strange action

PluckaPlucka Registered Users Posts: 123 ✭✭
when I use my electric kettle after a few seconds my 12 volt to 240 volt system switches off on for a split second but nothing actually stops working.Why is this happening?I'm not connected to the grid.


  • BB.BB. Super Moderators, Administrators Posts: 31,688 admin
    What is the DC bus voltage/input voltage to the AC inverter? 240 VAC electric kettles can run something like 1,300 Watts? That is >>100 amps at 12 VDC, and needs heavy/short cabling and  a good size battery bank (suggest >>500 AH @ 12 volts) to avoid pulling more current than the battery bank can supply (a single car battery can supply ~100 Amps for a few tens of seconds, but that is about it for less than 100 AH 12 volt battery).

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • PluckaPlucka Registered Users Posts: 123 ✭✭
    I have 12 volt 360 amp hour lithium batteries and the kettle is 900 watts,inverter is 1500watts ,surge 3000 watts. Would I be right to think  that the cables are not handling the sudden surge properly for a split second . This morning ,because it has been raining for two days,battery voltage was down to 13 volts and dropped to 11.8 volts while's the kettle was running and back up too 12.8 volts when it turned off
  • BB.BB. Super Moderators, Administrators Posts: 31,688 admin
    Resistance heaters typically do not have a large surge (there may be some, many elements can have lower resistance when cold).

    Placing a voltmeter right on the DC inputs to the AC inverter and see if it hits (typically) around 10.5 volts... Many will shutdown and stay off (non-inverting) and will not restart until the battery bus voltage hits something like 12.8 volts or so (inverter "assumes" the "dead battery" has been recharged again).

    Lithium batteries, typically, have very good high current output with much less voltage drop/sag vs Flooded Cell Lead Acid batteries. However, some BMS (battery management systems) may limit the actual maximum output current of the battery string/bank (as well as shut off the DC output if the battery/cell voltage is too high or too low).

    I have used a lot of "weasel wording" above (typical, many, assumes, etc.)--There is just way too many different vendors and products out there these days to make blanket statements that are "mostly true"... Between reading the manuals and doing some metering/experiments may tell you more.

    Just as an FYI, here is how to estimate your wiring voltage drop... Nominally, I suggest 0.5 volts max on a 12 volt bus at max continuous load. That would be discharging to 11.5 volts (loaded) on an FLA battery with 0.5 volt to inverter or 11.0 volts at inverter input (and if your inverter supplies 2x surge current, that would be a 1.0 volt drop on the same wiring).

    The math:
    • 900 Watts * 1/0.85 AC inverter eff * 1/10.5 typical inverter low battery cutoff voltage = 100.8 Amps at load
    Using the NEC wiring table (simplified):

    Assuming 2 AWG cabling (95-130 amp rated). Let's say you are using 6 feet (one way cable run) of 2 AWG DC cabling from battery to inverter. A simple voltage drop calculator:

    Gives us:
    Voltage drop: 0.094
    Voltage drop percentage: 0.79%
    Voltage at the end: 11.906
    About 0.1 volt drop... Now 2 AWG is pretty heavy cable... And other tables could suggest using 6 AWG for 100 amps (marine table):

    6 AWG cable, 6 feet, 100.8 amps:
    Voltage drop: 0.48
    Voltage drop percentage: 3.98%
    Voltage at the end: 11.52

    Which is pretty much my suggested 0.5 volt maximum drop (assuming 6 volt wire run).

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • PhotowhitPhotowhit Solar Expert Posts: 5,577 ✭✭✭✭✭
    I think Bill has very kindly said the voltage drop you are seeing is due to the wires between the lithium batteries and your inverter.....

    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former, 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
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