DeepCool DQ750 ST PSU Review

1. Introduction2. DeepCool DQ750 ST3. DeepCool DQ750 ST (External)4. DeepCool DQ750 ST (Internal)5. High Res Gallery6. Testing Methodology & Results7. Closing Thoughts8. View All Pages

Correctly testing power supplies is a complex procedure and KitGuru have configured a test bench which can deliver up to a 2,000 watt DC load. Due to public requests we have changed our temperature settings – previously we rated with ambient temperatures at 25C, we have increased ambient temperatures by 10c (to 35c) in our environment to greater reflect warmer internal chassis conditions.

We use combinations of the following hardware:
• SunMoon SM-268
• CSI3710A Programmable DC load (+3.3V and +5V outputs)
• CSI3711A Programmable DC load (+12V1, +12V2, +12V3, and +12V4)
• Extech Power Analyzer
• Extech MultiMaster MM570 digital multimeter
• Extech digital sound level meter
• Digital oscilloscope (20M S/s with 12 Bit ADC)
• Variable Autotransformer, 1.4 KVA

We test with the +12V in single rail mode.

DC Output Load Regulation
Combined DC Load	+3.3V		+5V		+12V		+5VSB		-12V
	A	V	A	V	A	V	A	V	A	V
75W	1.24	3.34	1.19	4.97	4.95	12.03	0.50	5.00	0.20	-12.00
150W	2.16	3.33	2.83	4.90	10.07	12.00	1.00	5.00	0.30	-12.01
375W	6.17	3.32	6.06	4.87	26.17	11.97	1.50	5.00	0.50	-12.02
565W	10.31	3.30	10.85	4.84	38.34	11.87	2.00	4.97	0.60	-12.03
750W	10.71	3.28	13.85	4.82	53.60	11.82	3.00	4.92	0.80	-12.05

Load regulation rates as a pass. I have seen much better results this year from other 750 watt units although there is nothing here to raise any major concerns.

DeepCool DQ750 ST	Maximum Load
	757W

We managed to reach around 757W before the unit would shut down gracefully. Or another 7 watts over the rated maximum.

Next we want to try Cross Loading. This basically means loads which are not balanced. If a PC for instance needs 500W on the +12V outputs but something like 30W via the combined 3.3V and +5V outputs then the voltage regulation can fluctuate badly.

Cross Load Testing	+3.3V		+5V		+12V		-12V		+5VSB
	A	V	A	V	A	V	A	V	A	V
734W	1.0	3.33	1.0	4.97	60.0	11.79	0.2	-12.00	0.50	5.00
154W	15.0	3.27	15.0	4.76	2.0	12.02	0.2	-12.01	0.50	4.97

The unit dealt with the cross loading test however there was quite a lot of movement on the +5V and +12V rails.

We then used an oscilloscope to measure AC ripple and noise present on the DC outputs. We set the oscilloscope time base to check for AC ripple at both high and low ends of the spectrum.

ATX12V V2.2 specification for DC output ripple and noise is defined in the ATX 12V power supply design guide.

ATX12V Ver 2.2 Noise/Ripple Tolerance
Output	Ripple (mV p-p)
+3.3V	50
+5V	50
+12V1	120
+12V2	120
-12V	120
+5VSB	50

Obviously when measuring AC noise and ripple on the DC outputs the cleaner (less recorded) means we have a better end result. We measured this AC signal amplitude to see how closely the unit complied with the ATX standard.

AC Ripple (mV p-p)
DC Load	+3.3V	+5V	+12V	5VSB
75W	5	10	15	10
150W	5	10	20	10
375W	10	15	35	15
565W	15	15	55	15
750W	15	20	75	25

Ripple suppression is decent, although far short of the best we have tested in recent months. The +12V rail peaks at 75mV under full load conditions which is a little higher than we would like to see.

Efficiency (%)
75W	87.66
150W	90.43
375W	91.92
565W	91.13
750W	90.21

The power supply delivers great efficiency results, peaking at close to 92% at 50% load. This drops to around 90% at full load.

We take the issue of noise very seriously at KitGuru and this is why we have built a special home brew system as a reference point when we test noise levels of various components. Why do this? Well this means we can eliminate secondary noise pollution in the test room and concentrate on components we are testing. It also brings us slightly closer to industry standards, such as DIN 45635.

Today to test the power supply we have taken it into our acoustics room environment and have set our Digital Sound Level Noise Decibel Meter Style 2 one meter away from the unit. We have no other fans running so we can effectively measure just the noise from the unit itself.

As this can be a little confusing for people, here are various dBa ratings in with real world situations to help describe the various levels.

KitGuru noise guide
10dBA – Normal Breathing/Rustling Leaves
20-25dBA – Whisper
30dBA – High Quality Computer fan
40dBA – A Bubbling Brook, or a Refrigerator
50dBA – Normal Conversation
60dBA – Laughter
70dBA – Vacuum Cleaner or Hairdryer
80dBA – City Traffic or a Garbage Disposal
90dBA – Motorcycle or Lawnmower
100dBA – MP3 Player at maximum output
110dBA – Orchestra
120dBA – Front row rock concert/Jet Engine
130dBA – Threshold of Pain
140dBA – Military Jet takeoff/Gunshot (close range)
160dBA – Instant Perforation of eardrum

Noise (dBA)
75W	<28.0
150W	<28.0
375W	30.8
565W	34.3
750W	37.3

At 375 watts demand the large fan starts to spin up a little, hitting a noise rating at close to 31dBa. When the fan spins up in the last 250 watts of power delivery, the noise levels increase noticeably.

This power supply is reasonably quiet when you are demanding 500 watts or less, which would be the general situation if you are using a system with a single, mid or even high end graphics card (R9 295X2 excluded).

Temperature (c)
	Intake	Exhaust
75W	36	41
150W	38	47
375W	39	52
565W	45	57
750W	47	62

The large fan maintains good thermals inside the chassis, peaking at +15c over intake at full load.

Maximum load	Efficiency
757W	89.94

For those interested, we measured efficiency when stressing the unit to breaking point. 89.94 percent efficiency at 757W … hardly practical, but interesting regardless.

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