mixing and matching of different size batt's

al128al128 Solar Expert Posts: 65 ✭✭✭✭
Hi there, folks:


I do have 6 units of 12/100ah batteries, that turned out ok (got them cheap, as they were used ones ... it was kindalike one of those "jump into the pool w/out knowing if there is any water in it" deals :D).


Now I got offered 2 units of 12/220ah batteries ...

I know that they can be used together, since they are all 12v ... but I seem to recall that there are better and worse charging configurations ... and possibly other things to watch out ...


I currently use only 12V loads, but will switch over my complete house within 2 months or so, on a 24V batt.bank.

could anybody lend me a hand here (best short term 12v configuration and long term 24v configuration)?


thx in advance,
Al

Comments

  • mike95490mike95490 Solar Expert Posts: 9,357 ✭✭✭✭✭
    Re: mixing and matching of different size batt's
    al128 wrote: »
    mixing and matching of different size batt's

    Not Recommended to mix the 100's & 220's
    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 ,

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: mixing and matching of different size batt's

    Mike's right (as usual). The difference in performance curves between a 100 Amp/hr and a 200 Amp/hr is huge. Never mind the age difference factor.

    I'd suggest setting them up as two separate banks with an 'A'/'B' switch if you want to get full potential and maximum battery life. I don't know how much array you've got or how well your existing bank charges, but it is possible to run two separate charge controllers from one array and have one CC per bank and then just switch the inverter as needed.

    As for going to 24V system ... Do you need consistent Wattage over 1200? Going to a higher system Voltage is only necessary if you need the Watts. And even then you might consider adding additional 12 V inverters if the load is cumulative and not singular (i.e. lights & misc. adding up to 2 kW as opposed to running some one thing that draws near 2 kW on its own).
  • icarusicarus Solar Expert Posts: 5,433 ✭✭✭✭
    Re: mixing and matching of different size batt's

    You COULD, although not recommended, wire the 100s in pairs, (so that would make 200) and then wire them in parallel. I done this with some older t-105's ~225 ah and some older L-16s.

    Tony
  • al128al128 Solar Expert Posts: 65 ✭✭✭✭
    Re: mixing and matching of different size batt's
    icarus wrote: »
    You COULD, although not recommended, wire the 100s in pairs, (so that would make 200) and then wire them in parallel. I done this with some older t-105's ~225 ah and some older L-16s.

    Tony

    i see your logic (as 2x100ah wired in parallel gives me a 200ah battery) ....

    the only thing that I am not sure about: how do you wire those parallel twins into a line where all batteries are parallel to begin with (1040ah/12v)???

    in other words: inhowfar would pairing them be different than just have them all in parallel in the string? ... or does your example just apply for the 24V scenario?

    thx again, your input is very appreciated
    al
  • icarusicarus Solar Expert Posts: 5,433 ✭✭✭✭
    Re: mixing and matching of different size batt's

    In my case all the batteries are 6 volt. so I have series and parallel in any given string to make 12vdc. With 12 volt batteries to start you simply have to wire the lower ah pair(s) + to +, - to -, and then pull off to the other (higher ah) battery(ies) negative off from the negative of one of the lower pair, and pull off the positive from the other batteries positive.

    Let's see if I can make this even less clear. Let's call your 100 ah batteries 1A, 2A etc. (this would be so much easier if I could draw on line!) Then lets call your 200 ah 1B.

    So you would first wire 1A and 2A pos-pos/neg-neg. (12vt 100ah +100ah=~200ah)

    Then you would wire the from the pos of 1A to the pos of 1B and then wire the neg of 2A to the neg of 1B. (200ah+200ah=400ah)

    This would work for as many batteries as you have in either A or B configuration, so long as any battery in A configuration is ~100 ah and any in any B configuration is ~200 ah.

    As I suggested earlier, it isn't a recommended technique but it will work,

    Tony
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: mixing and matching of different size batt's

    Pardon me for pointing this out but ...

    Wiring 100 Amp/hr batteries "in pairs" and then "in parallel" to the 200's is the same thing: parallel connections. You'll still just have 100's paralleled to 200's. This isn't a good idea. While the 100's will be taking on close to their maximum recommended charge rate, the 200's will be close to their minimum. The 100's will charge faster, get hotter, and lose more water. The 200's will probably not get fully charged and will sulphate prematurely.

    A difference of 20% Amp/hr rate between batteries in parallel may be tolerable. A difference of 100% isn't.
  • bryanlbryanl Solar Expert Posts: 175 ✭✭✭✭✭
    Re: mixing and matching of different size batt's

    re "The 100's will charge faster, get hotter, and lose more water." - I think this is not quite right.

    Battery charge acceptance depends upon their current charge state and internal impedance.

    If the batteries in a bank are of the same chemistry, they will 'track' each other's charge status and share current going in and out in proportion to their capacity. That is an inherent outcome of Kirschoff's laws and the manner by which the battery impedance changes with state of charge and age.

    Keeping all batteries in a bank as much alike as possible is more of a management and maintenance issue than it is a technical capacity or charging one.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: mixing and matching of different size batt's

    To paraphrase Oscar Wilde: I wish I was young enough to know everything. :p

    The internal resistance of a 100 Amp/hr battery isn't the same as that of a 200 Amp/hr battery. Connecting two 100's in parallel does not give the same charge/discharge performance of a 200. It may seem like it should, but in practice it doesn't. It's all tied up with the Peukart Effect: http://en.wikipedia.org/wiki/Peukert's_law

    But I guess 50 years of dealing with electricity in the real world is meaningless. Maybe I have received a few too many high-Voltage shocks. That could explain a lot; my brain does wander off down some strange paths from time to time. :p
  • bryanlbryanl Solar Expert Posts: 175 ✭✭✭✭✭
    Re: mixing and matching of different size batt's

    Peukert is a good reference as it gets to the same basic issue. The application could be a bit confusing in regards to current sharing between batteries in bank, though, I think. I do note that the Peukert coefficient is normalized to capacity and that is a factor to consider here.

    Perhaps a thought experiment. Using 6 cell lead acid batteries in similar condition or state of health, if you discharge a 100 AH battery to 12.2v resting and then apply 14.4v to it, would the charging current be the same as if you applied that same voltage to a 200 AH battery discharged to the same voltage?

    Or, take an old sulfated battery and consider its behavior. If we ignore the self discharge, which is really only a concern when sitting unused, it is easy to see that it takes very little for this battery to track whatever voltage is applied to it. When you load the battery, its voltage drops quite rapidly and when you charge it, it rises the same way. What you can see is that the sulfated battery will track the voltage applied to its terminals over the nominal range providing a little current if it drops and accepting a little if it rises. The extreme case would approach the same thing as having a block of wood with terminals on it.

    Another approach would delve into the "thick plates" bogeyman and I dare not tread there as beliefs there get into religious fervor that puts creationists to shame. It also gets back to Peukert. Oh well.

    I guess this discussion could also get into equalization and the purpose it serves and how (and why) it works. Then there is the practical example of the many situations where non-matched batteries are charged or used in parallel, particularly in RV's. It is not a clear cut thing.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: mixing and matching of different size batt's

    But Bryan, you are perfectly correct that there is no industry standards a battery must meet in order to wear the "Deep Cycle" label. More's the pity. But no manufacturer is going to commit to such specifications because there are too many variables.

    In order for paralleling batteries to truly work as a larger battery, each corresponding plate in the two lesser batteries would have to be connected. Even that is not right, because whereas the Amperage capacity is a function of the plate area, it is not a linear function.

    Too many variables again. Sometimes we just have to deal with the imperfect and sometimes vague information we're given, and try to make educated guesses as to what to do. :D
  • bryanlbryanl Solar Expert Posts: 175 ✭✭✭✭✭
    Re: mixing and matching of different size batt's

    I really don't think there is any call to make things personal.
    no manufacturer is going to commit to such specifications because there are too many variables.
    Yes, indeed. It is why we need to be careful about pronouncements and affirmations that may not have real substance. We need to avoid creating meaningless measures that leave out or dismiss important variables.

    The issue is about precision versus accuracy and properly understanding measurements and their limitations.

    Here, I don't think we are after the actual difference in capacity or current capabilities but rather whether or not paralleling dissimilar batteries is good or bad and why that might be so.

    Paralleling dissimilar batteries is another battery issue where some assertions made border on FUD mongering, IMHO. Assertions are made that apply only to cases of battery failure or extreme and constructed cases. This isn't constructive or helpful, IMHO.

    I have been hearing the warnings to not match batteries unless they are the same manufacturer's lot and date code for a long time. I have wondered why this might be so. I have tried to find out. I am still trying to learn. What I have discovered so far doesn't match the rhetoric I have heard in contexts such as this.

    It does appear that matching batteries in a bank is a good idea for maintenance and life issues but using mismatched batteries doesn't destroy anything, doesn't detract from performance, doesn't cause damage (with appropriate caveats).

    I'm open to hearing about ideas and concepts I haven't considered but they have to make sense to me and to fit in with what else I have found out to gain much traction in my gestalt on these ideas.
  • icarusicarus Solar Expert Posts: 5,433 ✭✭✭✭
    Re: mixing and matching of different size batt's

    I think a good short answer for the OP is this: There is no technical reason you can't mix and match batteries, but it is not recommended for a variety of reasons (most of which are over my head!).

    That said, nothing is going to blow up, nothing is going to die a pre-mature death. If you have a selection of batteries of various ages/sized/makers etc, feel free to wire them up if it gives you some perceived benefit. (especially larger ah capacity)

    How's that guys?

    Tony
  • BB.BB. Super Moderators, Administrators Posts: 32,004 admin
    Re: mixing and matching of different size batt's

    From yet another thread full of battery discussions:
    BB. wrote: »
    I ran across this page on why different types of batteries have different starting s.g. fills... Is pretty interesting:
    Specific Gravity vs Applications
    1.285 Heavily cycled batteries such as for forklifts (traction).
    1.260 Automotive (SLI)
    1.250 UPS – Standby with high momentary discharge current requirement.
    1.215 Geral applications such as power utility and telephone.

    As mentioned earlier, the specific gravity (spgr.) of a fully charged industrial battery, or traction battery, is generally 1.285, depending on the manufacturer and type. Some manufacturers use specific gravities as high as 1.320 in an attempt to gain additional Ah capacity, but at the cost of a shorter cycle life.

    ...

    Higher Gravity = vs Lower Gravity =
    More capacity / Less capacity
    Shorter life / Longer life
    Higher momentary discharge rates / Lower momentary discharge rates
    Less adaptable to "floating: operation / More adaptable to "floating" operation
    More standing loss / Less standing loss
    Also on that page is the formula between cell resting voltage and specific gravity:
    Specific gravity = single-cell open-circuit voltage - 0.845 (example: 2.13v – 0.845 = 1.285)
    Or
    Single-cell open circuit voltage = specific gravity + 0.845.

    Because specific gravity affects battery voltage--How different of battery matters too...

    (1.285-1.215) * 6 cells = 0.42 volts different between Max/Min S.G. fills for battery type.

    0.42 volts is (very roughly) almost equal to 40% capacity difference (based on 12 volt example) between batteries (1.285 filled battery vs a 1.215 filled battery)...

    With two such batteries in parallel--one is fully charged at 12.8 volts or so, the other 12.4 volts... One is going to gas more during charging (excessive charging is not a great thing to do continuously), and the other will carry more current when discharging (and age faster).

    And given that you really want matched battery capacity when put in series--the differences in aging will affect that balance over time.

    Add all of the other construction/additive/material differences that batteries can have--the question is how different are different batteries.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mike95490mike95490 Solar Expert Posts: 9,357 ✭✭✭✭✭
    Re: mixing and matching of different size batt's

    The OP wanted to know if it was OK.

    Sure, it's OK. Your batteries, you paid for them, you can do what you want.

    Just be sure they are all close to the same voltages before you start connecting them in parallel. Hooking a half-flat battery to a couple of full ones will test your fuses.

    I don't recommend mix-n-match batteries from different batches.

    I'm not going into "theory of why" because that is a long class. I think this site:
    http://www.smartgauge.co.uk/batt_con.html just begins to touch on the many factors that can play, in large battery banks.
    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 ,

  • al128al128 Solar Expert Posts: 65 ✭✭✭✭
    Re: mixing and matching of different size batt's

    hi there, OP here ;)


    ok then - how about a 2 bank setup ... what would be a smart configuration?

    I understand I will need 2 chargers (right?) ... but I could still use one inverter (being fed from both banks) ...

    I could manage to get the 2 banks into "reasonable close" AH sizes

    again, thx for your input
    al
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: mixing and matching of different size batt's
    al128 wrote: »
    hi there, OP here ;)


    ok then - how about a 2 bank setup ... what would be a smart configuration?

    Yes, it's what I recommended in the first place. :D The 200's in one bank, the 100's in another.
    I understand I will need 2 chargers (right?) ... but I could still use one inverter (being fed from both banks) ...

    It's easier that way, but not absolutely necessary. Another choice would be to use a controller with 'AUX' function that can switch charging (via relay) to the secondary bank. In this configuration use the 200's as the 'primary' bank and the 100's as the 'secondary', which would only be charged once the primary bank is in Float mode. Use an A/B switch on the inverter, switching to the secondary bank when/if needed.
    I could manage to get the 2 banks into "reasonable close" AH sizes

    again, thx for your input
    al

    You're welcome. And may I say the reason you get a half-dozen different answers to any question around here is because there are a half-dozen different answers; you just have to pick the one that best suits your needs.
  • BB.BB. Super Moderators, Administrators Posts: 32,004 admin
    Re: mixing and matching of different size batt's

    At this point--if the batteries are same mfg. and same construction type (i.e., all flooded cell deep cycle; and not a mix of automotive, flooded cell, and agm--for example))--I think this is being over-thought.

    Connect them in parallel (ideally, with fuses to each battery string) and go for it.

    You cannot use two chargers with the inverter(s) sharing the batteries (unless you use a blocking diode--which has its own issues).

    If you want to use an A/B switch to alternate between banks--you can... But I am not sure that it would be worth the cost for a few months of use. You got the batteries used/cheap--just "enjoy" them.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • stephendvstephendv Solar Expert Posts: 1,571 ✭✭
    Re: mixing and matching of different size batt's
    But Bryan, you are perfectly correct that there is no industry standards a battery must meet in order to wear the "Deep Cycle" label. More's the pity.

    Sure there is :D EN 60 254-1 or IEC 254-1 provide the testing procedures for measuring the cycle life of a battery discharged to 80%.

    Most forklift batteries should have this rating specified.
  • icarusicarus Solar Expert Posts: 5,433 ✭✭✭✭
    Re: mixing and matching of different size batt's

    Once again, Bill has it dialed. "I think that this is being over-thought"! [moderator edit: My spelling is bad enough without having it edited wrong on quoting. -Bill B.] ;):p (Icarus edit,, Sorry Bile!)

    I agree, sometime we engage in a search for solutions for problems that don't really exist. KISS, KISS, hugs Bill lol,

    Tony
  • bryanlbryanl Solar Expert Posts: 175 ✭✭✭✭✭
    Re: mixing and matching of different size batt's
    "I think that this is being over-thought"
    Bingo!

    industry standards and "EN 60 254-1 or IEC 254-1" can be fun but for what the OP is after I do think there needs to be a balance between blind obedience and "over-thought" for what we want to do.
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