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SilverStone ST45SF-G 450W SFX Form Factor PSU Review

Author: Lee Garbutt
Manufacturer: SilverStone

AC Ripple and Power Factor

AC Ripple and Noise on the DC Outputs

The amount of AC ripple and noise present on the DC 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.  I adjusted the O-scope time base to look for AC ripple at both low and high frequencies. 

The ATX12V V2.2 specification for DC output noise/ripple is defined in the ATX12V Power Supply Design Guide.

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Ideally we would like to see no AC ripple (repetitive) or noise (random) 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 the power supply complied with the ATX standard.  The following table lists the ripple/noise results during all of the load tests for the main output voltages of interest.

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While not as good as some high-end ATX PSUs, the SilverStone ST45SF-G still exhibited acceptable AC ripple suppression on all four of the primary DC outputs and stayed well within the recommended guidelines.

Power Factor (PF)

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.

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AC Volts x AC Amps = VA (Volt Amp)

Purely Resistive AC Load: VA = Watts (same as DC circuits)
Inductive/Reactive AC Load: VA x PF = Watts

AC Volts x AC Amps x PF = Watts

I measured the AC Power Factor with an Extech power analyzer at both 115 VAC and 240 VAC input voltages.  The SilverStone ST45SF-G uses Active PFC circuits so as expected; the majority of readings were close to 1.00 at the higher loads. 

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Note: PF and efficiency is not the same thing.  A power supply with active PFC is more environmentally friendly (doesn’t pollute the AC transmission grid with harmonics) and will draw less current, but it will not save you money on your monthly electric bill unless you are a commercial user whose bill is based on PF and usage. 

November 6, 2012 | 12:23 PM - Posted by Kenneth (not verified)

I bought a Silverstone Strider ST50F-P psu about 2 years ago for a home server build. I bought it specifically to fit into a Lian Li PC-V354 case which has the psu standing on end over the mobo while looking at it from the side. I wanted a nice short psu that wasn't going to be tasked with high demand of power and it fit the bill. If I were to do it all over again, I am not sure I would go with this unit that was reviewed. While it is 40mm shorter overall and would give me a little bit more room to work in that particular case, it also has a 40mm smaller fan. I use that fan to pull air from the inside to the outside and the size trade off would be pretty steep. I guess this would be nice for a mini ITX build where space is at a super premium but otherwise I would still grab something with more air flow.

November 9, 2012 | 05:27 AM - Posted by Justin 150 (not verified)

I think the noise is the main issue here. Seems very well designed.

If you are not pulling more than 150W on load then a pico-psu is probably a better option. Even at 225W the Silverstone seems pretty quiet but from there upwards the noise seems to increase pretty rapidly.

If needing 300W + and have the space there are better options

November 19, 2012 | 08:29 AM - Posted by Robert123 (not verified)

Perfect upgrade for the sg05 & 06. esp if you have the older 300w versions.

December 31, 2012 | 09:40 AM - Posted by David López (not verified)

Be careful!. I have SG06, and this Power supply modular need some depth extra mm, because the connector is big than normal version.
It can be fit, but you need to make a lot of force, and curve a lot the wires, isn't god the modular version because need more space.

Other part is that the sound is horrible!, make a lot of plus sound than the standard version, even at 60-90W only of consumption!.
If you need more than 140W is horrible loud!

I open the power supply, and first I try to mount the fan outside the power supply chassis, and decrease some little db, because the little grid on intake increase loud, and the grid on outside pard not increase as intake. This decrease a little, but not to much, but you need 15mm extra of space, and be care of obstruction fan, and lost warranty of you new power supply.....

Today I will go to buy a fan for replace, I check this models that can be well (3000rpm models):

The stock fan reach 3500rpm at 42db, but I don't know cfm. I not remember the trademark, I thinbk was similar than rfl, but I remember has 4 letters not three. Personality, for some around 4€ extra Silverstone can be put a better fan, and better control of speed, I not trust never more on Silverstone specifications.... they can be crazy when was putting silent on your specifications!

Other part is the rpm control have fails, bacause when increase the power consumption increase the rpm (and loud), but when you recover a low consumptions the rpm not decrease at the initial levels, and was more louder than the same consumption of before...

I made another easy mod that not need broke anything, I put a 60x60x25 silent fan rear the power supply extracting the air, I attached with prolimatech magnetic supports.

Because I think is better always that the pressure need to be positive, I put this extracting fan at low rpm, then the intake fan capabilities are better than this outtake fan capabilities.
For better dissipation the fresh air need to stay some seconds or miliseconds and arrive to all deepth of power supply. This is thinked normally for a good heat dissipation on cars, and I think is ok also for computer or all that need heat disipation.

If you not need more than 300W, the standard version is better. I have i7-3770T(80W), and also plus GTX 660(140W) the standard 300W Power supply is suficient, with plus margin for sata devices.

I buyed only for gold plus certification and for better quietness sound of the standard version, and I think a was make big mistake for this caprice....

If i know all this before, I never buyed, because is truth that I not need....