Batteries and Bulk Charging

nielniel Solar Expert Posts: 10,300 ✭✭✭✭
yes i thought this important enough to warrent it's own thread so that all could see. as some of you know i had been professing a maximum bulk charge current that was typically between 10 and 13% for all battery types. i am sorry and i was wrong on this account as crewzer had pointed out to me. i decided to email concorde on this question and see what they generally had to say about it.
i didn't get an email, but i got a personnal phone call from them. in the conversation i explained the problem and that i had been advising others wrongly on the forum. he said other batteries and types, other than concorde that is, are generally to be bulk charged to a maximum of 25 to 30% of capacity. on the lifelines i told him the way it was worded it seems it is unlimited for bulk current. he said it most certainly isn't unlimited, but he said before we go on here know that anybody using the lifelines for solar are violating the warranty as the sun xtenders are for that purpose. he then went on to say that you can for both the sun xtender and lifeline(non renewable charge source) give them an amp for an amp. that means a 100amp sun xtender will be able to have a 100amp bulk charge. this is a big difference from what i was thinking of these batteries before and is good news for all of us as it does give more options and ability to feed with more pvs without having to worry about overdoing it. as to the fast charge he basically said for the concordes that once the bulk is in (1hr!) the following absorb stage will just take slightly longer and that efficiency hasn't any bearing on it for the concordes. he couldn't say for other batteries, but i can say that of the nimh types that are fast charged they aren't charged as efficiently as their normal rate of charge and this reduces their battery life somewhat. this is minute and not worth worrying about though, for leadacids(good ones anyway) are more resiliant than nimh's.
one last note is that of the majority of battery failures he said he has seen, be it concordes or other battery manufacturers(from a different job), that the number one cause of failure is sulphation due to undercharging the battery and he went on to say that the number one cause for the sulphation was from having a load on the battery that sucked down the effective charge to the battery. you must account for not only incoming current to charge the battery, but know that if there's current to a load leaving the battery it takes away from the charge current by that much. i too have mentioned this on the boards before, but maybe not strong enough or often enough. this can go quite low percentage wise for the charge if there's any charge at all with loads on. example: you go to charge your 100amphr battery with 6amps, but you have a load on it drawing 4amps. your charge current is that difference between them and is 6-4=2amps effective charging current. it is now 2% and may never reach full charge causing sulphation if allowed to continue. in the same example, but with a small inverter on drawing 10amps this is a loss of 4amps from the battery and is effectively discharging.

Comments

  • crewzercrewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    Re: Batteries and Bulk Charging
    ...know that anybody using the lifelines for solar are violating the warranty as the sun xtenders are for that purpose.
    Niel,

    Interesting… Did he happen to mention what the differences between the two battery brands?

    Following up on VRLA (gel and AGM) battery charge rates, here’s another (positive) angle to consider. Although VRLA’s are technically capable of accepting relatively high charge currents, that doesn’t mean, in my view, that they must be used that way.

    For the purpose of this discussion, let’s assume the following off-grid scenario:

    Nominal system battery (VRLA) voltage: 12 V
    Average daily energy requirement: 2 kWh (167 Ah)
    Nominal battery bank capacity: 1,000 Ah (3 days autonomy down to 50% SOC)
    Average daily insolation for selected PV array tilt and azimuth: 4 hours
    Overall system efficiency: 67%
    Required PV array size: (2 kWh / (4 hours x 67%)) = ~750 W STC

    The expected mid-day charging current to the batteries (gel, in this case) would be something around 750 W STC x 87% (STC to PTC derating) x 95% (controller efficiency) x 97% (wiring efficiency) / 13.8 V = ~43.6 A, or 4.3% of the battery bank capacity.

    The 1,000 Ah battery bank is apparently capable of accepting a 30% (300 A) charge current. For this scenario, it would require a 5,150 W STC PV array, 5 MX-60 controllers  :-o , and a pile of big cable and breakers to supply that much charging current.

    So, is such a large system warranted just because the gel batteries can accept such a large charge current? I would say no, as a system that large would bulk charge the batteries very quickly and therefore spend a lot of time in a cost-ineffective idle (absorb and float) mode.

    Instead, an array in the 750 W – 1,000 W STC range as described above would be part of a balanced and cost-effective solution.  And, recommendations for solutions that are balanced and cost effective as well as that meet stated technical requirements is where we as a forum usually end up. Therefore, the 5% to 10% charge current recommendation that we so often use remains a valid and important element of our total design strategy.

    On this final point, it would seem to me that we do and will continue to agree.

    Regards,
    Jim / crewzer
  • System2System2 Posts: 6,290 admin
    Re: Batteries and Bulk Charging

    A more interesting point is charging from generators. Consider a system half as big as in the previous example, with a 500A battery bank. Add a VFX2612E inverter and a generator for charging in the 2-3 darkest months when there's little sun. The VFX2612E can deliver a charging current of 110A, or 22% of C. The question then is if the charging current needs to be reduced nor not. If one can charge the full 110A it would only take half the time for bulk compared to limiting to 11%/55A. This is a good thing as it considerably reduces run-time on the generator.

  • crewzercrewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    Re: Batteries and Bulk Charging
    A more interesting point is charging from generators.

    An excellent point indeed! I have to admit that, with my typical focus on solar energy generation, I don't give much thought to battery charging from generators.

    Thanks!
    Jim / crewzer
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Batteries and Bulk Charging

    crewzer,
    no we didn't have time to get into the differences between the 2 batteries, but he did say that the sun xtender is made for the more rigorous uses and abuses that renewable energy presents to batteries. i didn't say you have to go with more charge into the batteries, but only said that you can if you wish as the charging range is now wider. now we didn't exactly get into the cheap batteries that are around like the ones we had from wal mart, but i'd suspect that for each battery and manufacturer they can vary on their recommended max charge rates. somehow i feel the cheap ones are much lower on their max charge percentages and the 25-30% he talked of is a rough idea of what many batteries can do and specifics are to be obtained from those manufacturers. now by comparrison the sun xtender is rated 100% and would be on the 24hr amphr rating of the battery.
    jkirkebo,
    it would depend on the battery manufacturer and their recommendations for their batteries. this does indeed make it easier for the application of using generators to charge them up with and if the batteries are oked for 25% then 22% would fall within that charge range capacity. now using say 1 concorde sun extender pvx 1080t rated 108amphrs this battery could take that generator's full 110amp output if it has a loss inline that could drop 2 of those amps. btw charging from a generator i'm guessing is a condition legal for the lifeline warranty as it is a constant charge source.
    note in general,
    know what your battery manufacturer recommends before making a high percentage charge available to it. if they don't say on a website then email them. if you get no reply then stay within the previous safe zone of charging of 5-10% and again that does not account for any loads on the batteries during charge.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Batteries and Bulk Charging

    i do have to add that they did say the voltage regulation is critical and that it be there. this is just to be sure that others understand this is important in charging leadacid batteries and the recommendations of the manufacturer should be followed. i still say this holds true for many smaller pvs that many think would not hurt the battery. as to the really small ones why would most of you bother if it won't allow it to ever reach a full charge?
  • System2System2 Posts: 6,290 admin
    Re: Batteries and Bulk Charging

    I am concerned about the statement; "... anybody using the lifelines for solar are violating the warranty as the sun xtenders are for that purpose" .

    If you go to http://www.lifelinebatteries.com/, the last paragraph is as follows:

    "In addition, we are original equipment on Monaco, Vantare, Marathon, Parliament, Country Coach and Royal motorcoaches and recreational vehicles where inverters such as Heart, Trace, Xantrex, and Magnum apply heavy loads to batteries. Our Batteries efficient charge acceptance and low internal discharge make them ideal for photovoltaic (solar) and UPS applications where sealed batteries are desired.
    "

    Is this not a direct contradition to the phone call niel referred to?

    niel, do you have the name and number of the person that made that statement?



    The third paragraph found here http://store.solar-electric.com/cosuagmba.html, implies (warranty) the difference in the SunExtender and the Lifeline is the quality of construction.

    Quote:

    "SunExtender vs LifeLine batteries: Both are made by Concorde and are very similar in basic construction and technology. They carry a different warranty, and there are some slight differences internally. The LifeLine also usually have the SAE or dual type marine terminals instead of the bolt only terminals that most of the SunExtenders have. To a large extent in many applications, they are interchangable. You will NOT get the 5-year LifeLine warranty if you use SunExtender batteries in marine or RV applications, but the in general the SunExtender batteries are cheaper because you are not paying for that warranty."


    With the search I have done so far, I have not found anything to support lifelines for solar are violating the warranty, as the sun xtenders are for that purpose.


    Wayne
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Batteries and Bulk Charging

    again take this up with concorde as this is what they had told me so again don't blame the messenger.
  • System2System2 Posts: 6,290 admin
    Re: Batteries and Bulk Charging
    niel wrote:
    again take this up with concorde as this is what they had told me so again don't blame the messenger.


    The Concorde Lifeline vrs Sunextender warranties are discussed on the http://www.wind-sun.com/smf/index.php?topic=1550.0 thread.


    As per the other thread, I apologize to niel if it appears that I am blaming the messenger for the statement in question. I will infact take this up with Concorde, if a name and phone number, of the person that made the statement, is made available to me.



    Wayne
  • Patman3Patman3 Solar Expert Posts: 62 ✭✭✭✭
    Re: Batteries and Bulk Charging

    I'd stand BACK before putting 100 amps into any battery. Maybe I'm just chicken baaaa.
  • FrankFrank Solar Expert Posts: 54 ✭✭✭
    Re: Batteries and Bulk Charging

    I've put ~130 amps into my 660 AHr bank of Concorde's w/o any obvious problems (that's 30 amps A.C. charging a 24 VDC nominal bank). I don't charge off the grid very often (it does it automatically after a grid failuer if my inverter is in backup mode) and have now set the current rate to 15 amps (A.C.) which my generator can handle while powering the house.

    It's not unusual for boats to have big alternators; some as big as 130 amps. I've seen these going into 1 or (usually) 2 8D's which is quite high charge rate. Of course full output won't be needed if the batteries come quickly up to Bulk level.
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