Series/Parallel battery wiring

jonr
jonr Solar Expert Posts: 1,386 ✭✭✭✭
Say I have this setup (and I fix the issue with the wiring lengths not being equal). Wouldn't it provide better battery balancing if I also cross connected the 3 short jumpers in the middle of this diagram? Ie, it would force an averaging of the voltage drops across each two battery series and make it closer to exactly 1/2 of the entire banks voltage.

Attachment not found.

I am available for custom hardware/firmware development

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Comments

  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: Series/Parallel battery wiring
    jonr wrote: »
    Wouldn't it provide better battery balancing if I also cross connected the 3 short jumpers in the middle of this diagram?

    The only time I have seen that done is where the battery bank is being charged by two chargers that each work at half the battery bank voltage. If those batteries in your diagram were 12 volts, you would have a 24 volt battery bank. You could charge it with two 12 volt chargers. Grounding can be a bit of an issue that way.

    This technique is done with some higher voltage banks. It has been recommended by the midnite engineers for charging a 120 volt bank with two classics, each configured to charge 60 volts.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Series/Parallel battery wiring

    First thing spotted: that battery bank is 'laddered'. The positive and negative connections should come off opposite posts. But that really only works with two parallel strings. For three they should got to common connection point with equal length wires.

    As far as interconnections between batteries there is no advantage to it and may be a disadvantage in that it can create alternate paths that skip some batteries while putting more current to others; exactly what we try to avoid.

    I never saw the pictures, but one fellow on the forum tried to do what you are proposing. He got sparks for his efforts and went back to the standard wiring.
  • jonr
    jonr Solar Expert Posts: 1,386 ✭✭✭✭
    Re: Series/Parallel battery wiring

    Here is a case where the voltage imbalance between batteries in series caused a problem and adding cross connects plus an active voltage balancing device fixed it.

    The device is similar to the ones used to balance lithium battery banks. Lithium batteries actively balance based on voltage but will also test individual cells before building the pack and match cells to minimize imbalance.

    I am available for custom hardware/firmware development

  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: Series/Parallel battery wiring
    jonr wrote: »
    Here is a case where the voltage imbalance between batteries in series caused a problem and adding cross connects plus an active voltage balancing device fixed it.

    Nothing wrong with using a BMS (batt management system). They are usually not cost effective for lead acid (LA) batteries because the way we manage LA batteries is by overcharging them... they are (relative to lithium batteries) quite tolerant of overcharging.

    The battery cells that come off a production line are all a bit different and have slightly different need for charging. If a battery manufacturer specifies a charging protocol that will charge the average LA cell, half their cells will fail under warranty. Most battery manufacturers specify a charging protocol that will fully charge more than 99.9% of their cells. This means that for a typical LA battery most cells are routinely being overcharged.

    The link you provided shows an active voltage balancing system, but because it is voltage based it still will still lead to charge imbalance. Each 12 volt battery is still 6 cells in series with no cell balancing other than the usual overcharging. The problem of parallel batteries is not solved... just because you hold six 12 volt batteries at the same voltage doesn't mean that they will be equally charged.

    The weakest cell among the 36 cells will set the limits (performance & lifespan) for the entire bank. Your chance of having an outlier weak cell is almost three times as great as if you had a single string of 12 cells to make up the 24 volt battery bank.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • jonr
    jonr Solar Expert Posts: 1,386 ✭✭✭✭
    Re: Series/Parallel battery wiring

    I agree that within battery issues still exist and overcharging needs to be used to address that. But if battery A in a series string has a higher voltage, it prevents battery B from receiving as much voltage - so B may never get overcharged as it should be to balance individual cells. Controlling the intermediate voltage ensures that battery B receives the intended voltage (eq, 1/2 of the applied voltage). I'd pay $50 for that if it helps.
    vtmaps wrote: »
    just because you hold six 12 volt batteries at the same voltage doesn't mean that they will be equally charged.

    Isn't long term voltage a good indicator of SOC and SOC the value that needs to be controlled to prevent undercharging (ie, sulfation) problems?

    If I have 3 12V batteries properly wired in parallel in a 12V system (ie, all 3 always at the same voltage), what bad things happen in terms of charge imbalance?

    I am available for custom hardware/firmware development

  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: Series/Parallel battery wiring
    jonr wrote: »
    If I have 3 12V batteries properly wired in parallel in a 12V system (ie, all 3 always at the same voltage), what bad things happen in terms of charge imbalance?

    Stratification, sulfation, overheating, over gassing, grid corrosion, and more. Basically anything bad that can happen to an undercharged or overcharged battery.

    Two batteries at the same voltage do not necessarily receive the same current. I'm not saying that parallel batteries cannot work, but as the cells age and diverge in their characteristics the charge imbalance will grow. One of your 18 cells is already the weakest (even when they are brand new... they can't all be above average). That cell will set the limit for the whole bank.

    At first it is difficult to notice a problem because the good strings may mask the weak strings. If you have a DC clamp ammeter you can see if the battery strings are receiving equal current. As the divergence progresses you may find that after charging, one string is actually discharging into the other strings. As I mentioned earlier, the entire bank is only as good as its weakest cell. The unequal charging in a parallel system just makes things worse.

    So yes, parallel batteries can function well for awhile, but they are very likely to have a shorter lifespan than a single string. Things get really bad when one cell shorts out... that string will take most of the charging current and can go into thermal runaway. A shorted cell in one string can be caused by an open cell in another string... The string with the open cell receives no current and the remaining current is divided among the other strings. This higher current may cause overheating which causes warped plates which short out. This is why it is advisable to put fuses on each of the parallel strings in a battery bank.

    btw, even if you construct a battery bank with impossibly perfect wiring, and even if your battery cells are impossibly identical, you still have a system that is, at best, in an unstable equilibrium. If one string is a bit warmer than the others (inevitable) it will take more of the charging current which makes it warmer which makes it take more of the charging current which makes it warmer which makes it take more of the charging current...

    As I mentioned earlier, the reason multi cell (series and/or parallel) lead acid battery banks work at all is because of their tolerance to overcharging. If you hold them at a high enough voltage for long enough they will all usually get charged. The more cells you have the more likely you are to have an outlier weak cell. In your system with three parallel strings, you have almost three times the chance of having an outlier weak cell.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • jonr
    jonr Solar Expert Posts: 1,386 ✭✭✭✭
    Re: Series/Parallel battery wiring

    Is it ever worth it to balance banks by adding very small resistors? For example, in the example with three parallel pairs of batteries, series resistors could be used to make all 3 currents equal under typical conditions.

    Everything I read indicates that imbalances in paralleled batteries cause problems that are minor in comparison to the major problems that imbalanced series connected batteries can cause.

    I am available for custom hardware/firmware development

  • zoneblue
    zoneblue Solar Expert Posts: 1,220 ✭✭✭✭
    Re: Series/Parallel battery wiring

    That guy in that link had a dead battery in series with another, and he tried to fix it with an active device, duh.

    Its really a given that a bank of any kind of cells will only function correctly, if the indiv cells match in their internal resistance, and their capacity, within a fairly tight tolerance. Once that tolerance is breached the bank is considered end of life.

    One bad cell in a bank regardless of its position or typology spirals to death because it discharges first, then reverse polarises, destroying the cell.

    Lithium batterys are often parallelled relentlessly. But they are factory binned to ensure internal resistance and capacity match closely, and often certified to that effect. And their BMSs rigidly maintain a middle operation zone.

    Theres several reasons why i can think of not doing it with Lead banks.

    The main one is that being old tech, they are made to lower tolerances, and natural variation will cause issues at the bottom end in particular. Even if they started out fairly close, they may not stay that way. Parellel batterys should really have fusing to protect against plate shorts. The more cells in parallel the more fuses required, and the bigger the consequence of a plate short. Plate shorts are fairly easy to do with lead, because as the grids corode gunk falls to the bottom of the cell. Fuses in close proximity to the cells are problematic due to ignition risk. With lithium theres no liquid inside, and the only real cause of plate shorts is either physical damage, or over discharge, followed by over vigorous charge. This is one of the priamry scenarios BMS protect against.

    Lastly, parallel sets of longer series strings, impart an averaging effect, that means that current sharing between the strings is more likely to be more equal. With parallel banks uneven current sharing is a real issue, and is caused by differences in internal resistance. Add 8 in series with another 8, and those differences are much more likley to cancel out, than 16 cells in parallel. This still doesnt stop cell variations, but does help with overall string balance.

    None of these sound super convincing reasons as I write it, but together, i guess they add up to why its not done or recomended.
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


  • Blackcherry04
    Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    Re: Series/Parallel battery wiring

    Since 90% of the Batteries in the world are in a Parallel configuration, it only make sense that more of them have issues than those in Series, just a thought.
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: Series/Parallel battery wiring
    jonr wrote: »
    Is it ever worth it to balance banks by adding very small resistors? For example, in the example with three parallel pairs of batteries, series resistors could be used to make all 3 currents equal under typical conditions.

    sure. but the resister will have a voltage drop and the battery will not be at the same voltage as the other batteries. Try it... monitor what you are doing with an hydrometer.

    Your goal (with any battery bank, series or parallel) is to use the lowest voltages possible for the shortest time possible to charge your batteries. High voltages for long times are tough on a battery. The manufacturer gives a charging spec that will overcharge most cells, all because a few cells need more than the rest. With an hydrometer you can figure out what works for your batteries in your system in your environment.

    I'm glad that as I work out the details of charging my battery bank that I only have one string to manage.
    jonr wrote: »
    Everything I read indicates that imbalances in paralleled batteries cause problems that are minor in comparison to the major problems that imbalanced series connected batteries can cause.

    Imbalanced series connected batteries are certainly a problem. They all receive the same current, though. They can be monitored by voltage... much less fuss than checking SG. One of the practical problems of parallel banks is that when there is a high resistance bad cell, the string drops out but the other strings may mask the problem. While they are masking the problem real damage is being done to them. With a shorted cell in one string, the masking won't last as long before you notice something wrong. Hopefully you will notice something before the fire in the battery box.

    Parallel batteries should be fused. What size fuse? Great question! Too large ... it doesn't offer protection. Too small ... if one blows on a startup surge, they all blow.

    btw, all that fusing adds connections, points of failure, to your system.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • zoneblue
    zoneblue Solar Expert Posts: 1,220 ✭✭✭✭
    Re: Series/Parallel battery wiring
    Since 90% of the Batteries in the world are in a Parallel configuration, it only make sense that more of them have issues than those in Series, just a thought.

    None of the 4 different battery systems here contains any parallel strings. 2 vehicles, one electric fence, one RE system!
    vtmaps wrote: »
    I'm glad that as I work out the details of charging my battery bank that I only have one string to manage.

    Quite.
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


  • Blackcherry04
    Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    Re: Series/Parallel battery wiring
    zoneblue wrote: »
    None of the 4 different battery systems here contains any parallel strings. 2 vehicles, one electric fence, one RE system!
    Yeah and I bet they all have parallel plates attached to a common buss and sharing a common pool of electrolyte if they are FLA.
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: Series/Parallel battery wiring
    Yeah and I bet they all have parallel plates attached to a common buss and sharing a common pool of electrolyte if they are FLA.

    To pursue that thought to its logical extreme... even a 2 volt battery battery bank with only 1 pair of plates is a parallel battery bank. That would be due to heterogeneities in the plates. The most common real cause of single cell parallel is stratification, when the upper plate and the lower plate see different electrolyte concentrations.

    I'm sure that if whoever invented the LA battery had thought about all this, they wouldn't have bothered inventing it. :p

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Series/Parallel battery wiring

    People think batteries are not resistors. They are. People think wires and connectors are not resistors. They are. All resistors are variable, whether you want them to be or not. If you add more resistors of whatever type to a system be prepared for the increasing possibility of changing resistance and thus current and Voltage differences throughout the system.

    Best plan:
    1). Design system right so batteries meet load demands with as few components as possible.
    2). Make sure charging is sufficient for battery bank.
    3). Buy in-date batteries.
    4). Keep an eye on them.
    5). Get years of service without complex battery management systems.

    Plus you avoid showing signs from suffering OCD.
  • Blackcherry04
    Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    Re: Series/Parallel battery wiring
    People think batteries are not resistors. They are. People think wires and connectors are not resistors. They are. All resistors are variable, whether you want them to be or not. If you add more resistors of whatever type to a system be prepared for the increasing possibility of changing resistance and thus current and Voltage differences throughout the system.

    Best plan:
    1). Design system right so batteries meet load demands with as few components as possible.
    2). Make sure charging is sufficient for battery bank.
    3). Buy in-date batteries.
    4). Keep an eye on them.
    5). Get years of service without complex battery management systems.

    Plus you avoid showing signs from suffering OCD.
    Yep, thats why every connection is so important and attention to detail is a must. If one out of fifty connections on a parallel bank is flaky, there will be a issue. It's every cable, every crimp, every lug, every washer, every nut. It's doing the proper maintenance and being in tune with the system before it cascades into something you cannot correct.
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: Series/Parallel battery wiring
    Yep, thats why every connection is so important and attention to detail is a must. If one out of fifty connections on a parallel bank is flaky, there will be a issue. It's every cable, every crimp, every lug, every washer, every nut. It's doing the proper maintenance and being in tune with the system before it cascades into something you cannot correct.

    I totally agree, and I must say that a little OCD helps keep everything ship shape. --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • Blackcherry04
    Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    Re: Series/Parallel battery wiring

    Here is a perfect example of a problem. Surrette supplies a Stainless steel terminal nut with a captive lock washer. The nut is fine, the lock washer is made out of a different alloy and will disintegrate and rust under the nut giving you a bad connection if exposed to acid. Solution is the use a SS flange nut with the locking serrations molded into the nut. Attention to detail. It costs a few $$ per bank to do it right the first time and not deal with the problems.
  • Aguarancher
    Aguarancher Solar Expert Posts: 315 ✭✭✭
    Re: Series/Parallel battery wiring

    A couple of things when using SS fasteners is that while those split nuts will help in securing tight connections they are prone to galling and can make dis-assembly a problem. A little anti-seize on those threads will also help ease dis-assembly.
    Also any fastener exposed to sulfuric acid should be type 316 SS not type 304 or 308 which are commonly used.
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: Series/Parallel battery wiring
    Attention to detail. <snip> do it right the first time and not deal with the problems.

    On the subject of detail... for the newbies, tell us again about the fine details of aiming the vents in the battery caps....

    I always liked that... it's so obvious once you think of it. :cool:

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • Blackcherry04
    Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    Re: Series/Parallel battery wiring

    Bayonet Battery caps that have vents on one side will clock into the well 180 ° and lock with the vents either facing the connection or facing the other direction. You'll have less corrosion on your lugs by facing the vents away. Takes a little practice to do it the right way. It's like tapping the cap twice on the well before removing it, the first tap condenses the little droplets and the second will cause it to fall into the well. A old 5 gallon plastic lid makes a perfect place to sit all the caps as you remove them, I line them up in rows and it's just habit to replace them the way I take them out. The lid can sit on top of the batteries with out fear of a short.

    Call me a trained monkey, but I have less issues when I do repetitive tasks the same way every time. Time Motion study type of thing. If you check 99 cells and leave # 100 your looking for a problem.
  • jonr
    jonr Solar Expert Posts: 1,386 ✭✭✭✭
    Re: Series/Parallel battery wiring

    I find it interesting that when it comes to cable resistance, some people go on about how important it is to match all the path lengths, even if it adds additional connections. But as large or larger variations in internal resistance between different batteries are ignored. One might be better off measuring the batteries and stacking them such that the higher internal resistance ones have the shorter path lengths. This might provide better balancing with fewer parts.

    Also interesting when people resort to the "do it my way or you are xxx" name calling technique.

    I am available for custom hardware/firmware development

  • Blackcherry04
    Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    Re: Series/Parallel battery wiring
    jonr wrote: »
    I find it interesting that when it comes to cable resistance, some people go on about how important it is to match all the path lengths, even if it adds additional connections. But as large or larger variations in internal resistance between different batteries are ignored. One might be better off measuring the batteries and stacking them such that the higher internal resistance ones have the shorter path lengths. This might provide better balancing with fewer parts.

    Also interesting when people resort to the "do it my way or you are xxx" name calling technique.
    The question would be , Does the resistance remain during the life of the Battery ?? I shuffle the batteries position in banks of GC-2's once a year when I do service on the connections, it's the first battery on the positive connection that uses the most water and takes the hardest service the way these are cycled. May not be true in all battery banks.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Series/Parallel battery wiring

    You can easily control the resistance in the cables by making them the same length to begin with and not allowing corrosion or loose connections to creep in.
    Batteries are another story. The best you can hope for there is to start with as equal SG per cell as you can and try to maintain that. You are not going to be able to filter out the minor differences.

    Sometimes it a really good idea to listen to people who have fixed hundreds of systems and got them working right and lasting long. We actually know what we're talking about.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Series/Parallel battery wiring

    Resistance is "relative"... In general, when the cables are more than a few feet in length, the cables become the major resistive factor in parallel battery bank connections.

    It is a bit of tough question to answer... More (matched) resistance in the cables, the less variation in charging/discharging currents you will have in your parallel connections (i.e., variation in cell resistance/voltages is "swamped" by cable resistance). Using the wires as a known/controlled resistance makes them a "ballast" (sort of a current control element).

    On the other hand, the more resistance you have, the more losses you get (and voltage drop). Power = I2R -- So, if you double the current, you get 4x the losses due to heating.

    Many of the reasons many of us here are so concerned with "balanced system designs", anytime you go out of the "middle range" for your installation (over/undersized panels, battery bank, AC inverter, wiring, charge controllers, backup genset, etc.)--You are more likely to trip on some "secondary" effect that now comes up and bites you in the rear end.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • jonr
    jonr Solar Expert Posts: 1,386 ✭✭✭✭
    Re: Series/Parallel battery wiring
    BB. wrote: »
    More (matched) resistance in the cables,... the more resistance you have, the more losses you get (and voltage drop).

    If I go here (and get over my amusement at his opening points), I see that the recommended "balanced" wiring requires longer paths and therefor more resistance. So, for example, if one used method 3 as drawn (not as intended - keep the middle cables shorter) and put the higher internal resistance batteries in the middle, we could be talking about less resistance to achieve better balance.

    Clearly, "the batteries are all equal so the path lengths need to be too" isn't exactly correct. But it would be interesting to see actual numbers.
    anytime you go out of the "middle range" for your installation (over/undersized panels, battery bank, AC inverter, wiring, charge controllers, backup genset, etc.)--You are more likely to trip on some "secondary" effect that now comes up and bites you in the rear end.

    Agreed, and sometimes such designs are necessary. Which is why "just follow the cookbook" is sometimes a poor answer.

    I am available for custom hardware/firmware development

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Series/Parallel battery wiring

    And how do you measure that difference in resistance between batteries?
    Which, by the way, changes over time including moment to moment.
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Series/Parallel battery wiring

    jonr,
    if you want to you can take the reverse view of it that was pointed out to me once in that if you make the wire resistance higher, but still equal going to the battery strings that the small variances in resistance presented by the battery is more insignificant. you can try this with resistors if you like, but they need matched very very closely. this will bring the charge rate down to the batteries though and may inhibit their ability to discharge as well. this brings to mind the question then of why have this rating of ah of a battery bank if you limit it? limiting the charge could also cause problems in that the batteries won't recharge if low enough in % and it won't take much to reach that point.

    the device you mentioned i would question its ability to balance a battery bank. it may work, but do it right the first time by low resistance wires with good connections that are equal in length to keep resistances as identical and low as is possible. if you have trouble grasping at the principals behind all this then you maybe shouldn't change anything beyond what is widely prescribed or risk losing your batteries prematurely. it's fine to question and discuss it, but learn to accept a bit more readily what others do know.
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: Series/Parallel battery wiring
    jonr wrote: »
    So, for example, if one used method 3 as drawn (not as intended - keep the middle cables shorter) and put the higher internal resistance batteries in the middle, we could be talking about less resistance to achieve better balance.

    The problem is, you don't know what the issue is with the weak battery. Maybe it doesn't need a higher or lower voltage than the other batteries. Maybe it doesn't need more or less amperage than the other batteries. Maybe it needs more time, or time and some combination of different amps and volts.

    How much are you willing to overcharge all the other batteries to get the weak one charged up? Sometimes its best to just remove the weak battery from the bank and try to equalize it in isolation.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Series/Parallel battery wiring

    Low resistance is an indicator of low SOC. If you 'balance' this against higher resistance, higher SOC battery by adding resistance you reduce the amount of Voltage that will go to the low SOC battery and condemn it to death.

    If the batteries start out imbalanced you can not correct this in any way other than by charging them to a state of balance. That is why individual cell management would work, but is not practical to implement on FLA's (which have a high range of tolerance). Starting out with a proper commission charging and using equalization as needed will lead to long battery life.

    Do not assume the Smart Gauge diagrams are about adding wire resistance. Quite the opposite. The wires are going to be needed to connect the batteries used anyway. As such keeping them equal removes one potential variation in the string resistance, reducing any differences to just the batteries. The wiring resistance can be compensated for by adjusting the charge Voltage so that true V levels are achieved at the battery. Keep in mind also that the effect of the wiring resistance is greatest at low Voltage, high current (i.e. Bulk stage) and diminishes as battery Voltage increases and charge current drops.
  • jonr
    jonr Solar Expert Posts: 1,386 ✭✭✭✭
    Re: Series/Parallel battery wiring
    Low resistance is an indicator of low SOC. If you 'balance' this against higher resistance, higher SOC battery by adding resistance you reduce the amount of Voltage that will go to the low SOC battery and condemn it to death.
    Obviously one would not measure the batteries while in an unequal SOC and then use those resistance values to balance. They would all be equally charged first.
    Do not assume the Smart Gauge diagrams are about adding wire resistance. Quite the opposite. The wires are going to be needed to connect the batteries used anyway.

    They aren't "about" adding resistance, but that is a side effect that they do create. The balanced configurations have longer path lengths using more wire that wouldn't be used anyway.

    I am available for custom hardware/firmware development