Babe in the woods, help.

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  • crewzercrewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    Re: Babe in the woods, help.
    Perhaps Jim/Crewzer can (or somebody else) can address how accurately one needs to hold the proper battery voltages (temperature/float) for long battery life---Is it less than 0.1 vdc, or if it is +/- 0.3 vdc OK (I would tend to try and design for the less than 0.1 vdc range).

    VERY busy right now.... I'll come back to this later...

    Regards,
    Jim / crewzer
  • BrockBrock Solar Expert Posts: 631 ✭✭✭✭
    Re: Babe in the woods, help.

    Honestly as much as I like AGM and I would never switch back to GC batteries, BUT for someone starting out I often recommend GC batteries because they are less expensive from the get go and can take more abuse. I like to think of them as "training" batteries. So you go through a set or two, figure out what works and what doesn’t and then when your set move up to AGM's. GC’s are typically the cheapest per watt for a true deep cycle.

    In the long run AGM's or larger batteries will be cheaper because of the longer life span (more cycles), but if you kill a bank by accident it is much better to kill a bank of GC rather then a bank of AGM's.
    3kw solar PV, 8 L16's, xw 5548, Honda eu2000i, iota DLS-54-13, Leaf EV, 4 ton horizontal geothermal, grid tied - Green Bay, WI
  • System2System2 Posts: 6,290 admin
    Re: Babe in the woods, help.

    I think I just got the answer, but... "when" batts go bad, they ALL go? So if you screw up (say overcharge or too many complete drains), the whole bank is gone.
    Will the "healthy" recycle quota be the same in all batts in the bank? As a particular batt fails or weakens, it infects the rest? Can you check spec. gravity on each battery to catch a sickie? Is there an advantage in adding a string of batts at stepped times? SAy like 1 string of 4 GC (24V total), then a week (month?) later, another string, and so forth
    Also is it possible to partially tap a 24 V. bank to get 12 V? I don't mean pull a large load, more like tapping 2 6 Vs to power a light or radio.
    Thanks,
  • crewzercrewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    Re: Babe in the woods, help.
    In another conversation with a fellow HBtr., who has had a solar setup for a few years now. He "says", after trying both types, he now uses 6V golf car batts. Claims in the long run they 1. cost less than 12s. 2 perform better (says their more honest in amp delivery claims). 3. Are tougher and live longer when abused. He claims every system gets "some" abuse and GC batts actually give him less trouble (moe forgiving?). His claim that there are thousands of golf cars using them STILL, this is proof that nothing new can do as good an overal job, or else they wpuld have been phased out by now.

    This is rather uninformed thinking in my view. While there’s no doubt that 6V “golf cart” batteries are seemingly cost effective and indeed rugged, your fellow houseboater failed to address any of their drawbacks:

    1) Flooded-cell batteries vent explosive hydrogen gas as they’re charged. This is a major reason why engine and battery compartments must be ventilated before the motor is started. Properly managed, VRLA batteries (AGM and gel) do not outgas.
    2) When mixed together, salt water and battery acid create deadly chlorine gas. VRLA batteries are sealed and do not pose this hazard.
    3) Flooded-cell deep-cycle batteries require considerable maintenance (and maintenance access), such as removing the manifold caps to check electrolyte levels and add water. VRLA batteries do not require this maintenance. In fact, they can be installed on their sides, which may actually come in handy in a boat’s tight quarters.
    4) Flooded cell batteries are typically ~80% efficient (Wh out / Wh in). VRLA batteries are ~90% efficient, and this feature can help reduce other system costs in a solar energy system. For example, everything else being equal, a system using VRLA batteries requires an ~11% smaller PV array.
    5) Flooded-cell batteries are indeed relatively cheap to purchase. But, when you add in the cost for maintenance (labor and material costs) and recharging efficiency, especially for solar generated energy, I doubt that he could make a case for flooded-cell batteries being cheaper over their useful life.
    Perhaps Jim/Crewzer can (or somebody else) can address how accurately one needs to hold the proper battery voltages (temperature/float) for long battery life---Is it less than 0.1 vdc, or if it is +/- 0.3 vdc OK (I would tend to try and design for the less than 0.1 vdc range).

    East Penn, the manufacturer of Deka and MK batteries, asserts that correct float voltage is quite important. The difference between “optimal” and “maximum” float voltage for any given temperature range is only 0.3 V for a 12 V battery. Similarly, Exide specifies a very narrow float voltage range for their Absolyte IIP AGM batteries: 2.23 - 2.27 Vpc. For a 12 V battery, that would be 13.50 +/- 0.12 V

    HTH,
    Jim/crewzer
  • BB.BB. Super Moderators, Administrators Posts: 28,167 admin
    Re: Babe in the woods, help.

    First think... Don't ever "tap" the middle of a string of batteries... You will undercharge some and overcharge others... Yes, a small load on a big bank may not be noticeable--but just don't do it. Get a converter (24vdc to 12vdc or whatever you need) and do it right.

    In general, when you have one battery fail (usually will not take a charge or give current at rated voltage for vary long---less likely, but you can have cracked cases, terminals fail, one cell fail, rest are good)--if the battery bank is relatively new, replacing the battery will be worth the money--but what tends to happen is that the one new battery carries more of the load (in parallel connections) and will cycle deeper than the rest--and eventually will age until it is in the same life state as the rest of the string...

    If your string is near the end of its life and you have one or more failing batteries--generally that is the time to replace them all at once.

    Looking around this board you will find that it is recommended that you do everything possible to ensure that a group of parallel batteries all charge and discharge evenly (for example, a simple string of parallel batteries--the first battery in the string will have the lowest resistance and charge/discharge more than the last battery in the string). There are several strategies you can use to try and better balance the current between a group of paralleled batteries.

    Another option is to only use series connected batteries--then you don't have current sharing issues as you do in parallel banks. The short answer is that some folks see series connected batteries lasting longer, and others see no difference between series and parallel connected banks. For my two cents, it seems to be easier to detect a bad battery in a series string than in a parallel string.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: Babe in the woods, help.

    wow so many questions. i'll attempt some of this.

    "I think I just got the answer, but... "when" batts go bad, they ALL go? So if you screw up (say overcharge or too many complete drains), the whole bank is gone."
    pretty much when one goes bad it will cause the others to go bad too. if it is a case where a cell went slightly low, but the water is not past the plates it may be through constant maintenance to be kept good and not drag down the other cells in the battery and thusly the other batteries. that cell would be filled and an eq charge given to bring it up to snuff. agms do have special needs when it comes to eq charging and usually is not handled as a normal leadacid battery would be. a weak cell on an agm may always be weak because it cannot be filled.

    "Will the "healthy" recycle quota be the same in all batts in the bank?"
    i'm not sure what you meant here.

    "As a particular batt fails or weakens, it infects the rest?"
    i addressed that already and it's basically yes in time.

    "Can you check spec. gravity on each battery to catch a sickie?"
    again it's already addressed basically above and yes that routine maintenance will catch a sick cell/battery. voltage readings are also an indicator.

    "Is there an advantage in adding a string of batts at stepped times?"
    certainly not. it is better to not get the batteries at different times be they whole strings or not. adding another string within a month if the first string is well taken care off and not strained or abused is certainly ok. however, the more different the batteries or banks of batteries are the more the worst case will drag down the rest of the good ones. judgement is needed here on your part if it is to warant a new battery with the old or worthwhile to replace all of the batteries because of the derating that would take place.

    "Also is it possible to partially tap a 24 V. bank to get 12 V?"
    i would not do that as it will set up differences between the batteries that an eq charge would not handle well. eq charges are meant for minor differences between batteries in a bank or between the cells of a battery. when done often with larger differences this will kill a battery prematurely as it overcharges the good batteries or cells to revamp the low ones. voltage converters are usually used to facilitate this need.
    i also see i posted at the same time period as crewzer and bb. i'll let this ride and read theirs after. hope your questions are answered. in looking over their answers i will not dissagree at all with them and you can add all 3 of our replies together for yourself.
  • BB.BB. Super Moderators, Administrators Posts: 28,167 admin
    Re: Babe in the woods, help.

    And just to clarify, you cannot check the acid specific gravity in sealed/gelled/AGM type batteries--only in flooded cell type.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2System2 Posts: 6,290 admin
    Re: Babe in the woods, help.

    Yeah, I knew a sealed batt had to be checked differently. My questions were in relation to using GC batts and what I could do/expect IF I went that route. The out gassing IS a big problem for where I want to put them. I really need AGMs.
    Am I correct in my thinking here; If I want a 24V system and I want a 6 battery bank, I hook 3 strings of 2 12V batts (series connected), then wire these 3 strings parellel? (hope that came out right)
    As far as the small tolerences of chargeing the float, IS that realistic or manufacture lawer speak? Can those .1, .3, etc constantly varible rates be done with affordable controllers? Ya'll are keeping your batts that closely controlled? Amazing!
    Thanks,
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: Babe in the woods, help.

    those of us with agms have to do it or lose the battery life from our expensive agms. the same holds true for your golf cart batteries, but because they are venting to the air with the ability to retop it off little harm can be done to them. don't get me wrong here for if you go overboard with boiling them or fail to maintain them for long periods you'd have then wished you kept the same strict standards on them as we do for agms.
    you don't want to ignite hydrogen gas that has collected from the batteries outgassing. my father had the misfortune of a spark igniting the hydrogen fumes from his car battery, when he was alive, and that battery exploded on him. (no that's not what he went from for the record.) he got some burns from the hydrogen being on fire and some burns from the sulphuric acid hitting him.
    i believe you are saying it correctly as 2 batteries in series with 2 other banks of these seriesed batteries paralleled to each other.
    yup those are the kind of tolerances to be had as my tolerances go farther into the .00 range of voltages so that i have a better handle on the charge. temperature variations also slide these values + or - a tenth of a volt or 2 either way on top of the charge ranges given by battery manufacturers so it is larger than you think, but still somewhat critically tight too. battery manufacturers state the voltage ranges good for their batteries in absorb or float and yes they can be that limited.
  • BB.BB. Super Moderators, Administrators Posts: 28,167 admin
    Re: Babe in the woods, help.

    I would believe those voltage tolerances are what is really required to maintain long battery life. For long term float (storage) of batteries, many times folks are probably better off disconnecting the loads and just letting the batteries sit than to charge them at the wrong voltage. The battery chemistry is temperature sensitive and pretty exact.

    Yes, that is one way of making a 24 volt system.

    And a properly designed charging system will keep the float voltages that accurate (via remote sense leads and a remote battery temperature sensor).

    And overcharged AGM and other lead acid sealed batteries will outgas just like flooded cell batteries if overcharged (and you can't refill an overcharged sealed battery--so they are quickly destroyed).

    -Bill

    PS: What Niel said.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: Babe in the woods, help.

    bb we gotta stop posting at the same time. people will talk. :roll: :lol:
  • BB.BB. Super Moderators, Administrators Posts: 28,167 admin
    Re: Babe in the woods, help.

    Niel, as long as they don't talk and type--we're safe. :wink:

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: Babe in the woods, help.

    no problem as most people can't walk and chew gum either. well, ok they can, but they either trip or choke. :-(
  • crewzercrewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    Re: Babe in the woods, help.
    As far as the small tolerences of chargeing  the float, IS that realistic or manufacture lawer speak? Can those .1, .3, etc constantly varible rates be done with affordable controllers? Ya'll are keeping your batts that closely controlled? Amazing!

    Ah, one of my favorite questions/comments! :evil:

    There’s no doubt that 0.1 V seems pretty trivial from the broader perspective of a 12 V battery. However, when considering that a full 12 V battery measures ~12.7 V, and a ½ full battery measures ~12.2 V, then 0.1 V represents 10% of the rated capacity. Taken a step further, 0.1 V represents 20% of useable capacity if one is to not discharge below 50% SOC.

    This sort of regulation tolerance is fairly easy to come by. For example, the Morningstar ProStar and TriStar charge controllers include battery sense connections that measure battery voltage at the battery terminals so as to adjust regulation voltage for losses in the wiring to the batteries! Morningstar’s published 12v & 24 V regulation spec for the TriStar is +/- 0.05 V. The Outback MX60 charge controller's output voltage meter can be user-calibrated in 0.1 V increments.

    On a related topic, the good controllers will also adjust their regulation voltage for battery temperature when a remote battery temperature sensor is attached. The typical “temperature compensation” formula for a 12 V battery is -0.03 V / degree C.

    HTH,
    Jim / crewzer
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: Babe in the woods, help.

    shouldn't that read about .003v/degree c/cell? for most standard batteries it is about .005v/degree c/cell.
  • crewzercrewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    Re: Babe in the woods, help.

    The baseline formula is -0.005 V / degree C / 2 V cell. That would be -0.03 V / degree C for a 12 V (six cell) battery.

    Regards,
    Jim / crewzer
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