lead acid battery-- cycles and extending life

bohrahsbohrahs Registered Users Posts: 5
Off grid site. Using lead acid batteries.

Currently, by limiting usage I don't allow the batteries to fall below 80% (Trimetric battery monitor).

To extend the battery life is it better to allow the batteries to drain more before recharging to limit the number of cycles?

Thanks.

Hemendra

Comments

  • YehoshuaAgapaoYehoshuaAgapao Solar Expert Posts: 280 ✭✭
    Re: lead acid battery-- cycles and extending life

    If the batteries get over 25C (warm/hot climate), then keeping the batteries a cool as possible helps a lot. Extra ventilation (if on shaded concrete or while discharging), shading (if in sun), burying (if outdoors), placing in climate controlled space (if flooded, need good exhaust ventilation)
  • icarusicarus Solar Expert Posts: 5,248 ✭✭✭✭
    Re: lead acid battery-- cycles and extending life

    The batteries ought to be charged with enough current to stir the electrolyte such that it doesn't stratify.

    You might find these links useful:


    http://www.batteryfaq.org/

    http://www.solar-electric.com/deep-cycle-battery-faq.html

    Tony
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: lead acid battery-- cycles and extending life

    You can go a bit lower in SOC: 75% on average usually works out to the best balance over life. Keep in mind that loads do vary, so going down to 50% once in a while or needing only 10% now and then won't hurt. But it is not necessary nor recommended to do either 50% or 10% consistently.

    If you are comfortable with the system's performance at 80% minimum SOC it should be fine.
  • Rngr275Rngr275 Solar Expert Posts: 101 ✭✭✭✭
    Re: lead acid battery-- cycles and extending life
    You can go a bit lower in SOC: 75% on average usually works out to the best balance over life. Keep in mind that loads do vary, so going down to 50% once in a while or needing only 10% now and then won't hurt. But it is not necessary nor recommended to do either 50% or 10% consistently.

    If you are comfortable with the system's performance at 80% minimum SOC it should be fine.

    So should I be concerned that my system SOC is staying around 85-90%? And if so how do I fix that... throw a breaker every other day to allow for more discharge.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: lead acid battery-- cycles and extending life
    Rngr275 wrote: »
    So should I be concerned that my system SOC is staying around 85-90%? And if so how do I fix that... throw a breaker every other day to allow for more discharge.

    The main concern would be that you're not getting the best value out of your batteries. You could discharge them 10% more every day and get the same (and by some claims better) lifespan. The real world is not as precise as that, of course.

    Do you keep some things turned off to avoid higher DOD? Like TV's, PVR's, et cetera (shut off with switch on power line, not just device 'off')? If so try letting them 'run' full time and see how much effect the 'phantom loading' has on daily DOD.

    Otherwise you might want to calculate approximately how many more Watt hours that 10% more DOD would be and at least occasionally turn on some more loads. How about doing some more vacuuming from time to time? ;)
  • NorthGuyNorthGuy Solar Expert Posts: 1,925 ✭✭
    Re: lead acid battery-- cycles and extending life
    Rngr275 wrote: »
    So should I be concerned that my system SOC is staying around 85-90%? And if so how do I fix that... throw a breaker every other day to allow for more discharge.

    You can beef up your loads. You probably only use 7-10kWh/day - much less than what your panels can produce. If it's seasonal, you can install central air (will not be used in winter). If you have surplus year-round, you can buy an induction range. You will, however, need a second inverter in parallel to do that.
  • bohrahsbohrahs Registered Users Posts: 5
    Re: lead acid battery-- cycles and extending life

    I only use 3-4 kWh/day. I try to use water pumps, washing machine etc only when the sun is shining and batteries are under float. To bring down the average SOC to 75% could I use a toaster and an iron, or resistive loads are a no no?

    Hemendra
  • BB.BB. Super Moderators, Administrators Posts: 29,518 admin
    Re: lead acid battery-- cycles and extending life

    Type of loads really do not matter... What is more important is the amount of load...

    For a battery bank using Battery Capacity (20 hour rate) flooded cell, roughly:

    C/20 (20 hour discharge rate) -> gentle discharge, battery is efficient
    C/8 (8 hour discharge rate) -> About the maximum continuous rate for a "generic" flooded cell battery, less efficient discharging (battery can get pretty warm)
    C/5 -> pretty heavy discharge rate--Not recommended for long periods of time
    C/2.5 -> maximum recommended discharge rate (seconds to minutes)
    C/less than 2.5 hour rate--Battery voltage could collapse.

    Note that AGM/GEL batteries can support much higher discharge rates--But usually not really needed for typicall off grid home.

    So--That is the type/size of your battery bank (voltage, Amp*Hour Rating, flooded cell, or other).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: lead acid battery-- cycles and extending life

    Resistive loads are fine. In some ways they are less of a problem off grid than inductive loads.

    Toaster/iron do represent big draws though: typically 1200-1500 Watts. This can be a problem as an "all at once" current demand on a battery bank. You may be better off with a smaller load over a longer time to pull the batteries down. Keep in mind that a battery's actual capacity is less under a higher load than a lighter load. It's a little hard to wrap one's head around; that the capacity potential varies moment to moment depending on how much current is being drawn at the moment!
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: lead acid battery-- cycles and extending life

    note in addition to what bb said.
    gels generally are not able to support high charge/discharge rates and that not all vrla batteries are the same as to be able to lump them all together.
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