Antec SmartPower 2.0 SP-450 ATX Power Supply

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July 30, 2005 by Devon Cooke with Mike Chin

*POSTSCRIPT added Oct. 22, 2005*

Antec SmartPower 2.0 SP-450
450W ATX12V 2.0 Power Supply
Market Price ~US$60

Two years ago, most ATX PSUs in the retail market featured at least one 80mm fan. In the past year, the bottom mounted 120mm fan has become the norm, and 80mm fans have become almost rare among higher end retail PSUs. The Antec SmartPower 2.0 is a double anomaly because it uses two 80mm fans, one mounted at each end. It's only one of a small handful of models that use this this design, which has its advantages and disadvantages.

The "2.0" part of the SmartPower's name is important: The original SmartPower line is not ATX12V 2.0 compliant, and due to the higher demand on the 12V rail, they may have difficulty powering a current high-end system. There are three other models in the SmartPower 2.0 lineup: 350, 400 and 500. The 500 has an additional feature not found in the other models: Detachable output cables.

The SmartPower 2.0 is one of four power supply lines offered by Antec. TruePower 2.0, NeoPower, and Phantom are Antec's high-end, modular and fanless products, respectively. The SmartPower 2.0 is Antec's mainstream line, and is designed to meet the needs of the majority of users. It may not be able to boast that it is the best at anything, but there is one area where it beats all of Antec's other models: Price. Overclockers and gamers may turn their noses up at the SmartPower in favor of Antec's pricier models, but the SmartPower still does what a power supply is supposed to do: Supply power.

The classy, uncluttered, full-color box
suggests an experienced retail marketing team.

Feature Highlights of the Antec SmartPower 2.0 SP-450 (from Antec's web site)
ATX12V version 2.0 The latest major revision, supported by most recent power supplies.
ATX12V v2.0 compliance allows SmartPower 2.0 to consume up to 25% less power than standard power supplies, saving you money on your electric bill This is a claim based on Intel's minimum and recommended efficiency.
4 SATA Connectors support Serial ATA optical drives Yes, it supports optical drives, but you'll more likely be using them to power your hard drives.
Flow-through dual 80mm fans (one intake and one exhaust) See discussion of 80mm vs. 120mm fans below.
Unique Dual Fans Technology: Exhaust fan starts to spin when the power supply reaches certain temperatures to ensure proper airflow, the second fan spins on power up At low levels, only the internal "intake" fan is used, which should be good for noise levels. We'll find out how good..
Industrial grade protection prevents damage resulting from short circuits, power overloads, excessive current, low voltages and excessive voltages
"Industrial grade" doesn't really mean much, but more protection circuits are always welcome. Low voltage protection is unusual.
Increased 12V output capability for system components that consume more power from 12V rail "Increased" is relative to older power supplies based on ATX12V 1.x.
PF value greater than 90% (EU only) It's "EU only" because only the EU requires it.
Gold plated connector for superior conductivity Generally, gold plating has high conductivity and will not tarnish, but when mated with connectors with the more common nickel or tin plating, galvanic corrosion can occur over time, especially in humid environments.


SPECIFICATIONS: Antec SmartPower 2.0 SP-450
AC Input
115 / 230VAC @ 47-63Hz
DC Output
Minimum Output
Maximum Output
Maximum Combined

*There was some confusion about the specifications for the SmartPower 2.0. We managed to find three sources of specifications, each slightly different: The web site, the retail box, and the label on the unit itself. The variation between the three sources was minor; all of the actual line capacities were consistent. However, the combined maximum output for the +3.3V, +5V and the two +12V rails was different in each source. The web site lists the maximum as 410W, the box lists it as 430W, and no maximum is given on the actual unit. Depending on which source you believe, this puts the total output capacity (for all rails) at either 444W or 424W ? not quite the 450W listed in the marketing literature. For the purposes of this review, we give Antec the benefit of the doubt and treat the higher number as correct.

The specifications listed on the actual unit are incomplete: No maximum capacity is listed.


Intel's ATX12V V2.2 PSU Design Guide, the industry bible for PSU makers, states:

"In cases where expected current requirements is greater than 18A a second 12 V rail should be made available.

"The 12V rail on the 2 x 2 power connector should be a separate current limited output to meet the requirements of UL and EN 60950.

"12V1DC and 12V2DC should have separate current limit circuits to meet 240VA safety requirements."

It's important to remember that when there are two12V lines, they still draw from the same main source. It's not like there are two 120VAC:12VDC power conversion devices in a PSU, this would be way too costly and inefficient. There is only one, and the two rails draw from the same transformer. Each rail is coming from the same 12V source, but through its own "controlled gateway".

PSU makers' specs are misleading in that they rate the current capacity of each 12V rail independently. What really matters is the total 12V current: Generally, up to 20A is available on any one 12V line, assuming the total 12V current capacity is not exceeded.

An analogy that may help: Think of 12V1 and 12V2 as two identical water taps fed off short pipes joined in a Y-junction to a single larger pipe. The total amount of water flow available through the two pipes is always the same, it's dictated by the pressure behind the big pipe. Each of the two taps have a maximum potential water flow potential that is lower than the maximum available through both taps together. How much water flows through each pipe depends on how much each is open. The "position of the tap" in the PSU is dictated by the power demand of the components connected to it.

What the above means is that you don't need to worry about imbalances in power draw on the 12V lines -- as long as no single rail is asked to deliver more than 20A. PSU makers seem to mark each line for max current on a purely arbitrary basis. A PSU like the Antec Smart Power 2-450 rated for 32A max total on the 12V lines can be labelled many different ways:

12V1: 14A, 12V2: 18A
12V1: 15A, 12V2: 17A
12V1: 16A, 12V2: 16A
12V1: 17A, 12V2: 15A
12V1: 18A, 12V2: 14A

It could also be marked 19A + 13A or 20A + 12A, but being a cautious bunch, engineers will probably not specify more than 18A on any one line. This allows a 2A margin of error for the current limiting circuit. Antec's specs (and those of all dual 12V line PSUs) would be much more precise if it was appended with something like the following:

The maximum 12V current available is 32A. Over-Current Protection limits current delivery above 18A on either 12V1 or 12V2 rails. Up to 18A can be delivered on either 12V line, as long as the 32A maximum is not exceeded. OCP also limits the total DC output of the PSU to 444W.

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