Help Me Find The Right Uninterruptible Power Supply (UPS)

How to choose an uninterruptible power supply (UPS). An overview of capacity, output type, run time, and monitoring that can be used with any manufacturer.

There are many factors to consider when selecting an uninterruptible power supply (UPS). The basics are:

1. Capacity – How Much Of A Load Can I Place On A Battery Backup Uninterruptible Power Supply (UPS) Before It Doesn’t Work?

For example, if the device you would like backup power for has a label that says the input power is 120 volts, 3 amps, multiply 120 volts by 3 amps to get the wattage (360 watts). Then try to find a battery backup UPS with a capacity rating of at least 20% more than your device's wattage. In this case, 360 watts multiplied by 1.20 (360 watts times itself plus 20%) equals 432 watts

If we look at the passive backup power systems available, we have a 360 watt battery backup UPS and a 900 watt battery backup UPS which are the 2 models closest to our wattage load. We can't use the 360 watt battery backup UPS to backup this electronic device, because it will most likely overload the 360 watt battery backup UPS. Instead, we select the model with the capacity rating over our 432 watt figure. In this case, it would be the 900 watt model.

2. Output – What Are All These NEMA This And NEMA That References?

NEMA stands for National Electrical Manufacturer Association. It is a standard used to ensure quality, format, and features are consistent between products in electrical distribution, lighting, enclosures, etc. There are many of these, so we will cover the one that is used most commonly. 

The standard wall receptacle in the U.S. is a NEMA 5-15R (the R means receptacle). Anything that has a plug that fits in a standard wall outlet has a NEMA 5-15P (the P means plug). If your battery backup UPS says it has NEMA 5-15P (plug) input and NEMA 5-15R (receptacle) output, then you can plug it into a standard wall outlet for power and plug anything that uses a standard wall plug into the back of it for automatic backup power. Let's break down the meaning below. 

NEMA = National Electrical Manufacturer Association

5 = The voltage and format rating for this receptacle/plug. In this case the 5 means the outlet is meant for electronics that are powered by three wires (hot, neutral, and ground) that run at 125 volts maximum (110, 115, and 120 volt devices are typical and all use this receptacle/plug).

15 = The maximum amperage rating of the breaker typically associated with this outlet/plug.

R/P = R stands for receptacle and P stands for plug. 

3. Battery Backup Time – How Long Will The Uninterruptible Power Supply (UPS) Run When The Power Goes Out?

A lot of people are confused by this and think that the capacity rating of the battery backup UPS (for example 1 kVA / 700 Watt) determines the amount of battery backup power time they will have during an outage. IT DOES NOT. This rating is used to determine the maximum load that can be put on a battery backup UPS. In this case, the maximum load of the UPS is 700 watts. Yes, if you use 100 watts instead of 700 watts, the battery(ies) will last longer. 

The main determining factor of battery backup time is the NUMBER OF BATTERIES. There are a variety of other factors that impact the backup time like the amp hour rating of each battery, the voltage of each battery, the power factor of the inverter inside the battery backup UPS, etc., but the main thing to do to extend the battery backup time is to add batteries. You can do this by adding external battery packs to the main battery backup UPS which already has a set number of internal batteries. All of our online (double conversion) battery backup UPS models allow you to select and purchase additional external battery packs. 

4. Monitoring – Do I Need All These Fancy Lights And Displays?

In most cases, all you will need to know is the current load level and how much backup time is remaining. In basic models, simple LED lights show the amount of battery remaining and the current load level the battery backup UPS is supporting. This will assist you in determining how much time you have to safely shut down the attached equipment before emergency backup battery power is depleted on the battery backup UPS. 

If you want to monitor things like input/output frequency, input power load in VA/Watts, output power in VA/Watts, exact remaining backup power time in minutes, etc., high end battery backup UPS systems typically have these available on the front LCD screen. Our online (double conversion) battery backup UPS have a complete set of real-time statistics that can be viewed from the front LCD using the enter button to cycle through. 

For personalized assistance in finding the right battery backup UPS for your need, please contact us by chat (bottom right corner), email (, or phone (855-330-7799).