The FACTS about GPU mining electrical specifications

I just wanna add without reading all the comments that connector A is rated for x amps, you also have to taking into ambient temperature, this value changes as copper’s conductivity will decrease with higher ambient. Depends on setup environment, the voltage and current will go down wrt wire length and puts load stress on the PSU, make sure it’s a quality PSU.

2nd, if connector is “rated” for x amps, doesn’t mean you can’t exceed X+0.5 amp, you will see a slight voltage drop, and still safe for 24/7 hour operation for connector like sata and molex. Note: this do not apply to the crappy crimped wired one that come with the riser.

To see this, load a Molex cable down and see it for yourself. Make sure it’s 18 AWG wire like the ATX spec.
18 awg wire can handle 16A under ideal conditions and factors, for real world application, it can easy handle 60% of that, which is 11A! The other issue is the quality of the contact pin after the crimping, if you are using a quality psu made by flextronics or CWT the connectors them self are high quality.

Molex cables ARE rated at 11Amps on the 12 Volt rail. Therefore they can safely power two GPU’s as the PCIe specification limits PCI power draw to 5.5amps. Only early AMD 480 cards violated this specification and caused many burned cables in the process (they have since fixed via firmware update).

I will provide more information when I have time but felt it important to get this information out.

Below is a picture of SATA to Molex adapter. This adapter has been in service for at least 18 months. I specifically performed spectral micro CT and material decomposition on this adapter to look for defects and found none (was going to be part of a post, I will now provide those CT images). I do not use these cables on my production rigs, but still use them on my test rigs for convenience…

To my horror I found this after I left my test rig running some new software in my house!!! While I was away on a business trip.

Yes the yellow, 12V wire is clearly burned, Yes that shiny black blob is melted white plastic and possibly some black socket plastic. Yes there is black and gray soot up the length of the riser PCB and yes the Molex plug is permanently fused into the socket.

My home rigs have a smart smoke alarm, it never tripped. My home rigs are in a fireproof area with nothing to burn, but toxic smoke will still enter the HVAC system. I did get a GPU failure message from the rig but it restarted and just dropped the faulty GPU once it lost power, didn’t think about that possibility in my code, so I didn’t see the issue.

So here I am proclaiming the importance of safety to all my mining kin and I nearly killed my children with the very thing I have been warning about. I shut everything down yesterday… everything, and tried not to vomit the rest of the day.

I will try to collect myself this weekend and provide more useful information on this event.

2 Likes

Thanks @ZC93 for your sharing on molded SATA connection. I never thought of it. And yes, the amp rating is based on ambient temperature (30C). Again, we are never too sure of the purity of copper of our AWG 18 cables.

Based on your sharing and my research I summarize based on to expect the worst from manufacturer (add temperature correctional factor to equation x 80% safety margin).

Note:
My PSU has a max load of 2400w (Future orders will size down to 1800w). 8x PCIE cables with 2x PCIE 6+2P connectors on each cable; 4x Molex cables with 2x Molex 4P Connectors to each cable; and 5x SATA cables with 2x SATA 15P connectors on each cable.

Steps I take:

  1. Only build 9x GPU rig. 8x GPU will be powered up by 8x PCIE cables.
  2. Where possible, connect max PCIE 8P to GPU aux power.
  3. The same twisted cable, I connect the other PCIE 6P connector to the riser PCIE 6P connector.
  4. If the cable is not long enough to reach the bag, I add a PCIE extender cable to avoid putting stress at the twisted cable’s joint.
  5. 9th GPU, I use the 4x separate Molex cable. Will use TWO 2x Molex 4P to PCIE 6P adaptor cable.
  6. One of the PCIE 6P will connect to GPU aux power. The other PCIE 6P connects to riser PCIE 6P
  7. Will only use the PSU SATA cable to connect to HDD. No other things.

My calculated max load power before the cable will heat up more significantly based on 60C ambient temperature (worst scenario).

  1. GPU 1 to 8: 134w (DC). I will need to do TPD ensure not more than 134w and lower.
  2. GPU 9: 153w

(Sorry, I am new user can’t put more than 2x URL links for you)

URLs you can look into assuming all manufacturers follow the Standard Terminals:
http://www.tomshardware.co.uk/g00/power-supply-specifications-atx-reference,review-32338-12.html?i10c.encReferrer=aHR0cHM6Ly93d3cuZ29vZ2xlLmNvbS8%3D&i10c.ua=1

A more detailed info can be glimpsed from here on PCIE 6P and 8P actual max power load:

And here, old but still very relevant on PSU connectors:

Ambient temperature correctional factor as a reference, there is no common standard. Based it upon that manufacturer not using pure 100% copper. And assuming inside rig temperature can reach up to 60C worst scenario? My correctional factor is 0.58 x 80% safety margin.

Reference URL:

The summary below is based on SINGLE PSU CABLE. Be very alert of the colours. Each colour is from different voltage rail. 3.3V (orange), 5V (red), 12V (yellow). Some PSU may be missing 3.3V. Eventually all the rails will balance out the power draw with max draw of 75W from riser.

If you are using Molex connectors, always check both molex connectors of the adaptor you are using and PSU own molex cable has the different colored wires to calculate the max load correctly.

Minimize use of adaptors where possible to avoid voltage loss. Base your max load on the weakest link of the entire cable + adaptor if you are using any that your power budget is enough to power up the GPU and GPU need be tuned to further lower power draw.

Summary below:

  1. ATX 20P Cable: 251w (30C) / 116w (60C)

  2. ATX 20+4P Cable: 373w (30C) / 174w (60C)

  3. ATX 4P Cable: 192w (30C) / 89w (60C)

  4. ATX 8P (EPS) Cable: 336w (30C) / 156w (60C)

  5. PCIE 6P Cable: 192w (30C), 89w (60C)

  6. PCIE 8P Cable: 288w (30C), 134w (60C)

  7. SATA 15P Cable: 91w (30C), 42w (60C) - assuming it has 3.3V rail (orange cable)

  8. SATA 15P Cable: 76w (30C), 35w (60C) - assuming 3.3V rail missing

  9. MOLEX 4P Cable: 85w (30C), 39w (60C)

  10. 2x Molex 4P Connectors to PCIE 6P Adaptor: 170w (30C) / 78w (60C)

Note:

  1. Referring to Molex 4P Cable, it can support max load 85w. Means the plastic connector is able to withstand.
  2. In a Molex 4P however the cable on 5V and 12V rails have a max rating of 5A each.
  3. However, a 12V (yellow) AWG 18 cable can safely support 8A just like a PCIE cable.
  4. Hence, 2x Molex connectors connected to two different Molex cable will be able to provide load of 170w (30C) / 78w (60C)
  5. When I connect my 9th GPU using 2x of these adaptor to both GPU aux power (78w) and to riser (limited to 75w), total = 153w @ 60C

I don’t have any background in E&E. Above are based on months of research, reading and your feedback on the SATA 15P potential fire hazard. Really appreciate your sharings!

just one think iam not aware that you or me would be using the 3.3V rail nor the 5V rail for mining so u can drop them from your calculations right away basically you are interested for the 12V rail only else thats a lot of info u gathered :smiley:

1 Like

Agree. In my case is Molex + PCIE good enough. The ATX cable just to know is good enough whether there is any under-powered when I do CPU mining at the same time. :sweat_smile:

I know this is an Equihash forum. Worst scenario as long as this can work for Ethash, Equihash would not be a problem. :smile:

How much would an MSI RX 580 Armor 8G OC Graphics Card draw?

I use a watt meter power bar for the mining rigs i have in residential places in canada.

1440 Watts is the 80% limit to my knowledge.

Good tips.

What does those popular link mean, I thought we d better not choose risers with sata connector?