2x6-pin PCI-E to 8-pin PCI-E damages computer???

[Makalu]

So what's this about?

http://nvidia.custhelp.com/cgi-bin/nvidia.cfg/php/enduser/std_adp.php?p_faqid=2198&p_created=1212590319&p_sid=QiZDf-6j&p_accessibility=0&p_redirect=&p_lva=&p_sp=cF9zcmNoPTEmcF9zb3J0X2J5PSZwX2dyaWRzb3J0PSZwX 3Jvd19jbnQ9MjYsMjYmcF9wcm9kcz0yJnBfY2F0cz0wJnBfcHY 9MS4yJnBfY3Y9JnBfc2VhcmNoX3R5cGU9YW5zd2Vycy5zZWFyY 2hfbmwmcF9wYWdlPTEmcF9zZWFyY2hfdGV4dD1wb3dlcg**&p_li=&p_topview=1

Excessive ripple from connectors on different rails or what?

[Flanno]

I'd like to know too, as the card makers are shipping these 2x6pin pci-e to single 8pin pci-e connectors now. I posted about it a few threads down.

And noone is really sure what the story is over at the evga forums
http://evga.com/forums/tm.asp?m=418211&mpage=1&key=��

Originally when the gx2 came out some card makers shipped a single 6pin pci-e to 8pin pci-e cable. Now they have doubled up. So anyone with just 2x6pin pci-e cables on their psu, in order to power this card, has to sacrifice 2x4pin molex cables to accomodate the double molex to 6pin pci-e adaptor for the 6pin power on the card. And then use their 2x6pin pci-e cables on the psu with the 8pin adaptor for the 8pin power on the card. That's a lot of cables to power 1 card. And Nvidia say the single 6pin or double 6pin are bad. So why are they shipped with these uber expensive cards if there is a chance you could damage your psu and/or pc components ?

Can anyone offer an educated guess. Surely a psu that can do 18amps on 4 rails and a total 60amp rating on the 12v rail is enough ? Especially if you are using 2 x 6pin pci-e cables to power a single 8pin pci-e connector.

[Makalu]

ah ok...I read your other thread but didn't pick up on Nvidia saying anything about possible damage or to quote them "should not be used under any circumstances". Of course that's just in reference to the 2x6pin adapter.

I think the issue with the single 6-pin adapter is due to some PSU's not following the spec and using a full 6 wires from the connector to the PCB or possibly also because some PSU's put two connectors on one cable. Some PSU's only connect 3 or 4 of the possible 6 wires and they've got away with that because of the relatively low wattage draw on a single 6-pin connector in reality...I mean it seems that the max is about 5A and if the card requires more than that then Nvidia and ATI have simply added a second connector.

It could also be that some multi-rail PSU's would reach an individual rail OCP limit by running an 8-pin on a rail that was designed with a 6-pin in mind but the most current I've seen measured on an 8-pin in use so far is the one on the 9800GX2 carrying about 7A so I'm thinking it's because of wire limitations not rail limits.

[Flanno]

Thanks.

So in your educated opinion is it safer to use a single 6pin to 8pin or dual 6pin to 8pin.
The psu in question is in a Dell XPS630. I believe made by Delta, 750w, 18ampx4, and 60amp on 12v rail (I think). Has 2 6pin pci-e connectors, and is currently powering 2 x 8800gtx's with ease (using a pair of single 6pin to dual 6pin pci-e splitter cables)

[Makalu]

Well if it's not modular...which I think it isn't...and you can see a full six wires (three black grounds and three yellow +12V's) going from the connector into the PSU then it should be perfectly fine and safe to use the single 6pin to 8pin adapter. The 6pin is specified by PCI-SIG to carry 6.25A but it's rated by Molex to carry 9A. I'm not sure how much current the 8-pin connector on the GTX280 supplies but from reading a few power consumption measurements it sounds to be about 15A for the card total (180W) and I think it's safe to assume that the slot and the 6-pin each provide at least 4A so that would only leave 7A for the 8-pin to carry...that's a bit above the specification for a 6-pin but still well below the rating so yeah I'd go with that.

I can't really advise using the dual 6pin to 8pin adapter until somebody figures out why Nvidia is saying it can damage something. Assuming it's due to ripple across two different rails then it would be necessary to know for sure what the connector/rail distribution is on the PSU first...using two connectors that are both on the same rail would have identical ripple.

[Krohling]

The thing is... most PSUs with the 6+2 pin connectors the extra 2 pins are Grounds, and the "+2" are usually an extension of other 2 grounds from the "6" part of the connector.

Don't understand how 2 extra Grounds taken from elsewhere or taken from the same connector can provide more power if the number of +12V wires is the same.

The main concern should be: can your power supply provide enough juice @ the +12V rail(s)?

[Makalu]

well we had this discussion when the 8-pin connectors first started showing up with the 2 extra ground wire implementation and I think the conclusion was that an 8-pin can't provide more wattage then a 6-pin but it can provide more wattage with a lower voltage drop due to less resistance provided in the return path of the circuit by the two extra grounds.

But you do make a good point about some of the 8-pin or 6+2 pins reverting to still only three ground wires at some point in the circuit and that would really be the same as a 6-pin to 8-pin adapter so again I think their concern about using those is due to some PSU's not having a full three circuits connected to their 6-pins connectors.

[jonnyGURU]

I don't quite understand the warning myself.

Two PCIe connectors, if on different rails, would not increase ripple and noise because PCIe connectors are only ever on separate "virtual" rails and are never on truly separate rails.

Also, the "overload scenario" wouldn't come into play because whether you split the load across two rails, essentially doubling the OCP limit of each rail, at the adapter or at the card makes no difference. The load is being split regardless. It's not as if the traces for each connector on the card is going to separate parts of the card.

The limitation of the wires delivering the power is an interesting argument, but the wire used to deliver power to PCIe is capable of double the current the connector is actually designed to deliver. I've put a lot more than 75W on a PCIe connector with a load tester and the wire doesn't even get hot.

So I don't get it....

I would say, by far, that the dual 6-pin to 8-pin is much safer than a 6-to-8-pin.

[Makalu]

ok I was confused about ripple variations then...but while I'm on the subject what about combining two PCI-E connectors that are fed off of different transformers like in the 1kw+ CWT units?

The dual 6-pin to 8-pin would seem to be the better adapter since it would provide more current carrying capacity.

[jonnyGURU]

Yes. Usually when you tap off of different transformers you see the excess r&n, but PCIe's are always on the same transformer (correct me if I'm wrong).

[Makalu]

The Toughpower 1kw has PCI-E connectors on both transformers (12V3 and 12V4...the two rails with the 36A OCP) and I think some of the other CWT dual-transformers do something similar but I reckon it's a moot point since all of those PSU's have native 8-pins anyway and no need for the adapter.

[Bun-Bun]

The Toughpower 1kw has PCI-E connectors on both transformers (12V3 and 12V4...the two rails with the 36A OCP) and I think some of the other CWT dual-transformers do something similar but I reckon it's a moot point since all of those PSU's have native 8-pins anyway and no need for the adapter.

Theres two connectors on cards though so would it still not be possible to have two different transformers per card? Thus creating the same scenario?

There comment on those adapters really makes no sense.

[Makalu]

Yeah it is possible to do it with the native connectors and IIRC either the manual or a sticker near the modular interface on the Toughpower and/or Corsair HX1000 says to not power a two connector GPU off more than one rail so I doubt that Nvidia is rehashing a warning that's already been covered by the few PSU's with that possibility.

[Bun-Bun]

Maybe that is what they are concerned about...

However their statement is very ambiguous and considering they are saying that one should NEVER use this adapter and yet most of the card manufacturers are shipping it with them (and I am currently using the adapter on my rig until i get my 8 pin cable from corsair since I dont ahve a singe 6 pin to 8 adapter...) They should come out with a technical explanation as to why they are making that claim. With Nvidia saying never use it and the packaging with the cards saying "Not intended for the long term" I can see some problems quickly arising...

I can understand them saying adapters are not a good idea and a proper PSU should be purchased. But for them to say that a dual 6 pin adapter is a very bad thing while a single 6 pin is ok makes me wonder what the heck they are talking about...

Personally I don't care and I am going to keep using the adapter without worry.

[Makalu]

yeah it's very vague and I can't for the life of me figure out what it is they have in mind. Especially since the warning just says "could damage your computer" and doesn't even narrow it down to GPU or PSU damage or some other component.