SW4024 Blip

stmar Solar Expert Posts: 372 ✭✭✭
I have my system set up as a UPS, battery bank stays fully charged when grid is up. Normally we get a slight flicker of lights when system goes into Bulk if grid comes back up after being down. The other night my pellet stove motor cut off briefly, light flickered and sure enough system was in Bulk indicating that the grid had been down then came back on line. The problem with that is I was watching TV, signal comes through the internet router which is on the grid, and it did not falter so no way the grid was down. I looked at the Combox records and saw no faults or any obvious anomalies. Any ideas why the system would go into Bulk for no obvious reason? It did not take long for it to go to Absorption then Float, maybe 5 or 10 minutes.   


  • BB.
    BB. Super Moderators, Administrators Posts: 33,490 admin
    Can you tell us the actual battery bus voltage (i.e., 29.5 absorb, 27.6 volts float)?

    What brand/model/type of batteries (AGM, Flooded cell, etc.)? Age of battery bank? Average bank temperature?

    Do you see any "strange" bus voltage variations?

    Check the voltage of all batteries (i.e., across each 2/4/6/12 volt battery)? Are the batteries all near the same voltage or are there "large" variations?

    If flooded cell, have you checked/logged each cell sg?

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • stmar
    stmar Solar Expert Posts: 372 ✭✭✭
    Absorb = 28.8 Float 26.6
    4 Lifeline 12 volt 256ah AGM = 24 volt 512ah bank, about 3 years old, temp this time of year averages around 60F
    Can't see any extreme variations or anomalies. Battery voltages are within a few tenths, no large variations.

    System seems to be working as it should but I get a bit paranoid when something out of the ordinary happens. I am sure there is an explanation but may be above my pay grade.
  • RCinFLA
    RCinFLA Solar Expert Posts: 1,484 ✭✭✭✭
    edited February 2022 #4
    When grid goes down there are a couple of things that happen in SW4024.

    First there is normally a momentary overload on inverter from grid dropping which it detects and immediately opens connect relay releasing from grid.  If it is just a short glitch, ACin voltage is detected, and the inverter will still be in phase sync so it will almost immediately reconnect to grid.  The initial inverter overload usually dips the battery voltage enough to trigger a new bulk/absorb charge cycle whenever there is a grid glitch.

    The overload detection and relay bounce impart a small glitch in ACout.  

    How a given device rides across the glitch depends on the particular device.  Most electronic equipment has a power supply with AC-DC conversion which includes a DC filter capacitor.  Depending on size of filter cap and how much power the device is drawing it may easily ride across the glitch.

    You might find a situation on a desktop computer that when idling or running a light application load it rides through glitch but when playing a CPU/GPU intensive game consuming a lot of power it will cause computer to reset and restart.

    The inverter relay contacts take a beating from the high current openings and re-closings.  One of the common failures is 'welded relay' failure where relay contacts get fused together. 

  • stmar
    stmar Solar Expert Posts: 372 ✭✭✭
    Are you saying that the grid interruption may have been so brief that the router/internet did not react but the pellet stove motor did? I do have a surge suppressor on my main panel so hopefully that helps with the inrush after an outage, had real issues with that with my old Xantrex.