XW 4024 DC Under Voltage warning (W 48 )

bohrahsbohrahs Registered Users Posts: 5
Off grid location.

Inverter -- XW 4024
Battery -- 660 Ah flooded

I get a DC Under Voltage warning (W 48 ) whenever I use my microwave in the evenings when the system is not charging.

The SCP starts to beep about 10 seconds into the use and stops after the microwaving is done.

LBCO = 23.2 V
Cable length from the battery to the inverter = 4 ft
cable thickness, d = 12mm
microwave wattage = 1400 w

These are the readings (SCP and Trimetric ) before and during microwave use:

Before:
Voltage -- 24.7 V
Load -- 300 W
Battery Level -- 95%

During:
Voltage -- 23.8 V
Load -- 1727 W
Battery level -- 95%

After:
Voltage -- 24.6 V
Load -- 286 W
Battery level -- 95%

What could be causing this?

Hemendra

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: XW 4024 DC Under Voltage warning (W 48 )

    Checking the numbers says it should work fine.
    Your battery cables are 4/0 equivalent and only 4 feet long. They should handle 300 hundred Amps.
    The microwave should pull about 58 Amps (1400/24 = 58 ).
    That isn't 10% of the battery capacity either.
    So unless there's huge other loads drawing ...

    I'm thinking your batteries are three parallel strings of 220 Amp hour 6 Volt GC2's?

    This brings up the possibility of high resistance in the wiring of the battery bank: laddered connections, corroded terminals, unequal wiring length. Something like that.

    Have you checked the specific gravity on the batteries to be sure they really are getting fully charged? It is always possible the Trimetric is reading inaccurately. Check the SG first.
  • bohrahsbohrahs Registered Users Posts: 5
    Re: XW 4024 DC Under Voltage warning (W 48 )

    I have twelve 2-volt Volta DC470S/6 in series.

    will check the SG at 100% today.


    Hemendra
    Checking the numbers says it should work fine.
    Your battery cables are 4/0 equivalent and only 4 feet long. They should handle 300 hundred Amps.
    The microwave should pull about 58 Amps (1400/24 = 58 ).
    That isn't 10% of the battery capacity either.
    So unless there's huge other loads drawing ...

    I'm thinking your batteries are three parallel strings of 220 Amp hour 6 Volt GC2's?

    This brings up the possibility of high resistance in the wiring of the battery bank: laddered connections, corroded terminals, unequal wiring length. Something like that.

    Have you checked the specific gravity on the batteries to be sure they really are getting fully charged? It is always possible the Trimetric is reading inaccurately. Check the SG first.
  • BB.BB. Super Moderators, Administrators Posts: 32,608 admin
    Re: XW 4024 DC Under Voltage warning (W 48 )

    If you have a volt meter--Check the voltage of each cell under load, and check the voltage at the input lugs of the inverter.

    The batteries should be able to support ~23.0 volts, and the inverter could have its low voltage cutoff as low as 21.0 volts (allow for up to 2.0 volts drop across wiring--wprse case).

    At this point, looking for "differences"... A bunch of cells with normal voltage, and one or two cells significantly less.... A voltage drop across a cable or connection that is higher than anywhere else (corrosion, loose connection, etc.). Or a "hot" connection/wire (again, loose/dirty/corroded connection).

    What is the battery bank/room temperature? Did the system every "work correctly"? Are these new or older batteries, etc...?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • NorthGuyNorthGuy Solar Expert Posts: 1,913 ✭✭
    Re: XW 4024 DC Under Voltage warning (W 48 )

    The warning comes at 23V (according to docs). However, your LBCO is set higher than this. My guess is that your high LBCO causes warning at higher voltages. If that's true, setting LBCO to 22V should eliminate the warning.

    The voltage should drop under load. That is normal. Especially if batteries are not fully charged. You say they're at 95%, but 24.7V would rather indicate a battery that is somewhat discharged. Your drop, perhaps, is a little bit too big, but 1400W is about 10% of battery capacity and you would have a sizeable drop anyway.
  • bohrahsbohrahs Registered Users Posts: 5
    Re: XW 4024 DC Under Voltage warning (W 48 )

    Bill,

    The batteries are 3 months old. We had the low voltage warning problem from the start.

    These are the voltage readings:

    Scenario 1
    Battery Level = 98%
    Load = 950 watts
    PV input = 485 watts
    Battery temp = 26 C

    Voltage:
    1 -- 2.081
    2 -- 2.083
    3 -- 2.086
    4 -- 2.076
    5 -- 2.085
    6 -- 2.081
    7 -- 2.083
    8 -- 2.084
    9 -- 2.084
    10 -- 2.075
    11 -- 2.085
    12 -- 2.076

    voltage at the battery bank output = 24.97
    Voltage at the input lugs of the inverter = 24.92

    Scenario 2
    Battery Level = 92%
    Load = 970 watts
    PV input = 0 watts
    Battery temp = 27 C

    Voltage:
    1 -- 2.004
    2 -- 2.013
    3 -- 2.014
    4 -- 2.007
    5 -- 2.009
    6 -- 2.009
    7 -- 2.014
    8 -- 2.015
    9 -- 2.015
    10 -- 2.006
    11 -- 2.014
    12 -- 2.002

    voltage at the battery bank output = 24.05
    Voltage at the input lugs of the inverter = 23.94
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: XW 4024 DC Under Voltage warning (W 48 )

    It needs to be asked: what are the charging parameters for this battery bank set at? Particularly Absorb Voltage and time/end amps? Really your battery bank should be fully charged with a resting Voltage around 25.5, but it seems to be operating below 25 Volts all the time? This is why I am suspicious that they are not really at the SOC being reported by the meter.
  • BB.BB. Super Moderators, Administrators Posts: 32,608 admin
    Re: XW 4024 DC Under Voltage warning (W 48 )

    How are you measuring XX% state of charge? Battery Monitor? Hydrometer?

    The second measurement set at 92% SOC would seem to indicate that the bank is less than 92% state of charge, or is beginning to sulftate.

    Large batteries that are cycled below 80% SOC can need a fair amount of current and time to recharge--And sometimes higher voltage levels.

    How often are you having to replace water (distilled or equivalent) in the battery bank... Having to add some back every couple of months is probably about right. If you never have had to add water, they may be under charging.

    To fully charge a battery bank, you need to hold ~29 volts (depends on battery mfg. instructions) for 2-6 hours (2 hours if you don't discharge very deeply, 6 hours if deeply discharged). Some folks have found that they may need to add 0.5 volts to 2 volts to really get the battery bank fully recharged (again, depends on chemistry/battery construction).

    Check and log the temperature corrected specific gravity for all cells. And monitor one cell as you discharge and see what the S.G. levels are doing... Are you really using 10% of the battery state of charge, or are you cycling deeper than you expected.

    Battery variations (alloying with lead) can change behaviors... Batteries designed for Fork Lifts (very deep cycling) can use a lot of water and moderate voltages. Batteries designed for float service and low water usage (calcium) can need higher voltages to complete charging.

    A couple of good ways to tell when a lead acid battery is getting fully charged... As they approach 95-100% SOC, the battery will begin to "boil" or "fizz" (like a carbonated drink). If you have little gas being produced while the there is good current flow (over 2.5% of battery AH capacity), then it is not fully charged yet.

    Another is to monitor the battery charging current when holding absorb voltage (~29 volts)... You will see the charging current slowly drop over a couple of hours--To ~% to 1% or less of AH capacity (660 AH = 13.2 amps to 6.6 amps or less) and then "Level Off" (plateau) or stop dropping... At this point the battery bank should be full.

    If nothing like the above is happening, then you probably need more charging time or current. Are you using solar panels to charge or the XW Inverter/Charger connected to mains or generator to recharge the bank)?

    What is the size of your array (Vmp-array voltage, wattage, charging parameters -- Absorb Voltage, Absorb Timer, etc.)?

    Assuming all else is well--It sounds like dropping the LBCO voltage and checking how will the batteries are charging (specific gravity, charging parameters) are the two avenues of investigation I would suggest.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Dave AngeliniDave Angelini Solar Expert Posts: 6,138 ✭✭✭✭✭
    Re: XW 4024 DC Under Voltage warning (W 48 )

    Low battery cut out default is 22 volts after a 10 second delay. Check your setting first.
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

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