powered pci-e extenders are largely unnecessary

[eroxors]

Time to clear up the many wrong statements that people are making in this thread. I am the person who made the first powered PCIe extender and who documented why this is necessary: http://blog.zorinaq.com/?e=44

Firstly, the current drawn through the PCIe slot vary a lot depending on the card. Dual-GPU cards usually draw more than single-GPU ones (contrary to what someone said). Here are some of my own measurements with a clamp meter around the 12V lines of a PCIe extender, while Bitcoin mining:

HD 6990: 4.2 A
HD 5970: 4.1 A
HD 5870: 3.2 A
HD 6950: 2.5 A
HD 7970: 0.9 A

So for example the 7970 (and probably most other 7xxx series cards, but I have not tested them) draws so little power that they pretty much don't need powered extenders.

Also, eroxors, most of your cards are pretty low-end/mid-end. They likely all draw less than 3 Amp or so because your most power-consuming one seems to be the HD 5870 (3.2 A through the slot). Even if you had 4 of these cards, that's only 12.8 Amp total, so only 6.4 Amp per 12V wire of your 24-pin ATX adapter.

But most importantly, whether the 24-pin ATX connector overheats or not depends a lot on whether the Molex Mini-Fit Jr. pins in the PSU 24-pin plug have a single or double spring. You can tell by removing the pin from the plastic housing and seeing if it has one or two pairs of "dots" at the end. This one has two: http://www.alliedelec.com/images/products/Small/70090646.jpg The single spring pins (typically used by inexpensive PSUs) have a higher (edit: electrical) resistance and are more prone to causing the connector to burn out over time.

For example, in my farm of 4x5970 and 3x6990 machines from the old days, I noticed that upgrading from single-spring pins to double-spring pins pretty much made powered extenders unnecessary.

Finally, eroxors, you are right that the memory subsystem of Radeon cards (at least the 5xxx I tested years ago) is powered through the slot, not through the 6-pin or 8-pin power extenders. So Litecoin miners need powered extenders more than Bitcoin miners (at least for 5xxx and 6xxx cards, again the 7xxx series seems to draw so little from the slot, that powered extenders may not be necessary).

MrB to the rescue. Thanks for the clarification.

So powered extenders are:

a) unnecessary for 7xxx cards
b) unnecessary if adequate power supplies that have double-spring plugs are utilized
c) unnecessary for non-scrypt mining

I concede that there are applications that can warrant powered extenders, but stand by the "waste of time/money" designation. There is a clear profit motive for the product to be promoted the way it has been, which seems to be based on misinformation.

[gyverlb]

So powered extenders are:

a) unnecessary for 7xxx cards

I wouldn't bet even a cheap motherboard on this. You are referring to a post from someone extrapolating his experience with 7970s (and who didn't specify the tested models) to all 7xxx cards.

If fools base their setup on such limited information and burn all their systems at once they will have only themselves to blame.

If you don't have equipment to check for sources of problems (clamp meters and/or infrared imaging) or references of the very same setup already working for someone else, always validate a new setup on a single system before risking your whole mining operation : 48h of downtime for a rig and a single motherboard to replace may be manageable out of 10 rigs, all failing at once is a week-end lost replacing everything and probably a good part of a month worth of income lost...

[Kalen]

I have a 3-card setup, and due to heat issues, tried to use a unpowered riser on the middle card (5870). It booted, but always forced a reboot when mining. Tried a 2nd riser cable, same deal. Then tried a DIY Molex mod, with both cables. Was able to mine for about a few hours, then the card would crash. Trying again soon with a factory-made powered riser.

Anyway, not everyone has the technical expertise or tools to test PCB amps and stuff. So disagreeing with the thread title... out of an abundance of caution, its probably easier just to use a powered riser.

[GenTarkin]

so a 5850 & 5830 .. using x1 , one powered the 5830 not powered extender...the board should be fine?
The board itself even has a PCIe 6pin on it for additional PCIe power, but  not sure if thats routed to all PCIe slots or just the x16's

[mrb]

So powered extenders are:
a) unnecessary for 7xxx cards
b) unnecessary if adequate power supplies that have double-spring plugs are utilized
c) unnecessary for non-scrypt mining

I concede that there are applications that can warrant powered extenders, but stand by the "waste of time/money" designation. There is a clear profit motive for the product to be promoted the way it has been, which seems to be based on misinformation.

a) No, I only stated I tested the 7970. In fact lewlzminer above claims 3 Amp per 7950. So it seems my model of 7970 (a reference model) is not representative of the whole 7xxx series.
b) Yes. However I also suspect you need good quality mini-fit jr male terminals (on the motherboard's 24-pin connector) to benefit from the low electrical resistance of double-spring mini-fit jr female terminals (on the psu's 24-pin connector).
c) No. Again, many Bitcoin miners certainly do need powered extenders. I needed them even with my 4x5970 and 3x6990 running with downclocked memory (everything else at stock settings).

As to the profit motive of vendors: I don't know. I am not associated with any of them. I certainly did not start a conspiracy theory to entice users to buy powered extenders

[GenTarkin]

off the top of my head, not sure how much power the x1 slot provides, but I know a 5970 + my old socket 939 board w/ an unpowered extender cable .. ended a day later in a power component blowing near the PCIe slot area =(
Dead board.

[YipYip]

off the top of my head, not sure how much power the x1 slot provides, but I know a 5970 + my old socket 939 board w/ an unpowered extender cable .. ended a day later in a power component blowing near the PCIe slot area =(
Dead board.

I really appreciate all the input and for also the people who are saying they are not necessary etc

I think from my experience in that cards just dont show in the OS unless u bring it back to the board or goto a powered riser speaks for itself

And after experiencing multiple PSU's and a 1 dead mobo its time to say "thats enough of that shit"

When we are talking about $2k+ per rig of equipment and then not spending an extra $20 on 2 powered risers for a 4 card setup i think speaks for itself

The space shuttle O-Rings where the $20 equivalent to this story

[induktor]

I second YipYip

I won't risk a 600 $ GPU and 150 $ Mobo for a 15-20 $ powered extender!, I don't even have to think about it, just go for it.

I did notice that my 7950 mining BTC does not draw a lot from the PCIe 1x (Tested it with a TrueRMS clamp meter measuring max-min) without connecting the molex cable, current was under 1A, however when i mine LTC current goes to 1.8A, and I´m running at stock clock (925).
also notice that with LTC VRM temperature skyrocket!, close to 75C (when the GPU is under 60), in BTC VRM and GPU have the same temperature.

so yes, maybe for BTC is not absolutely necessary (still won't hurt), but for LTC I think it will be a good idea.

[fran2k]

So powered pci-e extenders aren't largely unnecessary: the combination of motherboard model, actual cards used, opencl kernel used, ram and gpu settings makes it impossible to predict what will happen without powered extenders unless you already tried the same combination. If it worked for you without them, consider yourself lucky.

Best option for me. Buy powered risers, try both options connected/unconnected, then decide.

[ewitte]

For a 16x slot I definately agree you shouldn't need a powered cable.  Smaller slots may be only speced for 25W.  I would not chance it.  I have one card in a 4/8x slot I get nervous about running LTC because memory has to run off the slot.  Don't want to burn out a dual 2011 motherboard that has 16 memory slots! The manual for the board states 25W max.

[endriuska]

I'm building a 18 card rig, hopefully 6 cards(6870) per rig and would any of you know if I should buy powered risers?  and do all of them must be powered? eg should i do 3 powered and 3 regular risers?

Thanks

[ewitte]

I wouldn't chance it for the ones running in 1/4/8x slots.  Compared to the cards the price is negligible.

[ModusPwnd]

How many cards per rig ?

I run 7 on one mobo without powered extenders.  No problem. 

[Fuzzy]

I burned the 12v pins on my Asus mobo running 5x 6950s last year using unpowered 1x risers...

I'd use powered risers just for peace of mind.


Note the mobo didn't have any optional on-board molex plugs either.

[endriuska]

so again, running 1x ports with powerisers is recommended and reg ones without is ok right?

thanks

[gyverlb]

so again, running 1x ports with powerisers is recommended and reg ones without is ok right?

thanks

This way at least you keep the load on the connectors in the officially supported range (until you overclock) and may invoke the warranty is something goes wrong.

[computerparts]

I see so many topics regarding powered extenders and their importance, but from my experience, they are a waste of time/money.

^This.  I've thought a time or two about creating this very topic.  I run 258 GPUs.

  How much did that set you back?