What Inverter Size Do I Need to Run a Laptop?

For many people, laptops are indispensable for work, play, communications and every day activities. So this brings up the matter of what inverter size is required to power a laptop? Well the answer is not quite cut and dried since there are a lot of factors to consider.

A 100W inverter can run a standard laptop, but more power is needed if you add a printer, router and speakers. High end gaming laptops will require at least a 400 watt inverter.

How to Calculate Inverter Size for a Laptop

To figure out the right inverter for your laptop, we have to do some math. Do not worry though as it is pretty straightforward.

The formula is:

Laptop watts + 20% = inverter size

A typical laptop for business applications uses 100 watts. Most inverters have an 85% efficiency rating, so you need to add at least 15% to run the laptop. For safety reasons, let us make that 20%.

100 + 20% = 120

So a 100 watt laptop needs 120 watts of inverter power to run. That is the minimum requirement though, and it won’t hurt to use a larger inverter. If you add a modem (10W), printer (10W) and speakers (20W), the entire system will need at least 150 watts of inverter power.

For a basic laptop, a 100 watt power inverter will be enough. The Ampeak 100 Power inverter is great for laptops and mobile devices, and you can use it a home in a car or RV.

Of course there are different types of laptops, but you can use the same formula for them. To get the best possible results, check the power consumption specs on your laptop, which should be in the manual.

The 20% addition in the formula can be modified depending on the inverter efficiency. In this case it is 20% because the inverter is 85% efficient. If you have a 90% efficient system, you can reduce this to 15% or 10%.

How Much Power Does a Laptop Computer Use?

Power consumption depends on several factors, the most important being the specs, the type and how you use it.

• The most portable laptops, or netbooks or chromebooks, use as little as 40 watts. You can run these on a portable solar panel easily. These are also called ultra portable or ultrabook laptops. Very little inverter power is required.
• A regular business laptop needs 60 to 100 watts, though some models might be in the 150 watt range.
• Gaming laptops need at least 250 watts inverter power, probably more. If you upgrade the system and add a powerful graphics card, RAM, CPU etc., power consumption can reach 300 watts or more.

Even a gaming laptop is more energy efficient than a heavy duty desktop gaming system though. A high end, customized gaming rig can use up to 800 watts and require a 1000 watt inverter. And that does not count the modem or other peripherals.

The bottom line is a laptop can be as basic or advanced as needed. A laptop used to write Word documents and browse the web will consume less power than a system that runs the latest games.

Usage is another factor. How many hours do you use it? Some people run their laptops for a few hours to write or prepare a presentation. Others may play games or watch movies for most of the day and through the night.

A gaming laptop that runs most of the day needs a more powerful inverter than a system that uses mostly Office applications. You have to consider how you use the laptop to determine what inverter is most appropriate.

Just like with solar power in general, it never hurts to have more power. If you are going to use other devices with your laptop, a larger inverter is worth considering as it will run longer. Having the best laptop solar chargers is also going to help of course.

How Many Batteries Does an Inverter Need to Run a Laptop?

The answer depends on how much power is available to the inverter. In an off grid system, the inverter is connected to a battery bank, which supplies the energy needed to run appliances.

The inverter battery bank determines how long you can run the laptop in a solar power system. A 12V 100ah deep cycle battery can power a 100 watt laptop for 5-6 hours, assuming it is the only load on the system.

A 12V 100ah battery holds 1200 watts (ah x volts = watts). Flooded lead acid batteries (FLA) have a 50% depth discharge (DOD) so only 600 watts are usable, meaning the inverter can run the laptop for 5-6 hours. We tried several and find the Weize 100ah 12V AGM to be very efficient.

These calculations assume the inverter and battery will only run a laptop If you add another appliance or other load, the inverter has to allocate resources to it. That will shorten the running time available for the laptop and the rest of the load.

Inverter Efficiency and Battery DOD Explained

When calculating battery runtime keep the inverter efficiency rating in mind. A 90% efficient inverter will use 10% more watts than the laptop requires, so a 100 watt laptop will use 110 watts. These will apply whether you use a pure sine or modified sine wave inverter.

If the battery has a 50% DOD, just divide the available watts in two. If you have a 250W laptop and a 12V 150ah battery, the laptop can run for approximately 3.6 hours, give or take a few minutes depending on the inverter rating.

150ah x 12V = 1800 watts
1800 watts / 2 = 900
900 / 250 = 3.6

You can follow these same steps regardless of the battery or laptop size. However you need to make some adjustments depending on the battery depth discharge rate.

In the example above we used 50% because it is typical for FLAs. But some deep cycle batteries like AGM have a 70% DOD.

70% of 1800 watts = 1260
1260 / 250 = 5.04

A 250W laptop connected to a 12V 150ah AGM battery can run for 5 hours compared to 3.6 hours on a 150ah FLA battery. This assumes the battery is not fully discharged. You can empty both batteries and get the same runtime. But doing so is not good for the battery so it is best to recharge at the recommended rate.

With a lithium battery you can get an even longer runtime, from 70% to 100%. Lithium batteries are more expensive, but it is the price to pay for that extra power.

Which Battery Should I Use with an Inverter?

It depends on your power requirements. Chances are that laptop is not the only device you will be running on the inverter. You have to consider the type of appliances you will use and for how long.

Deep cycle FLA batteries have limitations, but they are still the most popular due to their availability and low cost. For the most part your appliances will run fine on them. Just keep the 50% DOD limit and you will be fine.

And the discharge rate will not be much of an issue if you have solar panels. In off grid systems the panels keep the battery fully charged at all times, so even if a laptop and other devices run on the inverter, the battery does not lose power.

The battery only starts using its reserve power at night. However it gets recharged in the morning so you can keep using your laptop indefinitely as long as the panels keep the batteries charged.

In short, FLA and AGM batteries are good enough for most cases. if budget is not an issue and you want more power, lithium ion batteries are the best bet. If we are just talking about laptops though, any 12V deep cycle battery is enough.

5 Tips For Running a Laptop with an Inverter

• Modified vs. pure sine wave inverters. A pure sine wave inverter provides greater efficiency. There are some good quality modified sine wave inverters available which you can buy. If you are going to run sensitive and modern electronics on your system though, pure modified sine wave is ideal.
• Check the laptop power specs. This is going to save you a lot of time calculating and estimating the inverter requirements. You just need to add 20% to the laptop power consumption and your system is ready to go.
• Calculate the entire power load. Your laptop might only need 100 watts from the inverter, but what other appliances you will be running? Add them all up, including the efficiency rating and the battery DOD, and you have your inverter system.
• Leave room for upgrades. Laptops have to be replaced or upgraded at some point, and this means more power will be required. It is easier to upgrade a laptop than an inverter and battery bank, so make sure that your solar system has enough power to run whatever laptop you have now and possibly in the future.
• Do not run the inverter to the limit. If you added the total load for the laptop and everything else and it comes to say, 1000 watts an hour, the inverter must have 1200 to 1500 watts power. This is not just for the inefficiency, but also because pushing the inverter to its limit is not a good idea.

Conclusion

The nice thing about laptops today is you have a lot of options. From high powered machines to basic systems, there is one that should match your inverter and solar system specifications. And with today’s high powered inverters, getting that laptop to run is not going to be an issue.