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Every amp counts if you are off the grid. Take floor fans for example. We don’t really consider how much power it uses, but if your system runs on solar panels and batteries, power usage becomes important. So let us take a look at how many amps these fans consume.
A 120V floor fan draws 0.8 amps an hour or about 100 watts. If this fan is plugged into a 12V 100ah battery, it is going to draw 8.3 amps and will run for 10 to 12 hours.
How to Calculate Amps Used by Floor Fans
The easiest way is to look at the amperage rating. You can find this on the fan itself or the instructions. If the instructions are in watts, use this formula:
Watts / volts = amps
Most electric fans in the US are 110 or 120 volts. So if your floor fan is 100 watts:
100W / 120V = 0.8A
A typical floor fan draws less than 1 amp an hour. If you want to plug this into a deep cycle battery, the voltage will drop to 12V, 24V or 48V.
If you use the same 100W floor fan on a 12V 50ah battery, the numbers look like this:
100 / 12 = 8.3
The fan that pulls 0.8 amps off 120V now draws 8.3 amps from a 12V system.
The Ampere Time 12V 50ah battery can run this floor fan for 5 to 6 hours. 8.3 x 6 equals 49.8, but battery discharges are not 100% exact. If the fan pulls 5 amps an hour, it is a safe bet the battery is good for 10 hours. But anything more than 5A and the discharge accelerates.
Floor Fans vs. 12V Fans
If you want to save even more power, consider 12V fans. These are not converted from 120V but designed specifically to run at 12 volts.
A typical 12V fan draws .25A or 3 watts. Compare the 8.3 amps from a floor fan to the .25A of a 12V fan, and that 50ah battery will last way longer.
Of course there are also energy efficient floor fans available. Many are rated at 0.8 amps, but most of them use probably less than that. Even if it did use 0.8A, a good sized battery bank should last.
Given a choice it is better to have a 12V fan as it uses less power. But if you have a floor fan, it will still run.
How Many Batteries Do I Need to Run a Floor Fan?
The answer depends on the fan’s power consumption, how long you need to run the fan and the battery depth discharge.
A 150ah 12V battery can run a 100 watt floor fan for 15 to 17 hours. This runtime will completely discharge the battery. If you want to recharge at 50%, the fan runtime will be 7 to 8 hours.
These calculations assume the battery is only going to run the fan. If it is going to carry another load, adjust the battery runtime accordingly.
Take the same 100 watt floor fan but this time add a 100 watt laptop. This doubles the draw to 16.6 amps. From 15 to 17 hours the battery will only last 7 to 8 hours. If you follow the 50% DOD, the battery is good for 4 hours.
If you use a 12V fan the power requirements drop less. But if you load other appliances the demand goes up. Almost any battery will do if you are only going to run a floor fan. But if you run other appliances you will need a larger battery bank.
To make things easier, list all the appliances you want to run on the battery with the fan. Add the watts and convert it to amps. Next, determine how many hours you want to run all of them.
Suppose you want to load a fan, a TV and a couple of light bulbs for four hours. Assume the following:
- floor fan: 100W
- TV: 150W
- 2x light bulbs: 120W
- Total: 370W
The load is going to use 370 watts or 30 amps an hour. You need at least a 120ah battery. Double this to 240ah if you want to recharge the battery bank when capacity drops to 50%.
How Many Solar Panels Do I Need to Run a Floor Fan?
A 100W solar panel can power a floor fan. But due to inefficiency and weather variables, it is better to use a 150W solar panel for a 100W floor fan. You can also use the Newpowa 200W Solar Panel for additional power.
In theory a 100 watt solar panel is enough to run a 100 watt floor fan. But this assumes the panel rating matches the output, which does not always happen.
A 100 watt solar panel can generate 100 watts, but that is the maximum output. Most solar panels achieve peak output during summer at noon. For the rest of the day the output drops to less than 100 watts, which means there won’t be enough power to run the fan.
If you use a 150W solar panel it should be enough to generate the power a100W floor fan needs. As long as the sky is cloud free the fan will run.
However you will not be able to use the fan at night. That is why it is better to run appliances off a battery bank. Use solar panels to charge the batteries so the battery is always full.
This approach does two things. One it keeps the battery charged for longer periods. Two you don’t have to worry about cloudy skies or rain affecting the fan.
Do I Need an Inverter?
If you have a 120V floor fan and want to run it on a 12V battery bank, you need an inverter to convert the volts. You will also need an inverter if you are using a solar array.
Solar panels generate DC power. Most home appliances are AC so they won’t run. An inverter turns DC into AC before the current goes into the battery. Without an inverter you won’t be able to use the fan.
If you have a DC powered 12V floor fan, you can do without an inverter. You can connect DC powered devices directly to solar panels. But if the fan is running at 110V or 120V, you will still require an inverter to drop the voltage to 12V.
And if you are going tor power a lot of appliances on solar, an inverter is a necessity. Even if your floor fan is on DC, the rest of your appliances are dependent on AC power. So you must have an inverter to go along with your battery bank.
Tips For Using Fans on Batteries
If you have not already, buy an energy efficient floor fan. This is going to make a huge difference when it comes to power consumption.
Buying a new energy efficient fan is easy and cost effective. Fans are more affordable than AC, and the savings you get from it is the important thing. This applies not just to floor fans but other appliances you wan to run on batteries and solar power.
Buy from a reputable manufacturer. This ensures the fan consumes the power stated in its specs and not more. In fact, the most energy efficient fans use less power than the stated amount. A floor fan listed at .8 amps might consume 0.5 or less.
Calculate the runtime. Use the guidelines and examples given above. By knowing how long you need to run the floor fan and its amps, it is easy to figure out what battery size is needed.
Always assume you will use more power. If your calculations show you need 120 amp hours, get a 150ah battery. If you need 150ah, get a 175ah or a 200ah battery. It is better to have more power than not enough.
Having reserve capacity is also going to come in handy in case of power outage. With sufficient battery, you can run essential appliances comfortably.
The best thing about electric fans today is the number of options available. Whether you are on the grid or off, there is a floor fan that is going to suit your power requirements and budget.
I am an advocate of solar power. Through portablesolarexpert.com I want to share with all of you what I have learned and cotinue to learn about renewable energy.