Topic: Regarding risers and PSU cables - page 2. (Read 3638 times)

these problem started when AMD launched RX series GPU with only 6 pin powered and use up to 75w on the peak from pcie slot

i've been mining since HD5xx series, into HD7xxx and R9... there are no case of riser power cable melted, because those early gpu mostly use power only from GPU's power connector, and only little bit from PCIE slot


each gpu have different circuitry, bios and driver
some GPU split between GPU Core power (from GPU pcie connector) and GPU Memory Power (from PCIE Slot), some use shared power, by undervolting surely it help but gpu has their own allocation of power which i am not sure, that's why i will just take the safest option by using pcie powered riser

no i am not saying you can't, but it safer to use pcie power, I personally had use 3 riser in single molex which is ended up in PSU connector melted (the riser connector end was just fine), then I use 2 riser for single molex which most of the time just running fine, but some rig melted at some time when the room is hot enough, but until now i never had issue of melted connector when using pcie powered riser

I have a few hundred rigs that all call bullshit on this. All of them are setup with the risers powered off of molex to sata power on the atx power supply and all of the video cards off of high end server PSUs. Out of thousands and thousands of connectors I have never seen one have problems.

i don't have that deep knowledge of internal circuitry of PSU, what i did and assume is just to get into safest first than into the unknown
so i will just make (riser+gpu) on same PSU because i know that riser power and gpu power are somewhat connected inside gpu,

unlike on [ gpu <-> riser <-> motherboard ] connection, gpu and motherboard are power disconnected because when i see the riser pin trace it bypass the power pin from motherboard, and use their own power from molex/6-pin instead of from motherboard pcie slot

and also i have an experience on earliest day of gpu mining, when there are no powered riser available, i use different PSU for GPU and motherboard, and of course GPU are slotted directly into the motherboard since at that time there are no so called "gpu riser for mining", and then the motherboard just explode, taking that experience i never split PSU between power connected devices

This is so much great information that I had no idea about. Thank you so much, very informative and important!

In other words, you're saying that 6-pin connectors on the risers are needed. However, if that's the case, then how come it seems that most miners (well, that I've read about, perhaps not "big-time miners" though, but they do just fine with molex on their risers. Most cards use more power than the Pulse Mini. Of course, under volting is an option that many do so that would explain it.

Let's say the card uses 150W and since it's being powered by 6-pin cables, it also draw 75W from the PCI slot. Obviously that's not a good idea for molex cables then. However, if I under volt each card to make sure it never goes above 125W (lower of course to have some head room), it should be fine until the new 6-pin risers arrive, correct?

For example, if I under volt it enough to get to 110W max, would it still draw 75W from the 6-pin cable and then another 35W from the molex cable?

Thank you again for all your answers, you're extremely helpful!

Edit: Are you sure I can't use two molex risers on a single cable? Most people I've read about claim that it works just fine but that three is too many.

Thanks for clarification. What if I use a power cable joiner? Will that help with the single ground?

Currently both PSUs are plugged into the same surge protector.

Eventually they will be on the same PDU once I get that installed.

on most case it wont be a problem, as long as both PSU are connected to same ground wire, since both PSU ground ended up on the same home power plug it will be on the same earth ground, but on some case, there are different circuitry between two kind of PSU which make their ground is not equal or some other cause, then some problem

I have been using one PSU to power the risers and one PSU to power the GPU for all my mining machines. Never had a problem.
I use one of these to power the cards:
https://www.newegg.com/Product/Product.aspx?Item=9SIA7GT5NK5071

And then a 600-700w to power the motherboard, SSD, and risers. Would that normally cause a problem?

one dedicated molex cable for one riser is safe, but never use single cable for multiple riser in daisy chain

but personally i prefer to use 6-pin powered riser, not just because its safer, but molex powered riser are using 1x 12v (yellow) and 1x 5v (red) rail.
while pcie riser use 3x 12v (yellow) rail
most psu has limited 5v rail wattage, but huge 12v wattage (and mostly psu watt spec are for 12v rail, so 1000w psu means 1000w for 12v rail). if you ran out of 5v watt limit it could be problematic

GPU use 12v and 5v to power up, most 12v are taken from GPU power connector, and 5v (and some tiny 12v) are taken from PCIE-1X slot
on PCIE 6-pin powered riser it mising 5v pin, they convert 12v to 5v by using step down converter, highlighted in red box, so these riser only take 12v and convert some into 5v, so it does not use 5v rail from PSU, while Molex riser directly use 12v and 5v from PSU without any conversion




6-pin cable rated for 150w is actually not accurate, the story is initial pcie power cable is only 6-pin they rated it for 75w, but there's need to deliver more than 75w, so they changed the spec, pcie power should be rated 150w, to differentiate which cable can deliver 75w (older spec) or 150w they add 8-pin connector, which another 2 pin is not to deliver power, but only to signal GPU if these another 2 cables is connected it means the cable is on newer spec (150w), gpu can take up to 150w, but if only 6 pins are connected gpu only allowed to take 75w since the cable is assumed on older spec which is rated 75w

both 75w and 150w connector deliver power through 3x 12v pins, so it doesn't matter 6-pin or 8-pin connector since both are using 3 pin to deliver power, what matter is the diameter of cable (which is rated in awg), 18-16 awg wire can be configured for 6-pin, 6+2pin or 8 pin, but 24-20awg only allowed to be configured as 6-pin, since 24 awg wire each can't deliver more than 25w of power

most current PSU cable are using 18awg or 16awg, so it is safe to assume it can deliver up to 150w for 6-pin/8-pin connector

now about that 570 pulse mini, if the gpu use 6-pin connector, then the gpu will only take 75w from gpu power connector, so if i assume that "less than 150w" words are meant to be "it never exceed 150w, but it can take up to 150w" then when it take 150w, gpu will take 75w from 6-pin connector on gpu, and another 75w from the riser, since molex are rated 50w, its an overcurrent for molex connector

The molex cables are connected to the "PERIF1" and "PERIF2". It looks like 6-pins on the PSU but the other end of the "PERIF1" and "PERIF2" are molex cables.

The 6-pin cables that we're talking about are the ones that are used on GPU's. On the PSU they are connected to the ones on the right (the VGA1-6). So there are 6x 6-pin cables. Molex cables, however, only have two connectors on the PSU (the "PERIF1" and "PERIF2").

He was talking about splitting those 6 cables to make them 12 in order to use them for both the GPU's and risers.

I hope that makes more sense.

Hi all,
sorry for the silly wuestion, but of course I lack in knowledge of hardware, since I can't understand this point.
You said that every card+raiser need power supply, and you use PCIE 6-pin splitter for every card, so you have a total of 6 PCIE 6-pin cables. But if the connectors are only 2 in the PSU (in the picture OP posted I presume they are perif1 and 2, as he said), how do you connect them?
I know it is a dumb question, but I can't figure it out.
Thanks

That's great news if it's possible!

This also means that I should buy risers with molex connectors, I assume? That way I don't need to buy extra 6-pin splitters. Or is 6-pin splitters and use them still better than using molex cables?

Edit: I should mention that I've purchased six Sappphire RX 570 Pulse Mini. According to Sapphire they're drawing less than 150W. If the 6-pin cable is rated for 150W then molex with another 50W should be more than enough for those GPU's, correct?

@Uray

I just checked to make sure if it some overheating was happening as after reading what you told me I just got to check the cards on the riser. Normal heat, just like the one in the motherboard. Sata 4 pin cable is ok  too. I hope I will not burn anything by keeping this configuration but I have seen many mining videos on youtube that are on this exact configuration as mine.

yes you can, personally i have EVGA GQ series exactly like that, and done cable test using multimeter
if G2 and GQ are same then you can put sata/molex to that connector like i did, but i never had G2

Sorry if I wasn't clear with my message. I'll try to explain what I meant better.

The EVGA G2 1300 that I've purchased is modular and has two inputs for molex cables. Which means I could maybe run two risers per cable for a total of four risers.

However, the PSU also has inputs that are meant for SATA cables. The connector looks the same. Could I take one of the molex cables that came with my other EVGA G2 750 that I don't use and plug it into one of the SATA connectors on the 1300 PSU?

If you look at this image it might be clearer what I mean. The molex connectors are the ones called "PERF1" and "PERF2". To the left of those there are four connectors for SATA cables. Could I use another molex cable and plug it in to the SATA connectors instead?

https://www.evga.com/products/images/gallery/120-G2-1300-XR_XL_5.jpg

RX 480 is powered up by 8-pin pcie power and not 6-pin, I have it right in front of me so I am not wrong. The sata is only connected to the riser from the PSU and the card also get's power from the PSU via the 8-pin pcie cable. I have those running from a few weeks and I don't see any problem until now.

RX480 is powered by 6-pin pcie power not 8-pin so it definitely take up to 75w from the connector (since 6-pin pcie is max 75w, 25w for each pin), if the gpu take 133w then there are 133-75 = 58w gpu take from PCIE slot 1X, i am sure it is only for peak consumption of short period of time, it its continuously like this then sata power connector will be burn because sata only limited to 35w power delivery

so never use any sata power for gpu mining

A fully modular PSU like Corsair RM1000i comes directly with 8 PCIE cables that can be made 6 or 8 pin and it can support up to 8 GPU-s , it also come with 12 Sata cable connectors enough to power up many risers. I think the PSU is the most delicate part choosing when building a mining rig. This PSU supports easily up to 6 cards of RX 480,tested by me as one card max power draw I see in GPU-z latest version is 133 watt.

http://www.corsair.com/en-gb/rmi-series-rm1000i-1000-watt-80-plus-gold-certified-fully-modular-psu

yup that it is, only use pcie splitter that use at least 18 awg wire, 16 awg is better, but never use 20 or 24awg wire

if you want to use multiple PSU,, you shouldn't mix 1 PSU for riser and another for GPU.

GPU+Riser should be powered by same PSU, as there are electrical power connection between PCIE power socket on GPU and PCIE slot in Riser.
Power connector on riser is not to power up riser, it is to power up gpu via pcie-slot 1x connector which spec is allow gpu to take up to 72w from these pcie 1x slot, so sata powered riser is should not be allowed

splitting multiple psu between gpu and mothherboard is fine, splitting multiple psu between (gpu+riser) and another (gpu+riser) is fine too

Is this the cable?

http://www.ebay.com/itm/18AWG-6-pin-to-2x-6-2-pin-6-pin-8-pin-Power-Splitter-Cable-PCIE-PCI-Express-/361651807884?hash=item543420a68c:g:eEYAAOSw0fhXjlMJ