Battery Issues

dhill
dhill Solar Expert Posts: 47 ✭
in Off Grid Solar & Battery Systems #1
I've been running a system off grid for 10 years. I have Outback equip (3624 inverter, charge controller, mate) and 8 Trojan T15 connected in 2 strings for 24volts. My batteries aren't holding their charge after sundown. In one string the battery cases heat up, warm to the touch. I'm considering taking that string out of the mix. To what extent should the battery cases be warm. I can hold my hand over the top of the batteries and feel warmth. They are warm to touch but not hot. Is this an indication that the cells are dead. I add distilled water regularly as needed. The water level inside the cells has never dropped below the plates. I tried equalizing but didn't seem to get any results from that. Any advice or comments are appreciated. Thanks in advance.
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  • Blackcherry04
    Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    #2
    Re: Battery Issues

    Well, there is a point that Batteries do reach the end of their useful life. Since you didn't mention the SG level of the cells there is no way to know if the Equalization did any good or not. If you get a hydrometer and / or check them you'll know. You need to to check the voltage of each battery at rest to know if they are holding the charge. Splitting the bank apart might be a good idea to see if you can isolate the problem.
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  • NorthGuy
    NorthGuy Solar Expert Posts: 1,913 ✭✭
    #3
    Re: Battery Issues

    I'm curious, have you used these batteries for 10 years, or is it a newer set?

    I would measure voltages accross individual batteries to see if one of them has a shorted cell, in which case its voltage will be much lower than others.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #4
    Re: Battery Issues

    Uh, are you saying you've run the same set of T105's for ten years and now they won't hold charge over night? If so, you've set a record for battery longevity and it's time to get new ones.

    Take specific gravity readings of every cell. Consistently low (all cells) that does not respond to charging = dead batteries. Uneven SG readings between cells that does not respond to equalization = dead batteries. But without SG readings you don't know what you've got going on. Batteries do get warm when charging/discharging. It's a direct result of current flow. If they are low/dead their resistance will be low and the current will create more heat.

    (Insert usual caveats about not laddering batteries, using remote temp sensor, checking connections and wire size here.)
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  • dhill
    dhill Solar Expert Posts: 47 ✭
    #5
    Re: Battery Issues

    Thanks guys. I should have posted these batteries are 2 years old. They've been through some brutal summer temps in north Texas. The one thing I have not done is take the SG readings. Can you tell me how to do this? I'm competent at following directions even though I'm not necessarily technically knowledged.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #6
    Re: Battery Issues
    dhill wrote: »
    Thanks guys. I should have posted these batteries are 2 years old. They've been through some brutal summer temps in north Texas. The one thing I have not done is take the SG readings. Can you tell me how to do this? I'm competent at following directions even though I'm not necessarily technically knowledged.

    Have you got a hydrometer? Available from most auto supply stores. You just suck some electrolyte into it and the float will give you a reading like "1.275" (really fully charged) at the level of the fluid. "1.100" is a big problem. One cell reading "1.260" and another reading "1.175" in the same battery is a problem too; needs equalizing.

    Don't mix between cells, flush with distilled water after use.

    How you did any EQ without one I don't know.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #7
    Re: Battery Issues

    Here are the instructions from Trojan:

    http://www.trojanbattery.com/batterymaintenance/testing.aspx

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #8
    Re: Battery Issues
    dhill wrote: »
    In one string the battery cases heat up, warm to the touch. I'm considering taking that string out of the mix.

    You must separate the strings and do your testing, equalization, etc on just one string at a time.

    One of the many problems with having batteries in parallel is that when a single cell (in just one battery) fails, it can take down the whole bank. When the failure first occurs, the good string hides the problem. At this point, (after the sun sets or after you turn off the battery charger) one string of batteries is discharging into the other string. By the time you notice the problem you have harmed the rest of the bank.

    Going forward, if you are going to run parallel strings of batteries you should obtain a DC current clamp meter (about $60) and check the current in each string of batteries every week. The currents should be equal. It they are not equal, find and fix the problem long before you notice that your bank fails to hold a charge.

    So what to do now? Separate and test the strings (including SG). Equalize as needed. If you have a bad cell, replace the battery or replace the entire bank. That can be a tough call, it depends on the condition of the good batteries.

    When you do replace the bank (sooner or later), consider if a single string of L16 batteries (or other larger batteries) will work for you.

    One more thing... Do you have Outback's remote battery temperature sensor installed?

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #9
    Re: Battery Issues

    One inexpensive but "good enough" DC Clamp Meter (really an AC/DC clamp+general digital multi meter) that vtMaps was referring too was this one from Sears:

    http://www.sears.com/shc/s/p_10153_12605_03482369000P

    They are really handy for quick (and safe) diagnosing of solar array and battery string issues.

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