Differentiating between the Watt (W) and VA ratings is among the key problems many buyers face today. Without a proper understanding of the two terms, you cannot know the right UPS system to pick, and neither will you be able to select the recommended wires for the wiring system.
This article simplifies the meanings of VA and Watt ratings and also gets deeper into how you can use the information to plan well for your UPS purchase and installation project. Let’s walk together as we uncover every crucial detail for you.
Understanding The Fundamental Concepts of VA and Watts
To understand VA and Watts concepts, we would like first to explain the meaning of electrical power. We can define power as the rate at which a machine does some work. In the context of electrical appliances, we define the power rating as the rate at which a given device consumes electrical energy. Then finally, for UPS systems, power is the rate at which a UPS unit avails electrical energy for use by appliances.
As a UPS delivers power for use, a portion of it usually goes into doing the intended purpose which may include running a TV set, air conditioner, refrigerator, microwave oven, and many others. It’s always just a portion of what the UPS supplies because of efficiency issues. Simply put, no system can ever exhibit an ideal efficiency of 100%.
Where Do the VA and Watts Ratings Come In?
Well, as per the explanation we’ve given above, the VA (Short for Volt-Amperes) rating is the maximum amount of power a given UPS system can deliver for use. Experts also call the VA rating the Apparent Power. We calculate the VA rating by getting the product of the voltage (V) the UPS supplies and its current output, which is usually expressed in amperes (A).
Therefore, Power in VA = Voltage(V) * Current(A) = VA.
For example, a UPS system with a 230V and a 13A output rating has a VA equivalent to (Voltage * Current) = (230*13). This gives us 2990, which is approximately 3000VA. But again for simplicity, VA ratings above 1000 are always expressed in thousands. We can achieve that by dividing the respective values by 1000. So, the 3000VA becomes 3KVA.
Now that we’ve already shown you what VA means and how to calculate it, let’s proceed to the Watts rating. Contrary to VA, the Watts rating is the maximum usable amount of power that a given UPS unit can deliver. Since it is the actual usable power, we can also refer to the Watts rating as the Real Power of the UPS system.
So, What’s The Significance of Knowing VA and Watts Ratings?
The information about the Apparent Power (VA) and Real Power (Watts) of a UPS unit is beneficial to us in numerous ways. With the data about the VA rating and output voltage at hand, we can determine the maximum amount of electrical current the UPS can supply. Let’s look at a quick example to help you master the calculation better.
Considering a UPS system with a power rating of 1500VA. If it’s in Europe, the output voltage will likely be 230v.
Therefore, the maximum current in Amperes the UPS will deliver = (Power/Voltage) = (VA/V), which is = A. In our case, the Maximum Current = (1500VA/230V) = 6.5, which is approximately 7Amps. Knowing the current rating helps us to select the correct wire size for our wiring system and avoid any damage that can interfere with the UPS unit or the power system at large.
On the other hand, if it’s in the US or North America, the UPS will likely have an output voltage of 120V. So, in such a case, the maximum current = (VA/Voltage) = (1500VA/120), giving us 12.5, which is approximately 13 amps. You can see that we’ll need thicker wires for this second case because of the much higher current, and this confirms the importance of knowing the VA value of a UPS system.
While the VA rating dictates the magnitude of current a UPS delivers, the Watts rating is useful when determining the load capacity of the System. The Watts rating tells us the maximum load our UPS unit can run successfully, and this is also instrumental when choosing the ideal backup system for your project.
Introduction to The Concept of Power Factor (PF)
The Power Factor of a UPS system refers to the measure of how effective it is, in delivering useful (Real Power) for use by appliances. In other words, it’s the extent of the efficiency of a given UPS unit. The PF value ranges from 0 to 1, with zero not being the practical lowest value because no system can have an efficiency of 0.
We can also express the PF of a UPS as a percentage by multiplying the value by 100. The PF can be expressed mathematically as the ratio of Real Power (Watts) to Apparent Power (VA). Since it measures the efficiency, the Real Power of a UPS unit increases with an increase in the PF value and vice versa. You can always apply the below equation to determine the Watts rating of a UPS, given its VA rating and the PF value.
Power In Watts = (Power In VA * The Power Factor).
Therefore, Watts = VA*PF
Then as we have explained above, no machine has an efficiency of 0%, meaning the PF of a UPS unit cannot be 0. Generally, most UPS systems have PF values ranging from 0.6(60%) to 0.9(90%). Importantly, there are modern UPS systems that are extremely efficient and boast a PF value of 1.
From the equation Watts = VA*PF, a PF value of 1 makes the Watts and VA ratings of a UPS backup to be the same. In such a case, the Real Power becomes equal to the Apparent Power, and the unit will be able to run many devices or support those that require more power within its load capacity limit.
Calculating The Wattage Capacity of a 1000VA UPS
You need to master how to determine the Real Power (Watts) of a UPS system. The value shows the actual maximum load the UPS backup can support. Also, knowing how to calculate the Wattage capacity is crucial since the power consumption rating of most appliances is expressed in Watts. In this section, we will teach you how to calculate the Wattage capacity of a UPS system given its PF and VA rating.
Getting The Wattage Capacity of a Typical UPS
A typical UPS has PF ranging from 0.6 to about 0.9. Using the equation Watts = VA*PF, we can get the minimum and maximum Watts ratings of a 1000VA UPS as follows.
For minimum, the PF = 0.6. Therefore, Watts = 1000*0.6 = 600W. This value shows that despite a UPS having a higher VA rating of 1000, it can handle up to a maximum of only 600W. Surprisingly, this may never even be practical in real life as we cannot operate a UPS at its maximum load capacity.
Experts recommend always keeping the load capacity of a UPS unit at a maximum of 80% of the total capacity. That means the most practical load you can support with a 1000VA system = 600*0.8(80%) =480W. Therefore, the total load of all your appliances should not exceed 480W for a 1000VA and 0.6 PF UPS system.
On the maximum side, Watts = VA*PF = (1000*0.9), which gives us 900W. Again, in this case, the Apparent Power is 1000VA but the total Real Power the UPS can deliver is 900W. This is also the same as the total load capacity of the UPS and it will drop further to 900W*0.8(80%) = 720W if we factor in the recommended maximum utilization of 80% of the total load capacity.
Calculating the Watts Rating For Other PF Values
The Wattage capacity of a 1000VA UPS will be as follows for various PF values.Â
1. PF = 0.7
Watts = VA*PF = 1000*0.7 = 700W.
80% of load capacity = 700W*0.8(80%) = 560W
2.PF = 0.8
Watts = VA*PF = 1000*0.8 = 800W.
80% of load capacity = 800W*0.8(80%) = 640W
3. PF = 1 (Maximum Efficiency), VA rating will be = Watts Rating
Watts = VA*PF = 1000*1 = 1000W.
80% of load capacity = 1000W*0.8(80%) = 800W.
The resultant Watts values indicate that a higher Power Factor (PF) leads to higher real power ratings within the same VA rating. Therefore, to run higher loads more effectively, you should go for a UPS with a higher VA rating and power factor.
Some Key Practical Considerations
Before taking any UPS, check for the appliances it can safely and successfully support. Considering the device recommendations upfront helps to prevent surprise failures and ensure your power backup system works correctly. You also want to ensure you always operate appliances within the UPS unit’s Watts and VA ratings.Â
Besides not exceeding the maximum load capacity, experts recommend not ever hitting it. They suggest using only up to about 80% of the total load capacity to ensure the UPS doesn’t strain and serves you for more years.Â
What we’ve found to be the most effective so far is selecting a UPS whose load capacity is more than your intended load. This prevents unprecedented disappointments and gives you room to scale up your load in the future as necessary.
Monitoring the UPS load levels regularly will be a game-changer because it is the most seamless way to know whether the load is within the recommended limits.
Parting Shot
Many factors dictate the load in Watts a 1000VA UPS can support. However, the main one is the Power Factor, which is the measure of how a UPS is efficient in converting the Apparent Power to the real usable power your devices require to operate. Higher PF values are, therefore, highly recommended because they increase the Watt rating (Load Capacity).
For smooth operations and remarkable performance, select a UPS with higher VA and Watts ratings. Also, pick a unit with a higher PF, especially 0.9 and above, for maximum efficiency.
