Batteries in Series

firefly
firefly Solar Expert Posts: 66 ✭✭
in Off Grid Solar & Battery Systems #1
I have six 4 volt, 1104 amp/hr batteries run in series for 24 volts. Each connection is the same length of 4/0 cable. I am thinking that having the positive and negative connections come from opposite ends of the string, is the most efficient method. Is this correct, drawing #2?

Steven





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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: Batteries in Series

    Electrically it doesn't make any difference; the two layouts are the same.

    Physically it may make a difference, depending on the circumstances of the install. #1 would probably have shorter wiring over-all, and that is desirable. It is how mine are placed, with the RTS inbetween the two rows.
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  • firefly
    firefly Solar Expert Posts: 66 ✭✭
    #3
    Re: Batteries in Series

    Thanks Cariboocoot, I was just wondering which configuration would drain and charge the batteries more evenly.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #4
    Re: Batteries in Series

    They are identical in the sense that all are in series. The first one will (most likely) have shorter overall cable length. So lower installation costs and/or less voltage drop--So, for me, the first one is the winner.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Vic
    Vic Solar Expert Posts: 3,208 ✭✭✭✭
    #5
    Re: Batteries in Series

    Have always the diagram in the first example. It does keep the leads the shortest. Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
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  • NorthGuy
    NorthGuy Solar Expert Posts: 1,913 ✭✭
    #6
    Re: Batteries in Series

    It all depends on the exact position of terminals and how exactly wires are bent, which, in turn, depends on the orientation of terminals. Plus other things. For example, if the batteries are flooded you cannot block caps with the wires. The goal is to minimise the sum of lengths of the wires.

    Once you figure that all out, it's most likely that #1 will give you better results than #2, even though you will need to put an extra length of lead wire along the box.
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  • shockman
    shockman Solar Expert Posts: 113 ✭✭
    #7
    Re: Batteries in Series
    BB. wrote: »
    They are identical in the sense that all are in series. The first one will (most likely) have shorter overall cable length. So lower installation costs and/or less voltage drop--So, for me, the first one is the winner.

    -Bill

    Does pic #1 not go against the infamous Smartguage recommendation?? what am I missing? http://www.smartgauge.co.uk/batt_con.html
    4x240w panels,Classic 150 CC, 4x380AHR L16's, antique Trace 12V inverter
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #8
    Re: Batteries in Series
    shockman wrote: »
    Does pic #1 not go against the infamous Smartguage recommendation?? what am I missing? http://www.smartgauge.co.uk/batt_con.html

    Nope.
    Both illustrations are for one serial string of batteries.
    The Smart Gauge guide is for parallel connections of batteries.
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  • shockman
    shockman Solar Expert Posts: 113 ✭✭
    #9
    Re: Batteries in Series
    Cariboocoot wrote: »
    Nope.
    Both illustrations are for one serial string of batteries.
    The Smart Gauge guide is for parallel connections of batteries.

    Okay got ya! But now I'm not sure that I got the series/parrallel thing quite clear? in example #3 what if we substitute those 12v batts for 4x, 6v for a 12v system? what would the pic look like?
    4x240w panels,Classic 150 CC, 4x380AHR L16's, antique Trace 12V inverter
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #10
    Re: Batteries in Series

    Well for four 6 Volts configured for 12 Volts it would look something like this:
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  • ChrisOlson
    ChrisOlson Banned Posts: 1,807 ✭✭
    #11
    Re: Batteries in Series
    Cariboocoot wrote: »
    Well for four 6 Volts configured for 12 Volts it would look something like this:

    That is one of those things where "in theory there is no difference between theory and practice, but in practice there is".

    On our bank with 6 pretty substantial parallel strings (9.6 kWh per string) I did not make the string connects to the DC bus equal length. They vary by up to 3 feet difference between the shortest connects and the longest ones. Two years that way and never once have I seen where it makes one iota of difference in SOC between the batteries in different strings - both under load and under charging.**

    I even have the four Interstate SRM-4D batteries out of our fifth wheel RV hooked into our house bank to maintain them and work them over the winter instead of leaving them set idle. The cables hooking those into the bus are a full six feet longer than the shortest ones. I have monitored the charging and discharge of those 4D's, and even though they are much smaller (8.8 kWh) than the T12-250's they charge at the proper rates anyway during bulk and absorb.

    The charge rate for any string in parallel with another one, at any given voltage, is dependent on only one thing - internal resistance of the string or battery. The voltages between parallel strings or batteries always stay the same, regardless of the different lengths in cables, because we are not dealing with 100+ amps like you are in a series string - you're dealing with less than 20 amps on quite large wire and a voltage drop of .00000000001 volts does not make any difference with 20 amps on a AWG 2 bus connect that might be a few feet longer than another one.

    That's in practice - I've measured it, monitored it, documented it with different sized strings in parallel with zero problems noted.

    We now return you to your regularly scheduled theory. :D
    --
    Chris

    ** we used to have a 24V system with the same batteries and they were arranged in four battery parallel-series "groups" with a bus connect from each "group" to the DC bus. When we went to 48V I simply re-arranged the "groups" into series strings - same number of connects from the bus to the bank.
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #12
    Re: Batteries in Series
    ChrisOlson wrote: »
    That's in practice - I've measured it, monitored it, documented it with different sized strings in parallel with zero problems noted.

    We now return you to your regularly scheduled theory. :D

    "... which is already in progress."

    The results might be a little more visible with AGM batteries where the internal resistance of the batteries is a smaller part of the total string resistance.
    I agree that AWG 2 carrying only 20 amps gives pretty small numbers. A badly constructed end connector or a poor connection to a battery post could make more difference than the length of the cable itself, but you have clearly done due diligence on all of those elements too!

    A wiring pattern like the non-diagonal example at smartguage.com would make a lot more difference in voltage/current sharing than a difference in length of a cable connecting to a busbar.
    And of course it is the sum of the + and - cable lengths that counts, so the physical layout is important.
    Sometimes we theorists get carried away with "rules" that make a difference for some people's configuration but not others.

    Keep practicing!
    SMA SB 3000, old BP panels.
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  • ChrisOlson
    ChrisOlson Banned Posts: 1,807 ✭✭
    #13
    Re: Batteries in Series
    inetdog wrote: »
    The results might be a little more visible with AGM batteries where the internal resistance of the batteries is a smaller part of the total string resistance.

    Ouch! Do not do that. Batteries in parallel, just like batteries in series, have to be matched for proper absorb voltage. But unlike batteries in series, which all need to be matched for size and age, batteries in parallel (other than the noted exception above) can be mixed and matched, both in age and size.

    Do it in heavy duty trucks and gensets all the time where you'll see 6-8 Group 31 12V batteries in parallel for the starting bank. One battery goes bad, it makes the others work harder. But you weed out and only replace only the bad one - not the whole string - and the rest of the batteries in that string will still lead a long and happy life.

    The trouble with a parallel string is FINDING the bad one. There is only one way known and that is to disconnect them and test each one individually. Whereas in a series string a bad battery can be found fairly easily by simply checking voltage across posts - and if you find one that's different than the others you got a problem and need to dig deeper.
    --
    Chris
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #14
    Re: Batteries in Series

    *sigh* The question was in respect to Smart Gauge's method #3.
    Frankly with only 4 batteries method #2 works just fine.
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  • shockman
    shockman Solar Expert Posts: 113 ✭✭
    #15
    Re: Batteries in Series

    Attachment not found.
    Okay, I just had my 18yr old son make this drawing of my exsisting setup. I am going to put in 4 new L16's (380a/hr) and would like to know what fuses and or breakers to use and distribution blocks to clean up this mess. The inverter is a Trace 2012(2000w) and I will have approx. 1000w of solar and the small 160w mill. I would like to purchase all required bits and pcs from NAWS. I am hoping that I don't need an elec. box? unless recommended. Inverter is about 6ft away. I have lots of 0awg with crimped eyelets.
    If someone could draw a proper dia. with required fuses and dist. centers it would be a great help for when I place an order from NAWS (international shipping). My son says he hopes you have something better than Paint to draw it out with hehehe!
    Marc

    oops! dc lines and cc line also on pos. post also (of course)
    4x240w panels,Classic 150 CC, 4x380AHR L16's, antique Trace 12V inverter
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #16
    Re: Batteries in Series

    Man, that sure is a small drawing.
    What do you mean my eyes are old? :p

    First thing I see is "direct to inverter, no fuse" on the positive. Oops. Nope. Only the negative side doesn't need a fuse or breaker on it. Inverter and charge sources need proper circuit protection according to the expected current. Wire size is also dependent on current and length.

    Second thing I see is inverter on one set of terminals and charging on the other. Not really the way it's done. Diagonal opposite + and - yes, but for all things.

    Time for the next drawing.
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  • shockman
    shockman Solar Expert Posts: 113 ✭✭
    #17
    Re: Batteries in Series

    Don't know what happened to drawing?? it was much bigger on preview??? It is clickable to enlarge though :>)
    4x240w panels,Classic 150 CC, 4x380AHR L16's, antique Trace 12V inverter
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #18
    Re: Batteries in Series
    shockman wrote: »
    Don't know what happened to drawing?? it was much bigger on preview???

    looks fine to me as all one needs to do is click on it.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #19
    Re: Batteries in Series
    niel wrote: »
    looks fine to me as all one needs to do is click on it.

    It's still small. Oculist time I guess. :blush:

    Just to reiterate, it appears the wire sizes are not calculated. You may want larger than 0 AWG on your heavy lines for a 12 Volt system. Like 4/0.
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #20
    Re: Batteries in Series
    shockman wrote: »
    Don't know what happened to drawing?? it was much bigger on preview??? It is clickable to enlarge though :>)

    Not quite sure what the forum software bases its decision on, but in one case the entire image was placed inline, in the other case a reduced size thumbnail was inserted instead, with the full image being linked to it to display on a click.

    Possibly part of the difference is based on the size (in bytes) and type of the original image which was loaded into the post?
    Possibly one of the mods knows, or possibly it will take an admin or a power user to get the answer. :-)
    SMA SB 3000, old BP panels.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #21
    Re: Batteries in Series

    It appears the forum software is serving both a thumb nail and full image... I don't know if it was created that way or if the forum software did the thumb nail... Let's see if I can get a full sized image:

    attachment.php?attachmentid=4598&d=1361845700

    Looks like a did it as an "IMG" tag (I did a drag from the full image to the edit window here--but it did scale down by about 1/2) where the original post was done as an "ATTACHMENT" tag.

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