Charging Question (wasn't an "Inverter Question")

monoloco
monoloco Solar Expert Posts: 103 ✭✭
in Off Grid Solar & Battery Systems #1
I have an Outback FM60 and 24v bank of 8 305Ah Concorde AGM's, the float absorb voltage is set at 28.8, today just before going into float I saw the voltage spike up to 29.27. My question is: Is this normal? I wouldn't have noticed except my 24 volt Jabsco pump shut down due to (I think) over current. I'm just worried about overcharging my AGM's.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #2
    Re: Inverter Question

    It is probably not out of the ordinary and specifications. From this thread:
    Sulfated Lifeline Concorde AGM Batteries

    Concorde does spec 15.5 volts on a 12 volt battery for 8 hours to "recover" a sulphated battery...

    Obviously, 31.0 volts for 8 hours is not ideal (in general, "equalization"/high charging voltage/current is "hard" on a battery bank's overall life)--You should not be hurting your battery bank.

    Is the charge controller just not able to act "quickly" when clouds past in front of the array (takes a few seconds to adjust current flow), or not? I do not know.

    But we have had reports before about Xantrex XW hardware exceeding 70 volts (35 volts @ 24 volt bank) when there was a large solar array and quickly changing (other than a large array/inverter on a smaller battery bank, no other known causes that I remember reading about).

    The only other possible damage would be from over-voltage on any of your attached DC loads--But 30+ volts during equalization would be considered normal for a flooded cell battery bank.

    And why some 12 VDC adapters designed for cars (~12-14.2 volts) appear to fail on a PV solar battery system (10.5-15.5+ volts). It depends on the design of your loads.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • tallgirl
    tallgirl Solar Expert Posts: 413 ✭✭
    #3
    Re: Inverter Question

    You have to look at the length of time of the over voltage as well as the current. My bank, when completely full, rises 1 (0.94, actually) volt for each amp of current. I saw 61 volts yesterday, which equals about 9 amps on a 100% SoC bank. That's not enough current to do any harm for the 5 to 10 seconds it was that high.

    Remember that you're talking about hundreds of pounds of lead, if not thousands (I think my bank is on the order of 1,500 pounds or so). You don't want to be doing that for minutes on end, much less hours, but a few seconds isn't going to harm anything, other than any sensitive electronics.
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  • tallgirl
    tallgirl Solar Expert Posts: 413 ✭✭
    #4
    Re: Inverter Question
    BB. wrote: »
    But we have had reports before about Xantrex XW hardware exceeding 70 volts (35 volts @ 24 volt bank) when there was a large solar array and quickly changing (other than a large array/inverter on a smaller battery bank, no other known causes that I remember reading about).

    Even reasonably large-ish AGM banks will do it, but that's an AGM issue in general.
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  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,891 ✭✭✭✭✭✭
    #5
    Re: Inverter Question
    monoloco wrote: »
    I have an Outback FM60 and 24v bank of 8 305Ah Concorde AGM's, the float absorb voltage is set at 28.8, today just before going into float I saw the voltage spike up to 29.27. My question is: Is this normal? I wouldn't have noticed except my 24 volt Jabsco pump shut down due to (I think) over current. I'm just worried about overcharging my AGM's.

    You could put a voltmeter that logs on the voltage and then you will really be worried. I noticed a much faster response to load changes when I replaced the Outbacks with the XWcc. The Morningstar cc is even faster in my non scientific electric garage door opener test.
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

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  • monoloco
    monoloco Solar Expert Posts: 103 ✭✭
    #6
    Re:Charging Question (wasn't an "Inverter Question")

    Thanks for the replies, sorry for the title mistake it should have been Charging Question, I tried edit but it wouldn't let me edit the title. I went back and checked the log and it showed that I actually exceeded 30 volts. Would it be better to dial back the bulk/absorb voltage to 28.6 or 28.4? I don't know how these 24v pumps would even be useable with FLA batteries that charge at even a higher rate.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #7
    Re: Charging Question (wasn't an "Inverter Question")

    I changed the title on the opening post and your last post... Should "stick" with the new title now.

    Also, this newer version of Vbulletin software may let you edit your first post title by pressing the "Advanced Edit" button so you have all of the editing functions/options (not sure if permissions allow the post owner to edit titles and such).

    Check with the pump manufacturer... They would have to withstand at least 31 volts (during equalization) charging--So I would not worry about a few seconds or minutes of of <32 volts... Also check your inverter--It may shut down around 30-32 volts--if that is an issue...

    Dropping the absorb voltage, in general, may give you longer battery life (slow charge can be less damaging than fast charge)--but you are against the sun--X hours or so to get 100% of the available energy from the array into your battery banks... Running an undercharged battery bank has its own issues too.

    In the grand scheme of things, if nothing is getting damaged (pumps, electronics, etc.)--I would not dial back the charging voltage. That could lessen how quickly and how fully you recharge your battery bank (unless you are in float every day by noon anyway--then slowing the charge rate down by reducing charging voltage will not hurt anything--at least in summer--winter may be a different issue).

    Monitor your battery bank and make sure it is getting properly charged and adjust as needed--the generic advise.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • monoloco
    monoloco Solar Expert Posts: 103 ✭✭
    #8
    Re: Charging Question (wasn't an "Inverter Question")
    Dropping the absorb voltage, in general, may give you longer battery life (slow charge can be less damaging than fast charge)--but you are against the sun--X hours or so to get 100% of the available energy from the array into your battery banks... Running an undercharged battery bank has its own issues too.

    In the grand scheme of things, if nothing is getting damaged (pumps, electronics, etc.)--I would not dial back the charging voltage. That could lessen how quickly and how fully you recharge your battery bank (unless you are in float every day by noon anyway--then slowing the charge rate down by reducing charging voltage will not hurt anything--at least in summer--winter may be a different issue).

    Monitor your battery bank and make sure it is getting properly charged and adjust as needed--the generic advise.

    -Bill
    It is very sunny here and we don't use much power so we are usually in float by 11-12pm, with only a 750 watt array.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #9
    Re: Charging Question (wasn't an "Inverter Question")

    If your battery bank is getting above 90% state of charge several times a week---You should be fine.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #10
    Re: Charging Question (wasn't an "Inverter Question")

    you stated absorb/float at 14.4v per battery. you could go down to 14.3v if you would like and no harm or foul there, but a float voltage of 14.4v per battery is. that should be around 13.2v-13.3v per battery.
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  • monoloco
    monoloco Solar Expert Posts: 103 ✭✭
    #11
    Re: Charging Question (wasn't an "Inverter Question")
    niel wrote: »
    you stated absorb/float at 14.4v per battery. you could go down to 14.3v if you would like and no harm or foul there, but a float voltage of 14.4v per battery is. that should be around 13.2v-13.3v per battery.
    My bad, I meant to say bulk/absorb voltage was 28.8 float is set at 26.8 which is the high end of the recommended range.
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