Power supply with two 8-pin EPS connectors

[Mercantides]

I'm looking for a quieter power supply for my server:

• Asus EP2C602
  2 x Xeon E5-2670v1
  8 x 8GB PC3L-10600R (DDR-1333 @ 1.35V)
  3 hard drives
  EVGA 750 G1 - too loud at idle (100W)

Future plans:

• No more than 10 hard drives total
  1 or 2 low power GPUs for VMs, something like a 750ti

I've measured the power with a Kill A Watt meter. Idle draw is 100W with the drives spun up. Running prime95 gets the power draw up to 400W. Assuming 75W for each of the GPUs I'd be around 560W maximum draw from the wall, 500W after the efficiency loss. Realistically it'll never draw that much so the limiting factor in choosing the power supply is the fact it needs two 8-pin EPS connectors where most smaller power supplies only have one.

Here's the short list (sorted by prices in CAD)

• EVGA SuperNOVA G2 750 ($130)
  + Positive reviews here: viewtopic.php?f=6&t=68101
  
  SeaSonic X-650 (SS-650KM Active PFC F3) ($150)
  ? I'm unsure how quiet this is compared to newer units.
  
  be quiet! Dark Power Pro 11 550 ($155)
  + Positive discussion here: viewtopic.php?f=6&t=68708&p=596188
  - a bit on the expensive side for 550W
  
  EVGA SuperNOVA P2 750 ($160)
  + Positive reviews here: viewtopic.php?f=6&t=68747&p=596618
  ? $30 more than the G2, is it worth it?

I've ruled out:

• Corsair RMx, RMi Series
  - To get two EPS connectors you have to go up to the RM850 which are >= $200.
  
  Corsair HX750i ($175)
  - seems to expensive
  
  EVGA SuperNOVA 650 G2, 650 P2
  - These support two EPS but only using a single daisy-chained cable which I don't like and anyways is not long enough to reach both of the connectors on the motherboard.
  
  Seasonic G-550, S12G-550
  - Don't support two EPS connectors.
  
  SeaSonic G-650 (SSR-650RM) ($130)
  - Potentially loud: viewtopic.php?f=6&t=66596
  
  Seasonic S12G-650
  - Not modular
  
  Seasonic SS-660XP2 ($180)
  - seems too expensive

I think I've considered all of the possibilties but I'm wondering if I've missed any and I'm still not sure which on the short list I should get. The DPP 11 is enough for my planned needs but I might want a bit more headroom so the power supply can run a bit quieter or just in case I get some more power hungry cards. Although at that point I could always migrate the DPP 11 to another computer and get a new power supply for the server.

Any input to help me decide would be appreciated.

[Fire-Flare]

I ran a Seasonic X-650 in my rig a few years ago.

As I recall its fan only became noticeable in the summer months.

[CA_Steve]

Just a thought - EPS cable extensions are around $5. So, you could go with the EVGA P2 650 (currently $110 @ NCIX with rebate).

[Mercantides]

I ran a Seasonic X-650 in my rig a few years ago.

As I recall its fan only became noticeable in the summer months.

I've had an X-650 in my main rig for the past 5 years and I don't have any complaints.

Just a thought - EPS cable extensions are around $5. So, you could go with the EVGA P2 650 (currently $110 @ NCIX with rebate).

I hadn't considered this. Discounting the MIR by half and adding shipping for the EPS cable brings the price to ~$130. That might be the way to go, thanks for the suggestion. I'll sleep on it and decide tomorrow.

[Mercantides]

I think I'll go with the 650 P2.

I did a sanity check on using the daisy chained cable with an extension cable. The biggest concern is to make sure the connection at the power supply can handle the current load for both motherboard connections.

• EPS cable has 8 wires: 4 12V and 4 ground.
  Assuming that all power is being drawn through the EPS cable: 410W @ full load
  410W / 34A /4 = 8.5A per wire pair
  The real number will obviously be significantly lower as this doesn't consider power supply efficiency and power through the main motherboard connection.

Now to check that against the connector ratings.

• The EPS connector is Molex 39-01-2080 or equivalent. (http://www.molex.com/molex/products/dat ... USINGS.xml)
  Assuming 45750 terminals. (http://www.molex.com/pdm_docs/ps/PS-45750-001.pdf)
  From that data sheet the maximum current rating with the entire connector fully loaded, wire-to-board, dual row 8-pin, 18AWG is 8.5A per circuit. Wire-to-wire is 9A. So the 8.5A maximum I calculated above is right at the maximum rating.

Finally, out of curiosity I calculated the resistances and power.

• Resistance of 18AWG @ 25C is 6.510 ohm/kft = 0.5425 mohm/inch (http://www.interfacebus.com/AWG-table-o ... tance.html)
  Also from the same datasheet the contact resistance is no more than 10 mohm.
  The length of the EVGA EPS daisy chained cable is 700mm + 150mm = 27.5" + 5.9". Extension cable is 8"
  Total length is 27.5 + 5.9 + 8 = 41.4" = 22.5 mohm + 30 mohm for ps to cable, cable to cable, and cable to board
  Voltage drop is 8.5A * 52.5mohm = 446mV. About 4% on the 12V rail.
  Power dissipation is 8.5A * 446mV = 3.8W.
  Again this isn't very accurate because the current will be split in half at the first motherboard connection, the connector resistances are likely lower than 10mohm, and the estimation of current is also high.

Anyways, based on the above the 650 P2 should be fine for my use case.

[Mercantides]

I swapped in the 650 P2 a few weeks ago and it's been great. I still have a bit of noise from the hard drives but it's not enough to bother me.

[CA_Steve]

Cool beans.