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How to calculate run time of inverter

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bobdxcool

Member level 5
I have a 24volt inverter (2kva). There are two 12V, 200AH AGM (C20 at 27 degree c)batteries connected in series to the inverter input. Now, if I have a constant load of 2.5 amperes at 120V, how do I calculate the run time of the inverter for 70% DOD, 50% DOD, 30% DOD, 100% DOD ? Is there some forumula ? The power factor of the inverter is 0.8 and efficiency is 0.92. Also, how much time would it take to charge the batteries (40-50 amps charging current) back to 100% from 20%,30%,50%,70% of charge left ? I have a lead acid charger which can charge upto 50 amps.

The battery manufacturer says:
Charge Regime:
Batteries shall be charged in constant potential mode with current limit. Float charging voltage: 13.5 volts per module Boost charging voltage: 13.8 volts per module Current limit: 20.0 Amps to 50.0 Amps

Super Moderator
Staff member
Your batteries have 4800 Watt-hrs (24v x 200AH).

Your load draws 300 W. Efficiency is reduced 15 or 20 percent due to losses. Therefore say you draw 360W from the batteries.

Then your batteries might last 13.3 hrs, until they are 100% discharged.

To discharge to 50% DOD, then run for 6.7 hrs. Etc.

bobdxcool

Member level 5
Your batteries have 4800 Watt-hrs (24v x 200AH).

Your load draws 300 W. Efficiency is reduced 15 or 20 percent due to losses. Therefore say you draw 360W from the batteries.

Then your batteries might last 13.3 hrs, until they are 100% discharged.

To discharge to 50% DOD, then run for 6.7 hrs. Etc.

Thank you.
Also, how much time would it take to charge the batteries (40-50 amps charging current) back to 100% from 20%,30%,50%,70% of charge left ? I have a lead acid charger which can charge upto 50 amps.

Super Moderator
Staff member
Starting from 0% charge, charging at 50 A will take 4 hrs.

From 50% charge, 2 hrs. Etc.

These are only rough calculations.

Typical battery voltage when discharged is 10.5 V. It's best to avoid letting the battery drop below this point.

Typical voltage as charging ends is 14.4 V. After 24 hours it usually settles to 12.8 or so.

While the battery is discharging, you can take voltage readings and 'estimate' how much charge remains. This is only approximate, of course.

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