thanks a lot guys !! 
Topic: 6 x msi 7950 - can I use non powered risers? (Read 3131 times)
cool I get it fully now thanks a lot guys !!
thanks a lot guys !! 
You have to know EXACTLY how much juice each card is going to pull when under load in order to know whether or not you need powered risers.
Remember, 6pin PCI-e power connectors supply 75 watts and 8pin PCI-e connectors supply 100 watts. So, depending on which of these connections you have on your video cards will determine how much power will be drawn from your power supply. Anything above this amount will be drawn from the motherboard. For the PCI-e slots, 16x slots on your board will supply up to 75 watts of power. Anything less than a 16x slot will only supply up to 25 watts of power.
In my case, I use Sapphire 7950s that have (2) 6pin connections for power. So, they're getting 150 watts of power from the power supply, and the rest is coming from the motherboard.
Remember, 6pin PCI-e power connectors supply 75 watts and 8pin PCI-e connectors supply 100 watts. So, depending on which of these connections you have on your video cards will determine how much power will be drawn from your power supply. Anything above this amount will be drawn from the motherboard. For the PCI-e slots, 16x slots on your board will supply up to 75 watts of power. Anything less than a 16x slot will only supply up to 25 watts of power.
In my case, I use Sapphire 7950s that have (2) 6pin connections for power. So, they're getting 150 watts of power from the power supply, and the rest is coming from the motherboard.
Scrypt mining is much more power hungry than SHA256, usually up to 3x 7950's on non-powered risers is ok if you undervolt them and go easy on any overclocking, but any more than 3 and the additional cards will need powered risers otherwise you will burn out the 12v rail on the motherboard. There are numerous examples of this to be found if you search the forum. Depending on your cards you may even want to limit un-powered risers to 2 cards per motherboard to be safe. SHA256 is less power demanding as you can underclock the memory on the cards, which will lower the power consumption further.
I am building my first mining rig for bitcoins/litecions. I am using MSI 990XA-GD55 mothercard and I want to connect 6 radeons msi twin frozr 7950.
I was advised by somebody that there is no need for powered risers, because the mobo has 2x8pin + ATX24 connections for power supply.
Do you think it would burn mobo? please give a good explanation for your anwser
cheers
The 2x8pin is for the CPU, not for the PCI-E.I was advised by somebody that there is no need for powered risers, because the mobo has 2x8pin + ATX24 connections for power supply.
Do you think it would burn mobo? please give a good explanation for your anwser
cheers
So your mobo is the same as any other, pulling all the PCI-E juice from ATX24.
I would not do it. There are a couple guys around here that never do it and haven't had any problems, and there are numerous guys that have fried their motherboards. I ran a test on my 6 7970s and they draw 300 watts from the mobo at full load. 7950s wouldn't be that far behind. That's too much juice.
I think the thing you want to worry about is the amp draw on your 12v rails on the motherboard. These are going over the solder traces and there is probably an amperage limit that you can hit before things get too hot and turn into carbon.
Source: http://science.howstuffworks.com/environmental/energy/question501.htm
So the powered risers essentially bypass the thin hose on the motherboard and supply the voltage right at the card. It's a good theory and decent practice when applied properly. I wouldn't power all your risers, maybe a couple of them. Better yet, find out the amp rating on your rail(s) on the motherboard and then determine the amp draw from your video card and compare the two.
Quote
The three most basic units in electricity are voltage (V), current (I, uppercase "i") and resistance (r). Voltage is measured in volts, current is measured in amps and resistance is measured in ohms.
The voltage is equivalent to the water pressure, the current is equivalent to the flow rate, and the resistance is like the pipe size.
Let's see how this relation applies to the plumbing system. Let's say you have a tank of pressurized water connected to a hose that you are using to water the garden.
What happens if you increase the pressure in the tank? You probably can guess that this makes more water come out of the hose. The same is true of an electrical system: Increasing the voltage will make more current flow.
Let's say you increase the diameter of the hose and all of the fittings to the tank. You probably guessed that this also makes more water come out of the hose. This is like decreasing the resistance in an electrical system, which increases the current flow.
The voltage is equivalent to the water pressure, the current is equivalent to the flow rate, and the resistance is like the pipe size.
Let's see how this relation applies to the plumbing system. Let's say you have a tank of pressurized water connected to a hose that you are using to water the garden.
What happens if you increase the pressure in the tank? You probably can guess that this makes more water come out of the hose. The same is true of an electrical system: Increasing the voltage will make more current flow.
Let's say you increase the diameter of the hose and all of the fittings to the tank. You probably guessed that this also makes more water come out of the hose. This is like decreasing the resistance in an electrical system, which increases the current flow.
Source: http://science.howstuffworks.com/environmental/energy/question501.htm
So the powered risers essentially bypass the thin hose on the motherboard and supply the voltage right at the card. It's a good theory and decent practice when applied properly. I wouldn't power all your risers, maybe a couple of them. Better yet, find out the amp rating on your rail(s) on the motherboard and then determine the amp draw from your video card and compare the two.
I am building my first mining rig for bitcoins/litecions. I am using MSI 990XA-GD55 mothercard and I want to connect 6 radeons msi twin frozr 7950.
I was advised by somebody that there is no need for powered risers, because the mobo has 2x8pin + ATX24 connections for power supply.
Do you think it would burn mobo? please give a good explanation for your anwser
cheers
I was advised by somebody that there is no need for powered risers, because the mobo has 2x8pin + ATX24 connections for power supply.
Do you think it would burn mobo? please give a good explanation for your anwser
cheers
Jump to: