Calculating Battery Life for a 3000W Inverter Load

To determine how long a 12V 100Ah battery can power a 2500W load through a 3000W inverter before discharging below 10V, we can use the following steps:

Calculating the Current Draw

The current I drawn from the battery can be calculated using the formula:

where:

By substituting the values into the formula:

I 2500W / 12V ≈ 208.33A

Determining the Usable Capacity of the Battery

A typical lead-acid battery should not be discharged below 50% of its capacity to avoid damage. However, for this calculation, we will consider the total capacity. The total capacity of a 12V 100Ah battery is 100Ah.

We need to find out how many hours the battery can supply 208.33A before reaching a voltage of 10V:

Time Capacity / Current 100Ah / 208.33A ≈ 0.48 hours

To convert hours to minutes:

0.48 hours × 60 minutes/hour ≈ 29 minutes

Conclusion

Under these conditions, the 12V 100Ah battery can power a 2500W load for approximately 29 minutes before discharging below 10V.

Note: Actual performance may vary based on battery age, temperature, and inverter efficiency.

Important Considerations for Battery Usage

To calculate the discharge time, divide the battery capacity in amp-hours by the load current in amps. Then, adjust for efficiency factors and consider safety margins. Keep in mind that discharging a battery below 10V can reduce its lifespan. For precise calculations, consult battery specifications and consider professional advice.

Before considering the current setup, it is advisable to downsize the inverter to 1000 watts. This way, you can get about an hour of operation at 70% capacity.

If you are using a LiFePO4 battery, the recommended voltage is around 12.9V when the battery is 20% charged. At 90% charge, the voltage is around 13.3V. You should target around 12.9V for optimal performance.

Do not be concerned with the voltage; the usable capacity is what matters. Around 70% or 70Ah, the battery should be used.

Avoid abusing the battery; safely charging to 100% takes too long. For accurate calculations, do not use 80%.

The inverter should not run at 100% power. Around 700 watts would be more appropriate.

Typical losses in inverter circuitry and the effects of heat need to be considered. A good inverter with proper leads typically experiences a 5% loss.

Not all batteries are the same. Ensure you check the rated discharge capability of your battery. If it is not a LiFePO4 battery, this guideline does not apply.

If you need 2500W of power, you would require a minimum of three LiFePO4 100Ah batteries for about 45 minutes of operation.

Further Reading

Explore more about batteries in my Quora Profile! For more detailed information on battery specifications and usage, refer to additional resources available online.