Antec CP-850: Unique PSU with Top Performance

The CP-850 is 1.2″ too tall to fit into all but three of Antec’s top cases, so its popularity has to be be unnaturally limited. But the electrical and acoustic performance is superlative, especially in those cases, and it comes at an amazingly low price. White elephant or futuristic visionary?

August 29, 2009 by Mike
Chin

Product	CP-850 850W Power Supply
Manufacturer	Antec
Market Price	~US$125

The CP-850 was first shown by Antec to tech journalists all the way back at CES in the start of the year, then released to market in February. This power supply model is very unusual in that it has a form factor — CPX — which makes it compatible only with a handful of cases, namely the Twelve Hundred, P183 and P193 cases made by Antec. Partly because of its narrow target market, the CP-850 has not been quite as popular as it might have been with a more universal form factor.

It’s not as if Antec is lacking for power supplies. The brand has no fewer than eight different categories of PSUs for a total of some 29 different models. Several of these lines are quite powerful or high end; for example, the impressive flagship Signature series, TruePower Quattro, and the model on hand, the CP-850W. Exactly what Antec hopes to achieve with such a vast lineup of mostly ATX power supplies is a bit puzzling. Perhaps it’s a strategy of domination by SKU blanketing.

The CP-850 is another collborative result between Antec and Delta Electronics, a relationship that already produced the excellent Signature series PSUs. The CP-850 is unique enough, not only among Antec power supplies but among PSUs in general, that some examination of the marketing and technical blurbs are useful. Let go directly to the key features which sets this power supply apart. From Antec’s press release and marketing sheet:

"The CP-850’s new "CPX" expanded form factor allows for better circuit board layout, more room between components for airflow, and a straight-through air path that takes full advantage of the large 120mm Pulse Width Modulation (PWM) fan. The CPX form factor is thus able to provide quieter, cooler operation in addition to the CP-850’s preferred price-to-performance ratio… By breaking the mold of standardized power supply size restrictions, the CP-850 design is able to provide an excellent price-to-performance ratio. A silent rear 120mm PWM fan and dual PCB layout also ensure optimal cooling performance and reliability"

The use of a 120mm fan is no big deal; they’ve been around for years now, and even been exceeded in size by 135mm diameter fans. What is unique about the CP-850 is use of the fan not in a bottom position where the forced airflow must turn 90 degrees before it can exit the power supply, but placement on the back panel. It’s a fan position that allows air to flow straight through the PSU in any computer case. The design has many physical ramifications, the most important of which is that the PSU must be tall enough to fit a 120mm fan on the back, which makes it substantially taller than a standard ATX12V power supply, and it cannot be installed in the vast majority of cases on the market today. The aformentioned large cases — Twelve Hundred, P183 and P193 — were designed or modified specifically to be compatible with the CP-850. Alas, no other cases need apply for partnership with the CP-850. The other highlighted snippet about dual printed circuit board layout isn’t clear right away, but it becomes evident when the unit is opened up.

Our technical contact at Antec mentioned several aspects of the CP-850 design long before the sample arrived. Fundamentally, the straight-through airflow with the big fan and the dual PCBs keeps all the core heat-generating components in the center of a bigger casing; the lower thermal/power density has many benefits for reliability, cooling and cost:

• Not only can components be kept cooler with lower fan rpm, but they don’t have to be rated for as high temperature, and still be extremely reliable and long lived. Lower temperature rated components means lower cost.
• More room in the casing means the option to use larger parts, which again are less costly than smaller power electronic parts of the same rating.

These engineering efficiencies allow very high power capability and performance at modest cost. This is a good thing: Without the attraction of lower price, a PSU with a form factor that can only be used with three cases is unlikely to be seriously considered by most buyers. A search on the SPCR Shopping Engine as of late August 2009 shows the CP-850 to be available for as low as US$115, which is a real bargain among premier PSU brands of similar power rating. (Antec’s own Signature 850 comes in at $215 and Seasonic M12D-850 at $180.)

The photo on the retail box tells the story of the fan. Nicely packed in closed cell foam with detachable output and AC cables, and a paper user guide. It’s modular and comes with many detachable output cables, but many cables are permanently attached.

EXTERNAL TOUR

The CP-850 is naturally bigger than most other power supplies. Specifically, it is much taller, 4.7" instead of the usual <3.5". The reason fo the extra height is the 120x25mm fan, which is actually mounted on the outside of the unit, presumably to save on space inside.

The externally mounted 120mm diamater in-blowing fan dictates the height of the CP-850, which is about 1.2" taller than standard ATX12V PSU form factor. Both detachable and attached cables are sleeved, but they are not sleeved all the way into the PSU, which leaves a bit of an untidy visible jumble. There are only four connectors for detachable cables against seven permanently attached cables; it seems more "hardwired" than "modular". The side which faces outward is nicely open hex-mesh grill with a couple of supporting ribs in the middle. There are no vents other than the exhaust mesh. Two PCBs are visible through the exhaust mesh, one at the top and one at the bottom: This is the "Dual PCB layout" reference made by Antec. The label provide lots of information. The CP-850 has four separate current-limited 12VDC output lines. One can only presume a reasonable distribution of these lines to the various 12V outputs.

OUTPUT CABLES

The CP-850 comes with many output cables.

Some cables are ~3′ long.

Permanently wired, sleeved:

• 1 – 24" cable w/ ATX 20+4-pin motherboard connector
• 1 – 24" cable w/ AUX12V 4-pin connector
• 1 – 24" cable w/ EPS12V 8-pin connector
• 2 – 18" cable w/ PCIe 12V 6+2-pin connector
• 1 – 36" cable w/ 3x SATA connectors
• 1 – 36" cable w/ 3x 4-pin Molex and 1x floppy connector

Modular, sleeved:

• 2 – 18" cable w/ 6-pin PCI-Express connector
• 2 – 36" cable w/ 3x SATA connectors
• 2 – 36" cable w/ 3x 4-pin Molex connectors

INTERIOR

The casing is a bit different from most PSUs. Instead of the usual dual [-shaped clamshell, the bottom panel opens up with the removal of four screws.

Opening up the bottom panel reveals a bit of a surprise, pointed out by the green arrow. It’s an airflow guide. The curved bump, made of semi-rubbery, plastic sheet material, is meant to force more of the fan’s airflow to pass closer to the heatsinks, the black aluminum extrusions visible in the open PSU above. The second PCB can now be seen for what it is: A rectangular part covering perhaps a quarter of the available area. This view shows both the main PCB with heatsinks oriented to take advantage of the fan’s airflow direction, as well as the smaller PCB. Here’s the same angle as the previous photo, but with the small PCB unscrewed and flipped a bit to show its populated components. It was identified by Antec as the transient filter circuit. One thought is whether the extra wiring and soldering between the two PCBs could cause current losses or voltage drops, compared to single PCB designs. Certainly, resistance would be lower with one PCB. The green arrow above points to a 4-pin connector whose wires go to the PWM fan from a peripheral PCB. This must be the fan controller circuit — at least partly. The main portion of the PCB is difficult to examine without taking the entire unit apart, so let’s refer you to the review by OklahomaWolf at Johnnyguru.com for all the gory details. (Hint: The Wolf really geek-drooled over his sample. lol!) Protechnic / Magic is a fan brand Antec has not used in the past. The geometry of the 7-blade 120x25mm 0.52A fan looks good; the trailing edges of the blades are not parallel to the struts, which usually helps to minimize tonal noise. (See Fan Blade Geometry on page 3 of the Anatomy of the Silent Fan for more details.) The manufacturer states that it is a dual-ball bearing model rated for 12VDC, 93CFM, 2800 RPM, at 42 dBA.

TESTING

For a fuller understanding of ATX power supplies, please read
the reference article Power
Supply Fundamentals. Those who seek source materials
can find Intel’s various PSU design guides at Form
Factors.

For a complete rundown of testing equipment and procedures, please
refer to SPCR’s
PSU Test Platform V4.1. The testing system is a close simulation of
a moderate airflow mid-tower PC optimized for low noise.

Acoustic measurements are now performed in our anechoic chamber with ambient level of 10~11 dBA, with a PC-based spectrum analyzer comprised of SpectraPLUS software with ACO Pacific microphone and M-Audio digital audio interfaces.

In the test rig, the ambient temperature of the PSU varies proportionately
with its output load, which is exactly the way it is in a real PC environment.
But there is the added benefit of a high power load tester which allows incremental
load testing all the way to over 1000W.
Both fan noise and voltage are measured at various standard loads. It is, in
general, a very demanding test, as the operating ambient temperature of the
PSU often reaches >40°C at full power. This is impossible to achieve
with an open test bench setup.

The 120mm fan responsible for "case airflow" is deliberately
run at a steady low level (6~7V) when the system is run at "low"
loads. When the test loads become greater, the 120mm fan is turned up to a higher
speed, but one that doesn’t affect the noise level of the overall system. Anyone
who is running a system that draws ~400W or more would definitely want more than
20CFM of airflow through their case, and at this point, cooling is the main concern, not the noise level.

Great effort has been made to devise as realistic
an operating environment for the PSU as possible, but the thermal and noise
results obtained here still cannot be considered absolute. There are too many
variables in PCs and too many possible combinations of components for any single
test environment to provide infallible results. And there is always the bugaboo
of sample variance. These results are akin to a resume, a few detailed photographs,
and some short sound bites of someone you’ve never met. You’ll probably get
a pretty good overall representation, but it is not quite the same as an extended
meeting in person.

REAL SYSTEM POWER NEEDS: While we test the PSU to full
output in order to verify the manufacturer’s claims, real desktop PCs simply
do not require anywhere near this level of power. The most pertinent range of
DC output power is between about 40W and 300W, because it is the power range
where most systems will be working most of the time. To illustrate this point,
we
conducted system tests to measure the power draw of several actual systems
under idle and worst-case conditions. Our most power-hungry overclocked
130W TDP processor rig with an ATI Radeon X1950XTX-512 graphics card drew ~256W
DC peak from the power supply under full load — well within the capabilities
of any modern power supply. Please follow the link provided above to see the
details. It is true that very elaborate systems with the most power hungry dual
video cards today might draw as much as another 150~200W, but the total should
remain under 500W in extrapolations of our real world measurements.

INTERPRETING TEMPERATURE DATA

It important to keep in mind that PSU fan speed varies with temperature,
not output load. A power supply generates more heat as output increases, but
is not the only the only factor that affects fan speed. Ambient temperature
and case airflow have almost as much effect. Our test rig represents a challenging
thermal situation for a power supply: A large portion of the heat generated
inside the case must be exhausted through the power supply, which causes a corresponding
increase in fan speed.

When examining thermal data, the most important indicator of cooling
efficiency is the difference between intake and exhaust. Because
the heat generated in the PSU loader by the output of the PSU is always the
same for a given power level, the intake temperature should be roughly the same
between different tests. The only external variable is the ambient room temperature.
The temperature of the exhaust air from the PSU is affected by several factors:

The thermal rise in the power supply is really the
only indicator we have about all of the above. This is why the intake temperature
is important: It represents the ambient temperature around the power supply
itself. Subtracting the intake temperature from the exhaust temperature gives
a reasonable gauge of the effectiveness of the power supply’s cooling system.
This is the only temperature number that is comparable between different reviews,
as it is unaffected by the ambient temperature.

TEST RESULTS

Ambient conditions during testing were 24°C and 11 dBA. AC input was 118~122V,
60Hz. .

ANALYSIS

1. EFFICIENCY — This is a measure of AC-to-DC
conversion efficiency. The ATX12V v2.2 Power Supply Design Guide recommends 80% efficiency
or better at all output power loads. 80% efficiency
means that to deliver 80W DC output, a PSU draws 100W AC input, and 20W is lost
as heat within the PSU. Higher efficiency is preferred for reduced energy consumption
and cooler operation. It allows reduced cooling airflow, which translates
to lower noise.

Our CP-850 sample clearly met 80 Plus requirements. The 80% efficiency point was reached before 90W, which is low and very good for a PSU rated for 850W; 80 Plus only calls for 80% efficiency at 20% of capacity load, or 170W in this case. A broad efficiency peak of 83~85% was reached between 200W~500W, above which it fell off a bit. Our sample’s failure to maintain 80% efficiency at full load is by now a well-known consequence of SPCR’s torture chamber hot box, which subjects the PSU to an extreme level of heat. In contrast, 80 Plus tests PSUs in normal room temperature, under which conditions the 80 Plus tested sample reached 80.91% efficiency at full load.

2. VOLTAGE REGULATION refers to how stable the output voltages
are under various load conditions. The ATX12V Power Supply Design Guide calls
for the +12, +5V and +3.3V lines to be maintained within ±5%.

All the output lines were rock solid stable under all load conditions. The biggest variation was +0.1V on the 12V line at very load load. This represents +0.8%. The virtual absence of any drop in voltage below target at full load on all three main DC lines was most impressive.

3. AC RIPPLE refers to unwanted "noise"
artifacts in the DC output of a switching power supply. It’s usually very high
in frequency (in the order of 100s of kHz). The peak-to-peak value is measured.
The ATX12V Guide allows up to 120mV (peak-to-peak) of AC ripple on the +12V
line and 50mV on the +5V and +3.3V lines.

Ripple was vanishingly low on all the lines. At low loads at the start of testing, the 12V ripple actually did not often rise above 10 mV, and the lower voltage output lines stayed well in single digits. Only at extreme loads did some peaks reach above 20 mV on the 12V line. The maximum peaks seen for the +5V and +3.3V lines were in the teens. This is exceptionally low ripple noise.

4. POWER FACTOR is ideal when it measures 1.0. In the most
practical sense, PF is a measure of how "difficult" it is for the
electric utility to deliver the AC power into your power supply. High PF reduces
the AC current draw, which reduces stress on the electric wiring in your home
(and elsewhere up the line). It also means you can do with a smaller, cheaper
UPS backup; they are priced according to their VA (volt-ampere) rating. PF on our sample was close to the theroretical perfection of 1.0 at virtually all loads.

5. LOW LOAD PERFORMANCE is significant mainly to minimize energy waste and with system that demand very low power; the latter can cause some PSUs not to start. Standby power was very low with 0.4W draw. The unit powered up with no load, drawing 9.4W, suggesting it has a built-in loader to prevent low loads from causing trouble.

6. CROSSLOAD TEST – Basically the load on the 12V line was maximized while the load on all the other lines was minimized. Voltage regulation on all the lines remained excellent, and ripple stayed extremely low. There were no other changes.

7. 240 VAC INPUT – The power supply was set to 700W load with 120VAC through the
hefty variac in the lab. The variac was then dialed 10V lower every 5 minutes.
This is to check the stability of the PSU under brownout conditions where the
AC line voltage drops from the 110~120V norm. Most power supplies achieve higher efficiency
with higher AC input voltage. SPCR’s lab is equipped with a 240VAC line, which
was used to check power supply efficiency for the benefit of those who live
in 240VAC mains regions.

There were no surprises here. Our sample’s efficiency improved by nearly 3% at the higher VAC, and dropped a little less than 1% for each 10VAC drop. Voltage regulation and ripple were unchanged.

8. NOISE and FAN CONTROL

The voltage across the fan leads could not be monitored due to the use of PWM for the speed control. However, the reason we monitor the fan in the first place is for the noise, and SPL was well recorded here.

The noise level at startup was inaudible at 12 dBA@1m, at least from one meter distance. Only within about 6" of the unit could the fan or any electronic noise be heard. Amazingly, this sound level was maintained all the way to over 200W load. This is about as quiet as the Nexus Value 430 at low load, but the CP-850 maintains the low noise to a much higher power load, like the Seasonic M12D-850, 14 dBA@1m to over 300W.

The audio spectrum was benign and extremely low in amplitude to over 200W load.

The first sign of any audible increase occurred at 250W, when the SPL went up to 14 dBA@1m. It was not until 400W load that the noise finally became plainly audible at 26 dBA@1m. Beyond that power level, the fan ramped up in speed more or less linearly, reaching the maximum of 44-45 dBA by 600W load. The character of the fan was generally good, with a bit of chuffing at some middle speeds, but no obvious or annoying tonalities.

9. COOLING

The CP-850 kept itself very well cooled, especially at the highest loads. It was at 10°C rise or lower through the whole range until the maximum power load. The mere 12°C rise through the PSU at full 850W (for about 20 minutes after 2-3 hours of continuous load testing) was very impressive. It is, in fact, a record: The next coolest PSU at that load was the Seasonic M12D-850 with 19°C rise. Most others anywhere near this power level climb way past 20°C rise, and most move into double digit temperatures past ~400W. It’s probably safe to say that the superior cooling can be attributed to the combination of the powerful fan and the straight-through design which makes the airflow more effective.

COMPARISONS

The comparison table below shows the SPL versus Power Load data on all the PSUs tested in the anechoic chamber thus far.

The green colored blocks are 30 dBA@1m or greater SPL readings. The PSU that stayed quiet (under 30 dBA) to the highest load is not in this table because it has not been tested in the anechoic chamber: The Zalman ZM1000, which stayed below 30 dBA to almost 600W load. Its idle noise was not low enough, however, to match many of the PSUs in the above table; its measured SPL in the live test room was 20 dBA@1m, which would put it higher than any PSUs measured better than 16~18 dBA in the anechoic chamber.

Caution: Please keep in mind that the data in the above table is specific to the conditions of our test setup. Change the cooling configuration, the ambient temperature and any number of other factors, and you could change the point at which the fans start speeding up, as well as the rate of the rise in speed. The baseline SPL is accurate, however, probably to within 1 dBA.

As pointed out on the previous page, when employed in one of Antec compatible cases, the CP-850 will probably stay quieter to a higher power level than any other fan-cooled PSU.

CONCLUSIONS

The Antec CP-850 is a superlative power supply by almost any standard. Its electrical performance is up at the level of its more expensive brethren, the Signature 650 and 850, and Seasonic’s flagship, the M12D-850: Voltage regulation is extremely tight for all the lines at all loads, and the ripple noise is amazingly low. (An Aside: The CP-850’s performance makes me ponder again whether the best PSUs, going back even a couple of years, aren’t already much better than they need to be. Is there really any benefit to having 1% tolerance for the 12V line? Or 20mv ripple instead of 120mv?) Efficiency is not quite up to the best, but it’s nothing to be embarassed about.

The noise performance is excellent, with the <400W performance matching or bettering virtually every PSU tested thus far. Above 500W load in our heat box, the noise level goes over 40 dBA@1m, or about the norm for PSUs rated this high. It has the virtue keeping itself extremely cool, however, cooler than any other PSU we’ve tested at such high loads.

A serious consideration is that in each of the three compatible Antec cases, the CP-850 mounts on the bottom, and the intake for the PSU is quite separate from the rest of the system. In the P193 and P183, the PSU is in an entirely separate thermal chamber, and in the model 1200, a direct path can be maintained to the directly opposite, wide-open front vent. This means that our extreme hot box test conditions never apply to the CP-850; in other words, SPCR’s test environment is unrealistically hot for the CP-850. Our atypical spot check with a room ambient thermal test showed the CP-850 would reach only 24 dBA@1m at 700W load in a 27°C working environment. This is ridiculously quiet for such high power output.

The above is an obviously unfair advantage for the CP-850… but what of it? Antec has used an integrated systems approach for its CP-850 and its best cases, and if that approach is an advantage over all other case/PSU combinations, then, all the more power to Antec! It’s not uncommon for enthusiasts to frequently replace the motherboard and components that mount onto it — such as CPU, RAM and video card — while the case and PSU are retained. There would be ample reason to take that approach with the CP-850 and one of the compatible Antec cases.

For the quiet-seeking computer gaming enthusiast, the CP-850 (along with any of the three compatible cases) is something of a godsend. Fantastically stable power, super low noise at any power load, long expected reliability due to excellent cooling, modular cabling, and all at a price that’s no higher than many high end 6~700W models. That you’re limited to one of three well-executed high cases from Antec — one mostly for silence (P183), one mostly for gaming (1200) and one that’s really an ultimate everyman case (P193) — is not exactly a hardship either.

The CP-850 is non-standard, but compelling, and in its typical application, as powerful and quiet a PSU as anyone will ever need. It could become a game-changing product if compatible cases become more widespread. Should Antec manage to persuade any PSU or case makers to produce CPX-conforming products, it might help breath a new lease on life on the embattled ATX tower case sector. No, ATX is not about to roll over and die any time soon, but it is in a period of decline as smaller, ready-made PCs increasingly dominate along with laptops. Kudo to Antec for taking a chance and creating a unique, compelling product.

Our thanks to Antec for the CP-850 sample.

SPCR Editor’s Choice Award

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SPCR Articles of Related Interest:
Power Supply Fundamentals
SPCR PSU Test Rig V.4
Recommended PSUs

Nexus NX-8500

Coolermaster Silent Pro M700W
Chill Innovation CP-700M
Seasonic M12D-850

Zalman ZM1000-HP
Antec P183 Case

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