Summary

PC Power & Cooling is one of the most respected names in the PC power supply industry. In this review we will be taking an in-depth look at two of their newest units, the Silencer 360 ATX and the Silencer 410 ATX. The Silencer line was specifically designed for users seeking a powerful yet quiet power supply. In addition to the 360 ATX and 410 ATX, a Silencer 310 ATX is also available. These new models are advertised as being ultra-quiet, feature active PFC (Power Factor Correction) and now come with black enclosures.

PC Power & Cooling Silencer 360 ATX and Silencer 410 ATX power supplies

We evaluated both Silencer power supplies on features and performance. A full range of equipment was used to test each power supply under controlled load conditions. In addition to measuring the power going in and coming out we looked at voltage regulation, electrical noise (AC ripple), airflow, sound level, efficiency and cost.

There are three ATX power supplies available in the Silencer line: 310 watt, 360 watt, and 410 watt models. Not surprisingly, from the outside the only apparent difference between our 360 watt and 410 watt review samples is the name plate. But what I did find surprising was that on the inside they also appear almost identical. Upon closer inspection I noted the 410 had a few slightly larger components (heatsink, capacitor and fuse) and an extra capacitor that the 360 doesn't have.

PC Power & Cooling's new line of Silencer ATX power supplies offer more features and cost significantly less than the older Silencer 400 ATX, which was based on the Turbo-Cool 425 watt chassis. Overall, the two Silencer power supplies reviewed produced very good results. Both Silencer ATX units exhibited good voltage regulation with excellent stability and low AC ripple. (However, I would like to see the 3.3 VDC rail a little higher.) Both of the units tested include active power factor correction and produced above average efficiencies while operating under a moderately heavy load. I also like the look of the new black cases and fan grill. The following table summarizes the data collected during testing for the Silencer 360 ATX and Silencer 410 ATX power supplies.

For a more detailed technical review of the two PC Power & Cooling Silencer ATX power supplies, read the detailed review below.

Introduction

We evaluated both the Silencer 360 ATX and Silencer 410 ATX power supplies on features and performance. A full range of equipment was used to test each power supply under controlled load conditions. In addition to measuring the power going in and coming out we looked at voltage regulation, electrical noise (AC ripple), airflow, sound level, efficiency and cost. Here is a block diagram of the test bench setup and a list of the equipment I used during testing.

• FLUKE 87-III True RMS digital multimeter (Accuracy +/- 0.05% of 3-digit reading)
• WattsUp? Pro – digital wattmeter and power analyzer (Accuracy 3% of displayed value)
• Hitachi V-650F 60 MHz dual trace oscilloscope (Accuracy +/- 3% of input range)
• Powerstat Variable Autotransformer, 1.4 KVA, 0-140 VAC
• FLUKE  52-II digital thermometer (Accuracy +/- 0.3°C/0.5°F)
• Extech Model 407736 digital sound level meter (Accuracy +/- 1.5 dB)
• AccuLab V1-10kg digital balance (Accuracy +/- 1g)
• Homemade power supply load tester – selectable load, up to 300 watts

To be ATX compliant, a power supply must be designed and built according to a set of standards created by Intel ( ATX Specification – Version 2.1 ), which along with motherboard specifications also defines the size, form factor, connectors, voltage outputs, etc., that a power supply must incorporate.  More detailed information can be found in the ATX12V Power Supply Design Guide . 

The switching-mode power supplies used in modern PCs are designed to convert alternating current (AC) into direct current (DC) used by the computer's internal components.  A standard ATX power supply will produce three different voltages to power the motherboard, CPU, memory, hard drives, optical drives, etc.  These are: +3.3 volts, +5 volts, and +12 volts.  In addition, the PSU also generates several other voltages: -12 volts and +5 volts STBY (note: the -5 volt output was removed in ATX12V rev. 1.3).

Establishing a controlled load is critical to testing and evaluating a PC power supply.  I built my own power supply load tester using 11 wire-wound, ceramic resistors of various sizes.  This unit can place up to a ~300 watt load onto the power supply being tested.  Different combinations of resistors can be switched in or out to select various loads.  I will be using a 240 watt combined load to simulate a medium to heavily loaded typical PC.

The tester connects to the power supply thru the 20-pin ATX motherboard connector and two 4-pin Molex drive connectors. 

 Here is the Ohm's Law key if you are trying to remember how the different variables relate... :)

First Impressions

Like all PC Power & Cooling power supplies, the Silencers come securely packaged in a plain cardboard box. In addition to the power supply each box contains a set of Installation Instructions, mounting screws and a power cord.

These new Silencers come sporting a black matte finish with a black fan grill. An On-Off switch is now included on the back panel. 

There is no manual line voltage selector switch because the unit auto-detects the incoming voltage level.  This is a nice feature that avoids the potential damage that can be caused by inadvertently (or intentionally) setting a manual line voltage selector switch to the wrong voltage.

The PC Power & Cooling Silencer power supplies come with a full compliment of connectors including two dedicated Serial ATA drive connectors. 

(1)  ATX12V Main motherboard connector (20 pin)

(1)  12V Power connector Ì¢åå P4 (4 pin)

(8)  Peripheral HDD connectors (4 pin)

(1)  Peripheral FDD connector (4 pin)

(2)  Serial ATA power connectors (15 pin)

The wiring harnesses all measure approximately 17" long and none of them are sleeved.

Silencer ATX Power Supplies

There are three ATX power supplies available in the Silencer line: 310 watt, 360 watt, and 410 watt models. Not surprisingly, from the outside the only apparent difference between our 360 watt and 410 watt review samples is the name plate. But what I did find surprising was that on the inside they also appear almost identical. Upon closer inspection I noted the 410 had a few slightly larger components (heatsink, capacitor and fuse) and an extra capacitor that the 360 doesn't have.

PC Power & Cooling also decided to eliminate the unused -5 VDC output, which has been removed from the ATX12V rev. 1.3 guidelines. (Some older ISA cards used -5 VDC.)

The Silencer 360 and 410 incorporate the same 80 mm rear mounted, variable speed, exhaust fan. The Nidec fan is rated for a maximum airflow of 34 CFM with a noise rating of 20-32 dBA. Under relatively light loads the fan is very quiet & virtually inaudible. As the PSU load (and internal temperatures) increases, the fan speeds up and can become quite noticeable.

The specifications for the higher capacity Silencer 410 ATX are almost identical to the 360 ATX except for the maximum current ratings on the +3.3V, +5V, and +12V outputs.

The Silencer 410 looks almost identical to the 360 except for a few slightly larger components and an additional capacitor. As mentioned above, the major difference between the 360 and 410 is the increased amperage capacity on the +3.3V, +5V and +12 VDC outputs. Here are some pictures of the Silencer 410 ATX power supply with the cover removed.

And finally, here are a couple pictures of the Silencer 360 ATX and 410 ATX side by side for comparison. As you can see, they are almost as hard to tell apart looking inside as they are from the outside. (Note the slightly larger heatsink inside the Silencer 410 ATX.)

Testing - Physical Weight

One of the basic measures of any ATX power supply is the unit's overall physical weight. This may seem rather simplistic but it generally holds that more components and larger heatsinks equal a better PSU. Both Silencer power supplies were weighed on a digital balance.

I was a little surprised to find that both of the Silencer power supplies weighed a little less than an average ATX power supply in the ~400 watt range, including an older PC Power & Cooling Silencer 400 ATX I have from a year ago (2,131 g).

Testing - DC Output Voltage Regulation

To simulate real world operation, each power supply was connected to the load tester, supplied with 115 VAC, and allowed to burn-in for 24 hrs before voltage readings were taken. In this test we are interested in seeing how well a PSU can maintain the various output voltages while under a moderately heavy load. The DC output voltages were measured with a FLUKE digital multimeter at the ATX connector. 

The ATX tolerance for voltages states how much each output (rail) is allowed to fluctuate. PC Power & Cooling specifies ±5% for all outputs except for the -12 V output, which is ±10%.

The following table lists the DC voltage regulation results for the two Silencer PSUs.

As you can see, all of the DC outputs were held well within the ATX specification while operating under a 240 watt combined load. They were also rock solid with virtually no fluctuations during testing. I would prefer to see slightly higher values on the +3.3V lines however they are still well within tolerance.

Of particular interest are the three main power rails (+3.3V, +5V and +12V) and the 5VSB line. Maintaining these outputs at optimum levels is important to the reliable operation of any PC. If you push components (overclock/over-volt) then they become even more critical.

Testing - AC Ripple on DC Outputs

The amount of AC ripple present on the outputs was checked using an oscilloscope. This AC component may be present in the KHz range where most switching power supplies operate or it may be more prevalent at the 60 Hz line frequency. In each case, I adjusted the O-scope time base to look for AC ripple at both low and high frequencies. 

40 mV P-P on the +12 VDC output of the Silencer 360 ATX

The ATX specification for DC output noise/ripple is defined in the ATX12V Power Supply Design Guide.

Ideally we would like to see no AC noise on the DC outputs – the cleaner the better!  But in reality there will always be some present. I measured the amplitude of the AC signal (in millivolts, peak-to-peak) to see how well each power supply complied with the ATX standard. The following table lists the ripple/noise results during our 240 w load tests. The four main output voltages of interest (+3.3 V, +5.0 V, +12 V and +5 VSB) were recorded for each power supply after the 24 hr burn-in period.

Both of the Silencer power supplies exhibited very good AC ripple suppression on all of the measured outputs.

Testing - Input Voltage Line Regulation

During the previous load tests we set the AC input voltage to 115 VAC. This is an optimum value for most of the power supplies under test. To find out how well each Silencer power supply can handle under and over voltage conditions on the AC mains, I lowered the input voltage to 100 VAC and then raised it to 130 VAC with a Variac (variable autotransformer). Once again we are interested in seeing how well each PSU can maintain the various output voltages as the input line voltage fluctuates +/- 13% (+/- 15 VAC).

Both PSUs produced excellent line regulation with varying input voltage. 

Testing - Power Factor (PF)

Power factor (PF) is one of those mysterious properties of AC that even most electrical engineers have a hard time explaining. A thorough technical discussion goes beyond the scope of this review (not to mention this author's understanding).

Power factor is defined as the ratio of true power (measured in watts) to apparent power (measured in Volt Amps). It measures how effectively AC power is being used by a device. The difference between true power and apparent power is expressed as the power factor and results from the way true power and apparent power are measured. Ideally we would like to have true power and apparent power equal to one another, which would result in a PF of 1.00 or 100% effective power utilization. 

True power (also referred to as working power) defines power that produces work, heat and light. We see true power in DC circuits and in AC circuits that are powering purely resistive loads like a resistance heater or light bulb.

Apparent power is found only in AC circuits. Along with true power it also takes into account the extra power needed to create the alternating magnetic fields inside inductors (transformers and motors) and to charge capacitors. Devices that incorporate inductance and capacitance in an AC circuit are referred to as reactive loads. Reactive power does not produce any work. Nearly all AC devices include some form of reactive load, which causes the PF to be less than 1 and the apparent power to always be greater than the true power.

Apparent power can easily be found by multiplying the AC voltage times the AC current using the RMS (Root Mean Square) values. Apparent Power = Volts (RMS) x Amps (RMS) = VA

The basic formula for true power includes the power factor (the power factor compensates for the extra reactive power). True Power = Volts (RMS) x Amps (RMS) x PF = Watts

When AC is applied to a purely resistive load, the current rises and falls in almost perfect harmony with the voltage. Plotting a graph of the AC voltage and current will result in two classic sine waves that are in alignment with each other. But power supplies are not resistive loads. They include inductors and capacitors among other things, which result in a complex reactive load. A reactive load causes the alternating current to become out of phase with the alternating voltage. A load with predominantly inductive reactance will cause the current sine wave to lag behind the voltage sine wave by a certain amount (phase angle). When the two sine waves are in perfect alignment (purely resistive load) the Power Factor is 1.00. The more the current lags behind the voltage, the smaller the Power Factor value becomes. Having the current out of phase with the voltage can also induce harmonic distortions back onto the power lines.

For example, when AC is used to power a light bulb (resistive load), electricity flows thru the filament and is converted into heat and light. Under these conditions the true power and apparent power are essentially the same so the PF ~ 1. All of the incoming AC power is being effectively used. If that same AC has to first go thru a transformer or power supply (reactive load) before reaching the light bulb filament, extra current is required to create the magnetic fields inside the inductors and keep the PSU's capacitors charged. 

The added reactive power causes the apparent power to now be greater than the true power, which in turn decreases the PF to something less than 1.00. This extra reactive power does no real work so is factored out (power factor) when the true power of the circuit is measured.

Switching mode power supplies can have a detrimental affect on the AC mains because of the reactive load they induce and by the harmonic distortions they generate. This type of power supply can draw highly distorted current from the AC mains, which may adversely affect other equipment on the same circuit.

Reactance and waveform distortions work together causing the PSU to draw more power than is actually converted into DC power and heat. With a PF of 0.66, a power supply will use 50% more power (100 watts / 150 VA = 0.66 PF) than it converts into DC power and heat.

Some PC switching mode PSUs contain Power Factor Correction (PFC) components and circuits.  Passive PFC typically adds a capacitor onto the AC input while Active PFC incorporates more sophisticated circuitry. Active PFC is usually only found in higher wattage and more expensive units and is required in many European Union countries. A power supply that does not have any PFC will normally exhibit a PF of <0.70 and will generate significant harmonics, which can distort the AC source waveform. Power supplies with active PFC will have power factors >0.95 with minimal harmonics.

Active PFC (PF=0.99)       Passive PFC (PF=0.75)           No PFC (PF= 0.55)

What this really means to the end user is that a PSU with PFC will pull less current from the AC mains to generate the same amount of DC power as a similar non-PFC unit. For commercial users who are billed based on VA usage and PF, this may save you money. However, most residential users are billed per kilowatt-hour, which ignores the load's reactive power component. Because of this a PSU with active PFC won't save the typical residential user any money on their electric bills.  However if you have a room full of computers operating on a single circuit, equipping them with PFC power supplies will draw significantly less current (therefore allowing more computers :)

I measured the AC Power Factor with a WattsUp? Pro power analyzer.  Both of the Silencer units incorporate active power factor correction circuits, which resulted in a PF reading of 0.99. 

The average AC current draw for the two Silencer units was approximately 2.9 Amps. This is considerably lower than the 4.2~4.5 Amps average AC current drawn by most non-PFC power supplies in the same size range operating under the same load. So our tests support the theory that incorporating active PFC does significantly reduce a power supply's AC current draw.

One final note on power factor: a power supply that incorporates active PFC circuitry might seem to be more efficient than one that does not have PFC. It's true a PFC power supply will pull less current than one without PFC but because of the way power supply efficiency is calculated, it is technically not more efficient than a comparable unit without PFC. This is because true power (watts) is used in the efficiency calculation, not apparent power (VA). A power supply with active PFC is more effective at converting electrical power but is not necessarily more efficient.

A power supply with active PFC is also more environmentally friendly (doesn't pollute the AC transmission grid) and will use less current, but it will not save you money unless you are a commercial user whose bill is based on PF and usage. As we will see in the next section, the two Silencer power supplies with active PFC were only slightly more efficient than average non-PFC units even though they pulled substantially less current while operating under the same load. 

Testing - Efficiency

The efficiency of a power supply is defined by the power output divided by the power input and is usually expressed as a percentage. If a PSU were a 100% efficient (which none are) 400 watts of AC power going in would result in 400 watts of DC power coming out. In the real world there are always inefficiencies and power is lost in the form of heat during the conversion process.

According to the ATX12V Power Supply Design Guide, power supply efficiency should be a minimum of 70% at full load, 60% under a typical load, and 50% while under a light load. The input voltage was set to 115 VAC. I measured the AC power input with a WattsUp? Pro watt meter and calculated the combined DC power output by summing the products of all the DC outputs (volts x amps).

As you can see, both of the PC Power & Cooling Silencer PSUs exceeded the recommended 60%~70% range for a “typical” load (240 watts).  Spending a little more money up front to purchase an efficient power supply may very well pay for itself over the lifetime of the PC.

As mentioned in the previous section, having active PFC onboard does not “technically” make a power supply more efficient because efficiency is based on true power – watts, not apparent power – VA. In fact, active PFC can have a slight negative affect on overall PSU efficiency due to the extra circuitry. However, having a power supply with active PFC will reduce the computer's overall current draw and is more environmentally friendly to the AC distribution system.

Testing - Differential Temperature and Noise

The differential temperature across both Silencer power supplies was calculated by subtracting the ambient room air temperature (T in) from the temperature of the warm exhaust air flowing out of the power supply (T out). Thermocouples were placed at the air inlet and exhaust outlet of each power supply. The ambient room air temperature was 24¬"+C (75¬"+F) +/- 0.5¬"+C during testing.

T in = temperature of air entering power supply

T out = temperature of air exhausting from power supply

T-ch = T out - T in

Both of the Silencer power supplies use a temperature-controlled fan that speeds up as the load (internal heat generation) increases.

Sound pressure level readings were taken 3' in front of the PSU under test in an otherwise quiet room. Each power supply was placed on a foam rubber mouse pad during testing. The ambient noise level was ~30 dBA.  To my ears, anything over 40 dBA becomes noticeable and must be considered a potential noise source. 

The two Silencer power supplies were virtually silent while operating under a light load (<100 watts) but became slightly noisy when operated under a moderately heavy load requiring the single 80 mm fan to speed up to maintain adequate cooling. 

Price and Conclusions

Price - $/Watt

And finally we have pricing. The following table lists retail price for each power supply as shown on PC Power & Cooling's website (June, 2004). I have also included the average cost per watt. 

Any one who is familiar with PC Power & Cooling's traditional prices will immediately recognize that these new Silencer units are much less expensive than in previous years!

Conclusions

PC Power & Cooling's new line of Silencer ATX power supplies offer more features and cost significantly less than the older Silencer 400 ATX, which was based on the Turbo-Cool 425 watt chassis. Overall, the two Silencer power supplies reviewed produced very good results. 

Both Silencer ATX units exhibited good voltage regulation with excellent stability and low AC ripple. (However, I would like to see the 3.3 VDC rail a little higher.) Both of the units tested include active power factor correction and produced above average efficiencies while operating under a moderately heavy load. I also like the look of the new black cases and fan grill.

The following table summarizes the data collected during testing for the Silencer 360 ATX and Silencer 410 ATX power supplies.

While operating under a moderately light load the two Silencers were very quiet & almost inaudible. However, when operating under a heavy load and/or relatively warm ambient room temperatures with poor case cooling, then expect the fan to run at higher RPM and become noticeable.

Strengths:

• Excellent DC voltage stability
• Very low AC ripple (noise) on DC outputs
• Good DC voltage regulation (all rails within spec)
• Active power factor correction (PF = 0.99)
• Above average efficiency (>70% with typical load)
• Auto voltage select and Power On-Off rocker switch
• Very quiet while operating under moderately light load
• Serial ATA drive connectors
• 100,000 hr MTBF, backed by a 3-year warranty
• Low cost

Weaknesses:

• 3.3 VDC output on the low side (but still within the ATX spec)
• Cooling fan can become noticeable at high speed (heavy load)
• No nylon mesh sleeving on cables

The new Silencer ATX power supplies are a nice addition to PC Power & Cooling's full lineup of power supplies and accessories. These new units offer a lot of features and good value.

I would like to thank PC Power & Cooling for sending us these two power supplies to review. Check out a Silencer ATX or other high-quality power supply or cooling accessory the next time you are ready to build a new system or upgrade an existing one.