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PFC - Is it necessary?

E

extreme4377

Limp Gawd
Joined
Mar 6, 2005
Messages
372
Is PFC a necessity for PSU's? I noticed that none of the Antec TruePower II power supplies have PFC. What is it and what does it do? And is it needed?
 
Some more on PFC:
http://www.silentpcreview.com/article28-page5.html


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 divided by Apparent Power. 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? No, the power factor correction is usually 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...
 
The Seasonic has weak 12V rails even combined. Ill have to take a look at the more powerful line of Seasonic's. Otherwise, I might just spring for the NeoPower 480W. Any suggestions?
 
davidhammock200 said:
The Seasonic S-12 600W is SLI Certified & should be about $132. ;)
Click to expand...

Thanks but why would I need a 600W SLI cert. PSU for my system? Im looking for a good solid 400-500W PSU with modular connections(Excluding the 24pin and other 4 pin mobo connector), good, strong rails, and quiet performance.
 
extreme4377 said:
Thanks but why would I need a 600W SLI cert. PSU for my system? Im looking for a good solid 400-500W PSU with modular connections(Excluding the 24pin and other 4 pin mobo connector), good, strong rails, and quiet performance.
Click to expand...
Responding to your post:
The Seasonic has weak 12V rails even combined. Ill have to take a look at the more powerful line of Seasonic's. Otherwise, I might just spring for the NeoPower 480W. Any suggestions?
Click to expand...
Neither the Seasonic S-12 500W or 600W have "weak +12V rails".

Dave ;)
 
Right, I know. Im just saying why would I need all that power? The NeoPower 480 is a good solution. Any drawbacks Im missing of the neopower?
 
extreme4377 said:
Right, I know. Im just saying why would I need all that power? The NeoPower 480 is a good solution. Any drawbacks Im missing of the neopower?
Click to expand...
None, a very good PSU with 3% load regulation & a max combined of +12V@32A. ;)
 
I have a NeoPower 480 running in a P4 box right now, and it delivers good power in the old rowhome in which I live.

Just be warned of the following caveats to the modular design:

•Modular plugs create electrical resistance, and, therefore, reduces total power delivered. Granted, it's only a small reduction in power, but it affects the rating of the power supply (if I remember correctly, on the side of the unit, Antec rates the overall power delivered at peak as 460 watts).

•There are only three connectors on the PSU for component cables to be attached to (the fourth one is "Fan Only" if I remember correctly). I thought that this would have been more than enough for 2 optical drives, one SATA hard drive, a ZIP, and a 6800 GT. However, due to the rather short lengths of the wires provided and the full sized Thermaltake Tsunami in which all of these components live, I wound up having to make sacrifices in order to get everything cabled correctly. I made the inside of the case as clean as possible, but I've had better experiences in wire-tidiness with standard design power supplies. I hope you don't have a PCI Express graphics card: since the wire for PCI-E must be dedicated, that leaves you with only two connectors for component wires.

If you must have modular, might I suggest looking at the new NeoHE models simply because they have more connectors on the PSU. I've read only one review from SPCR, and they seem to like it, though they found the efficiency not up to snuff.

The NeoPower 480 is good, don't get me wrong. In practice, however, I think that there are better PSU's out there.

Hope this helps.
 
Thanks for the input bro. Im now looking at the OCZ Modstream 520W. I am still eyeing the Neo480 but Im on the fence. Although, you may have just pushed me off into OCZ land
 
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