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cheburns

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Is it worth shelling out the extra dough to get a PSU that is APFC... How do you make that decision of whether its worth it or not what are the real benefits and are they worth the money? I just don't know enough about PSUs myself (first build)

Thanks
 
A good description for APFC is seen in one article that explains how the current is cleaned so that less power is consumed.

Today on our bench are two supplies that in many respects are identical, but in a few are not. As you'll see from the upcoming photos, their designs differ as well as the circuitry within. The real difference here though, is the addition of APFC, or "Active Power Fault Correction". The purpose behind this technology is to sweep clean the power that enters your supply, so that it can consume less of it under a load, which makes for cooler operation, as well as a lesser draw from the wall. What will this mean to the consumer? It's a promise of lesser power consumption on a way to a green lifestyle. Our two guinea pigs for today's experiment were provided kindly by Ultra Products. They will be tested against each other in the standard way (the use of OCCT to look for ripples), as well as have their inrush current monitored via the use of a "Kill-a-watt" meter we've borrowed for this review. It'll help us to see how much the supplies are drawing under a load, allowing us to see if APFC really does work, or if it's more marketing hype than technological leap.
http://www.motherboards.org/reviews/hardware/1608_1.html

Basically it acts like a power conditioner for supplies and is commonly seen for ac use as well. The make and model supply you should be looking at will depend on the type of build you are planning. The lists for both good and bad makes and models of supplies(always needing revission of course) can seen below.


Good:
Antec(except Smart Power models) - Astec - AOpen - Channel Well - Coolermaster - Enermax(except Liberty models)
- Enlight - Fortron Source (Sparkle) - HEC - OCZ Technology - PC Power & Cooling - PowerMan
- Seasonic - SilverStone - Sunbeam - Tagan(older models) - TTGI/SuperFlower - Vantec - Zippy / Emacs - Verax - XCLIO - Zalman
- Corsair - Ultra

Bad:
Allied - Antec Smart Power models seem to lack(recommend True Power or NeoHE) - Aspire - CoolMax - DEER - Enermax Liberty models - ePower - EYE-T
- KingStar - L&C - Linkworld - Logisys - PowerMagic - PowerUp - Powmax - Q-Tec - Raidmax - Skyhawk - Star
- Turbolink - ThermalTake(complaints heard some good some ???) - Rosewill - SilenX ??? ToPower(newer models)
 
This is from www.silentpcreview.com, and is about the best benefits focused, nontechnical description of PFC I've seen:
POWER FACTOR CORRECTION

Increasingly, switched mode power supplies (SMPS) are designed with an active power factor correction (PFC) input stage. This is mainly to meet new regulations aimed at restricting the harmonic content of the load current drawn from power lines. Both users and power companies benefit from PFC, as does the environment.

Power Factor Correction (PFC) can be defined as the reduction of the harmonic content, and/or the aligning of the phase angle of incoming current so that it is in phase with the line voltage. Mathematically, Power Factor (PF) is equal to Real Power (Watts) divided by Apparent Power (Volt*Ampere). The basic concept is to make the input look like a pure resistor. Resistors have a power factor of 1 (unity). This allows the power distribution system to operate at maximum efficiency, which reduces energy consumption.

Non-PFC power supplies use a capacitive filter at the AC input. This results in rectification of the AC line, causes high peak currents at the crests of the AC voltage. These peak currents lead to excessive voltage drops in the wiring and imbalance problems in the three-phase power delivery system. The full energy potential of the AC line is not utilized. Nonlinear peak currents also distort output voltage and create harmonics. There is an international standard for controlling harmonics (IEC100-3-2) and PFC is mandatory for home appliances consuming 70W or more power in EU nations as of January, 2001.

PFC circuits are classified into two types: active and passive.

Passive PFC uses passive elements such as a ferrite core inductor on the input source to create a countering reactance. While easily applied to the existing power circuitry without much modification, the power factor is low (60 - 80%), the AC input must be chosen (115VAC / 230VAC), and the harmonics produced from the difference between the capacitance and the inductance are hard to control. Significant electromagnetic noise can result.

Active PFC uses switching regulator technology with active elements such as IC, FET and diodes, to create a PFC circuit This circuit has a theoretical power factor of over 95%, reduces total harmonics noticeably, and automatically adjusts for AC input voltage. However, it requires a complex EMI filter and an input source circuit, and is more costly to build.

The benefits of high PF for the user comes from the reduced AC current drawn by high PF PSUs, not in any savings from electricity bills, except in the case of commercial utility users who do pay for V(oltage) x A(mperes). There are two broad consequences:

Less stress on the AC electrical wiring: The lower current drawn by a high PF power supply means that there is less stress on the electrical wiring of the building. This can be a big plus in the case of older building with lower capacity AC wiring. It is certainly easy to see the benefits in a enterprise setting where dozens or hundreds of PCs are drawing power. If the total current load from the IT department could be reduced by 30% or more, this would be very signficant in direct electricity savings, reduced airconditioning cost, and possible avoidance of building AC re-wiring.

Lower UPS costs: Lower current draw also means that smaller capacity Uninterruptible Power Supply (UPS) units can be used. As UPS units are priced in direct proportion to their current capacity (VA), a PF of 0.98 versus one of 0.6 can traslate into a 40% reduction in purchase cost. Again, in an enterprise setting with hundreds or thousands of PCs, the savings can be very significant.

PFC Myths

There are myths about power factor correction that continue to be propagated by well-meaning people. Let's tackle the two most common ones:

Does higher PF reduce my electricity bill? No, if you are a home user. If you are an enterprise running hundreds of PCs and pay not only for power but also VA, then yes. For more details, see PFC discussion above.

Does PFC make a power supply more efficient? Not in the normal way that power supply efficiency is defined, which is the power loss (to heat) as a percentage of total AC input in AC-to-DC conversion. However, in the sense that Apparent AC power (VA) is lowered, PFC does reduce energy consumption.

Power factor correction is applied by an input circuit which uses a small amount of input power. With two PSUs that are identical, equipping one with PFC will cause a typical efficiency drop of 2~4%. Many PSUs that have Active PFC also have high efficiency, as APFC is usually found on higher quality PSUs, but the two are not intrinsically related.
Click to expand...
Some more useful info: http://www.dansdata.com/gz028.htm

In short, I wouldn't consider it an essential feature. Active PFC will help your power company, but won't do all that much for you (although there are some benefits if you're intending to use a UPS). Most of the better (non-budget) PSUs will include it, however.
 
Agreed on that! Look over the specs on some of the makes and models seen in the "good" list and you will see most will have this. But it can also be seen on others as well such as the Antec TP3 550w a friend ordered to replace the TP2 loaned to him seen at http://www.newegg.com/Product/Product.aspx?Item=N82E16817371002

(hopefully it will turn out to be the TP2 not 3 since the order was apparently placed after I told him to go for the TP2 model?)
 
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