Battery Bank Configuration

quiquequique Solar Expert Posts: 252 ✭✭
I have a battery bank which was 4 batteries of 6V each, in series parallel to give 12V power to my inverter. I added 4 more batteries and for some reason i did this as in the picture:

bank.jpg

If read from top to bottom:

1. you see the + and - where the terminals connect to the inverter
2. the first row of batteries, original bank, 2 6V batteries in series
3. the second row of batts, original bank, 2 6V batteries in series
{first and second row are connected in parallel}
4. the third row of batts, new addition, 2 6V batteries in series
5. the fourth row of batts, new addition, 2 6V batteries in series
{this is where i changed things a bit}

basically the last 2 rows, 3 & 4 enclosed in the rectangle, were the recent additions.

Would this be a problem?

Comments

  • mike95490mike95490 Solar Expert Posts: 8,489 ✭✭✭✭✭
    Re: Battery Bank Configuration

    Yes, you have a problem. Butr it has an easy fix. Just move your positive lead from the top right terminal, to the lower right terminal (as in your pics). That then distributes the power equally between ALL the batteries. The way it is currently, the top pair see 70% of all the load demand, and the bottom pair, see little demand.
    This article explains pretty clearly, the benifits of wireing on the diagonal :
    http://www.smartgauge.co.uk/batt_con.html
    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 ,

  • quiquequique Solar Expert Posts: 252 ✭✭
    Re: Battery Bank Configuration

    ok i saw the drawing, i kinda understand why. The other suggestion made to me was connecting each successive battery in parallel with each other, which in my drawing would correspond to:

    Moving the left-bottom dashed connection up one slot and the right-bottom dashed connection up one slot as well.

    Would the effect be the same as what you suggest?
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Battery Bank Configuration

    The idea is to balance the charge/discharge across all batteries so that one set doesn't end up supplying most of the power while the other just 'tags along'. The 'piggy-back' wiring doesn't do this. Connecting the charge controller and inverter 'diagonally' across the whole bank helps keep wire lengths even, and thus resistance equal.

    Your first set of four should be wired this way. If you are adding a second set it gets more complicated. For one thing, age/usage difference in the batteries can mean significant difference in their power potential. Adding new batteries on to a set that is already a few years old is not recommended. You could set up a second bank, and switch between them as needed with a battery switch:

    http://store.solar-electric.com/basw1300amp.html

    For very large Amp/hour banks it is better to use larger capacity single batteries rather than hook lots of smaller ones together (fewer connections, fewer wires). Otherwise they should be cabled to a common connect point with equal-length wire, and from there to the CC/inverter.

    I'd recommend you get a hydrometer and check the state of your existing batteries (assuming they are flooded cell) before adding new ones on.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Battery Bank Configuration

    i think you are trying for the 4th method in mike's link, but are getting confused. draw out method 4 and take it to your battery bank and wire it as such. paralleling with old batteries will drag the new set down to the same level as the older set and be very sure your charge source can handle the extra battery power as the charge rate should be at a 5% minimum rate.
  • mshen11mshen11 Solar Expert Posts: 185 ✭✭✭✭✭
    Re: Battery Bank Configuration

    trying not to hijack the thread with more questions...

    how do you size the wire that interconnects the battery? do you get the awg wire that is compatible w/ the total amp-hr of the string or the total amp-hr of individual battery?
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Battery Bank Configuration

    it would be similar to that of the load wires, but i recommend going at least 2 gauge numbers thicker. for instance, if you have let's say #4 for your inverter wires then go at least #2 for battery interconnects. some may just think of the interconnects as an extension of the load wires too and add it to the load wire length, but i think adding lower resistance at the battery bank improves the general function of the battery bank to act more as one battery.
  • mike95490mike95490 Solar Expert Posts: 8,489 ✭✭✭✭✭
    Re: Battery Bank Configuration

    The "Load" should be able to "see" all the parallel batteries through the same resistance, which is why the length and style of the wire is important. The gauge should be the same throughout the battery pack interconnects. If you vary gauge between batteries, it WILL affect loading and battery life.
    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 ,

  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Battery Bank Configuration

    the wire does not have to be the same throughout the whole system (meaning the same as the load wires would be) as it can be made to be thicker for the battery interconnects just to clarify. as far as the battery interconnects are concerned then what mike said is true that if you go with a particular gauge then all interconnects should be of that same gauge #.
    i hope this clarifies what i viewed as a possible misreading of what mike said.
  • quiquequique Solar Expert Posts: 252 ✭✭
    Re: Battery Bank Configuration

    ok so here is what i did...can someone check it to see if its ok? :)
  • quiquequique Solar Expert Posts: 252 ✭✭
    Re: Battery Bank Configuration

    here is the link to my modified wiring, forgot to add itwiring.jpg
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Battery Bank Configuration

    not quite there yet.
    as you see the photo the top batteries going from left to right are to be numbers 1 to 4 for reference. you currently have the battery bank - tap on the 2nd battery from the top left and you should place it at the 1st battery on the top left. you also have the battery bank + tap on the 4th battery from the top left and that needs moved to the 3rd battery from the top left.
    i must say you confused things some with alternating the battery directions and drawing on the picture.
  • mike95490mike95490 Solar Expert Posts: 8,489 ✭✭✭✭✭
    Re: Battery Bank Configuration

    That pic with the tangled connections, just made my eyes sore, and I gave up.
    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 ,

  • Solar GuppySolar Guppy Solar Expert Posts: 1,962 ✭✭✭
    Re: Battery Bank Configuration

    Your interconnecting wire is WAY undersized ... looks like 10 gauge ( green wires )

    It all should be the same gauge
  • everlandfarmeverlandfarm Registered Users Posts: 5
    Re: Battery Bank Configuration

    I'm confused??? In a parallel circuite voltage is constant, so comments about rewiring when you have a parallel series circuit, two batteries in series, then in Parallel with the others achieving 12 volts. Your drawing clearly shows the 12V banks in paralel , so comments about only the "top ones" being used confuses me. My comments are made under the assumption that the load wires and the interconecting battery wires are the same size. IF the wires between the batteries aren't the same size as the load wires, then voltage drop would come into play and "could" cause the batteries to discharge unevenly. Oh, the wiring for the "series" portion, where the two battieries are series to make 12V need only be 1/4 the size of the main wiring running down both sides of the bank. Obviously, these series connections only see 1/4 of the current.

    I'm assuming that the battery wiring is stranded and not solid due to "skin effect" as it's a high current DC circuit? Oh, skin effect is the fat that current travels on the outer "skin" of a conductor, thereby one solid wire has much less skin than a stranded one. The current would be traveling on the skin of many smaller conductors which are twisted together the net result being a lot more skin for the current to travel on. Look at a resistance chart for solid vs stranded wire. (this is totally false for dc or low frequency ac for power as the current will only tend to do that when excursions beyond power frequencies and into radio frequencies are made and it is a gradual progression as to the current on the surface with the higher the frequency is.--niel)

    Also remember the old electricians trick, two #14's" in parallel give you the equivalent resistance of a #7 [note--this is not true. Wire AWG is approximately 3 AWG reduction for every doubling of wire cross-sectional area--so 14-3=11 AWG ... Also paralleling wires do not always share current correctly; poor/dirty/bad connections can prevent current sharing and cause the "low resistance" path to overheat/fail--Bill B. moderator]. Why not just buy a 6 or 8? Cost, a spool of 14 is lots cheaper than the others and you can fabricate what you need. Putting n the connectors must be carefully done as you culd end up with a high resistance connection resulting in an unwanted voltage drop. That's easily checked though, just measure from battery terminal (terminal-not connector) to terminal with a meter and you should see no or very minimal dc voltage, if you do see voltage, your wire or connectors are suspect.

    To put it in perspective, let's say you have 40 amps being drawn from the batteries. If you have a bad connection resulting in only a half ohm of resistance, that's a 20volt drop and you only have 24 to start with. E=IR, E being voltage, I beng current, and R being resistance, so 40X.5= 20Volts.

    Ev
  • quiquequique Solar Expert Posts: 252 ✭✭
    Re: Battery Bank Configuration

    Niel,

    thanks, i know i confused things by changing the direction of the separate banks. The only reason why i did that was because my cables from the inverter wouldnt reach if i had done it otherwise.

    THanks for the tip (and patience reading my drawing).

    As for the gauge in wires someone mentioned, i am aware of that. The day after i took that picture i bought the correct wires, i was just using them as temp. Also i believe someone mentioned about using old batteries and new ones. My old ones are 6 months old, and i cleaned them up well, refilled them and everything and actually mixed and matched them in the battery banks.

    Thanks!
  • WindsunWindsun Solar Expert Posts: 1,164 ✭✭
    Re: Battery Bank Configuration
    I'm assuming that the battery wiring is stranded and not solid due to "skin effect" as it's a high current DC circuit? Oh, skin effect is the fat that current travels on the outer "skin" of a conductor, thereby one solid wire has much less skin than a stranded one. The current would be traveling on the skin of many smaller conductors which are twisted together the net result being a lot more skin for the current to travel on. Look at a resistance chart for solid vs stranded wire.

    Also remember the old electricians trick, two #14's" in parallel give you the equivalent resistance of a #7. Why not just buy a 6 or 8? Cost, a spool of 14 is lots cheaper than the others and you can fabricate what you need.

    1. Skin effect has almost no effect at standard 60 Hz frequencies until you get up to around 650 kcmil wire size, or the equivalent of about 3/4" solid copper wire. For AWG 4/0 cable, the max frequency for 100% skin depth comes out to 125 Hz. Stranded wire vs solid wire has no effect on skin effect, as the strands are not insulated from each other and act as a single conductor.

    The only time you would ever see skin effect in stranded wire is with Litz wire, where each strand is insulated and is almost never seen outside of some specialized electronics applications.

    2. That "old electricians trick" has gotten a lot of people in trouble, because it simply is not true. Puttiing 2 #14 wires in parallel is equal to #11 AWG, not #7. The cross sectional area of #14 is 2.08 mm, the cross sectional area of #7 is 10.55 - or 5 times as much.
  • quiquequique Solar Expert Posts: 252 ✭✭
    Re: Battery Bank Configuration

    Niel,

    one more thing. I drew out and corrected the picture so that its easier to read, actually, let me load it up. wiring2.jpg.

    That would mean both + and - taps to the inverter come from the same 'line' of batteries. does that matter? or would it be better to take it from the parallel line of batteries, meaning, (-) from #1 but (+) from #3 instead of #7?
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Battery Bank Configuration

    Considering that you have four banks of batteries, it would be best to run separate cables of equal length from each one to a central connection point and from there to the inverter/charge controller.

    Stating the obvious: keep the wires as short and fat as possible. :D
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Battery Bank Configuration

    quique,
    marc brings up good points of wire equality and low resistance with larger wire thicknesses, but i'm trying to bring you to see how the symmetry will be to get equality from the fat short equal wires first. it seems the confusing picture may have even thrown me. this diagram is better if it's how you actually have it and didn't confuse yourself.

    eliminate the main red connection from battery 7 to battery 1 and place it from battery 8 to battery 2. power shall be taken from the battery bank at battery 3 for the + and battery 2 for the -.

    does this clarify it?
  • quiquequique Solar Expert Posts: 252 ✭✭
    Re: Battery Bank Configuration

    EXACTLY what i was thinking! thanks niel!

    and yes, i did change the wires!
  • everlandfarmeverlandfarm Registered Users Posts: 5
    Re: Battery Bank Configuration
    Windsun wrote: »
    1. Skin effect has almost no effect at standard 60 Hz frequencies until you get up to around 650 kcmil wire size, or the equivalent of about 3/4" solid copper wire. For AWG 4/0 cable, the max frequency for 100% skin depth comes out to 125 Hz. Stranded wire vs solid wire has no effect on skin effect, as the strands are not insulated from each other and act as a single conductor.

    The only time you would ever see skin effect in stranded wire is with Litz wire, where each strand is insulated and is almost never seen outside of some specialized electronics applications.

    2. That "old electricians trick" has gotten a lot of people in trouble, because it simply is not true. Puttiing 2 #14 wires in parallel is equal to #11 AWG, not #7. The cross sectional area of #14 is 2.08 mm, the cross sectional area of #7 is 10.55 - or 5 times as much.

    Hmmm, True, but we're talking about DC current from a battery, so not sure what your reference to 60HZ is about? You do agree that stranded wire has lower resistance than solid?

    Sigh, thought that this was "solar beginners corner?" Most beginners don't spend a ton of $$ investing in top of the line gear to start experimenting with alternate energy sources. Your comment about cross sectional area is valid. I was only trying to provide some alternatives. Further I believe I not only commented on good connections in that scenario, but also provided info on checking for voltage drops but provided a simple math exercise to show the importance of solid connections.

    So, you beginners out there, if you feel that you need additional copper in your wiring the proper way is to spend a lot of $$ on large stranded wire. Alternatively, you can also parallel in additional wires to achieve the same result. Your hobby, your $$.
  • BB.BB. Super Moderators, Administrators Posts: 29,797 admin
    Re: Battery Bank Configuration

    I believe stranded and solid 14 awg wire would have the same DC resistance (from my experience, stranded wire has a larger diameter because of all the "air space" between the conductors which should end up with exactly the same copper cross-section).

    Stranded wire, in "higher frequency" applications experiences a "skin effect" where at higher frequencies, the current tends to migrate out to the surface of the wire. Hence the mention of 60 and 120 Hz (typically inverters take power in little chunks from the battery--at 2x the fundamental frequency). So--for larger wiring and inverters--there can be a skin effect at the lower frequencies.

    I would assume that solar panel connections to GT inverters would see a DC current flow (rather than 60/120 Hz current spikes).

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