Power supplies of the 80 PLUS Gold category, which most often become the heroes of reviews, are designed largely the same and guarantee a certain level of quality for the appropriate amount of money. However, there is room on the market for more affordable solutions. It is budget devices that, due to inevitable savings on components, require the most careful selection.
Let’s take a look at one such model under the Formula V Line brand – an inexpensive 80 PLUS Bronze 750 W power supply that has modular cables and boasts a 12VHPWR connector.
⇡#Technical characteristics, design, price
Despite the fact that the Formula V Line APMM-750BM has an active PFC, the device is certified according to the 80 PLUS 230V EU standard, which means it is designed for an input voltage of at least 200 V and does not guarantee operation when it drops below this level. The description of the new product contains the phrases “ATX 3.1 Ready” and “PCIe 5.1 Compatible”, but there is no usual claim in such cases for the possibility of briefly exceeding the full output power by 100, and the power through the 12+4 connector by 200%. It is reasonable to assume that such a possibility does not exist. The maximum power of a 12 V line is 675 W, and the power supply reaches up to 750 using small lines.
The Formula V Line product is assembled in a housing that is spacious for its power and has a depth of 160 mm. A distinctive design feature of the APMM-750BM is its abundant perforation. By and large, the four sides of the case represent a cage, which is blown through by a 140 mm fan. The ability to control the fan operating mode is not provided.
Despite the promise of PCI Express 5.1 compatibility, the 16+4 connector complies with the PCI Express 5.0 power specification. That is, it is 12VHPWR, not 12V-2×6. Sense 0 and Sense 1 pins are shorted to ground, indicating 600 W of available power – overly optimistic given the total reserve of 675 W on the 12-volt line. In addition to 12VHPWR, the APMM-750BM has only three universal connectors for powering the CPU or video cards and two for cables with SATA and Molex power connectors.
The cables themselves have a ribbon shape and the cross-section of all conductors is 18AWG. In the 16+4 cable, the cross-section of the supply conductors is increased to 16AWG.
Formula V Line APMM-750BM is sold for an adequate price for its characteristics, starting from RUB 7,620.
⇡#Internal organization
Looking at the power supply’s price and 80 PLUS Bronze certification, you wouldn’t expect the APMM-750BM to be state-of-the-art. The device combines old and new solutions in certain circuits, and the quantitative characteristics of certain components are predictably reduced compared to more expensive analogues. We were unable to determine the OEM supplier of the printed circuit board.
The EMI filter is a two-stage one, consisting of two X-capacitors, four Y-capacitors and two common-mode chokes. There is a fuse and an NTC thermistor to limit inrush currents. But there is no relay, so the thermistor is always connected to the circuit and dissipates a certain amount of power when the power supply is running. Surge protection using a varistor is also not implemented. We also note that for some reason the rectifier on the primary side is not screwed to the nearby radiator or even in contact with it.
The main converter has a forward topology with two transistors (double forward), which partly explains the “bronze” efficiency of the APMM-750BM. But there is an active PFC block.
The rectifier on the secondary side is assembled the old fashioned way, using Schottky diodes. Small lines of 3.3 and 5 V are formed by DC-DC converters, but a group stabilization choke has been added to them (another of the outgoing solutions). A supervisor chip that provides protection against overvoltage, undervoltage and short circuit is present.
The inscriptions on the APMM-750BM case mention a Japanese capacitor in the singular, and this is not a mistake. It is used in a PFC circuit and has a fairly small capacitance of 390uF. The remaining electrolytic capacitors that we were able to identify were manufactured by Chinese companies Hangcon and Chengx.
The switchboard is connected to the main PCB by a bundle of wires. The fan has no identification marks, but, according to the power supply passport, it operates on a hydrodynamic bearing.
⇡#Testing methodology
The testing methodology adopted in 3DNews is described in a separate article, which is recommended for reading to understand the design of computer power supplies and their most important characteristics. Refer to it to find out why it is needed and how this or that component mentioned in the review works, and how to interpret the test results.
⇡#Test results
Tests have confirmed that this is nothing more than a “bronze” power supply with efficiency at key load values of 87, 91 and 86%. For a full load of 750 W, small lines of 3.3 and 5 V had to be used, hence the sharp drop in energy efficiency. And when they account for a significant share of power consumption, the APMM-750BM can already qualify for the basic category of the 80 PLUS standard.
The APMM-750BM fan always rotates, and its speed is kept at about 1,000 rpm. under load up to 90%. The last 75 W of power was achieved through small lines, so the power supply had to raise the fan speed to almost 1,800 rpm.
The 12V line voltage under low load is overestimated by about 4%, which is probably done specifically in order to maintain the required minimum as power increases. The ATX 3.0/3.1 specification allows you to increase it by even 7%. But the 3.3 and 5 V lines are outside the permissible range of -5/+5%.
The ripple amplitude on the 12 V and 5 V lines under a full load of 750 W is 70–80 mV, which is acceptable for the first, but, again, is outside the standard for the second.
⇡#Conclusions
When it comes to power supplies at such a price as the Formula V Line APMM-750BM, you need to understand that the operating scenarios of the device are limited not only by its full power (in this case, 750 W). Considering the poor regulation and filtering of small lines, and even their low load in modern PCs, the Formula V Line APMM-750BM is more likely a 675 W power supply. The presence of a 12VHPWR connector in this case is a nice bonus, but of course you cannot count on powering flagship video cards and meeting the strict requirements of ATX 3.0/3.1 for short-term overload.
Fortunately, the parameters of the 12 V line of the Formula V Line APMM-750BM are within standard limits, and the declared power corresponds to reality. The cables are removable, their cross-section is not underestimated. Sometimes this is all that is required from the power supply.