Matching batt. voltage for pairs in bank

sunbunnysunbunny Solar Expert Posts: 59 ✭✭✭✭
I'm full of questions today .

My 10 twelve volt/100 amp AGM batteries have been wired up the best I could to a ProStar 15 and 2 small panels. They were not in use much. One day almost 2 months ago, the controller said 15.1 volts and it was cloudy. Seemed kind of high to me so I disconnected them all from each other. I've been checking them and they are all within .12 of 13 volts, now. They are home and getting charged while I get ready to put the bank in place. ( 2 were too low but I have 4 others...)

I'm pretty sure it doesn't matter very much but it made me wonder if each pair should be similar voltage OR add up to similar voltage ??

Thanks

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Matching batt. voltage for pairs in bank

    Similar Voltage is just that: similar. In other words a "12 Volt" battery is a "12 Volt" battery even though one may read 12.75 and another may read 12.65. Small Voltage differences aren't very relevant. Large Voltage differences can be an indicator of a problem such as uneven current distribution, bad connections, shorted cell, or sulphation.

    The thing that matters most is that they are the same type of batteries. When you mix batteries of different capacities even though they are the same Voltage they will not each charge the same. if the difference is great enough all will suffer for it.

    A couple of things:

    You have ten 12 Volt batteries in parallel? That is asking for trouble. Pretty much impossible to get the current even throughout, which means those small Voltage difference will become larger differences over time as the batteries fail.

    Seeing 15 Volts on a cloudy day is not as odd as you think: there's this phenomenon called "edge of cloud effect" which actually focuses sun on the panels increasing insolation and thus power output. This can momentarily push Voltage above normal. It's generally not anything to worry about.
  • sunbunnysunbunny Solar Expert Posts: 59 ✭✭✭✭
    Re: Matching batt. voltage for pairs in bank

    Thanks, 'Coot.
    It was a Very cloudy day.

    The batteries were all paralleled with leads taken off opposite ends. The only other choice was to let them sit with no charging at all. They stayed very even. They are all the same model battery; received used. One battery developed corrosion on one terminal and it has a low charge: 12 even. I'll try to bring it up but for now, it and another (12.45) are out.

    The 4 batteries I got later have been on a regular auto type charger with an AGM setting several times and are only around 12.6/7
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Matching batt. voltage for pairs in bank

    12.6 or 12.7 is pretty normal Voltage. You have a major problem when the Voltage is off by 10% or more. You're looking at 1% differences here, and most meters aren't even that accurate.

    The more batteries you have in a bank the more difficult it becomes to manage them. That's why for greater stored capacity it is better to go with larger individual batteries and/or up the Voltage.

    Some basic info: http://forum.solar-electric.com/showthread.php?15989-Battery-System-Voltages-and-equivalent-power
  • sunbunnysunbunny Solar Expert Posts: 59 ✭✭✭✭
    Re: Matching batt. voltage for pairs in bank

    Yes, I've read lots of posts about battery sizing and uneven charging of 3+ strings in a bank. These were a gift so I'm going to make the best I can of it. They will be on 1-2-both-off battery switches.
    I have my next set picked out and there likely won't be 12 of them or 6 pairs and I'll have some hardware left over.
    I made the battery box big enough for 16" tall batteries :) If I have to make different wires... well the price of wire is small compared to the batteries.

    Thanks
  • Marc KurthMarc Kurth Solar Expert Posts: 757 ✭✭✭✭
    Re: Matching batt. voltage for pairs in bank

    Normal standing voltages can vary between different battery manufacturers. With Concorde AGM's for example, a fully charged battery is 12.8v to 13.0v (measured with no load, no charging within 2-3 hours) Other manufacturers may have different standard voltage values. When I see a Concorde at 12.6v or 12.7v, I know that the battery is not fully charged and/or has sulfated.

    I don't know what brand battery you have, but I would not feel comfortable with a sustained 15.1v to a 12v Concorde AGM unless the battery temperature was very, very cold.
    I always have more questions than answers. That's the nature of life.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Matching batt. voltage for pairs in bank

    I don't believe the 15 Volts was sustained, therefor not a problem with AGM's. You would definitely not want to run them there for an hour or two during Absorb!
  • sunbunnysunbunny Solar Expert Posts: 59 ✭✭✭✭
    Re: Matching batt. voltage for pairs in bank

    They are Concordes. Thanks Marc Kurth, I didn't feel comfortable seeing over 15. My friend who gave me the batteries and sets up this brand in remote monitoring situations, says it's not unusual but I didn't want to go off and leave them. Perhaps the one bad battery was causing the problem.

    Sooo.... I guess I'll stop trying to charge that 12.00 one... it was taking 15.7 from the automotive charger that has an AGM setting ( at about 9.75 amps). It was not warming up but it also wasn't charging.
    I have the others paired up and I'm going to use my new Iota charger from NAWS to charge them :)
  • sunbunnysunbunny Solar Expert Posts: 59 ✭✭✭✭
    Re: Matching batt. voltage for pairs in bank

    Another reply so my 'signature' will show up.

    And the 15.1 volt display was there for a few hours.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Matching batt. voltage for pairs in bank
    sunbunny wrote: »
    Another reply so my 'signature' will show up.

    And the 15.1 volt display was there for a few hours.

    That is not good.
    Nor should it be possible with a solar charge controller.
  • Marc KurthMarc Kurth Solar Expert Posts: 757 ✭✭✭✭
    Re: Matching batt. voltage for pairs in bank
    That is not good.
    Nor should it be possible with a solar charge controller.

    As usual, I have to agree with you, Sir.

    Sunbunny, pay close attention to what he says. I don't post here very often, but I most certainly respect cariboocoot's knowledge and experience!

    With a 1040T at a stable temperature between 65F and 85F:
    Charge it at a constant 14.2v to 14.4v (no more than 14.6v) until the current draw drops to .5 to 1.0 amps. THAT is when it is fully charged and NOT before that.
    (Use temperature compensation when outside of this range - it is NOT optional)

    I will grin while adding: Hitting them with 15v+ was a good move to desulfate your used batteries. Some of these swap-out batteries are a good deal, some are not. Here is how I would qualify it, based on a Concorde battery:

    - Fully charge the battery at the PROPER voltage, with a high available current if the battery wants it
    - Let it stand for 2-3 hours
    - Look for 12.8v to 13.0v

    1) If the battery voltage is a bit low after charging, it is MOST LIKELY sulfated. Time to equalize it gently with a constant voltage, or to smack it with a constant current recondition. Depending upon severity, it may take several runs of "equalizing" to bring it back - if it is possible at all.

    As a gross generalization, when a customer brings in a PVX-1040T sitting at 10v or higher, I can bring them back up to 60% to 95% caapacity, depending on how long they sat

    2) If the battery voltage is VERY low, and/or continues to pull a high current when it shouldn't - you may have lost a cell. Time to replace.

    3) If the battery static voltage is in the proper range, but the capacity obviously just isn't there, it is either worn out from cycling - or it was overcharged over a long time period and it dried out. Time to recyle it.

    Just my opinion,
    The other Marc
    I always have more questions than answers. That's the nature of life.
  • sunbunnysunbunny Solar Expert Posts: 59 ✭✭✭✭
    Re: Matching batt. voltage for pairs in bank

    Thanks very much, The Other Marc :)
    It's sounding like I need a much fancier charger than I've been dealing with.
    I haven't much faith in my Sears charger even if it does have an AGM setting, I don't think it's giving them the right voltage. The Iota with IQ4 seems much better.
    The 10 batteries that were on the small PV system might have been roasted by it or rescued by it... After 'resting' for 2 months, they are mostly at 13.0. I should load test them..

    My PV system will be going soon and the charge controller has a bettery temp sensor so that will help and I'll also have a seperate meter.

    Is there a stand alone charger that you would recomend ?
    My friend bought a whole storage unit of the batteries so this brand/model Might be in my future for a long time.

    Thanks !

    Edit: I just checked again. The Iota is giving the pair 28.4 and 8+ amps . The Sears had charged them twice in one week and never shown more than 13.3 on a single batt.. The Sears on another single was showing 13.1. I disconnected it but didn't smash it :)
  • Marc KurthMarc Kurth Solar Expert Posts: 757 ✭✭✭✭
    Re: Matching batt. voltage for pairs in bank

    I'm not a fan of IOTA chargers for a whole bunch of reasons, but I'm not here to promote or bash a product. (They make a good converter, but look closely at how their Bulk phase voltage is higher that the Absorb - then think about it)

    I will say that:
    - Your batteries pulling over 8 amps at 28.4v is a good sign - they are taking a charge at the specified voltage. This is a good thing to see when dealing with used batteries! Hopefully, your charger has the IQ :-) to drop to the float voltage when the load drops very low - like under 1 amp. Keep an eye on them - be sure you see a tapering current being drawn by the batteries. My bet is that they will drop to float too soon, leaving the battery undercharged.

    - IOTA's float voltage of 13.6v is a tad bit high at 75F to 85F for the PVX-1040T. Short term, no big deal at all. For longer term, I'd rather see you top off the charge and let the batteries stand alone. When the voltage drops to 12.65v or 12.7v, boost them again. That will take 3-6 months if the batteries are healthy.

    - Undercharging causes more premature failures than any other two things that we see. Undercharging can be too low of a voltage, too low of a current, not charging long enough to see the reduction in amperage, or leaving the battery sitting at lower charge levels.

    Based on the voltages that you are reporting, the ambient temperature of where your batteries spent their previous and future time will determine how much life they have left.

    The other Marc
    I always have more questions than answers. That's the nature of life.
  • sunbunnysunbunny Solar Expert Posts: 59 ✭✭✭✭
    Re: Matching batt. voltage for pairs in bank

    Thanks again, TO Marc !
    I am a little concerned about the temperature history of the batteries but I think they were used in a below ground enclosure. Storage might be another story but they were all 12.6v when I got them a year ago. They have been kept cool and charged since. I would be surprised if they got to 75F in the future unless it was from charging. They are at about 60F right now.
    Thanks for the advice. 'Charge them the best I can and let them sit' is exactly my plan. The solar charge controller is programable so that will help get them just right. Until then I don't have any control over the charge parameters.
  • Blackcherry04Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    Re: Matching batt. voltage for pairs in bank

    Just some information about a IOTA with IQ-4. I find they work quite well and even if their algorithm and voltage's seems weird, it works fine. While they do not follow the traditional 3 stage format they do use the 3 variables of Battery charging, Voltage, Time and Current. I have installed them for many customers in the last 3-4 years and find them bullet proof. They will maintain their rated output hour after hour.

    ABSORPTION STAGE
    After the Bulk Stage, the IQ4 then moves to the Absorption Stage (14.2V for a 12V battery). This mode will continue for up to 480 minutes (8 hours) to ensure that the battery receives a complete charge.

    FLOAT STAGE
    During the Float Stage, the IQ4 reduces the DLS charge voltage. This reduced voltage maintains the full charge while minimizing 'gassing' of the battery. The IQ4's float stage prevents boiling and bulging of the battery caused when the battery is exposed to higher charging voltages for too long.

    EQUALIZATION STAGE
    If the batteries remain in a "float stage" for a seven-day period, the IQ4 will switch the DLS charger into a pre-programmed Equalization Stage. This protects the life of your battery by dissolving any sulfate layer on the battery's internal plates and avoids stratification that can occur when a battery has not been in use for extended periods.

    Absorption Phase
    (2.366V per cell) 14.2V 28.4V 56.8V
    Float Phase
    (2.266V per cell) 13.6V 27.2V 54.4V
    Equalization Phase
    (2.466V per cell) 14.8V 29.6V 59.2V

    My preference is for buying the plain DLS and the IQ-4 as a plug in option. As I posted before there is a 10 turn potentiometer where the voltage can be adjusted. The only issue is the output voltages are a ratio to each other. If you lower the voltage say .2 it lowers all 3. If you crank it wide open and and insert the hi plug in the jack you can adjust it to a true equalization voltage ( 15.5 V or 32 V ) I have never tested the 48V model. The way I judge it is the batteries maintained by them use very little water and the SG's stay spot on. Just a little .02 on them.
    .
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