Introduction
ZM750-HP is a 750 W power supply from Zalman featuring a modular cabling system, a 120-mm fan and a heat-pipe-based heatsink to cool down the secondary rectifiers. We had already reviewed the 600 W model from this series, ZM600-HP, and liked it a lot. Let’s see if the 750 W model is also great.
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Figure 1: Zalman ZM750-HP.
This power supply is small, being 6 ½” deep (16.5 cm), while we’ve seen some products on the same power range using a bigger form factor, 7 3/32” (18 cm) deep.
As mentioned, this product has a 120-mm fan (dual ball bearing) on its bottom side, which is our preferred configuration.
Besides the main motherboard cable (20/24-pin connector) and the ATX12V/EPS12V cable (two ATX12V connectors that together form an EPS12V connector) this power supply has also one auxiliary power cable for video cards (6-pin connector) and one SATA power cable (with three SATA power plugs) coming directly from inside its housing.
This power supply comes also with a 6/8-pin auxiliary video card power cable, two SATA power cables with three SATA plugs each, three peripheral power cables with three standard peripheral power plugs each, one adaptor to convert any standard peripheral power plug into two floppy disk drive power plugs and a power adaptor for fans with speed control, i.e. you can choose to connect the fan to the +12 V wire (full speed) or to the +5 V wire (a little bit less than half the speed).
All wires used on this power supply are 16 AWG, which are thicker than the traditional 18 AWG wires used – which is outstanding. The only wire that isn’t 16 AWG is the -12 V wire (22 AWG), but this is far from being an issue since this output can handle very little current.
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Figure 2: Zalman ZM750-HP.
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Figure 3: Cables that come with the product.
ZM750-HP features active PFC, allowing Zalman to sell it in Europe. As for efficiency, Zalman says this unit has a maximum 86% efficiency. We think it is strange a manufacturer mentioning the maximum value for efficiency but not the minimum.
Like ZM600-HP, this power supply is manufactured by FSP, which is the company also in charge of power supplies from several other manufacturers, in particular OCZ GameXStream and StealthXStream series.
Let’s now take an in-depth look inside this power supply.
A Look Inside ZM750-HP
We decided to disassemble this power supply to see how it looks like inside, what is the design used and what components are used. Please read our Anatomy of Switching Power Supplies tutorial to understand how a power supply works inside and to compare this power supply to others.
This power supply has the exact same internal layout as Zalman ZM600-HP, but of course we expect to see some difference on the semiconductors used.
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Figure 4: Overall look.
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Figure 5: Overall look.
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Figure 6: Overall look.
Transient Filtering Stage
As we mentioned on other articles and reviews, the first place we like to take a look when opening a power supply to have a hint about its quality is its filtering stage. The recommend components for this stage are two ferrite coils, two ceramic capacitors (Y capacitors, usually blue), one metalized polyester capacitor (X capacitor, yellow component on the pictures below) and one MOV (Metal-Oxide Varistor). Very low-end power supplies use fewer components than that, usually removing the MOV and the first coil.
This power supply has one extra coil, one extra X capacitor and two extra Y capacitors, plus an extra X capacitor after the rectification bridges. It, however, does not have a MOV, component in charge of removing spikes coming from the power grid.
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Figure 7: Transient filtering stage (part 1).
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Figure 8: Transient filtering stage (part 2).
Now let’s have a more detailed discussion on the components used on ZM750-HP.
Primary Analysis
Let’s now take an in-depth look on the primary stage from ZM750-HP. For a better understanding, please read our Anatomy of Switching Power Supplies tutorial.
This power supply uses two GBU806 rectifying bridges connected in parallel on its primary, each one capable of delivering up to 8 A at 100º C for a total current limit of 16 A. Here we could see the first difference between ZM750-HP and ZM600-HP: the 600 W model uses two GBU606 bridges, which have a lower current limit (6 A each for 12 A total).
This is more than adequate rating for a 750 W power supply. The reason why is that at 115 V this unit would be able to pull up to 1,840 W from the power grid; assuming 80% efficiency, the bridges would allow this unit to deliver up to 1,472 W without burning these components. Of course we are only talking about these components and the real limit will depend on all other components from the power supply.
Like ZM600-HP, the reviewed model uses three power MOSFET transistors on its active PFC circuit, instead of just two like usual. The transistors used are three FCPF20N60, each one capable of delivering up to 12.5 A at 100º C (or 20 A at 25º C, see the difference temperature makes) in continuous mode or up to 60 A in pulse mode. The ZM600-HP we reviewed used different transistors, SPA20N60C3, which have similar specs: 13.1 A at 100º C or 20.7 A at 25º C. Thus we think the difference on the transistors here wasn’t technical but rather a business decision (different vendors, Fairchild vs. Infineon, respectively).
The active PFC capacitor is Taiwanese from OST and labeled at 85º C.
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Figure 9: Active PFC transistors and diode.
This power supply uses another two FCPF20N60 power MOSFET transistors on the traditional two-transistor forward configuration on its switching section. The 600 W model uses different transistors here, FQPF18N50V2, with a little bit lower continuous current limits (12.1 A at 100º C and 18 A at 25º C) but with a higher current limit in pulse mode (72 A at 25º C).
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Figure 10: Switching transistors and rectifying bridges.
The primary is controlled by a CM6800 integrated circuit installed on a small printed circuit board. This component is the most popular PWM/PFC combo controller.
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Figure 11: PFC/PWM controller.
So even though ZM600-HP and ZM750-HP use the exact same design on the primary, they use different semiconductors, in special rectifying bridges with higher current limits. Let’s see if the same thing happens on the secondary side.
Secondary Analysis
Zalman ZM750-HP has eight Schottky rectifiers on its secondary, four for the +12 V output, two for the +5 V output and two for the +3.3 V output. This configuration is identical to the one used by other power supplies based on the same project of ZM750-HP, like ZM600-HP, OCZ StealthXStream 600 W and OCZ GameXStream 700. But let’s see whether or not the components are identical.
The +12 V output is produced by four SBR30A45CT Schottky Rectifiers, each one capable of handling up to 30 A at 110º C (15 A per internal diode). The maximum theoretical current the +12 V line can deliver is given by the formula I / (1 - D) where D is the duty cycle used and I is the maximum current supported by the rectifying diode (which in this case is made by four 15 A diodes in parallel). Just as an exercise, we can assume a typical duty cycle of 30%. This would give us a maximum theoretical current of 86 A or 1,029 W for the +12 V output. The maximum current this line can really deliver will depend on other components, in particular the coil used.
The +5 V output is produced by two MBR3045CT Schottky Rectifiers, which is basically the same component with a different name (different vendor). The maximum theoretical current the +5 V line can deliver is given by the formula I / (1 - D) where D is the duty cycle used and I is the maximum current supported by the rectifying diode (which in this case is made by two 15 A diodes in parallel). Just as an exercise, we can assume a typical duty cycle of 30%. This would give us a maximum theoretical current of 43 A or 214 W for the +5 V output. The maximum current this line can really deliver will depend on other components, in particular the coil used.
The +3.3 V output is produced by another two MBR3045CT Schottky Rectifiers. The maximum theoretical current the +3.3 V line can deliver is given by the formula I / (1 - D) where D is the duty cycle used and I is the maximum current supported by the rectifying diode (which in this case is made by two 15 A diodes in parallel). Just as an exercise, we can assume a typical duty cycle of 30%. This would give us a maximum theoretical current of 43 A or 141 W for the +3.3 V output. The maximum current this line can really deliver will depend on other components, in particular the coil used.
As you can see, the rectifiers are clearly overspec'ed, especially the ones in charge of the +12 V outputs.
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Figure 12: +12 V rectifiers, +5 V rectifier and +3.3 V rectifier.
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Figure 13: +3.3 V rectifier, +5 V rectifier and +12 V rectifiers.
These are the same rectifiers used on Zalman ZM600-HP and OCZ GameXStream 700 W, while OCZ StealthXStream 600 W uses rectifiers with lower current limits (20 A per device, 10 A per internal diode) on the +12 V output.
So the main difference between Zalman ZM750-HP and ZM600-HP is on the primary side, not on the secondary.
The outputs are monitored by a PS232 integrated circuit, which supports the following protections: over current (OCP), under voltage (UVP) and over voltage (OVP). Any other protection that this unit may have is implemented outside this integrated circuit.
All the electrolytic capacitors from the secondary are Taiwanese from Capxon and Teapo, and labeled at 105º C as usual.
Power Distribution
On Figure 14 you can see this power supply label containing all its power specs.
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Figure 14: Power supply label.
This power supply features four +12 V virtual rails distributed like this:
- +12V1 (yellow with blue stripe wire): ATX12V/EPS12V connector.
- +12V2 (yellow with green stripe wire): Auxiliary video card power cable from the modular cabling system.
- +12V3 (solid yellow wire): Main motherboard connector, SATA and peripheral power plugs from the modular cabling system.
- +12V4 (yellow with black stripe wire): Auxiliary video card power cable coming from inside the power supply and SATA power cable coming from inside the power supply.
We think this distribution is satisfactory.
Let’s now see if this power supply can really deliver 750 W.
Load Tests
We made several tests with this power supply as described in the article Hardware Secrets Power Supply Test Methodology.
First we tested this power supply with five different loads patterns, trying to pull around 20%, 40%, 60%, 80% and 100% of its labeled maximum capacity (under “% Max Load” we list the actual percentage that was used), watching how the reviewed unit behaved under each load. On the table below we list the load patterns we used and the results for each load.
If you add all the powers listed for each test you may find a value different from what posted under “Total” below. Since each output can have a slight variation (e.g. +5 V output working at 5.10 V) the actual total amount of power being delivered is slightly different from the calculated value. On “Total” row we are using the real amount of power being delivered, as measured by our load tester.
+12V1 and +12V2 are the two independent +12V inputs from our load tester and during out tests the +12V1 input was connected to the power supply +12V3 (main motherboard cable and peripheral power connectors) and +12V4 rails (video card auxiliary power connector), while the +12V2 input was connected to the power supply +12V1 rail (EPS12V connector).
By the way, this pattern is similar to the one we used with Corsair TX750W.
Input | Test 1 | Test 2 | Test 3 | Test 4 | Test 5 |
+12V1 | 5 A (60 W) | 11 A (132 W) | 17 A (204 W) | 24 A (288 W) | 33 A (396 W) |
+12V2 | 5 A (60 W) | 10 A (120 W) | 15 A (180 W) | 20 A (240 W) | 22 A (264 W) |
+5V | 2 A (10 W) | 4 A (20 W) | 6 A (30 W) | 8 A (40 W) | 8 A (40 W) |
+3.3 V | 2 A (6.6 W) | 4 A (13.2 W) | 6 A (19.8 W) | 8 A (26.4 W) | 8 A (26.4 W) |
+5VSB | 1 A (5 W) | 1 A (5 W) | 1.5 A (7.5 W) | 2 A (10 W) | 2.5 A (12.5 W) |
-12 V | 0.5 A (6 W) | 0.5 A (6 W) | 0.5 A (6 W) | 0.5 A (6 W) | 0.8 A (9.6 W) |
Total | 148.9 W | 297.9 W | 448.1 W | 608.6 W | 740.0 W |
% Max Load | 19.9% | 39.7% | 59.7% | 81.1% | 98.7% |
Room Temp. | 47.0º C | 46.9º C | 47.3º C | 48.3º C | 52.1º C |
PSU Temp. | 48.3º C | 48.9º C | 47.7º C | 50.2º C | 52.8º C |
Voltage Stability | Pass | Pass | Pass | Pass | Pass |
Ripple and Noise | Pass | Pass | Pass | Pass | Pass |
AC Power | 168 W | 332 W | 502 W | 699 W | 873 W |
Efficiency | 88.6% | 89.7% | 89.3% | 87.1% | 84.8% |
Final Result | Pass | Pass | Pass | Pass | Pass |
Zalman ZM750-HP proved to be an outstanding product. Efficiency when delivering between 40% and 60% of its labeled power (between 300 W and 450 W) was at 89% and the lowest efficiency we’ve seen was when the unit was delivering 740 W, at practically 85%, which is a number far from low.
Voltage stability was impressive, with all outputs – including -12 V – always within 3% from their nominal values (the maximum allowed is 5%; 10% for -12V).
Noise level was always below the maximum allowed, even though we’d prefer to see lower numbers for the +5 V and +3.3 V outputs. Below you can see noise level when we were pulling 740 W (test number five) from this power supply. Just to remember, the maximum allowed for the +12 V outputs is 120 mV peak-to-peak and the maximum allowed for the +5 V and +3.3 V outputs is 50 mV peak-to-peak.
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Figure 15: Noise level at +12V1 input from our load tester with the reviewed unit delivering 740 W (51.4 mV).
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Figure 16: Noise level at +12V2 input from our load tester with the reviewed unit delivering 740 W (54.6 mV).
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Figure 17: Noise level at +5 V input from our load tester with the reviewed unit delivering 740 W (30.4 mV).
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Figure 18: Noise level at +3.3 V input from our load tester with the reviewed unit delivering 740 W (29.6 mV).
Let’s now see if we could pull even more power from ZM750-HP
Overload Tests
Before overloading power supplies we always test first if the over current protection (OCP) circuit is active and at what level it is configured.
OCP kicked in when we tried to pull more than 24 A from +12V2 input from our load tester (which was connected to the power supply +12V1 thru the ATX12V/EPS12V cable). The label says that each rail has a limit of 20 A, so OCP was configured the way we like: close to the limit printed on the label.
Below you can see the maximum values we could pull from this power supply. If we tried to pull more than that the power supply wouldn’t turn on, showing that one of its protections was in action, which is terrific.
Input | Maximum |
+12V1 | 33 A (396 W) |
+12V2 | 24 A (288 W) |
+5V | 18 A (90 W) |
+3.3 V | 18 A (59.4 W) |
+5VSB | 2.5 A (12.5 W) |
-12 V | 0.8 A (9.6 W) |
Total | 851.6 W |
% Max Load | 113.5% |
Room Temp. | 49.8º C |
PSU Temp. | 50.9º C |
AC Power | 1,040 W |
Efficiency | 81.8% |
As you can see even during this extreme condition efficiency was above 80%, which is nice. And, like we mentioned, the power supply won’t burn if you try to pull more than it can handle: it will simply shut down.
Main Features
Zalman ZM750-HP power supply main specs include:
- Nominal labeled power: 750 W.
- Measured maximum power: 851 W at 50º C.
- Labeled efficiency: 86% maximum.
- Measured efficiency: Between 85% and 90%.
- Active PFC: Yes.
- Modular Cabling System: Yes.
- Motherboard Power Connectors: One 20/24-pin connector and two ATX12V connectors that together form an EPS12V connector.
- Video Card Power Connectors: One 6-pin connector and one 6/8-pin connector.
- Peripheral Power Connectors: Nine in three cables.
- Floppy Disk Drive Power Connectors: Two (converted from one standard peripheral power plug).
- SATA Power Connectors: Nine in three cables.
- Protections: over voltage (OVP, not tested), over current (OCP, tested and working), over temperature (OTP, not tested) and short-circuit (SCP, tested and working).
- Warranty: 3 years.
- Real manufacturer: FSP
- More Information: http://www.zalmanusa.com
- Average price in the US: USD 125.00.
* Researched at Newegg.com on the day we published this review.
Conclusions
Zalman ZM750-HP is an excellent 750 W power supply. It can deliver up to 850 W at 50º C, has high efficiency (up to 90%) even when delivering its labeled power (85% at 750 W), electrical noise level inside specs and outstanding voltage stability, probably due to its thicker wires (16 AWG instead of 18 AWG). And what is great, it comes with a very attractive price tag for a 750 W product that can deliver what is promises and plus some more (Zalman says this unit can deliver up to 86% efficiency, but this is an understatement).
Even though it has far more peripheral cables you will ever need (nine SATA power plugs and nine standard peripheral power plugs) it comes with only two power cables for video cards. This is the only flaw from this product. It can easily power two very high-end video cards like GeForce GTX 260, GTX 280, Radeon HD 4870, etc but you won’t be able to install two of these card in SLI or CrossFire mode directly. Since these video cards require two auxiliary power connectors each, you will need to use adaptors to convert some of the standard peripheral power plugs into video card auxiliary power plugs.
Corsair TX750W, for example, is cheaper and does not have this problem (it comes with four video card cables), but provides lower efficiency and higher noise levels.
This is the reason we are giving this product our “Silver Award” instead of Golden, as we think a product on this power range must have four auxiliary power connectors for video cards.
Internally ZM750-HP uses the same project as Zalman ZM600-HP, OCZ StealthXStream 600 W and OCZ GameXStream 700. While the secondary from ZM750-HP is identical to the secondary from ZM600-HP and GameXStream 700 W (StealthXStream 600 W uses rectifiers with lower current limits), the primary is different, using components with higher current limits, especially the rectifying bridges (16 A vs. 12 A).
Originally at http://www.hardwaresecrets.com/article/661
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