to charge or not to charge? (inactive batt.)

notsobrightnotsobright Solar Expert Posts: 247 ✭✭
is it better to disconnect a battery with full charge if its not being used or just let it charge everyday?

thanks

Comments

  • icarusicarus Solar Expert Posts: 5,248 ✭✭✭✭
    Re: to charge or not to charge? (inactive batt.)

    It is best to fully charge a battery and store it with a float charge,, assuming you have a way to do a proper float charge. (How are you proposing to, as you say, "charge it every day?"

    Tony
  • notsobrightnotsobright Solar Expert Posts: 247 ✭✭
    Re: to charge or not to charge? (inactive batt.)
    icarus wrote: »
    It is best to fully charge a battery and store it with a float charge,, assuming you have a way to do a proper float charge. (How are you proposing to, as you say, "charge it every day?"

    Tony


    so youre saying its better to charge than not. seems like even a float charge would be wearing the battery if its not really needed, no?


    Im just trying to determin if I should just dissconnect my back-up battery and check it every now and then or just let the controller handle it 24/7

    thanks
  • BB.BB. Super Moderators, Administrators Posts: 29,518 admin
    Re: to charge or not to charge? (inactive batt.)

    A float charge (between roughly 12.7 and 13.6 volts or so) does not really charge the battery or cause electrolysis (limits water usage to a very small amount).

    If you don't have a float charger handy, but have 120 VAC from grid power available--I have taken a standard wall brick type battery charger and put it on a 24 hour lamp timer... I usually set the timer for ~1 hour per day of charging. So far, it seems to keep the car batteries I have done this to nice and charged and not using much water (one car has computers, clocks, On-Star, Lojack, etc. for a ~0.18 amp load--for that one, I set the timer for 4 hours per day)...

    Storing the battery between 80-100% charge is fine--The problem is to remember to reconnect the battery before it drops below 80% charge and begins to sulfate (permanent damage). Or, as happens to me, I forget to remove the charger and cook the battery.

    Your mileage may vary.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: to charge or not to charge? (inactive batt.)

    to be clear,
    sulfation will start with a battery that stays below 100% soc. imho it is not good to store a battery without a full charge to it or without a float charge for extended periods of time.
    as to the float charge it is necessary to keep the battery up as it will lose capacity just sitting there. if it stayed charged i would agree with bb and say to store it without any charge to it. as long as there is regulation to keep the battery from taking on more than it needs to maintain, you will be fine leaving a float charge to it. figure 1-2% of the ah battery capacity is good for the float charge if one only wishes to have minimal pvs on it.
    now you didn't specify the length of this storage as up to a month without a float won't kill it if it was fully charged to begin with and depending on the battery it may be able to go further than a month, though i don't recommend it.
  • notsobrightnotsobright Solar Expert Posts: 247 ✭✭
    Re: to charge or not to charge? (inactive batt.)

    does the controller just go to float as the sun comes out each day if the battery allready has a full charge or does it cycle through the 3 stages anyway?

    again, Im just trying to determin if I should just dissconnect my back-up battery and check it every now and then or just let the controller handle it 24/7

    I shouldnt need some other charger to float the battery since the controller has a float stage should I?

    Ive been disconnecting it but the durration of inactivity is usually no longer than a month and the battery is an AGM.

    I started disconnecting when I noticed the battery was resting at 13.15v, thats after sitting more than 8 hours (overnight)

    but also my thinking was that if Im not using it and its resting with a full charge then even a float is an unessesary cycle and may be contributing to excessive wear, no?

    thanks
  • BB.BB. Super Moderators, Administrators Posts: 29,518 admin
    Re: to charge or not to charge? (inactive batt.)

    NSB,

    If your charger has a float stage, and you measure less than 13.6 volts or so most of the day--Then you are probably fine leaving the battery/solar charger/etc. connected.

    However, since the battery is AGM--they also store well (upwards of 4-6 months) without being recharged too...

    I think, at this point, it is your choice as too which you want to do...

    One of AGM's wear issues is the catalyst inside (the caps, typically) does erode as it recombines hydrogen and oxygen from charging (and a bit from floating too). Charging once per month may help extend the life of your catalyst.

    Otherwise, for a long battery life--at what temperature you store the battery will probably have more effect on its total life. Basically, the rule of thumb is a battery (or almost any common item) will age 2x faster for every increase of 10 degrees C (18 degrees F). And conversely, the life will be 2x longer for every 10C drop in storage/operating temperature.

    If you have a place to store the battery that is significantly cooler than where it is normally operating, moving it to that cool location (such as a basement floor and charging once every 1-4 months) would probably give you a (usefully?) longer battery life than if the battery where in a hot shed and exposed to thermal cycling (hot days, cold nights--another killer for mechanical/electrical/electronic devices).

    Otherwise, accept that you will have to replace your battery(ies) every 3-7+ years (depending on battery quality, size, usage)... For an emergency backup system--you don't want to pull fire it up 5 years from now and find the battery has only 10% of the capacity that you need to carry you through the storm/disaster.

    So there is an argument that you want the full system up and running, with planned cycles (once a month to once a year or so) to ensure everything is operating correctly--before stuff hits the fan. There have been some comments here too that batteries need to be exercised/cycled (perhaps to 50% state of charge) occasionally for good life/function too.

    Given that a you would expect 500 or more cycles from a 50% discharge/charge cycle--do this a dozen times a year will probably not be the death of a battery (40 years of cycle life--vs probably 3-7+ years of shelf/float life).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • KamalaKamala Solar Expert Posts: 452 ✭✭
    AGM float

    We are talking about AGM batteries. I have four 6Vs in a 12V bank. They are in service nine months out of the year in a rather small RV.

    During those nine months they are cycled only for 2 or 3 days per week. The days per week of cycling may increase four or five times during the 9 month service period due to holidays or vacations and during this time I allow the controller float them.

    When the RV is to be stored prior to winter, I have decided to disconnect the bank from the RV after it has been fully charged. That is, the bank is connected to nothing.

    As BB. said, AGMs can be stored (fully charged) for four to six months with little self discharge. Perhaps longer during my cold Wisconsin winter.

    The most significant factor of AGM maintenance is to make certain that they NEVER are over charged. If they are, the safety caps will pass gas thereby diluting the electrolyte. Which cannot be replaced.
  • RCinFLARCinFLA Solar Expert Posts: 1,280 ✭✭✭
    Re: to charge or not to charge? (inactive batt.)

    A lead acid battery is 'wearing' from the day electrolyte is installed and positive plate is formed. All you can do is minimize the wear.

    Floating is the generally accepted practice. 13.2 to 13.6 vdc.

    There is an optimum (compromise) point that keeps the negative plate from sulfating too much and the positive grid from oxidizing too much. Too high a float voltage accelerates positive grid corrosion, too low a float voltage results in gradual sulfation of negative plates.

    There is variation on this optimum based on quality of positive grid structure, thickness of the positive plates, and separator quality. If it is a true deep cycle with thick positive plates it can take float at the higher end that further reduces the negative plate sulfation. A thick positve plate has 'reserve' lead that support the excess lead dioxide created by higher float voltage.

    A battery left on float for years will likely become unusable due to high resistance caused by positive grid corrosion. A battery left unconnected and 'topped off' every month or two will likely be sulfated on negative plate eating up usable capacity.
  • bryanlbryanl Solar Expert Posts: 175 ✭✭✭✭✭
    Re: to charge or not to charge? (inactive batt.)
    There is an optimum (compromise) point that keeps the negative plate from sulfating too much and the positive grid from oxidizing too much. Too high a float voltage accelerates positive grid corrosion, too low a float voltage results in gradual sulfation of negative plates.
    Which is why float alone is no longer modern practice. There are at least two methods I know of for active sulfation inhibition. One was described in Home Power mag about ten years ago and is used by the BatteryMINDer line. I believe this same method is used in some Victor battery chargers. It uses an AC signal for the effect.

    The other method is that used in the Progressive Dynamics ChargeWizard and WFCO RV converters. This uses a periodic charge bump coupled with a low float voltage.

    Perhaps a third method might be regular exercise. This is where a battery gets discharged down 30% to 50% and then promptly recharged vigorously and fully.

    I think the lack of active sulfation inhibition plus low charge rates are reasons why some low use solar systems can be hard on batteries. This also gets into when equalization is needed.
  • notsobrightnotsobright Solar Expert Posts: 247 ✭✭
    Re: to charge or not to charge? (inactive batt.)

    you guys are great! Im learning alot from all of you.

    I think for the way Im using my system I will keep disconnecting after full charge.

    the longest disconnection would be mabey 2 months but I generally just throw a switch to check the voltage so I'll reconnect when needed.

    I remember when trying to decide which battery to buy when I was looking at the Concord AGMs I asked the rep what would be best in my solar RV.

    I was told the go with the Lifeline RV/Marine because the other (forget the name) solar type batteries they had for renewable energy would not be warrantied in an RV installation.

    when I asked why I was told because the RV/Marine type was designed with thicker plates because of the vibrations associated with RV/Marine use.

    now I wonder if the Lifeline might just be a better choice even in a solar aplication since it has thicker plates. (or so Im told by the company rep)

    just thought I would toss that out there.

    thanks
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: to charge or not to charge? (inactive batt.)

    nsb,
    being we are talking agms you may get away with the 2 month periods without a float charge to it. i still don't recommend it and i disagree totally with storing agms without a charge to them for 4-6 months because sulfation will still occur and it just does not occur only when below 80% soc. if the batteries are convenient to you then throw a float charge on them for a day every couple of weeks. concordes are durable batteries in any case, but one does want to see it treated as best as you reasonably can. i also heard, but never read that these things just don't sulfate and unless i hear or see first hand info from the company to the contrary i will assume they can sulfate. in any case info on general battery storage seems lacking on their website, but i'm quite sure many boaters and rvers leave the batteries uncharged for long timeperiods. i can't say what their ampacity is after such long periods as i'm sure this affects it and probably cycle life too.
    i was also told for my situation putting solar to batteries here that they would not warrant the lifelines as that's what they said they designed the sunxtender for and that is for solar. i guess the exception is when the battery goes mobile.
  • KamalaKamala Solar Expert Posts: 452 ✭✭
    Re: to charge or not to charge? (inactive batt.)

    This is an issue I am really wrestling with. When I picked up my batteries from a local wholesaler, I had a discussion with the owner about how I was going to use these batteries. I described my application and was admonished to disconnect the batteries when not in use (full charge assumed.) I explained that I had customizable smart charge capability and would leave them hooked up as his eyes glazed over.

    The only reason that I was talking to the owner was that the manager was on vacation. He could not find my batteries in his price list. The burley, grimy (no slight intended, he was very cordial and very helpful and has my respect) warehouse worker (the only other employee present, as far as I could tell) threw the price at him off the top of his head as he skidded by on the forklift. So much for the owner's recommendations.

    Then, after I stored the camper last fall on grid supported float, I began to worry as the weeks passed that I may be overcharging. A couple of threads here contributed to the magnitude of that worry.

    So, in February, I visited the storage site (only one hour from my home) and disconnected the batteries. Before I did so, I checked the TriMetric for high battery volts. It was over 15V. This concerned me until I realized that the winter temperatures had gone below -15°F. So maybe that's OK.

    BB.'s suggestion of a simple "lighting" timer might be the best way to address this issue.... for me. Seems ineloquent though.:roll:

    BTW... the setup so far this year has performed superbly. :D

    Craig
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: to charge or not to charge? (inactive batt.)

    kamala,
    if charged from the grid i agree that it could possibly be too much, but solar will not float charge 24/7.:D
  • KamalaKamala Solar Expert Posts: 452 ✭✭
    Re: to charge or not to charge? (inactive batt.)

    Ah. So. I see. The OP is ALL solar. :blush:

    But I'm still wrestling... but less vigorously8).
  • bryanlbryanl Solar Expert Posts: 175 ✭✭✭✭✭
    Re: to charge or not to charge? (inactive batt.)

    re: "when I asked why I was told because the RV/Marine type was designed with thicker plates because of the vibrations associated with RV/Marine use." -- ah! one of the common myths. I found that this belief is so religious here you cannot question it here in any form or fashion else the Spanish Inquisition starts to look tame.

    Batteries are manufactured with the primary trade-offs between cost, capacity, and ruggedness. The range for the batteries used in smaller solar systems is really rather small (just look at the manufacturer's spec sheets), especially when compared to differences you can get due to use profile, age, temperature, or cycle to cycle variance.

    You can measure the equivalent of 'plate thickness' or useless lead if you want. Just look at the energy density. From what I have seen (spec sheets again and I know many here just hate to depend on those when it comes to religious items like this), you'll see commonly available lead acid batteries all stay close to 22 watt hours per pound. I have seen one AGM that was bragging about "thick plates" and was down to 19 wh/lb but that wasn't aimed at this market.

    Strength in batteries comes from the materials used and how they are fashioned into battery structures. Often just making things bigger and heavier just makes them more subject to breaking.
    being we are talking agms you may get away with the 2 month periods without a float charge to it. i still don't recommend it and i disagree totally with storing agms without a charge to them for 4-6 months because sulfation will still occur and it just does not occur only when below 80% soc.
    AGM's at least don't suffer electrolyte stratification but Niel's advice seems to be that of folks who like long battery life and know how to get it from batteries that have intermittent use.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: to charge or not to charge? (inactive batt.)

    Random observations on the issue.

    Batteries prefer to be kept charged, but not over-charged. The quality of the charging system and the accuracy of its settings will determine whether batteries left hooked up will be properly maintained or boiled to death.

    RV/Marine batteries have thicker plates - thicker than automotive batteries and thicker than AGM's. This has nothing to do with ruggedness. AGM's are usually more rugged than any FLA type, as the plates are sandwiched between the mats. Very few incidents of AGM's suffering any type of mechanical internal failure. The plate thickness is to deliver greater power over time; more material to erode in the natural discharge/charge process (do not confuse 'erode' with 'corrode'). The plate design is also different: RV/Marine have a hybrid of the spongeform, high-Amperage delivering plates as used in auto batteries and the 'more solid' plates of a deep cycle (which is actually sort of waffle or wavy in shape, not to be confused with the massive plates of the 20-year monsters used mainly in telecom).

    Curiously, deep cycle batteries do like to be cycled occasionally. In fact they don't reach their full power potential without being discharged and recharged a few times. Seasonal use should be fine. As for maintaining the charge, either a good solar set-up with 3-stage capability or an occasional 'check and charge' (monthly) will keep them happy. Since batteries can fail without warning or reason anyway, you are probably agonizing over a minor detail.

    Not that my opinion matters much. I'm only trying to give people the benefit of my decades of experience. :D
  • bryanlbryanl Solar Expert Posts: 175 ✭✭✭✭✭
    Re: to charge or not to charge? (inactive batt.)

    re: "RV/Marine batteries have thicker plates - thicker than automotive batteries and thicker than AGM's." -- absolutely amazing. I provide a measure and it makes no difference in the belief or its expression. I could provide pictures as well but what good would that do against this sort of religious belief?

    But perhaps we are talking different regimes? I look at the line cards and don't see a difference that exceeds that found in individual batteries. That doesn't mean there are no differences at all, just that the differences are minor compared to anything one can see in normal uses.

    re: "Curiously, deep cycle batteries do like to be cycled occasionally. In fact they don't reach their full power potential without being discharged and recharged a few times." -- this is true for all lead acid batteries. It has to do with surface area and what happens to the plate structures in use.

    All batteries need proper exercise. A problem in many light use solar systems is that the cycles aren't typically deep enough (> 30% or so) to provide this and the result is a need for equalization. There is a reason for this, too, and it has to do with sulfate buildup. This is also related to why most RV applications don't need a proper equalization.

    When it comes to batteries, I suggest folks look for measure and solid rationale and be very very careful of blanket assertions.
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