This is a very difficult question to answer due to the fact that we are using different voltage outputs and devices rarely consume the maximum Amps listed in their specifications at a constant rate. Theoretically you can use the following calculations however in most cases you will get far better backup times from your UPS.
Please see our case studies as they may give you a better indication of the backup times you can expect - Case Studies
On most of your devices you will find the Voltage and maximum Amp rating either on the back of the device or on the DC power supply which was provided with your device. It is preferable to use the specifications that are on the device itself.
In our example we will use two devices with different voltages as specified below:
- Internet Router - 12V 1.0A
- Passive PoE Access Point - 15V 0.5A
Use an online Watt calculator such as RapidTables to calculate your device Watts:
Internet Router:
Access Point:
Adding the Watts together you will give you the total wattage that these two devices will use in an hour (12W + 7.5W = 19.5W)
You can now calculate the theoretical time in minutes the UPS will provide power to these devices using the following formula (UPS Wh rating \ total watt used in hour * 60 Minuets) In other words, for this scenario using a 75Wh UPS the calculation will look like this:
75Wh \ 19.5W * 60 Minutes = 230 minutes
As stated previously you should in most cases have far better times than depicted in this calculation. As an example you can compare the max watt calculated requirement and the actual POC usage in one of our CCTV deployment case studies.
Note: These calculations are only to provide a rough estimate and does not take into consideration other factors such as internal losses, temperature etc.