Topic: Building my psus, need some quick numbers crunched. (Read 2061 times)

Many thanks indeed, that's cleared a few things up with me, I was always wondering why the two additional pins were *both* ground connectors and there was no other 12V feed.

Great info

+1

The 6-pin connector was designed for a 75W load but the physical connector is capable of delivering 200W safely (due to type of connector and guage of wiring used).  When the standard was ratified GPU weren't pulling more than 200W so the spec was designed at 75W.  The MB slot can deliver 75W and 6-pin connector can deliver 75W.  An "extreme" video card could use 2 to get 225W total.  More than enough right?

However after the 6-pin ATX PCIe standard was ratified AMD & NVidia hit a wall and needed more power.  Now the 6-pin connector technically could jhandle 200W but many power supplies had been built expecting no more than 75W load so just allowing >75W on same connector would be dangerous.   Yeah it created a lot of "WTF???" in the industry as it was only 6 months after the 6-pin hit the market that AMD/NVidia came back saying we need more power.

Since the 6pin can deliver 200W (if power supply can handle it) the 8-pin design is simply an incompatible connector to ensure one doesn't damage the powersupply by overloading it.  The 8-pin was chosen so it can break away and form 6+2 connector.  The two additional ground lines reduce resistance which lowers the voltage drop improving efficiency.   As a safety feature the video card w/ 8 pin connector checks for presence of ground on one of the new ground wires (a sense line).  If it doesn't detect a ground (the last two pins are not connected) it doesn't power up because that means it is being powered with a 6 pin connector and it could damage the powersupply it it tried to pull full 150W load.

If you have a powersupply w/ only 6-pin connector but it can deliver 12.5A (some can, some can't) you can just use a 6-pin to 8-pin adapter and it will work fine.  Just check the amperage rating for each rail to ensure the PS can really deliver 12.5A.

So that is likely way more than you wanted to know about the convoluted mess than AMD/Nvidia made of the ATX powersupply standard.  Hindsight being 20/20 likely they would have simply made the 6-pin spec require powersupplies to deliver 12.5A (150W) from the beginning and then there would have been no need for a second connector. However that is in the past and now we are stuck with it.
 
On edit:  Edited for clarification and to pontificate.

They're supposed to be rated for a higher wattage(150 vs 75 or something along those lines) not that i can say why adding more grounds would do that

a quick question about PCIe connectors...
what is the actual function of the 8 pin PCIe connector since all it does is add 2 more ground wires?
6 pin already has the same number of 12v power pins as there is ground so what is the point of adding more ground pins?

That magic black smoke is named Hexus, and he is hell bent on destroying ferngully.

I have some cards that are damaged from idiots and I use them to test stuff like this out. Thing ran, but then I pulled down the office system while I went out to dinner (pulled from wall) and came back to find the building next to my office on fire....so I have a few days until I can play again.
NOTE: Fire was coffee pot in an auto shop related. Not mining or my fault

Yes I believe so.  That is a very non-stand method of marking connectors but based on item description and the sticker in photo I think the other poster is correct that it is 12V potential between the 12v- and 12v+ connectors. 


If it were me I would check w/ multimeter BEFORE connecting any video cards. If you don't have one a Radioshack/Amazon $20 model if fine for what we will be testing.   Connect the (+) lead of multimeter to 12V+ connector and (-) lead of multimeter to 12V- connector.  The multimeter should read +12V. 

If it reads 24 volts then don't connect it to a video card you will instantly destroy it.
If it reads -12 volts then likely you have the leads reversed.  Double check that you have leads and connectors right. 

Remember to power a video card you need
a) 12V
b) flowing in the direction from the yellow wires -> black wires.

If voltage is wrong or direction of current is wrong you will destroy the card (likely instantaneously).


Nice idea for cheap power supplies.  If I were building more rigs I would look into those. 

Yep. It's just an special power supply because it isn't tied to ground. You could do cool things like tie several of them together in series to get a higher voltage, or connect V+ to ground and get -12V on V-.

http://www.ebay.com/itm/190576601798?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649#ht_2559wt_902

That is what I have. So black to 12v- and yellow to 12v+?

NO the black wire is ground.  There is 12V differential between 12V wire and ground (0v)  (12V - 0V).  Video card runs on 12V potential.  So you connect +12V line and common ground (0V) and you get 12V of potential across the video card and that makes it go.  Current flows from source of high potential (+12V line) to source of low potential (ground line).  The GPU and other components are between the +12V and ground connections so the current flows through the video card components to reach the low potential (ground).  To reduce the current across each wire the 6pin uses 3 circuits in parallel.  The 8 pin uses 4 circuits in parallel.



If you connect +12V and -12V line you just created 24V of potential. Are you trying to blow up someone's video card? Push 24V into video card and the magic black smoke that makes computer parts go will leak out.

Ok, just came across your post in this thread by chance: https://bitcointalksearch.org/topic/crazyness-build-time-48670

I realize now what kind of power supply you are using. Is it the Meanwell S-250-12? Judging by this datasheet, that one has two outputs labeled +V and -V with a floating ground. When you say + and - 12V, you mean that there is a total difference in potential of 12V between those pins. On an ATX supply there are many outputs, all labeled relative to the GND pin at 0V. So, between +12V and -12V, there is a 24V difference in potential. Semantics, maybe, but with a huge difference in meaning.

Ok, now that that's clear, back to your original question: how many cards can you run off this? The datasheet says you have 29A to play with. Unless the power supply is screwed up, it shouldn't blow up if you overload it because it has built in protection. It should just shut down nicely. I think you might get 2 cards running on it. Have you measured the power consumption of your cards, or do you have a multimeter that could do this? If so, you could put it in series with a single card and measure the current exactly.

Good luck!

EDIT: Oops, you posted while I was writing this!

Ok, well I have it wired as yellow -> 12v+ and black to 12v-. And yes you are right, they are 0v, but this psu dose not have 0v or multivoltage so it has 12v- becaues there is only 12v +
And I have the system running right now on 3 5770s (there are only 3 12+ and 3 12- so I didnt want to chance it) system is running great.
Config is as follows

Foxcon A7DA-S 3.0 AM3
(1) Antec Earthwatts 650w 80+ Bronze
------> Powering the motherboard, 250gb segate IDE HDD and a Asus5850
(1) Shakaru Speacial 360w 90+ at wall via Kill-A-Watt (NICE!)
------> Powering 3 XFX 5770

5.63amp/612w

MH/s 1137 avg on CGminer 2.0.5

Someone know what the card draw on the non pcie given power to a 5830, 5970 and a 5870 is?

Sorry, shakaru, this is not correct. The black wires are 0V. There is a blue wire on the 20- or 24-pin motherboard connector that carries -12V. On the other hand, there might be a way to use the -12V rail if you're really careful.

Does the PSU list the maximum current output on each rail?

You know thoese black wires on the 6pin................12v-
The yellow ..12v+

you can facepalm all you want until you slap your self silly.

tell me how would u use the -12v on a video card?

Facepalm

well the -12v will be useless to you...
so what ever the wattage of that output you will need to suptract from the 360w
if 50% of that power is used to power the -12v
that would only leave your with 180W...
you might get 2 5830 on one powersupply...

another thing to consider is the efficiency of the power supply.
for long term running (like mining) you want an efficient one if your paying for electricity.

Bought my self a few 4.7amp 360w dedicated 12v psus. Now on the back there are 3 12v- and 3 12v+ then your neut,live and ground. Now could anyone know how many card I can attach to this before I blow one up?
My main hardware are eitehr 5830s or 5770s, so that would be what I am working with. I tested out a single 5830 on it and ran like a dream! Hoping I can get atleast 3 on it. Hope....