 from MX60

    MikeO

  4. #4
    Join Date
    Jul 2007
    Location
    Quetico, Ontario
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    5,024

    Default Re: Help Please: 12V battery and 24V panel

    There are a number of voltages that are relevant.

    A "12 volt panel" might have a maximum voltage of ~25 volts (Voc) (open circuit voltage) and a voltage around 17-18 (vmp) You need a voltage significantly above battery voltage to be able to charge a battery,, hence the 17-18 Vmp (Voltage @ maximum power)

    So in fact I have never heard of a 18 volt panel (though they may exist), are probably looking at the 2 voltage numbers of the same panel.

    A 24 volt panel will have numbers ~ double those above.

    Tony

    PS Welcome to the site,,, there are some very smart folks here. The real common sense is here,,, and perhaps home power magazine. Folks here have reinvented the wheel here so that others don't have to over and over again.
    Please note, being a moderator does not add any weight to my opinions 300 watts Siemens/BP panels,plus a Sun 90,, making ~400. ~30 amps into Rogue MPT-3024, 450 ah of Trojan T-105, Morningstar ts300 inverter, a Tri-Metric meter.a collection of antique generators, plus 2 Honda eu-1000i's (also a BS2512 IX controller) and assorted other stuff!

  5. #5
    Join Date
    Jun 2003
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    pittsburgh, pa
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    10,079

    Default Re: Help Please: 12V battery and 24V panel

    i would like to know how you know it is an 18v pv? are you measuring the voltage when it's aimed at the sun without any batteries or other loads connected? what is the make and model # of the pvs and your batteries too?
    as was mentioned a 12v pv can have around 17-18v nominal as the excess is needed to impress a charge to the battery and over varying conditions. this is compatible with your battery voltage, but the charge controller (regulator) is needed and preferably with a battery temperature sensor.
    in addition, you should be certain you will have enough pv amps for the charge percentage to roughly fall within 5-13% of the battery amphours (ah) based on a 20hr rate. this is not cold cranking amps as that is a rating for starting batteries and starting batteries should not be used in solar applications. you also need to know that you will be replacing all of the power you are expecting to use from the battery with pvs or you will have a constant undercharge condition and destroy the battery through sulfation. one last note on a battery is that it should not be drained beyond 50% as that will hasten the death of the battery and many opt to not exceed 20 or 25% dod (amount discharged) to improve the battery lifespan.
    in going with 2 batteries in series (batteries should be identical and about the same age) you will need more than 1 12v pv as 2 would then minimally be needed with a controller that is operating at 24v. this will not run 12v items and a converter will be needed to downconvert from 24v to 12v and should be able to supply enough current as your 12v loads would maximally require.
    you can parallel identical batteries as well and eliminate the converter's need and this would double your battery capacity if going with 2 of them. this would also double your charge requirements so this means doubling your pvs.
    fusing should also be used to and from the batteries and proper wire size to carry your power with little loss. switches are an option, but must be rated for the dc current you will pass through it.
    i generalized this somewhat, but even at that it's allot. hope i didn't leave anything out.
    Last edited by niel; May 26th, 2009 at 20:44 PDT.
    NIEL

  6. #6

    Default Re: Help Please: 12V battery and 24V panel

    Hi there,
    If the sailboat is sailing at sea ( salt water ) then be aware to use only marine pv panels. the price is higher but the standard equipment is not salt water proof.

    Greetings from Greece
    Last edited by BB.; May 27th, 2009 at 7:01 PDT. Reason: Help with English a bit....

  7. #7
    Join Date
    Sep 2006
    Location
    Willits, CA
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    5,407

    Default Re: Help Please: 12V battery and 24V panel

    2) If I were to put a second 12v battery in my boat and connect them appropriately to achive a 24V battery bank, will I still be able to run my existing 12V lighting, radios, vhf, and gps, or would I risk overloading those components?
    If you attempt to power a 12V device from 24V, it will fail quickly.

    You could run matched loads off each 12V battery, such as Port & Starboard lights You run the risk of not depleting both batteries evenly, and then while rechargeing, overcharging one, and not fully charging the other.

    Instead of having to buy all new 24V devices, you could from the onset, get a pair of 6V, group 27, batteries, wire in series, and have a large 12v system. You will need to scale up your charging capacity too, to keep from undercharging the batteries.
    http://tinyurl.com/LMR-Solar
    http://tinyurl.com/LMR-BigLug
    http://tinyurl.com/LMR-NiFe

    Grundfos 10 SO5-9 with 3 wire Franklin motor (1/2hp 240V 1ph # 214505 ) on a timer for 3 hr noontime run - Runs off PV
    Powerfab poletop PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe battery | 15, Evergreen 205w "12V" PV | Midnight ePanel || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT

  8. #8
    Larry N Guest

    Default Re: Help Please: 12V battery and 24V panel

    Greetings and thanks for being so kind and responding to my questions so quickly.

    It sounds as though in theory my hunch was correct in that I could in fact use a 120W 24V solar panel to charge the 12V battery on my sailboat as long as I put a converter between the panel and battery to "down convert" the 24V to 12V. I think it was MikeO who reccomended a Morningstar charge controller. If I have completely misunderstood the theory I hope someone will corrct me.

    I guess I could go with the 24V panel and 2- 12V batterys wired in series (I think series is the correct term) but all my electrical components on the boat are rated for 12V and I would probably be sending to much power. Does that sound reasonable?

    Let me try to answer a couple of the questions that were asked of me.
    1)I live in North fForida so we get a heafty amount of sunshine most of the year although you couldn't tell it based on the last 2 weeks of rain and overcast skies.
    2)I'm not sure of the estimated power comsumption for the boat as I have just aquired her. Bilge pump, 12v fans, vhf radio, am/fm cd player, led interior lights at night, anchorage/running lights, thats about it. I will need to figure hours and amperage but certainly noting elaborate will be in use.
    3) Not sure of my battery make but do know it is a 12V Group 27 deep cycle marine battery.
    4) In regard to the 18V panel, the only proof I have that it is in fact 18V is the manufacturers spec sheet. The manufacturer is a Chinese company named "Suntary". His specs are as follows: Module Type SM120-18 - Rated Power 120Wp - Voc 21.4v - Vm 17.5v Im 6.86A
    5) His specs for the 24V panel are: Module Type SM120-24 - Rated Power 120Wp - Voc 29.4v - Vm 23.5v Im 5.11A

    I personally like the 24V panel better as the deminsions are a beter fit for my boat.
    Not sure if this information is helpful or is enough for someone with a lot more knowledge than me to give a solid opinion but the info was asked for so I felt obliged to provide it Would anyone be willing to estimate a fair price for each of the above panels? That would be helpful for me to know if the manufacturer is negotiating in good faith or trying to over charge me.
    Thanks and looking forward to your knowledgeable replies...Larry

  9. #9
    Join Date
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    Default Re: Help Please: 12V battery and 24V panel

    Your "18 vdc " panel is a 12 vdc panel, as evidenced by the ~17.5vdc vmp. The Vmp for the 24vdc panel is too low to power a 24 volt system,,, you could wire a string of batteries (3x6) to be 18vdc nominal and it might work for that.

    Tony
    Last edited by icarus; May 27th, 2009 at 19:51 PDT.
    Please note, being a moderator does not add any weight to my opinions 300 watts Siemens/BP panels,plus a Sun 90,, making ~400. ~30 amps into Rogue MPT-3024, 450 ah of Trojan T-105, Morningstar ts300 inverter, a Tri-Metric meter.a collection of antique generators, plus 2 Honda eu-1000i's (also a BS2512 IX controller) and assorted other stuff!

  10. #10
    Join Date
    Jun 2003
    Location
    pittsburgh, pa
    Posts
    10,079

    Default Re: Help Please: 12V battery and 24V panel

    sorry, but that 24v pv as you called it is not going to cut it with a vmp output of 23.5v when you have a 24v battery system. this may be a good 18v pv, but the other pv mentioned is a 12v pv that has the 18v out rating. the controller regulates the pv output to properly charge the battery. if the battery is a 24v battery and is to operate 12v items, that is when a converter is used in addition to all of the other stuff.
    NIEL

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