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Thread: Battery voltage drop under load

  1. #1

    Default Battery voltage drop under load

    I have just completed the install of my RV's solar electrical system.

    I've got 6 used 6Volt Crown industrial batteries. Each is rated at 325AH. That should be a total of 975AH for the 12 volt system.

    They are all charged up to 1.225 or higher SG and measure about 12.4 volts for each set.

    However, when I turn on the lights and am running a 225 watt load, the voltage drops to 11.9 volts.

    If I try to run a 1000 watt load, the voltage drops to 10.5 volts.

    My guess is that the batteries are sulfated and can't supply much output.

    Does this make sense? Or am I missing something?

    Tom

  2. #2
    Join Date
    Sep 2006
    Location
    Willits, CA
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    5,624

    Default Re: Battery voltage drop under load

    sulfated is a good guess. Try a couple deep discharges (down about 60%) and recharges, see if that will knock off some of the sulphate. How old are they ?
    http://tinyurl.com/LMR-Solar
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    Grundfos 10 SO5-9 with 3 wire Franklin motor (1/2hp 240V 1ph # 214505 ) on a timer for 3 hr noontime run - Runs off PV
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  3. #3
    Join Date
    Jun 2003
    Location
    pittsburgh, pa
    Posts
    10,247

    Default Re: Battery voltage drop under load

    allow the battery to get fully charged. the voltage will appear well over 14v on its way to a full charge.
    NIEL

  4. #4

    Default Re: Battery voltage drop under load

    One of the biggest problems we see with used batteries (even if they are "new") is that they sat around for a long time partically charged. That nearly always causes some sulfation, which sounds like the problem you are having.

    Someplace on the batteries there should be a date code that will tell you when they were actually manufactured.
    Northern Arizona Wind & Sun Forum & Website Administrator

  5. #5

    Default Re: Battery voltage drop under load

    They are all charged up to 1.225 or higher SG
    Check you manufactures recommendation, but 1.225 is not charged in my book, 1.255 >1.275 would be more like it.

    Have a good one
    Tim

  6. #6

    Default Re: Battery voltage drop under load

    These were made in 2007 and 2008.

    So can sulfation be reversed?


    Tom
    35ft Toy Hauler. 2 200W Sun Elect. Solar panels feeding an FM80 into 6 6V Crown CR325 batteries.

  7. #7
    Join Date
    Feb 2010
    Location
    South of Erie, North of Pittsburgh PA
    Posts
    943

    Default Re: Battery voltage drop under load

    Quote Originally Posted by Windsun View Post
    One of the biggest problems we see with used batteries (even if they are "new") is that they sat around for a long time partically charged. That nearly always causes some sulfation, which sounds like the problem you are having.

    Someplace on the batteries there should be a date code that will tell you when they were actually manufactured.
    If you are going to buy batterys, should you ask about the manufacture date? How old of a manufacture date should you accept ? I see in your store you recomend the Crown batterys. I have 2 distributors in the 80 to 90 mile distance from me. Are the trojans any better? I can,t see how they could be since the crown has thicker plates and is lots cheaper to buy. Since I live in Pa the freight from az. would eat me up if I bought from your co. Or do you sell them and I would pick up at the distributor close by me? Slarvic

  8. #8
    Join Date
    Jun 2003
    Location
    pittsburgh, pa
    Posts
    10,247

    Default Re: Battery voltage drop under load

    it is hard to say just how much sulfation may or may not be there, but without putting a full charge on the batteries you are going to windup with junk for batteries for sure. some say it can be reversed, but don't count on it as that is not proven technology. a good rough guess would be about 14.5v, but here is the page for charging crown batteries,
    http://www.crownbattery.com/?page=su...gingprocedures

    solarvic,
    they usually don't answer sales questions on the forum. you could call them up and have them answer any concerns you may have with the differences between buying from them and a local guy.
    NIEL

  9. #9

    Default Re: Battery voltage drop under load

    Can sulfation be reversed,
    A cut from a rolls manual, But as I said before, I do not think you have had your batteries fully charged (which you need to do before EQ) I would start with a good normal charge , watching the sg`s until they stop rising, then do an EQ till the SG`s stop rising, that should also give a better idea of battery condition before attempting corrective EQ
    Have a good one
    Tim

    Equalization - Corrective

    Corrective equalization needs to be performed if symptoms arise such as a constantly running generator (low capacity) or the battery bank will “not hold a charge”. These symptoms are typical of a heavily sulfated battery. If a battery is not being fully charged on a regular basis or limited equalization is performed using a generator (see Bulletin 611, Generators, Inverters and Equalization) sulfation will occur from “deficit” cycling. This undercharge condition can take months before it becomes a major and noticeable problem. This under charge condition is caused when batteries are deficit cycled. The bank receives less of a charge each cycle and starts to sulfate. Eventually the sulfate will cause a resistance to charge and a “false high voltage” reading will occur. The “false high voltage” is measured by the charge controller, which further lowers the charging current to maintain the voltage set point. This further increases the undercharge condition. This is one reason why specific gravity measurements are so important as “false high voltage” readings can be misleading. See Bulletin 609, Voltage, SG and State of Charge for information on how to correctly interpret voltage readings.

    Amperage hour meters can compound the problem and cause people to believe they are returning the correct amount of energy back into the batteries to maintain a good state of charge. Amp-hr meters should be thought of as simply a fuel gauge that does not measure state of charge directly but indirectly. The state of charge is determined by using an equation (peukert's equation). Sometimes there can be fundamental errors with factors used in these calculations. You should always confirm, at least initially, state of charge by taking a specific gravity measurement of one cell when it is thought the bank is fully charged.
    Corrective Equalization - Method

    Corrective Equalization can take a very long time depending on the degree of sulfation. It is not recommended to equalize with a generator as some generators produce low grade AC that is not properly filtered by the inverter. This is especially true at higher voltages.

    1. If you have hydrocaps remove during equalization.
    2. Set charging controls to the highest voltage allowable by the charge controller (inverter). If the bank is severely sulfated or available current is very limited, charge control can be removed or by-passed. Temperature should be monitored very, very closely and keep below 125ºF.
    3. Charge at a low DC current (5 A per 100 AH of battery capacity). If grid power is not available use solar panels or a good DC source when possible. At high voltages, charging with generator can be difficult and hard on the inverter.
    4. Once an hour, measure and record the specific gravity and temperature of a test cell. If the temperature rises above 115ºF (46ºC) and approaches 125ºF (52ºC) remove the batteries from charge. (For temperature measurement choose a center cell, if applicable).
    5. If severely sulfated, it may take many hours for the specific gravity to rise.
    6. Once the specific gravity begins to rise the bank voltage will most likely drop or the charging current will increase. The charging current may need to be lowered if temperature approaches 125ºF (46ºC). If the charge controller was by passed, it should now be used or put back in line.
    7. Continue measuring the specific gravity until 1.265 is reached.
    8. Charge for another 3 hours. Add water to maintain the electrolyte above the plates.
    9. Allow bank to cool and check and record the specific gravity of each cell. The gravities should be 1.265 ± 0.005 or lower. Check the cell electrolyte levels and add water IF necessary.

    To avoid this situation it is recommended that a specific gravity reading of one pilot cell is measured and recorded on a regular basis when it is thought that the bank is fully charged. The measurement should be compared to previous readings. If the measurement is lower than the previous reading a longer absorption time and higher voltage setting should be used. Note as stated above, the longer the absorption time and the higher the bulk voltage, the more water will be consumed but less equalization will be required. Note: the specific gravity should rise as the cells use water. Look for trends in the specific gravity over a period of time and make very small adjustments as necessary.

    Caution: If you have HYDROCAPS, remove during equalization.

  10. #10
    Join Date
    Jun 2007
    Location
    Williams Lake, BC
    Posts
    3,000

    Default Re: Battery voltage drop under load

    What kind/brand of charger are you using ? what is its amp rating?

    EJ
    100% Off Grid @ 51* 46' N lat 124* 44' W long

    New House system: coming - 2 arrays @ 2240W
    CL150&Epanel 2 @140 W 12v PVs , 24V C&D AT-15P AGM @ 950Ah
    + CL150 2@120W 12 V panels, 24V C&D AT-15P AGM @ 950Ah
    Cotek ST1500W inverter, TBS 30a-24v Omni-charger, Honda Eu3000is,

    Guest cabin system: 3 - 70W panels to SB 2000e CC, with 2 - 100 ah 12v SAFT wet NiCd's , 600W TSW Inverter

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