Bulk and Absorb times drastically decreasing along with run times.

Audiomaker
Audiomaker Solar Expert Posts: 100 ✭✭
in Off Grid Solar & Battery Systems #1
Yep, title says it all.

48v bank. 2 strings of 4 12v grp 27 100ah FLA's being charged by a Xantrex XW6048.

In the last week I've noticed the charge times are reduced, and the charge frequency is up (i.e....generator is cycling more often).

As of this morning, the charger stays in bulk for all of 15 minutes, absorbs for another 10 or so, then the system shuts down the generator at about 4 amps @ 59v.

Basically the charger is reaching it's 3-4 amp range where it normally shuts off waaay too fast. Kinda like what I've known as a "surface charge".

Thoughts? Remedies?

Sean
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Comments

  • Mountain Don
    Mountain Don Solar Expert Posts: 494 ✭✭✭
    #2
    Sounds like the batteries are no good. When FLA's get to end of useful life they take very little time to reach what appears to be a full charge. Unfortunately their capacity is actually very little and hence you find they supply very little output. New batteries would solve.... How old are they? You would do much better to change to a different battery, one that is truly a deep cycle battery.
    Northern NM, 624 watts PV, The Kid CC, GC-2 batteries @ 24 VDC, Outback VFX3524M
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  • Audiomaker
    Audiomaker Solar Expert Posts: 100 ✭✭
    #3
    They are a year old.
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  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    #4
    disconnect one string and check it alone and then do the other one alone.. it will show you if there any variance between strings, there may be more than one bad one...
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #5
    Check the voltage arcoss each battery when charging/discharging/resting... If there is one or two that stand out with a "different" voltage--It may be the "bad" battery.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Audiomaker
    Audiomaker Solar Expert Posts: 100 ✭✭
    #6
    Ok, I got voltages of around 12.5v overall with one at 12.7v. They weren't fully charged, but I was checking water and planning to equalize so I didn't want to fully charge at that point.

    So would the higher voltage, or lower voltage "stand out" be the bad battery? I know that'a a lame question, but I have to ask just to be sure.


    Secondly, after reading on the net, I'm definitely experiencing the symptoms of sulfating.

    This is probably due to my non-stop cycling to less than full in my generator setup.

    The batt's go through their charge cycle (which is getting shorter and shorter quickly), and drop off in voltage very fast. I'm to half capacity (read by voltage) in 20 min @ 300w load.

    So... question is...

    If I leave the water cap's off for a few days, and increase my bulk and absorption voltages to 62v, what destruction will I do if checking the water a few times a day (it would cycle this about 6-8 times per day)?

    The idea is to turn the bulk and absorption stages into semi-equalize stages to see if I can knock off the sulfacation..

    Ideas?

    P.S. Can I float at 62-64 volts for a day or two?
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #7
    High voltage during charging could be bad.

    Low voltage during discharge possibly bad. Looking for 1 to 2 volt difference if bad cell.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Blackcherry04
    Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    #8
    Before you talk about Equalization, do you have a Hydrometer ?? I see no SG levels mentioned, you can't do a equalization without one, it'd be a guess in the dark at best.

    DO NOT TAKE THE TOPS OFF !!! You'll blow out your electrolyte.
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  • Audiomaker
    Audiomaker Solar Expert Posts: 100 ✭✭
    #9
    BB. wrote: »
    High voltage during charging could be bad.

    Low voltage during discharge possibly bad. Looking for 1 to 2 volt difference if bad cell.

    -Bill

    That was taken just sitting... disconnected.
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  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    #10
    How long was it since it was being charged? Normal time span is ~3 hrs or more, this allows for dissipation of 'surface charge'
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
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  • Audiomaker
    Audiomaker Solar Expert Posts: 100 ✭✭
    #11
    Well, upped the bulk and (1hr) absorb voltages to 65v after running a 6hr EQ. Capacity seems to be increasing slowly. Once again trying to find what a small bank likes when continuously short cycled.

    That's a 200ah 48v bank @ 20a with an average of 300w being pulled non stop... it either is charging or inverting. Doubling the bank would certainly help but not everyone can do that.

    I don't think the batt's liked the 6-8 cycles per day to 70-80% and were sulfating... I think.

    I'm kind of in a "save what I can" mode right now, but on the next set I think I'll keep the voltage up if Im doing short absorb times like this.

    Nursing lead acid batteries is such a pain.
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  • Mountain Don
    Mountain Don Solar Expert Posts: 494 ✭✭✭
    #12
    Audiomaker wrote: »
    Well, upped the bulk and (1hr) absorb voltages...........

    With only a 1 hour absorb there is a good chance FLA batteries will never get a real full charge.
    Northern NM, 624 watts PV, The Kid CC, GC-2 batteries @ 24 VDC, Outback VFX3524M
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  • Audiomaker
    Audiomaker Solar Expert Posts: 100 ✭✭
    #13
    Mountain Don wrote: »

    With only a 1 hour absorb there is a good chance FLA batteries will never get a real full charge.

    Agree.

    It's polite to the generator however but I suspect sulphates the bank pretty quickly, which is why I increased the voltage for that hour.
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