SG rising up on ROLLS

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maok
maok Registered Users Posts: 20
Hi, I am just a new one in the world of of-grid, so I have many questions.
main one:

is it normal that the SG rises so slowly, that after 5 hours of charging 24 A, it almost didnt move?and after completed PWM, the SG is max 1,250.
I have 12V 530Ah.

when you , guys, can notice, that SG is rising up? is it after some hours charging, or next day, when the battery cooled down?

have I little current to battery?

batteries are 1 month new.

thanks a lot for answers..

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  • hillbilly
    hillbilly Solar Expert Posts: 334 ✭✭
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    Re: SG rising up on ROLLS

    Not a ton of specifics on your system, so just a couple of questions:
    Yes SG levels do rise gradually, and 1.250 is not all that low for normal charging, particularly if they have not been cycled a lot yet. The SG levels should rise as the battery recharges, although it sometimes doesn't show immediately, what was the SG level before charging? 1 month old batteries may not be fully broken in yet, did you follow any sort of charging parameters when you first acquired them? When you say "5 hrs of charging at 24 amps" that doesn't mean a lot: how discharged were the batteries before the charging, what was the voltage level was absorb set for, and how long were they held at that voltage... etc? That current should be sufficient to charge the batteries, but may very well take a long time to do it if they are substantially discharged. Is this charging via PV, generator, or both?
    Fill in a few more blanks...
  • BB.
    BB. Super Moderators, Administrators Posts: 33,493 admin
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    Re: SG rising up on ROLLS

    Roughly, we "recommend" 5%-13% of the battery's C/20 (~40 Hour rating) for charging current... For yours:

    24 amps / 530 AH = 0.045 = 4.5% rate of charge.

    This is a relatively low charging current so it can take awhile to recharge your bank. Basically, you are at C/20 rate of charge (5%), so for every 5% change in State of Charge, it will take 1 hour of 24 amps to recover.

    Roughly, from the Battery FAQ, you are looking at ~0.015 Specific Gravity [fixed--was 0.15--missing a "0"] for every 10% change in State of Charge (~2 hours on your 24 amp charge rate).

    If you are pumping in 24 amps, and you see no change in specific gravity after ~2 hours (at 5% charge rate/24 amps)--then your battery cells have pretty much reached 100% capacity (from the Rolls Charging FAQ, they say full charge is ~1.265-1.275).

    In theory, ~25C batteries, charging at ~24 AH and 14.2-14.7 volts. Once the batteries are mostly charged, you should hold the 14.x volts for ~2-3 hours, Then stop charging or reduce to float voltage of 13.2-13.4 volts.

    5 Hours of charging at 24 amps should move the SG by ~0.025 [fixed] points (assuming your battery was at ~75% state of charge or less). If your battery SG started out near 1.250 and hardly moved (and you see bubling in the battery, and you know that ~24 amps where flowing)--Then you pretty much have done an Equalization and the SG reading you saw will be the maximum for your battery set.

    By the way, what was the voltage at the battery bank over the last 5 hours while you where running 24 amps into the bank (14.x or 15.5-16.0 volts)?

    At 15.5+ volts, that would hve been equalization. If 14.x volts, I would guess that the charging current should have reduced automatically to well below 24 amps (bulk/absorb charging).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • maok
    maok Registered Users Posts: 20
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    Re: SG rising up on ROLLS

    Thanks for answers..

    now I am writing every change, so I will see more clear in that / I hope/
    so..

    yesterday the SG was 1,190 to 1,200 in all cells. open voltage 12,10V.
    then I started to charge at 14,7V and 24A.
    already after 5 hours started PWM on my Tristar controler, and current slowly moved
    down to 10 A through 1,5 hour.
    after this charging, the SG rised only of 0,010.

    I am asking myself, why the PWM started so soon, when I cherge on so low current?
    it looks like the voltage is rising up faster than is normal..

    maok
  • BB.
    BB. Super Moderators, Administrators Posts: 33,493 admin
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    Re: SG rising up on ROLLS

    Note: I made a mistake in typing the SG change per 10%... Should be 0.015 not 0.150 (and 0.025 not 0.250) like I originally typed.

    Do you have a remote battery temperature sensor for your charge controller? It was found that the smaller MPPT charge controller (15 amp) really needed the RBTS. The controller tends to run hotter than the battery bank which suppresses the output voltage otherwise.

    I don't know anything on the Tristar MPPT controller--How do you know it is on PWM (light?) vs just normal reduction due to less sunlight.

    Also, what is the voltage on the controller output terminals vs battery bank. Although, it sounds like everything is OK now that you are seeing 14.7 volts on the battery bank during charging (and the controller would be reducing charging current at that time).

    What is the load like? From the SG and resting battery voltage, it sounds like you are discharging down to ~60% State of Charge (using 40% of the battery bank capacity).

    530 AH * 40% = 212 Amp*Hours consumed (approximate guess)

    At a 20 amp average charge--that would take 10+ hours of recharging...

    Really need to know what your nightly loads are... It sounds like you are pulling 2-3 times more energy from your battery bank than your existing solar panels are able to output during the day (especially in winter).

    Do you have any measurements of your nightly load? (I could be all wrong here--just guessing).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • maok
    maok Registered Users Posts: 20
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    Re: SG rising up on ROLLS

    hi,

    now is almost no sun in Slovakia. exactly, I didnt see the sun for two weeks.
    so I am charging with a gasoline generator.
    my night consumptions are zero. Whole electricity is off. but daily I spend around 4 amps through 18 hours. so it is around 65Ah daily.

    now I made measurment from yesterday every hour.

    on the start it SG was 1,190-1,200.
    than I charged 5 hours at 20-24 Amps.
    then I equalized it 10 hours at 15,8V and 16Amps.
    after this time the SG measurments was 1,255 - 1,275.

    do you think is it OK?

    now I wil carrefuly measure my consumption and I will see.


    but I am scared, that on normal bulk voltage 14,7 it would not full charge , becuse already after 5 hours of bulk charging, the amperage start to drop downd.

    so we will see now, after this "deadly" equalization what will hapend...

    thanks for reply

    maok
  • BB.
    BB. Super Moderators, Administrators Posts: 33,493 admin
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    Re: SG rising up on ROLLS

    14.7 volts is fine... And you will see the battery/charge controller accepting less current as it gets fully charged. As long as you reach at least 90% state of charge every few days, and don't stay below ~75% state of charge for more than a day--you should be fine in normal operation.

    Regarding charging, if you use 65 Amp*Hours in a night, you should be replacing ~110% at most during the charging (~73 AH).

    Don't try to get to 100% state of charge every day... That is probably approaching an overcharging issue.

    By the way, how is the water usage? You should be replacing some every month... Zero water usage or nearly exposed plates every month is not right.

    I have to go now...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • maok
    maok Registered Users Posts: 20
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    Re: SG rising up on ROLLS

    thanks,

    I counted, that I sended 267AH to the battery. on the start the battery was at 50% and on the end of the charging /15 hours/, it was nearly 100%./ ampermeter showed 6Amps into bat./ and SG was also near 100%.
    so its more or less matching the right numbers..

    so now I am measuring all my consumtion, and tomorow I will see.

    but I think about to buy stronger AC/DC converter /60 A/ , to charge batt. faster.
    it could be the solution.

    .. yes, when it is charging PWM, I can see it on the light /green is blinking/

    maok
  • BB.
    BB. Super Moderators, Administrators Posts: 33,493 admin
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    Re: SG rising up on ROLLS

    In general, any charge rate between 5% and 13% is fine... However, when running a genset, you probably want to output load on the genset to be near 50% of the generator's rated capacity (if not a bit higher). Should end up being more fuel efficient for you (generators are typically pretty fuel efficient from 50%-100% rated load. Below 50%, the fuel flow remains at ~50% fuel flow even if it is outputting 5% rated power).

    You can run into issues where it would be difficult to get more than 50% rated capacity out of the generator with many battery chargers. The older battery charger designs have poor Power Factor (the AC current wave form is not in phase with the AC voltage and/or the current wave form does not look like a sine wave). Poor power factor will make the battery charger "look larger electrially" than it actually is.

    Power Factor for AC battery chargers is not usually stated--So without actually measuring it is a bit of a gamble to figure out what any charger's power factor may be. If you find one listed as "Power Factor Corrected" -- that should be a good sign.

    I am sorry--Power Factor is a bit technical and if English is your second language you may want to look it up in some local references (you are doing better in English than I do at times--and English is my only language :cool: ).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • maok
    maok Registered Users Posts: 20
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    Re: SG rising up on ROLLS

    Hi,

    yes , you are right. now is not very effincient my charging from my genset , because it runs around 10% of its rated power.

    but, what about the batteries, it looks like , the long equalization helped a lot.

    I spent 34Ah after charging, what is around 8% of batt. capacity, and the SG droped down of 0,005. so now is SG from 1,255 till 1,265.

    and open voltage was after this 12,57.

    so, we will see later, but it looks better..

    thanks a lot..

    Maok;)
  • maok
    maok Registered Users Posts: 20
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    Re: SG rising up on ROLLS

    ...the story is still going on...

    so, the battery was filled with the power using the long durating equalization.
    then I discharged around 35 % /175Ah/. SG droped down to 65%. I was OK.
    but next day I started to charcg again with 24 Amps. It took around 5 hours, till PWM starts to push down the current. also this was OK, when I counted the total power. /175AH versus 155Ah/. So everything looked like the batteries are almost finished the charging.
    but then I measured the SG, and it was only at 1,240. so what is going on here?

    shall I need to equalize every time when I will want to charge battery to full state?:confused:
    my charging voltage is 14,8V

    thaaanks a lot for the answers..

    Maok
  • hillbilly
    hillbilly Solar Expert Posts: 334 ✭✭
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    Re: SG rising up on ROLLS

    If you mean that you put in 155AH when you had discharged 175AH then your SG level doesn't sound off at all, depending on a few factors you quite likely would need to recharge 200+AH to get your SG levels back up to 100%. Your SG levels are indicating a 80% SOC roughly, and 155AH/200+/-AH is between 75-80%.
    Sounds like you just weren't quite done charging them, did you notice what your charging current had dropped down to, and was it still dropping? That 5 hours of charging, how much of that time were the batteries at 14.8V?
    You would need a few hours at that voltage level, and the charging current would need to drop down to somewhere in the neighborhood of 2% of the batteries 20hr rated capacity for them to be recharged. It's quite common off the grid that you wont get this each and every day, it's more critical to make sure that this does happen on a regular (but not daily) basis.
  • maok
    maok Registered Users Posts: 20
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    Re: SG rising up on ROLLS

    hi, thanks for reply.
    my battery is 530 Ah at 100hour and 400Ah at 20 hour.
    so you meant, that 2% will be from 400? it would be 8A? or? /I am very new in this world of charging/
    I saw on my meter 8A, and then 6A. ..it would mean that battery was fully charged?
    14,8V was around 2 hours. it was PWM.

    maybe the SG doesnt change on the upper side of batt. beacause the acid is havier than water, and it will mix up only when equalizing? I dont know. everybody is writing, that SG starts to rise in the moment of starting charging. uff..

    thanks

    maok:confused:
  • BB.
    BB. Super Moderators, Administrators Posts: 33,493 admin
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    Re: SG rising up on ROLLS

    It takes awhile (couple hours?) for the electrolyte to mix after charging... And, for tall batteries especially, the electrolyte can "stratify" or be high sg at the bottom of the battery and low at the top of the battery.

    Basically, if you charge > 90% every few days or at least once per week and equalize once per month (if needed with low/unbalanced sg readings among cells), and recharge if the sg falls below ~75% within a day to, at least, above ~80%--you should be doing fine.

    And keep an eye on how much distilled water you have to add to the battery bank per month. None--probably not charging enough; some--just about right on average; plates almost exposed--you are probably overcharing.

    Overcharging is not healthy for battery banks (causes damage to positive plates/grids). And running for days/weeks below ~75% (sulfates harden and battery capacity is reduced).

    As long as you are in the 80%-90+% area most of the time (with excursions from 75-50% recharged within a day or so)--you should have good battery life.

    Don't try for a 100% daily charge (except when equalizing once every month +/- a couple weeks). It is inefficient (especially when charging on a genset) and can lead to heavy water use and positive plate/grid damage.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • maok
    maok Registered Users Posts: 20
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    Re: SG rising up on ROLLS

    step by step I am going to more understanding of this stuff.
    thanks to you all..

    maok