When to turn off your inverter?

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System
System Posts: 2,511 admin
in Off Grid Solar & Battery Systems #1
When using deep cycle batteries with your inverter is it safe to run your loads until the inverter begins to give a low voltage sound for example when it reaches 11V it starts to beep then you would turn off the inverter? Or should you check the voltage and turn it off before the alarm sound comes on say for example when the battery is reading 11.9V under load then you should turn off the inverter?

Reason why I asked this is because I want to know what voltage reading should you work with for the battery to know the safe discharge for deep cycle battery. Is it when the battery is under a load or when it is unloaded? Due to the fact that when a battery is under a load and say for example it is showing 11.8V when you remove the load from the battery the battery voltage rises up again sometimes greatly depending on the load that was on it.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
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    Re: When to turn off your inverter?

    Right you are: loads will draw Voltage down. Especially on a 12 Volt system. Sometimes a sudden load will create such a drag that the inverter "thinks" the Voltage is too low and will shut down.

    Voltage isn't an ideal method of determining State Of Charge. But it is important because of the low Voltage shut-down. In this case the Voltage under load is what matters. 10.5 Volts is basically dead for a 12V battery, so an 11 Volt shut-down point is really as low as you'd ever want to get.

    If you find this happening often and/or if there is a significant Voltage shift from a load coming on you need to re-evaluate your system. It may not be heavy enough for the loads, or there may be a wiring problem (undersized DC cables will aggravate this condition drastically).
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  • Windsun
    Windsun Solar Expert Posts: 1,164 ✭✭
    #3
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    Re: When to turn off your inverter?

    .8 volt difference between loaded and unloaded seems pretty high. Where did you measure that at - right at the battery? If so, they might have a pretty high internal resistance - or maybe just cheap batteries with small internal busbars to save on Lead.
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  • boB
    boB Solar Expert Posts: 1,030 ✭✭✭✭
    #4
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    Re: When to turn off your inverter?

    Remember too, that battery cable inductance can affect the voltage readings under load. and won't be affected by how large the cable wire size is. Length and cable routing will though. Make sure the cables, if very long, are wound together or at least held close together as best as possible to reduce inductance effects.

    It may not this but can't always be sure unless it's tried. Shouldn't affect the voltage reading at the battery itself usually but certainly at the inverter terminals.
    Sometimes the peak voltage can go way up due to resonance from the cable inductance and the filter capacitors in the inverter across the battery terminals.

    boB
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