Recharging My Battery Bank

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Iguana Greg
Iguana Greg Registered Users Posts: 8 ✭
in Solar Beginners Corner #1
I am working on a new project down here in Nicaragua. There is a current battery bank for the inverter system. It has 4 12Vdc 270Ahr batteries in parallel setup. When I took over the project they had three battery chargers hooked up on three different batteries. They wer all still setup in parallel. I believed that you connected the positive charger terminal to the first Pos. on the setup and connected the neg. to the last neg. post one the battery setup. Having multiple battery chargers set up on each battery is ok? Perhaps ok but not ideal???

I have always used one charger for all batteries in the setup. And if I used two chargers I simply put them on the same battery terminal as the first battery charger setup.

Any thoughts would be greatly appreciated. I have to use the battery charges for now as we are rearranging the solar panel configuration.

Thank you for your time and responses.
Greg
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #2
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    Re: Recharging My Battery Bank

    Check out this artical about wireing on the diagonal
    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 ||
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #3
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    Re: Recharging My Battery Bank

    If you have an accurate DC digital volt meter--Measure the voltage of each battery under heavy loading or charging. If the voltage difference is 0.01 volts or less, then your wiring is sharing ok.

    If the voltage difference is 0.10 or greater, then your batteries are not properly sharing current and not charging/discharging together.

    Mike's link how to wire a battery bank addresses the current sharing issues.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Iguana Greg
    Iguana Greg Registered Users Posts: 8 ✭
    #4
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    Re: Recharging My Battery Bank

    Thanks Guys........But when actually recharging the bank I should put the wires from the charger on the same ones that feed the inverter, correct? And if more then one charger is used it simply gets added to the same wires as the first charger is hooked on to, Correct or does not matter.

    Thanks again,

    Greg
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #5
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    Re: Recharging My Battery Bank

    What matters is the voltage on each battery. The wiring link makes the sharing of current more consistent.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • JESSICA
    JESSICA Solar Expert Posts: 289 ✭✭
    #6
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    Re: Recharging My Battery Bank
    mike90045 wrote: »
    Check out this artical about wireing on the diagonal

    “Tire rotation is an important maintenance duty that extends the life of your tires and ensures safe driving…” [From Edmunds.com)

    I was wandering: If our batteries are wired as in the first diagram, and if, as the article says, because of laziness or sheer ignorance we do not want to change that method, Would it help if we rotate the batteries, say, every 6 months, so that each battery takes its turn, as it were, in the process of being worked out?
    Would "battery rotation" extend the useful life of each battery?

    Hope I made myself understandable.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #7
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    Re: Recharging My Battery Bank

    Batteries are big, heavy, and relatively dangerous to work on. It would be better to design the battery wiring correctly the first time.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Ralph Day
    Ralph Day Solar Expert Posts: 1,019 ✭✭✭✭
    #8
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    Re: Recharging My Battery Bank

    Yes you made yourself understandable, and my back hurts just thinking about doing that!:cry:

    Ralph
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #9
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    Re: Recharging My Battery Bank

    physically rotating the batteries can help, but as said try to do it right by keeping things wired correctly and as evenly as possible. i have mentioned this before as sometimes the end batteries seem to take more, abuse, use, or whatever you want to refer to it as, in time. try to go outside to inside and visa-versa if you can and not just bumping them in line by 1. very accurate voltage and specific gravity readings can also be an indicator as to arranging with lower to higher and visa-versa. i don't see the need to do this that often if you elect to do it and every year or 2 should be fine.
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  • JESSICA
    JESSICA Solar Expert Posts: 289 ✭✭
    #10
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    Re: Recharging My Battery Bank
    mike90045 wrote: »
    Check out this artical about wireing on the diagonal

    Ok, I accept your rebuke.
    Now, 2 more questions:
      If I change the wiring to method 4 (diagram 4), will it make any difference, given that my batteries are about 3 years old?
      Where exactly do I connect the cables coming from the charge controller?

    Thanks.

    P.S. : I never suggested physically rotating batteries; moving the cables would do the trick.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #11
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    Re: Recharging My Battery Bank

    "P.S. : I never suggested physically rotating batteries; moving the cables would do the trick."

    ok no problem as doing it by wiring can yield a similar result. now if you have more than a few batteries and the wires can reach to rearrange that far then maybe the wires are needlessly too long and introducing a bit of extra interconnection resistance. of course, all interconnections should be made as short as possible with keeping good functionality along with being equal in length and is part of doing it right.
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  • JESSICA
    JESSICA Solar Expert Posts: 289 ✭✭
    #12
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    Re: Recharging My Battery Bank

    Thank you, Niel.

    Nevertheless, my questions went unanswered:

    Would it help my old batteries if now I rewire them according to method # 4?

    Where should I connect input (controller) cables to battery bank?

    I have only 4 batteries, now connected as in diagram # 1.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #13
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    Re: Recharging My Battery Bank

    Yes, properly wiring the batteries will only help them--even if they are three years old.

    Next, check the specific gravity of each cell... If the specific gravity difference (between high and low cells) is >0.030 (some people say > 0.015), then run an equalization charge (~15 volts for a 12 volt battery bank--if you have "sensitive" 12 volt devices like laptop 12 volt charge adapters, disconnect them before hitting your battery bank with 15 volts to limit the risk of damaging the 12 volt devices).

    Every 30 to 60 minutes, recheck the SG of the high/low cells... Once they stop moving up in Specific Gravity--Then stop equalization and log the results--Call this 100% charged for your battery bank.

    Do not over equalize the battery banks--Over Equalizing batteries is hard on them too.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #14
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    Re: Recharging My Battery Bank

    you can go to method 4 if you would like, but methods 2 and 3 are fine too. #2 would benefit from the rearranging once a year or so, moreso than #3. #3 is probably done the most and is easier to follow for most people. make all wires of equal length to attach to the common point which some make that common point an oversized buss for easy connections. some of the wires will seem to be long when they connect to the middle batteries, but that length needs to be equal to the outer wire lengths. make the outer wires about what is needed without much excess to keep resistances down and of course all will not only be the same length, but the same gauge as well just for clarification.
    does that help?
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  • JESSICA
    JESSICA Solar Expert Posts: 289 ✭✭
    #15
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    Re: Recharging My Battery Bank
    niel wrote: »
    make all wires of equal length to attach to the common point which some make that common point an oversized buss for easy connections. some of the wires will seem to be long when they connect to the middle batteries, but that length needs to be equal to the outer wire lengths. .
    does that help?

    Yes, it helps.
    But please, bear with me here, since I am a little dumb: Is that " common point which some make... an oversized buss" the point where both, input cables form controller and output cables to inverter, are connected? If so, how in heaven do I connect so many terminals in just one place?
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  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    #16
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    Re: Recharging My Battery Bank
    JESSICA wrote: »
    Yes, it helps.
    But please, bear with me here, since I am a little dumb: Is that " common point which some make... an oversized buss" the point where both, input cables form controller and output cables to inverter, are connected? If so, how in heaven do I connect so many terminals in just one place?

    This page has a good illustration of oversize bus bars:

    http://2manytoyz.com/battbank.html
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  • techntrek
    techntrek Solar Expert Posts: 1,372 ✭✭✭
    #17
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    Re: Recharging My Battery Bank

    I'm curious why method #2 still shows a slight imbalance between the outer 2 batts and the inner 2. The current from all batteries must travel through the same number of connections/wires (the same argument they use for method #4).
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
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  • Iguana Greg
    Iguana Greg Registered Users Posts: 8 ✭
    #18
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    Re: Recharging My Battery Bank

    Well said.........if you are lazy then why would you want to move around 4 - 158lb. batteries every 6 months.

    Thanks for your help everyone.

    More post to come.

    GB
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  • JESSICA
    JESSICA Solar Expert Posts: 289 ✭✭
    #19
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    Re: Recharging My Battery Bank
    dwh wrote: »
    This page has a good illustration of oversize bus bars:

    http://2manytoyz.com/battbank.html

    Great!

    What is the amp. rate for the buss bars?
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  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    #20
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    Re: Recharging My Battery Bank
    JESSICA wrote: »
    Great!

    What is the amp. rate for the buss bars?

    I have no idea. The dimensions are on that page though, and there are standard calculations to figure out the ampacity of copper bars.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #21
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    Re: Recharging My Battery Bank
    JESSICA wrote: »
    Yes, it helps.
    But please, bear with me here, since I am a little dumb: Is that " common point which some make... an oversized buss" the point where both, input cables form controller and output cables to inverter, are connected? If so, how in heaven do I connect so many terminals in just one place?

    yes, and a large buss is how. i recommend buss ampacities being at least x2 of the largest wire size in the system to help keep resistive differences down between connected wires.
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  • JESSICA
    JESSICA Solar Expert Posts: 289 ✭✭
    #22
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    Re: Recharging My Battery Bank

    When I was ready to re-wire my batteries according to the diagram already discussed, I realized, again, my ignorance. Those diagrams are for batteries wired in parallel, and my batteries are wired in series, to get 24 volts at the end. (4 batteries x 6 volts each).

    Is there a correct way (diagram) to re-wire my batteries in a balanced way?
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #23
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    Re: Recharging My Battery Bank

    If you have just 4x6v batteries wired in series--It is "naturally" balanced and you have no issue (no alternative current paths).

    If you have, for example 8x6v batteries for 24 volts--Then you series wire (and fuse/breaker) the 4x6v string, and then treat the 24 volt string just like a "single battery" in the Smart Gauge diagrams.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • JESSICA
    JESSICA Solar Expert Posts: 289 ✭✭
    #24
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    Re: Recharging My Battery Bank
    BB. wrote: »
    If you have just 4x6v batteries wired in series--It is "naturally" balanced and you have no issue (no alternative current paths).

    If you have, for example 8x6v batteries for 24 volts--Then you series wire (and fuse/breaker) the 4x6v string, and then treat the 24 volt string just like a "single battery" in the Smart Gauge diagrams.

    -Bill

    Thanks, Bill.

    Anyhow, I guess all cables (from each battery to the other one) must be the same length. Am I right?
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #25
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    Re: Recharging My Battery Bank

    For a single pure series bank... No, it does not matter--You don't need to match cable lengths (easier to stock spares if all are the same length--but you don't want "excess cable" in your bank wiring either--extra resistance and more cable in the way as you check electrolyte levels, etc.).

    If you have, for example, two banks... Where you need symmetry is for the current flow path in each bank...

    For example, you can have 5 cables for each string, a mix of 2 short and 3 long... It does not matter if it is L-S-L-S-L or L-L-S-S-L or whatever cable order between the two parallel strings--just that the total resistance is the same between parallel banks.

    What you don't want L-L-L-L-L for one bank and S-S-S-S-S for the other parallel bank.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #26
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    Re: Recharging My Battery Bank

    short answer is series does not matter, but parallel does need equality. in the case of 2 or more parallel series strings they must be made to be equal in each series so as to be able to parallel. that equality as bill pointed out is resistance and not necessarily wire length, but making lengths equal is one way of getting equality in resistance.
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