Battery Life

Hi, I'm new here and appreciate any info/advice anyone can offer.
I've lived off-grid for 16 years and for the last 7 have been responsible for the care and feeding of a 12V, 1700 amp hour fork-lift battery bank which is charged by my solar array.

My concern is that I've been overcharging the batteries. They are designed to discharge to 20%, but I've never ever allowed them to discharge more than 60%, using a generator to bring them back up to between 90 and 100%.

The solar array puts out about 25-30 amps, while the generator charges at 130-150, and it's not a trickle charge, it's full-bore right off.

So, have I "ruined" the bank? Currently (sorry), it has a resting charge of 12.2V, which I know is low, but it's winter here, so I'm unsure. Should I begin allowing the bank to discharge lower, incrementally perhaps, or keep doing what I'm doing?

Thanks,
Jenny

Comments

  • mike95490mike95490 Solar Expert Posts: 7,283 ✭✭✭✭
    Re: Battery Life

    Don't let it get lower. Do you know how to do an equalize charge ?

    Overcharging would cause lots of boil-off of water, have you had to add lots of water ?
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • BB.BB. Super Moderators Posts: 26,837 admin
    Re: Battery Life

    If you can, find any information from the battery mfg. on the "care and feeding" of their battery.

    Regarding your charging current--normally, somewhere between 5-13% of the 20 Hour rate (in Amp*Hours) is the recommended battery charging current...

    For yours, 170 amps would be just fine--so you are not improperly charging using your genset (unless you are leaving the generator running for hours, "boiling" your batteries).

    The 30 amps from your solar array is, pretty much, just a trickle charger.

    If you have not yet, read one or more battery FAQs (like this one).

    Some things to aim for:
    • Don't let your battery sit below 75% State Of Charge for days at a time. Will cause "sulfation" to harden.
    • Do equalize with the genset once or twice per month (and/or install a larger $olar Array.
    • Undercharging and Overcharging are both damaging overtime
    • Keep water levels at recommended levels (don't let dry out or over fill)
    • Use distilled water (or filtered rainwater, etc.). Do not use untreated stream/lake/well water.
    If you don't have them already, get a hydrometer and thermometer to measure your specific gravity (usually once a month or so, once you have your system stable).

    I also try to push the installation of a battery monitor. As close as you can get to a "gas gauge" for a battery. The Trimetric is a good, low cost unit. The Xantrex I like because they include a programmable output that you can use to warn if the batteries are over discharged or use to turn off your inverter, etc.

    It is difficult to tell how much life you have left in your battery bank... Monitoring the specific gravity of your electrolyte vs how much power you are consuming will give you an idea of how much battery capacity you have left.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2System2 Posts: 6,290 admin
    Re: Battery Life

    Thanks Mike and Bill

    Mike, yes I do equalize, usually ever 60 days. No, I haven't had to add an inordinate amount of water.

    Bill, I did read the FAQ page (which is how I ended up here) and it's great because it's in English. My solar guy is wonderful, but he answers my questions in "engineer-speak" and over time I've just stopped asking. I do equalize, use distilled water, don't overfill and keep an eye on the water level. The batteries never sit below 75% for days, ever. I have a TriMetric, which is the main way I track and what I've used to guide my gen usage. My primary concern is that I've overcharged them over time. I'll take your suggestion about checking the specific gravity and see what happens.

    Thanks again to both of you. What a great resource.

    Jenny
  • BB.BB. Super Moderators Posts: 26,837 admin
    Re: Battery Life

    Sounds like you are doing everything correctly.

    Not often we can say that here--I have destroyed more than my fair share of storage batteries from neglect before I got educated. (perhaps equalizing more often would be helpful overall--equalizing/"boiling" helps keep the electrolyte properly mixed--especially useful in in large/tall batteries--electrolyte can stratify over time).

    Generally, once your charge gets the batteries to "bubbling"--then timing the equalize (per the mfgr's recommend time) is all you need to do. If you are adding some water every month or two--it sounds like you are properly charging (adding no water or a lot every month are both bad signs). Can't do much more.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • icarusicarus Solar Expert Posts: 5,090 ✭✭✭✭
    Re: Battery Life

    How old is the string? Have you tested each battery in the string and each cell in each battery? Have you made sure that your cables are good, and that you are drawing from the right point(s) of the battery bank? Some wiring configurations are better than others. (Do a search here, there are some pretty good wiring diagrams somewhere on this site).

    Hydrometer testing all the cells can begin to isolate what the problem may be. If all the cells are low and won't charge,, you probably wrecked the string,, but one bad cell can over stress the entire string. I like to look at the Specific gravity on my every couple of weeks to head off trouble.

    Good luck,

    Tony
  • icarusicarus Solar Expert Posts: 5,090 ✭✭✭✭
    Re: Battery Life

    Wow! We off gridders have our own section now! I am overwhelmed!

    Thanks guys,

    Tony
  • wild01wild01 Solar Expert Posts: 90 ✭✭✭
    Re: Battery Life

    you might check the batteries manufacturer recommended "finishing amps" should be on the manufacturers web site this is the minimum amps that a forklift battery should be charged at. It won't really hurt them to be charged at less, but because of their high internal resistance they won't really be taking much of a charge. Also I've noticed that forklift batteries tend to have a much lower voltage when fully charged then one might think they should. mine will hit 13 when fully charged and being equalized, but if i turn on a 15 watt cfl it'll drop strait to 12.1. it's always done this and I can still take it to 80% dod and use the expecter number of amp hours day after day.
  • System2System2 Posts: 6,290 admin
    Re: Battery Life

    Thanks wild01, that's been my experience as well, and I've wondered about it. I'll gen charge them up, they'll go as high as 15V and then rocket back down fairly quickly. So they have "high internal resistance"?. Makes sense. I'll start letting them discharge more then. They've never "stretched their legs" with deep discharge. I'm just hoping I haven't killed their little cells by not letting them discharge deeper.

    Jenny
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