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PSU Wattage: rated vs. what it actually does

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November 26, 2004 10:11:45 PM

Can somebody inform me about the ratings on PSU's? Some say they put out 500W, but I've heard that some of them really don't do this all the time. Also, Antec puts out power supplies with the "true" rating, such as true 430, which is what I have. How can I tell whether what I'm getting really puts out what it says? Thanks.

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November 27, 2004 8:15:31 AM

You can't. Antec was one of the early players to destroy the rating system with their lower end power supplies dropping voltage around 70% of their rated load. Antec then came out with the "True Power" which actually put out what it was rated at, and now people claim Antec's "always been" a fine company.

Different companies have different duty cycles they rate their power supplies at. Fortron Source for example rates their supplies at 70% of the cuttoff load (the point when the power supply trips it's overload protection circuit). So they tend to put out far more than their rating. Antec's True Power put out a little more than their rating. Enermax puts out about the same as it's rated at. Enlight as I recall puts out just a hair less than it's rated at. And cheaper power supplies tend to be anyone's guess, but that guess had better be low.

Another thing about cheaper supplies is they don't filter the current as well, which can lead to stability problems and shortened component life. And they tend to use inferior capacitors, which means the power supply itself will likely fail within a short period of time (2 months to 2 years, rather than 5-15 years of the good ones).

There are other power supplies at or near the top, I'd read some reviews.

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November 29, 2004 4:34:58 AM

Are you saying that Fortron Source is the best power supply company? Another thing, pardon my noobness lol, but what's a duty cycle?
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November 29, 2004 4:36:39 AM

There are better power supplies than Fortron Source, but you'll pay a premium for them.

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November 29, 2004 6:52:15 PM

Duty cycle can mean different things for different purposes. Generally it's the time or amount that a product can be expected to reliably perform its function (having nothing to do with warranty of course). Or, how long it can be expected to be useful before obsolescence (sp?).

In this case, he's using it to mean the supply can reliably and stably put out 'X' amount of power, for 'Y' amount of time. Like a cheap one will say it puts out 500w, but doesn't say it will break down after an hour of doing 500w, while a high quality one would say 500w and mean 500w 24/7 for 2 years. These are just for example, I don't know what they really are.

Mike.
December 13, 2004 9:40:36 AM

"True Power" simply means that each of the main voltages is independently regulated and has nothing to do with how much power the supply can put out.

Duty cycle doesn't apply to the power rating, only to the MTBF reliability rating, where most manufacturers specify it at 70% of full rated power while some use 100%. Many power supplies are designed to trip their overcurrent protection at about 30% above the maximum amp ratings, but that doesn't mean they can put out 30% more than their rated power because they may not regulate the voltages adequately at such high loads. The only way to find the actual maximum power capacity is by measuring it, which normally requires the use of load resistors because computer equipment rarely draws over 250-300W.
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