batteries dead?

Jeromeds
Jeromeds Registered Users Posts: 13
Two months ago I installed (4) interstate batteries in cabin after keeping charged (IOTA 3 stage) all winter. They have 350 watts of solar panel on (2) 220AH two year old and (2) 220AH three year old in series (12v). Upon my return this week the inverter alarm was buzzing and after resetting I check the specific gravity which where in the "red" at about 1.125. I charged with Gen and IOTA to 13.4 but the Specific gravity didn't improve. Is this an indication that the batteries are toast?

Comments

  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: batteries dead?

    At what voltage does the inverter alarm sound? Many inverters have a low voltage cut off or alarm that is designed to protect the inverter, but is too low to save the battery.

    Just for the future, why was the inverter left turned on? Were there loads? What brand/model inverter? Is the low voltage disconnect adjustable?
    I charged with Gen and IOTA to 13.4 but the Specific gravity didn't improve. Is this an indication that the batteries are toast?
    Did the batteries make gas? If not they may be stratified, which means the SG you measured was from dilute acid near the top. Try getting the voltage up higher.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: batteries dead?

    Okay, first let's get the battery bank configuration figured out. You have four 6 Volt 220 Amp hour batteries. Two parallel strings of two in series for 440 Amp hours @ 12 Volts. Does that sound right?

    What size was the battery charger used to keep them charged all winter? It should be 45 Amp @ 12 Volt. And how was this run all winter if you weren't there? (We have had horror stories of people plugging the charger in to the inverter which was run off the batteries being charged by the charger. This does not work.)

    350 Watts of panel is about half what a battery bank that size needs.

    SG of 1.125 is dead. Charging to 13.8 Volts is not going to improve it. You need to charge to 14.4 Volts and keep it there for three or four hours.

    Unfortunately since the batteries went dead and were that way for an unknown amount of time the chances of recovery are very slim.
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: batteries dead?
    And how was this run all winter if you weren't there?

    I think he had the batteries at home (on grid) on trickle charge all winter. He just took them to the off grid cabin two months ago. When he found them dead this week he used generator & iota to try to recharge them. I think his big mistake was leaving the inverter on for two months while he wasn't there.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • Jeromeds
    Jeromeds Registered Users Posts: 13
    Re: batteries dead?

    Clear answer. Batteries moved and maintained with 45 amp Iota and 110 V grid then reinstalled beginning of season with 4 hours minimum of typical direct sun/cloud. I inadvertantly left inverter the 60 days away. Will the 350 watt array being too small for 440 AH combined battery @12v result in killing use or new batteries? Hard to get a balance considering limited finances. Thanks for imput.
  • Jeromeds
    Jeromeds Registered Users Posts: 13
    Re: batteries dead?

    Current array is 80w+135w+140 for 355watt @77% gives me aobut 4.5% of 440ah battery bank. Are you recommending another panel (or two less batteries) for optimal balance? What's the formula?A lesson learned.
    thanks
  • BB.
    BB. Super Moderators, Administrators Posts: 33,433 admin
    Re: batteries dead?

    Recommend around 5% to 13% solar array... Less than 5% and a heaviely used bank--probably will need lots of generator help.

    Over 13% will work (upwards of 25% should be OK), but unless you use a lot of power during the day, the system will sit at float for much of the time (of course, if you are using power during the winter, more panels will help reduce generator usage).

    The problem is--350 watts of panels and, is it 4 hours of "noon time sun" or just sun from 10am to 2pm sun?... But in any case, an estimate of power generated would be:

    350 watts * 4 hours of noon time sun * 0.52 system efficiency = 728 Watt*Hours (of AC power) nominal per day

    An inverter can easily draw from 6 watts to 20+ watts 24x7 (depending on brand/model/configuration/etc.)... Say 15 watts:

    15 watts * 24 hours = 360 watt*hours with an unloaded inverter

    If you had a couple cloudy days (or if you only have 10a-2p sun), or there where some loads on the inverter--Very good chance that your system was simply drained because the inverter was not turned off... And simply exceeded the power generated by the array (batteries have self discharge too--which can draw addition power too).

    Easily, you could use 2-3x the current array wattage--But that is your choice. If this will be a heavily used system, going to 10% array will help (or actually measure your loads and run the calculations+based on amount of sun for your area).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset