What is EPS12v and PFC in power supplies? And why is 12V rail more used now?

[BCinSC]

Researching PSUs for some Barton 3200+ crunchers and can't find what these are. Plus, recommendations for decent inexpensive PSUs appreciated.

 

[Elcs]

Most people will reccommend Antec or Enermax. They can be a bit expensive but they are pretty much top dog when it comes down to it.

Thermaltake, despite some mishaps in other market segments produce some fine power supplies. The only complaint I have with my 420W PurePower is that it isnt perfect..... but really thats just me worried that a Vcore fluctuation will fry my processor. I think you'd struggle to find a negative review of the Thermaltake PSU's.

Anandtech did an article a long while back on PSU's and they explained PFC.... Id dig it out but Im prepping for Uni

 

[BCinSC]

Found it and it's not relevant to US folks.

 

[Viper96720]

EPS12V PS is needed by some server boards. It's an SSI spec Server System Infrastructure.

 

[BCinSC]

Reading the various articles on AT, SE, Toms, etc, I've learned that P4 and Athlon system make more use of 12V+ rail than prior generations - powering the CPU itself, which has gone down in voltage requirement, not up. Why is this?

 

[Matthias99]

powering the CPU itself, which has don't in voltage requirement, not up. Why is this?

Huh?

The 12V rail is used more nowadays because more components are drawing more amps in the system. It's much tougher to deliver a lot of power over a 3V or 5V line, and today's processors need it.

 

[BCinSC]

Wow. Wicked typo. Sorry. But you understood what I was getting at. And why can't 5V or 3.3v handle it? Their amps are double those of 12V rail on current PSUs

 

[Zepper]

Look at total power not just amps (5Vx30A=150W, 12Vx15A=180W.) Also voltage regulators (those little ICs with three legs near the CPU with all the big caps around 'em on your mobo) are more stable (and slightly more efficient) with a higher input voltage relative to the output voltage.
. Mobos that use 12V rail to power the CPU will have the P4 Aux power connector (4-pin square) - Found on the great majority of Intel mobos and most NV. Just picking up steam on boards for AMD w/ other chipsets (VIA, SiS, etc) even though AMD has recommended it from the beginning of the Athlon/Duron and maybe before that. I will no longer buy a mobo without the P4 Aux connector and look for 15A or more of +12V in my PSUs.
.bh.

 

[BCinSC]

Just took a gander at an old Gateway G6-233 system, with a 200W PSU that has a 'whopping' 6A on the 12V rail.

 

[Mark R]

First of all:

EPS12V is an alternative to ATX which is used for high-power systems (e.g. Dual CPU motherboards). An EPS supply uses a 24 pin molex connector to connect to the motherboard. ATX uses a 20 pin connector. Some EPS supplys have an adaptor to convert the EPS connector into ATX. EPS supplies also have the square 4 pin molex connector which supplies 12V to the CPU(s).

PFC (power factor correction) is of dubious relevance to home users. It is irrelevant to European users; PFC has been a legal requirement for PC PSUs for many years - and therefore all EU supplies are PFC. I'll explain very briefly why PFC might be relevant:
A convetional PSU has a low power factor, that means it takes more amps from the mains than you would expect it to. Let's say your pimpin' new PC needs 220W of power - you would expect it to take 2A, but without PFC it may take 3A. It still uses 220 W. However, if you run an office or a server rack, or hold a big LAN party, then the extra amps need to be taken into account, or you'll overload your power strips, or trip circuit breakers. Most electricity suppliers (especially to homes) charge only for the actual energy used (i.e. Watt hours) and ignore the number of amps needed to achieve this. Some suppliers may charge for the amps used, but for domestic use this is uncommon. If you pay for kWh on your bill, then you do not pay for low power factor. If you pay for kVAh then you do.

The +5 or 3.3V supplies could handle the power for the CPU, but there would be problems getting the power to the voltage regulator for the CPU. Supplying a CPU from 5V would require more than 2x the amps needed at 12V - this leads to lower power quality, needs thicker wires from the PSU, better quality connectors, thicker traces on the motherboard, etc.

It's easier to do this with 12V, especially as the ATX spec was not designed for such high currents on the 5V line. I've seen several motherboards (using high-performance CPUs (athlons) powered by 5V) where the 5V pins on the ATX connector have got so hot that the plastic connector had melted.

 

[Zepper]

I think your explanation of Power Factor Correction is wrong. Here's my view:
. Active PFC lines up the current load curve with the voltage curve - i.e. makes the load look more resistive. Therefore the average power usage as seen by the kWH meter will be slightly less over time. Over a large number of PSUs such as in universities, corporations etc. it could show a decent savings - for one or two psu's the savings would be negligible. In Europe, socialist clowns as they are, it's not large users saving, but not having to create new supply that's the issue.
.bh.

 

[Mark R]

Active PFC lines up the current load curve with the voltage curve - i.e. makes the load look more resistive.

PFC of ay kind (active or passive) lines up current with voltage - this means that more work can be done for each amp (on average).

Therefore the average power usage as seen by the kWH meter will be slightly less over time.

No, that's not right.

The key point about PFC is that it does not change the number of watts needed - you still need the same amount of power to do the same amount of work. kWh meters (like in your home) only measure watts (hence the name). If you connect 2 otherwise identical PSUs to a kWh meter (one with PFC, one without) they should both register identical loads. (Actually, I'd expect the PSU with active PFC to use more - the active PFC circuit is an entire SMPS in itself, and will typically need 10-20 W just for itself).

You need a kVAh meter to show a saving with PFC (these meters measure average voltage and average current and multiply them together). Normally, the cost to electricity companies of installing 2 meters (one kWh and one kVAh) is not worth it except for their largest customers - so they don't bother to charge for low power factor, particularly as it's really only an issue for industry where big industrial motors can take huge loads at very low power factor.