Transient Response Tests
Advanced Transient Response Tests
For details on our transient response testing, please click here.
In these tests, we monitor the response of the PSU in two different scenarios. First, a transient load (10A at +12V, 5A at 5V, 5A at 3.3V and 0.5A at 5VSB) is applied to the PSU for 200ms while it works at 20-percent load. In the second scenario, the PSU is hit by the same transient load while operating at 50-percent load. In both tests, we use our oscilloscope to measure the voltage drops caused by the transient load. The voltages should remain within the ATX specification's regulation limits.
These tests are crucial because they simulate the transient loads a PSU is likely to handle (such as booting a RAID array or an instant 100-percent load of CPU/GPUs). We call these tests "Advanced Transient Response Tests," and they are designed to be tough to master.
Advanced Transient Response at 20 Percent
| Voltage | Before | After | Change | Pass/Fail |
|---|---|---|---|---|
| 12V | 12.232V | 12.122V | 0.90% | Pass |
| 5V | 5.089V | 5.012V | 1.51% | Pass |
| 3.3V | 3.353V | 3.194V | 4.74% | Pass |
| 5VSB | 5.004V | 4.978V | 0.52% | Pass |
Advanced Transient Response at 50 Percent
| Voltage | Before | After | Change | Pass/Fail |
|---|---|---|---|---|
| 12V | 12.172V | 12.061V | 0.91% | Pass |
| 5V | 5.071V | 4.990V | 1.60% | Pass |
| 3.3V | 3.322V | 3.170V | 4.58% | Pass |
| 5VSB | 4.970V | 4.929V | 0.82% | Pass |
The 5V and 5VSB rails do pretty well in our tests, but we would have liked to see lower deviations at +12V, which managed to stay within one percent in both tests. Things didn’t go well for the 3.3V rail, though. It exceeded 4.5 percent deviation on both tests and took last place in the corresponding comparison chart.
Below are the oscilloscope screenshots we took during Advanced Transient Response Testing.
Transient Response At 20-Percent Load
Transient Response At 50-Percent Load
Turn-On Transient Tests
In the next set of tests, we measure the response of the PSU in simpler scenarios of transient load: during the power-on phase of the PSU.
For the first measurement, we turn off the PSU, dial in the maximum current the 5VSB can output and then switch on the PSU. In the second test, we dial the maximum load +12V can handle and start the PSU while it's in standby mode. In the last test, while the PSU is completely switched off (we cut off the power or switch the PSU off by flipping its on/off switch), we dial the maximum load the +12V rail can handle before switching the PSU on from the loader and restoring the power. The ATX specifications state that recorded spikes on all rails should not exceed 10 percent of their nominal values (+10 percent for 12V is 13.2V, and 5.5V for 5V).
Also where do you base this? That the PG signal is simple to cheat and the manufacturers actually do this? From the moment the mainboards take seriously into account PG if this was the case then most likely there would be huge problems with lots of them. According to the ATX spec PG is de-asserted to a low state when any of the main rails falls out of 5% v. reg. Simply as that.
It just gives room for 1 ms till the PG signal sees the change at least in the ATX spec.
As for the thermal camera how it can show things hotter than it is? The scale is for this reason and from the moment the camera sees something from a different angle and a different region the scale is changing automatically. Nothing I can do about it. This is why I provide also actual temperature readings on all IR images.
So the design is nothing new and this is a Seasonic rebrand with minor differences at the internals (most likely the caps selection as I stated above).
The fixed cables are the ones that will always be in use for any system using a 750W power supply, so the ability to disconnect those cables would not be beneficial. In fact it would lead to higher cost and also an extra point of failure and a slight loss of efficiency since a connector can never quite match an uninterrupted cable.
Loss of efficiency isn't a reason any more, on the contrary with bus bars or thick cables transferring power to the modular PCB energy losses can be minimized. In addition no cables block the secondary side caps, something that besides increasing their lifetime also allows for more relaxed fan profiles and better airflow inside the chassis.
Also the cost of a semi-modular to fully modular isn't high and in a 750 W PSU that costs 140 bucks already the cost reason doesn't stand (for fully modular design).
You cannot easily change them because other cables are often incompatible - there is no common standard for modular PSU cables. Using incompatible cables can be downright dangerous. Here is a cautionary tale.
Also I still cannot understand how the connector on the PSU end adds complexity and reduces cable flexibility! Cable flexibility depends on the gauges' thickness and not on the cables modularity design (or not).
Anyway I believe I made my opinion clear on why I prefer fully-modular PSUs.