How to Easily Size A Portable Power System

Choosing the right size for a portable power system doesn’t have to be a head-scratcher. Imagine the confidence of knowing exactly how much power you need, whether you’re out in the wild, parked in an RV under the stars, or getting ready for any power hiccups at home. Read along this guide to sizing a portable power system to your needs.

From keeping your devices charged to ensuring you’ve got enough juice for the essentials, the right-sized system can make all the difference between a smooth experience and a power nightmare. Dive in for a quick, simple guide to help you stay powered up, wherever life takes you!

---

Step 1: List Your Devices and Their Power Needs

First, make a list of the devices you want to power. In our example for a 3-day camping trip, the list includes phones, laptops, lights, and a mini-fridge. Our list may be completely different depending on your application and lifestyle.

Each device has a power rating, typically measured in watts (W), which you can usually find on the device label, charger, or in the user manual. Here’s an example of some everyday items and their wattages:

• Phone charger: ~10W
• Laptop: ~50W
• LED light: ~5W
• Mini fridge: ~60W

Step 2: Estimate Your Daily Usage

Next, estimate how many hours you’ll use each device per day. Multiply the wattage by the usage hours to get the daily energy needed in watt-hours (Wh).

For example, if you plan to charge a 10W phone for 3 hours:

10W × 3-hours = 30Wh per day

Repeat this calculation for each device, then add up the watt-hours for your daily total.

Example Daily Calculation:

• Phone charger: 10W x 3 hours = 30 Wh
• Laptop: 50W x 4 hours = 200 Wh
• LED light: 5W x 4 hours = 20 Wh
• Mini fridge: 60W x 24 hours = 1,440 Wh

Total Daily Wh: 30 + 200 + 20 + 1,440 = 1,690 Wh

For ease, we can round this up to 1,700 Wh per day. You can round up as needed to make any math easier and numbers easier to remember.

Step 3: Multiply by the Number of Days

Now, multiply your daily total by the number of days you’ll be off the grid or without power. or example, if you’re camping adventure is for three days:

1,700Wh per day × 3-days = 5,100 Wh

This result indicates that you’ll need a portable power system capable of supplying at least 5,100 Wh over three days. But we’re not done yet, there are some other factors to consider.

Step 4: Account for Voltage Differences and Inverter Losses

Some devices, such as laptops and household appliances, require adjustments because they operate at different voltages (e.g., 18-20V for laptops or 120V for AC devices). Most portable power systems output 12V and 120VAC, but it’s all derived from the internal battery. To ensure these devices run efficiently, we need to account for their voltage requirements and the energy lost in converting DC to AC.

Laptop Power Adjustment Example

For laptops that operate at 18-20V DC, multiply the calculated watt-hours by 1.6 as a simple rule of thumb to account for voltage differences. Let’s apply this to our previous laptop calculation:

50W × 4-hours × 3-days = 600Wh x 1.6 = 960WH (adjusted)

So, instead of 600 Wh, plan for 960Wh to ensure you have enough power.

Inverter Loss for AC Devices

Devices that run on 120V AC (such as a mini-fridge) require power to be converted from DC to AC. This conversion typically results in approximately 10-25% energy loss due to inverter inefficiencies, which all inverters have regardless of manufacturer. o account for this, multiply the watt-hours by 1.25.

For example, let’s calculate the adjusted power needed for a mini-fridge:

60W × 24-hours x 3-days = 4,320WH x 1.25 = 5,400Wh (adjusted)

Step 5: Add a 20-30% Buffer for Extra Assurance

Finally, it’s wise to add an extra 20-30% to your total watt-hours to account for unexpected usage, inefficiencies, and real-life variability in device power needs. his additional buffer ensures you don’t run out of power if your plans change.

For example, if our adjusted total for a 3-day trip is 6,510 Wh, we’ll multiply by 1.25 for a final buffer ( see the table below for all the adjusted WH needed).;

6,510WH × 1.25 = 8,138 WH

This final number represents the total Wh your portable power system should provide to ensure reliable power for the entire duration.

---

Quick Summary Table

Device	Wattage x Hours x Days	Adjusted Total Wh
Phone Charger	10W x 3 hours x 3 days	90 Wh
Laptop	(50W x 4 hours x 3 days) x 1.6	960 Wh
LED Light	5W x 4 hours x 3 days	60 Wh
Mini Fridge	(60W x 24 hours x 3 days) x 1.25	5,400 Wh
Total	All devices Listed for Trip	6,510 Wh
With Buffer	Peace of Mind	8,138 Wh

---

Ready to Get Powered Up?

With this guide, you’re ready to confidently size your portable power system. Whether it’s for a camping trip, an RV road trip, or home emergency preparedness, knowing your power needs helps you make the best choice for a reliable, ready-to-go energy source. Remember: it’s all about planning for what you know—and preparing for the unexpected.

---

References

1. U.S. Department of Energy (DOE) – Energy Efficiency and Power Calculations: https://www.energy.gov/
2. National Institute of Standards and Technology (NIST) – Voltage Conversion Factors and Electrical Standards: https://www.nist.gov/
3. Solar Energy Industries Association (SEIA) – Inverter Efficiency and Power Losses: https://www.seia.org/
4. Ready.gov – Emergency Preparedness and Power Needs: https://www.ready.gov/