Introduction

A decade ago, the 80 Plus program was introduced with the aim of promoting the development of more efficient and environmentally friendly computer power supplies units (PSUs). When it was officially included in the Energy Star 4.0 specification requirements in 2007, the program really took off, with every manufacturer who had not already certified their units sprinting to do so.

In 2008, it was already easy and fairly cheap to produce 80 Plus certified PSUs, making the original 80 Plus program somewhat obsolete, but the original standard was revised to include differing tiers of efficiency, starting with the 80 Plus Bronze, Silver, and Gold certifications. Two more levels, Platinum and Titanium, were introduced later. These "badges of honor" drove the manufacturers to funnel money into research in order to create better and more efficient units, and they significantly helped their marketing departments as well. Today, users can easily find 80 Plus Gold certified units at very reasonable prices for their home computers, and 80 Plus Titanium certified units for servers have already been available for a couple of years.

The race for more powerful and more efficient PSUs continues to this date, as every manufacturer is trying to get ahead of the competition by either developing more efficient units, or by producing cheaper units with the same level of efficiency. Today we will look at Corsair's attempt to show us who's the true king of the hill, as we are going to review the AX1500i, a fully digital 1500 Watts PSU with an 80 Plus Titanium certification and an impressive list of features.

The AX1500i is one of the first 80 Plus Titanium certified consumer PSUs, as well as one of the most powerful units currently available. These facts do help explain the rather insane retail price of $450, perhaps, but there's no question that this is a very niche product. With such a price tag and power output, the AX1500i is intended only for very advanced users and hardcore gamers who are willing to pay as much as a small home/office PC costs just to get the best PSU possible. However, this segment of the market is very demanding as well – does the Corsair AX1500i has what it takes to please such users? We will find out in this review.

Packaging and bundle

The black, serious cardboard box of the AX1500i somehow hints at the proportions of the power supply. It is not deeper or taller than typical PSU packaging, but it is much wider. Information on the most vital features and performance aspects of the AX1500i can be found on the rear of the box.

For a product of this class, the bundle can definitely be described as substandard. There is only a set of four black screws, a case badge, and a C19 power cable. Note that the vast majority of consumer-grade PSUs are making use of C13 cables; C19 cables are more commonly found on servers and larger electronic appliances. Beyond the above, there are no cable ties, no cable straps, and no other accessories whatsoever included with the AX1500i, which is very strange for a product with such a price tag.

Every single cable of the AX1500i, including the 24-pin ATX cable, is a flat, ribbon-like cable with no sleeving. All of the connectors and wires are black, making them perfect for those builders that they do not want their PSU cables to stand out visually.

External Appearance

Without a doubt, the AX1500i has an imposing presence. It is based on the same subtle visual theme as the rest of the AX series, but the 22.5 cm (8.86 in) long chassis is definitely eye-catching. It goes without saying that the AX1500i will not easily fit inside small cases and compact designs, but that's hardly a problem as this clearly is not a product meant to power anything less than the most advanced gaming computers and workstations. Decorative stickers can be seen on both sides of the chassis, while the sticker with the electrical specifications can be found at the top. The fan guard is a combination of circular and parallel wires, visually complimented by the embossed parallel lines design of the chassis.

The front of the chassis is littered with the many modular cable connectors, as well as the Corsair Link USB connector and a self-test button. The back is plain, with just the C19 cable plug and a small switch to be found. The switch does appear very small for a unit of this size but actually the AC input does not go through the switch, as with most designs; the switch electronically isolates the AC input by deactivating the inrush current relay. This is a neat trick and actually improves efficiency a little bit as well, as there are no losses on the contacts of the switch.

Internal Design

The 140 mm fan responsible for the cooling of this monster is a Corsair-branded NR140P fluid dynamic bearing fan. There is little information about this particular fan to be found in Corsair's website but, after testing the fan, our instrumentation shows that it has a maximum speed of about 2100 RPM and a maximum volume flow of about 75 CFM.

Unsurprisingly, Flextronics is the OEM behind the creation of the AX1500i and it is somewhat similar to the smaller AX1200i. However, there are great differences as well; in order to improve the efficiency to meet 80 Plus Titanium standards, Corsair essentially made the entire unit digital.

The build quality is exceptional, with an immaculate soldering job and a ridiculous amount of glue used to mechanically secure the components and minimize high frequency vibration noises. In fact there is so much glue that many components are literally buried inside lumps of grey stuff. Unfortunately, due to the excessive use of glue, we could not fully identify the number of AC filtering components. We were able to count six Y capacitors, four X capacitors, and three filtering inductors, which is already more than enough, but we suspect that even more of them are hidden under the lumps of glue.

Elsewhere, a metallic shield guards against EMI. It is also worth mentioning that thread locker glue has been used on almost every screw and metallic clips are used to ensure the tight contact of transistors onto the heatsinks, which is definitely not something we see every day – as a matter of fact, not even most top-tier units are so well made.

The major changes over the AX1200i, as well as over any other PSU that we have seen to date, are located at the primary rectifier and PFC circuit. Instead of using a rectifier bridge, Corsair is using two transistors for rectification and they have eliminated the PFC diode, replacing it with a digitally controlled circuit that allows for the generation of higher quality waveforms. As for the passive PFC components, there are four large coils and two Nippon Chemi-Con 680 μF capacitors. And when we get to the secondary capacitors, chaos ensues. There are electrolytic capacitors from at least three brands (Nippon Chemi-Con, Rubycon, and Nichicon) and solid capacitors from at least two manufacturers (CapXon and Teapo), and we may have missed some under the mountains of glue.

The second major change lies at the generation of the DC voltage lines. Unlike most other advanced units that generate only a single 12 V line and then convert all minor lines from it, the AX1500i has two virtual LLC converters. The major LLC converter generates the massive 12 V line and the secondary converter generates the 5 V line. The 3.3 V line is then derived from the 5 V line via a typical DC-to-DC converter. Due to the insane amperage, Corsair had to use large metallic bars to distribute the ground on the connector's PCB. A metallic bar also collects the freshly generated 12 V line, but it is then transferred onto the secondary PCB via seven thick wires.

Corsair Link

A couple of years ago, Corsair introduced the Link software that allowed for the monitoring and even partial control of compatible devices. It can be used to monitor and log system parameters, such as the CPU temperature and the speed of fans, as well as to perform certain actions when the appropriate hardware is used. For instance, you can program the lighting of the Hydro H100i to change according to the temperature reading.

With the AX1500i, Corsair Link can be used to monitor just about every primary parameter; voltage, amperage, and power on both the input and outputs, as well as the internal temperature and the speed of the cooling fan. The user can also create virtual OCPs, limiting the maximum current through certain connectors. As far as accuracy is concerned, the software readings usually are a bit off, but they are precise enough to be useful to the end user. You can see in the following pictures that we are using Link to depict the stability of the AX1500i when the input voltage is changed while the unit is operational; the AX1500i simply kept working without a glitch both when the voltage took a dive from 230 VAC to 127 VAC and when it went up to 248 VAC.

While the software worked well for us, we should mention that the version of Corsair Link with support for the AX1500i is still a Beta, so glitches and software issues could arise. We didn't encounter any during the limited time of our testing, however.

Cold Test Results

For the testing of PSUs, we use high precision electronic loads with a maximum power draw of 2700 Watts, a Rigol DS5042M 40MHz oscilloscope, an Extech 380803 power analyzer, two high precision UNI-T UT-325 digital thermometers, an Extech HD600 SPL meter, a self-designed hotbox, and various other bits and parts. For a thorough explanation of our testing methodology and more details on our equipment, please refer to our How We Test PSUs – 2014 Pipeline post.

The Corsair AX1500i delivered record-breaking performance at room temperature, with an impressive average conversion efficiency within the nominal load range (20% to 100%) of 94.9%. The maximum conversion efficiency is exactly 96.7% at 50% load, which is more than adequate for an 80 Plus Titanium certification under 230VAC input.

For 110VAC grids, the 80 Plus Titanium certification is more lenient, dictating an efficiency of at least 94% and thus the AX1500i should easily surpass it. Perhaps the most important point that we can make regarding the efficiency of the AX1500i is the low-load efficiency, which is at 85.6% at just 5% load, an astonishing figure considering that there are hardly any computer PSUs that will surpass 78% efficiency at 5% load. Of course, 5% load in this case is still 75W, and there are many PCs that idle at levels far below that value.

The cooling system of the Corsair AX1500i is based on "smart" thermal management, with the fan not turning on at all before it is necessary. Considering its output, the AX1500i is an astoundingly cool running unit, allowing it to operate without the help of the fan under loads that surpass the entire output of typical consumer/gaming PSUs. When the fan does start however, it does not remain quiet for long, with its speed increasing alongside the load. In the unlikely event that the AX1500i remains loaded at 80% capacity (or more) for several minutes, the fan is clearly audible from many meters away.

Hot Test Results

From the tables below, we can see that the output power quality of the Corsair AX1500i is simply setting new performance records. Our instrumentation recorded a maximum ripple of just 16mV on the 12V line under maximum load, while drawing 107.2 Amperes from it! Cross loading the voltage lines had virtually zero effect on the stability of the unit, courtesy of the dual LLC PSU design we mentioned in the Internal Design section. Finally, the voltage regulation is remarkable, with the worst and best results being 0.5% and a mere 0.15% on the 5V and 12V lines, respectively!

High ambient temperature have a miniscule impact on the energy conversion efficiency of the Corsair AX1500i, reducing the average nominal load (20-100%) efficiency down to 94.6% and the maximum efficiency of the PSU to 96.5%. The overall efficiency drop is a mere 0.3% percent over a temperature rise of 25°C, which is simply amazing, displaying both the effectiveness of the design and the quality of the active components. As such, the conversion losses remained nearly unaffected despite the much higher ambient temperature.

Overall, the behavior of the cooling system inside our hot box was similar to our "cool" testing results, with the sole exception being that the fan turns on at a much lower load than before. It also gets noticeably louder, but considering the massive power output, the AX1500i did not get hot at all, suggesting that the thermal control circuit is programmed to maintain low operating temperatures under any circumstance. We would be hard-pressed to find such low temperature readings even in reviews of units with half the capacity of the AX1500i.

Conclusion

The AX1500i is definitely a special kind of product. It aims not for a particular group of users, but for the cream of hardcore overclockers, enthusiasts, gamers, and professionals. In other words, it targets users that both have crazy power requirements and, at the same time, require excellent overall performance. Of course, if you do not possess a very power-hungry system with multiple high end GPUs and CPUs, the massive output of the AX1500i would not make any sense to begin with.

Both externally and internally, the AX1500i has been very carefully designed and built. It is aesthetically appealing without being extravagant and the fully modular design is appreciable on a unit with so many cables. Only the size of the chassis could become a problem in smaller cases but we can hardly imagine someone purchasing a $450 PSU with the purpose of installing it inside a run of the mill case. Inside the AX1500i, Corsair uses fine quality components and has one of the most detailed assembly jobs ever performed. They really cut no corners when designing and building this power supply.

When it comes to performance, the Corsair AX1500i is almost frightening. Starting with the efficiency, as the 80 Plus Titanium certification is one of the primary selling points of this product, the AX1500i has a higher average efficiency than the top efficiency many 80 Plus Platinum units can achieve. It also has exceptionally high efficiency at low loads, which is very useful for a unit of this output, as the power requirements of even the most power hungry systems while idling are just a few percent of this unit's capacity. The quality of the output is also breathtaking, with very low voltage ripple even under massive loads and unparalleled regulation. Furthermore, due to the high efficiency, the AX1500i emits only very low volumes of heat, allowing it to operate virtually fanless across a large portion of its capacity range. The Corsair AX1500i undoubtedly delivers the best all-around performance that we have seen to this date.

With the release of the AX1500i, to our eyes, Corsair has simply tried to create the very best power supply possible, regardless of the cost and market potential. They did succeed on breaking almost every performance record we can come up with for a consumer-grade PSU... but that includes the record for being the most expensive unit a consumer can currently buy.

With a retail price of $450, this is definitely not a product aiming for the masses. Using any 1500W PSU to power even a high-end gaming PC, let alone a basic Home/Office PC, would be the very definition of the word "overkill". Corsair's AX1500i is a PSU meant for the most advanced gaming computers and workstations, and only for those users that are willing to spend a few hundred extra bucks in order to get the very best there is.

It's doubtful most of us will ever use such a product, but just as the 80 Plus program brought higher efficiency power supplies to the masses, products like the AX1500i will inevitably have a "trickle down" effect. Seven years ago the cost of a good 80 Plus Bronze 1000W PSU ranged from around $250 to over $300. Such power supplies were mostly overkill even then, but today you can find them for less than half the price, and higher efficiency 80 Plus Gold PSUs aren't much more. It may take some time to get there, but undoubtedly we will see much of the technology in the AX1500i makes it's way into more reasonable products. You have to start somewhere, and R&D often starts at the top.