What Exactly Does the Wattage Rating on a Power Supply Unit Mean? Your PSU is rated 80 Plus Bronze and for 650 watts, but what exactly does that mean? Read on to see how wattage and power efficiency ratings translate to real world use. Today’s Question & Answer session comes to us courtesy of SuperUser—a subdivision of Stack Exchange, a community-drive grouping of Q&A web sites. SuperUser reader TK Kocheran is curious about power supplies: If I have a system running at ~500W of power draw, will there be any tangible difference in the outlet wattage draw between a 1200W power supply vs, say, a a 800W power supply? Does the wattage only imply the max available wattage to the system? What is the difference? And what, for that matter, do the 80 Plus designations mean on modern PSUs? Contributors Mixxiphoid and Hennes share some insight into the PSU labeling methods. The wattage of your power supply is what it could potentially supply. However, in practice the supply won’t ever make that.

I always count 60% of the capacity as the truly maximum capacity. Today however, there are also bronze, silver, gold, platinum power supplies which guarantee a certain amount (minimum of 80%) of efficiency. See this link for a summary of 80 PLUS labels.cost of new air conditioner unit 2013 Example: If your 1200W supply has a 80 PLUS label on it, it will supply probably 1200W but will consume 1500W. how much is an air conditioning unit for a houseI think you 800W supply will be sufficient, but it won’t guarantee you safety.ac units for mobile homes Hennes explains the value of a system-appropriate PSU: The wattage implies the maximum available wattage to the system. However note that the PSU draws AC power from the wall socket, converts it to some other DC voltages, and provides those to your system.

There is some loss during this conversion. How much depends on the quality of your PSU and on how much power you draw from it. Almost any PSU is very inefficient when you draw less then 20% of max rated power from it. Almost any PSU has less than peak efficiency when you draw close to the max rated power from it. Almost any PSU has their optimum efficiency around 40% to 60% of maximum load. Thus if you get a PSU which is ‘just large enough’ or ‘way to big’ it is likely to be less efficient. [But note that your PC does not consume a fixed or constant level of power. At idle, when not much is happening, the DC power consumed will be low. Perform a lot of processing and I/O operations, then power demand goes high.] A nice example of areal world efficiency graph is this: will there be any tangible difference in the outlet wattage draw between a 1200W power supply vs, say, a a 800W power supply? The 800 Watt PSU would run at 62.5% of max rating. That is a good value.

The 1200 Watt PSU would run at only 41% of its maximum rating. That is still within the normally accepted range, but at the low end. If your system is not going to change than the 800 Watt PSu is the better choice. Note that even with a good (bronze+ or silver rated PSU) you are still loosing about 15% during conversion. 15% of 500 Watt means that your computer would use 500 Watt, but the PSU would draw 588 Watt from the wall socket. Clearly, you should aim to have your PSU sized appropriately for your system–putting a high-load PSU into a basic desktop machine doesn’t increase your safety margin and decreases your efficiency costing you more money in the long run. Have a useful link or comment to add to the discussion? Sound off in the comments below. Want to read more answers from other tech-savvy Stack Exchange users? Check out the full discussion thread here.Have you seen this ad while driving through the streets of Pakistan? Every time I see it, it makes me a little bit angrier.

For those of you who do not understand Urdu or Hindi, the ad’s tag line is “Pankhay ke tarha chalayen” i.e. Run it (or use it) like a fan. This line encourages users to think that by using the Gree Inverter air conditioner, they will use the same amount of electricity as a ceiling fan. Considering the severe energy crisis we are facing in Pakistan at the moment, with a 30% shortage of supply compared to electricity demand, this advertisement is very irresponsible. In addition, it is making a statement that is a lie, or at least a selective truth. And it is a lie that many consumers believe, as has been seen by discussions on many Pakistani forums. Moderately efficient 56″ ceiling fans use 80W of electricity. If you run one efficient ceiling fan for 10 hours every day, at the end of the month, you will end up paying Rs. 240-500 for your electricity bill per fan based on whether you are a domestic or commercial customer, and what electricity tariff you are paying. However, a  Gree 1 ton AC (12000 BTU) that does not use an inverter, consumes on average about 1080-1250W of power, based on the model, as you can see on our air conditioner comparison page.

The best inverter air conditioners in the market consume on average 450-500W of power per ton. Is Gree saying that its inverter air conditioners use 80% less power than the most energy efficient models in the world? It cannot really be saying that since even in the ad shown above, Gree says that the AC uses up to 60% less than what we assume are the non-inverter air conditioners that Gree manufactures. That means, in the best case scenario, Gree’s inverter AC uses 432W of power on average. If you look at Gree’s specifications for its inverter AC, shown below, you can see that the lowest amount of power that their 1 ton inverter AC uses is 220W. Now 220W is nearly 3 times higher than a moderately efficient ceiling fan. What is important for Gree to clarify is under which circumstances does the inverter AC use just 220W of power. Is that the case when there is not much difference between the temperature outside and inside the room, for instance in our mild winters? Is it when the dehumidifier  or “Dry” option (a very important part of feeling cool) is turned off?

Please clarify to us what is the average amount of power that the 1 ton inverter AC will consume on an average summer day (34-36 degrees Centigrade) in Pakistan if the AC is set to cool the room to 26 degree Centigrade. Even if we assume that the Gree inverter air conditioner is as efficient as the best ACs in the world, then a 1 ton unit will use 500W of power on average. That means that when this air conditioner is run for 10 hours every day, then at the end of the month your electricity costs for running this AC will be between Rs. 1500-3150 per month. While this may be 30-50% lower than what your air conditioner is currently costing you, it is still 6 times higher than what a ceiling fan will cost in electricity bills. Gree actually does produce moderately efficient air conditioners. They are a good product in our Pakistani market, which overflows with inefficient appliances. However, please do not disrespect the intelligence of your consumers or the trust we place in you, nor produce advertisements that encourage irresponsible and ignorant behaviour from Pakistanis.