At what voltage is 50% AH rating?

bc buck
bc buck Registered Users Posts: 59 ✭✭
I am setting up a new Prosine 2.0 inverter charger on my 12 volt 260 ah battery bank. One of the parameters ask at what voltage do I want the prosine to shut down for low voltage. At what voltage is your wet cell battery considered at 50% ah while under a 15 amp load?

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    There is a nice chart here:

    http://forum.solar-electric.com/forum/solar-news-reviews-product-announcements/solar-information-links-sources-event-announcements/4426-working-thread-for-solar-beginner-post-faq?p=194303#post194303

    Probably, I would start at 12.0 volts and if you have too many shutdowns, drop it to 11.5 volts.

    Battery voltage for lead acid is not a very accurate method of determining state of charge under charge/load/no current/temperature/age...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    bc buck wrote: »
    I am setting up a new Prosine 2.0 inverter charger on my 12 volt 260 ah battery bank. One of the parameters ask at what voltage do I want the prosine to shut down for low voltage. At what voltage is your wet cell battery considered at 50% ah while under a 15 amp load?

    Most lead acid batteries are at about 50% SOC when their RESTING voltage is at nominal voltage, i.e. 12.0 volts for a 12 volt battery.

    Run your batteries down, disconnect them, wait a couple of hours, and measure the voltage. Do this until you get your RESTING voltage down to 12.0 volts. Then connect them, turn on a 15 amp load, wait a minute, and measure the voltage. That is your answer.

    There is a problem with this approach to setting the LVD (low volt disconnect).... if you leave a 1 amp load turned on, by the time your battery gets to the LVD voltage it will be well below 50% SOC.

    How long do your 15 amp loads last? Many inverters have adjustable timing for LVD.... i.e. the inverter doesn't shut down until the LVD has been reached for a period of time. My 24 volt system has a LVD of 24.0 volts for 1 minute. This means I can use my circular saw (which usually pulls the voltage down to about 23.3 volts) for less than a minute. For longer cuts I turn on the generator.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • Alaska Man
    Alaska Man Solar Expert Posts: 252 ✭✭
    Same here, if it's set to close or to short you will get LVD when the fridge cycles or other short heavy draws. I have mine set at 11.5 Volts for a minute too. My pig of an inverter has a constant 2+ amp draw.
  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Alaska Man wrote: »
    Same here, if it's set to close or to short you will get LVD when the fridge cycles or other short heavy draws. I have mine set at 11.5 Volts for a minute too. My pig of an inverter has a constant 2+ amp draw.
    If a fridge or freezer has a defrost timer, it will not be happy with an inverter that has a "sleep" mode where it does not supply power in the absence of a minimum load.

    SMA SB 3000, old BP panels.
  • South Africa
    South Africa Solar Expert Posts: 295 ✭✭✭
    I got a Victron Battery monitor to calculate the SOC.
    5kVA Victron Multiplus II, 5.2kW array, 14kWh DIYLifepo4 bank, all grid-tied.