Inverter shutting off under load

PluckaPlucka Posts: 60Registered Users ✭✭
At 12.5 volts my 3000 watt inverter shuts down when I switch my kettle [900 watt ] on -same with the toaster but will run the fridge or freezer and continue to a lower voltage on my lithium batteries.Is this normal or is there a problem ?

Comments

  • karrakkarrak Posts: 307Solar Expert ✭✭✭✭
    edited June 29 #2
    A no load voltage of ~12.5V for a 4S LFP (LiFePO4) battery equates to an SOC of ~11%[edit:original 5% was a mistake] . At this low SOC the output voltage will drop very quickly under a high load.

    Is it the Inverter or the BMS shutting the inverter down? Could you give me more details about your BMS and the LV cutoff for the inverter

    Simon
    Off-Grid with LFP (LiFePO4) battery, battery Installed April 2013
    32x90Ah Winston cells 4p8s (24V), 4kW Latronics Inverter, 1160W of Solar Panels, homemade MPPT controller
    Homemade BMS https://github.com/simat/BatteryMonitor
     

  • PhotowhitPhotowhit Posts: 4,731Solar Expert ✭✭✭✭
    We have often noted that 3000 watt inverter or anything over 1500 watts is difficult since you must use very large cables due to the voltage drop on smaller cables. How far is your inverter from the battery bank and what size cables are you using?
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, ForkLift battery. Off grid for @13 of last 14 years. 1000 watts being added to current CC, @2700 watts to be added with an additional CC.
  • PluckaPlucka Posts: 60Registered Users ✭✭
    Under light load I've seen the voltage at 11.9 volts.I think it's the bms that is doing the shut down.The whole 360 amp/hr lithium setup is very compact and the cables don't get warm.I don't know the cutoff for the inverter as the manual gives no figures for anything
  • karrakkarrak Posts: 307Solar Expert ✭✭✭✭
    I hope this graph is of some use.


    11.9V at a load of 0.05C (~200W for your system) for a 4s 12V LFP battery equates to 2975mV/cell which equates to an SOC ~3%, a voltage of 12.5V (3125mV/cell) with a load of ~900W (~0.2C) equates to an SOC of ~11% (I made a mistake in my first post). Any variation it the internal resistance/impedance of the individual cells will result in a larger voltage difference between the cells so with no load we can get a situation where all the cells are at the same voltage but at a load of 0.5C the difference between the cells could be 0.050V or even higher. In this case the average cell voltage could be ~3.1V but the lowest cell could be ~2.8V or lower. Any mismatch in the balance of the cells will also add to this voltage difference.

    It is a good idea to keep the cell voltage greater than 3.2V (12.8V for a 12V battery) or SOC greater than 20% to extend the life of the battery and use the last 20% as an reserve. If you are getting down to these low voltages frequently I would look at increasing the number of solar panels you have on your system.

    Simon

    Off-Grid with LFP (LiFePO4) battery, battery Installed April 2013
    32x90Ah Winston cells 4p8s (24V), 4kW Latronics Inverter, 1160W of Solar Panels, homemade MPPT controller
    Homemade BMS https://github.com/simat/BatteryMonitor
     

  • PluckaPlucka Posts: 60Registered Users ✭✭
    Thank you Simon,I'm looking at getting another 200 watt panel to put on the side of the van so it can be adjusted to the sun rather than having them flat on the roof.
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