How Long Will A 12 Volt Battery Run A Fan? (A Short Guide)

Last Updated: March 3, 2023

Wondering how long a 12v battery will power a fan during summer camping? You're in the right place.

This is going to be a short but on-the-point guide to figuring out the 12v battery runtime on any size fan.

To determine how long will a 12v battery run a fan will depend on a few factors:

Battery Capacity (Ah)
Battery DoD limit
Fan wattage consumption
Inverter efficiency

How Long Will A 12 Volt Battery Run A Fan? in short, a 12v 70Ah lead-acid battery (with a 50% DoD limit) will run a portable 12v 50W DC fan for about 8.4 hours.

Need a simple solution? Use Our battery runtime calculator to find out.

Table Of Contents show

Calculate how long a 12v battery will power fan

Now let's dive deep into some calculation stuff so again you'd never have to use any calculator to figure out the backup time of your battery.

12v Battery Capacity in watts

There are mainly 3 types of batteries, lead-acid, AGM, and lithium.

Lead-acid, and AGM batteries have a DoD (depth of discharge) limit of 50%. Which means you can only discharge them half. But the lithium (LiFePO4) batteries can be fully discharged up to 100%.

This was just a basic overview of batteries if you're a noob. Now let's get into some calculation stuff.

First, let's calculate the battery capacity in watts from amp-hours (because the fan's capacity is measured in watts).

Battery capacity in Watt-hours = Battery Ah * Battery Volts

For Example

Let's suppose you have a 12v 100Ah lead-acid battery.

100*12 = 1200Wh or 1.2kWh

To calculate the useable Wh multiply the value by 2 for lead-acid, AGM, and gel battery types (Because of their 50% depth of discharge limit).

1200 * 0.5 = 600Wh

You have 600 Wh of useable power stored in a 12v 100Ah lead-acid battery.

This guy has explained wonderfully about batteries. watch this if you're a beginner.

Inverter Efficiency

An inverter will be required to run an AC fan (which consumes 120-220V input). But some small fans required DC current (12v) which you can run directly from a 12v battery.

When converting DC into AC there will be some power loss because usually, inverters are only 85-90% efficient.

This means a 100W inverter will consume 100W DC power from the battery bank and only will be able to output 85-90 AC watts.

So if you're running an AC or DC fan with an inverter with a 12v battery then minimize the DC to AC conversion loss from battery watt-hour capacity.

For example:

Let's continue with the previous example. 12v 100Ah lead-acid battery.

600 * 0.85 (for 85% inverter efficiency) = 510 AC watts

You would get 510 AC watts from a 12v 100Ah lead-acid battery with a 50% depth of discharge limit.

Related Post: Solar DC Watts To AC Watts Calculator

How Long Will A 12 Volt Car or Deep Cycle Battery Run A Fan? Chart

Here's a chart showing how long a 12v 50Ah lead-acid battery will run a fan.

Fan Type	Wattage Consumption	Est. Runtime (hrs) on 12v 50Ah Battery (50% DoD limit)
12v Small Portable DC Fan	10 watt	30 hrs
12v Medium Portable DC Fan	30 watt	10 hrs
12v Ceiling DC Fan	60 watt	5 hrs
Medium AC Fan	70 watt	3.6 hrs
Ceiling AC Fan	130 watt	1.9 hrs

_{^{chart - How long will a car battery run fan}}

Note: Check the input wattage consumption of your fan in the product description session (usually located on the back side of every fan) and make the calculations for you accordingly.

What size inverter do I need to run a fan?

There is one rule of thumb. Multiply the wattage consumption of your fan by 1.2 when selecting the size of an inverter.

For example, to run a 50W fan you would need a 60-watt inverter.

But yes obviously you're not just gonna run a fan with an inverter. So keep in mind the above rule of thumb to select the size of an inverter according to your need.

Summary

To calculate how long a car or 12v battery will run a fan, Divide the battery amp-hours by the fan input amps. but it will completely discharge the battery which you can achieve only with a lithium battery, if you have a lead-acid, AGM, or Gel battery type then the runtime will be half.

I hope this short guide was helpful to you, if you still have any queries LEAVE A COMMENT or contact us. Thank You!

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Chris Tsitouris

Chris Tsitouris is a renewable energy professional with 10+ years of experience as Director of Engineering at Solar Spectrum, previously working as Project Manager at SunPower and Energy Analyst at the National Renewable Energy Laboratory. As a thought leader, Chris has authored numerous articles and research papers.