Questions About Dual PSU Setup

[bo122081]

Setting up a rig, and I have 2 600W PSUs already in my house not in use, so I was considering just going dual PSU with those on the rig rather than buying an 800+W PSU, since the 600 likely won't be enough.
What are the technical concerns here, I have no worked with Dual PSU setups before. I hear problems arising from possibility of one GPU getting power from more than 1 of the 2 PSUs.
Would I have to employ powered risers to avoid this, or is there an easier way?

Also, with multiple GPU setups, would I need to be using powered risers to avoid power issues regardless? Or can I run 3-5 GPUs off a board 'normally' without power issues as long as the PSU is pushing enough W?

Sorry for the newb questions, but running more than 2 GPU and/or 1 PSU is new territory for me, and I'm not exactly an electrical engineer.

[Zanatos666]

Firstly, the question about powered vs non-powered risers depends on what kind of coin you are mining.  BTC, you dont need powered risers, LTC you absolutely do. 

As for as dual PSU's, couldnt tell you, but I will tell you what I would do.  Its just electricity to them from what I know of, so I would have my normal PSU setup, but my second one, in order to get it running, will need an ATX connection.  You can pick up cheap PSU testers that you can connect to the second PSU that will turn it on.  Then I would have one PSU feeding its PCI-E connectors to one card, and the other PSU to the other card.  All in some open air care or configuration.  And thats it.  Each card would be getting enough power from the PSU's and can mine just fine.  Nothing else fancy would need done I dont think.

[bo122081]

Firstly, the question about powered vs non-powered risers depends on what kind of coin you are mining.  BTC, you dont need powered risers, LTC you absolutely do.  

As for as dual PSU's, couldnt tell you, but I will tell you what I would do.  Its just electricity to them from what I know of, so I would have my normal PSU setup, but my second one, in order to get it running, will need an ATX connection.  You can pick up cheap PSU testers that you can connect to the second PSU that will turn it on.  Then I would have one PSU feeding its PCI-E connectors to one card, and the other PSU to the other card.  All in some open air care or configuration.  And thats it.  Each card would be getting enough power from the PSU's and can mine just fine.  Nothing else fancy would need done I dont think.

What about if you're not using risers? for mining LTC on multiple cards should I get some powered risers regardless if I need risers or not?

So, as long as you have the square PCIE power plugs for each card coming off just 1 PSU (which, afaik, most cards only have 1 plug?), then you're good? Is the 'problem' with multiple PSU powering multiple cards an outdated concern, or is that just if you're not using powered risers? Meaning I need to use powered risers?

As to starting the secondary PSU, there's a ton of guides on how to make the second one start, or I might just buy one of the pre-made dual PSU adapters you can find online.

[Takeshi_Kovacs]

Setting up a rig, and I have 2 600W PSUs already in my house not in use, so I was considering just going dual PSU with those on the rig rather than buying an 800+W PSU, since the 600 likely won't be enough.
What are the technical concerns here, I have no worked with Dual PSU setups before. I hear problems arising from possibility of one GPU getting power from more than 1 of the 2 PSUs.
Would I have to employ powered risers to avoid this, or is there an easier way?

Also, with multiple GPU setups, would I need to be using powered risers to avoid power issues regardless? Or can I run 3-5 GPUs off a board 'normally' without power issues as long as the PSU is pushing enough W?

Sorry for the newb questions, but running more than 2 GPU and/or 1 PSU is new territory for me, and I'm not exactly an electrical engineer.

If you have newish graphics cards with on-card power connectors then it is easy and you do not need powered risers. Suppose you have one mobo and three graphics cards. You connect your first psu to the mobo and to the additional power connectors on the first graphics card. You then connect the second psu to the power connectors on each of the other two graphics cards and you are good to go. You will of course have to find a way to get the second PSU to turn on but a paperclip between two of the connectors on the 20/24 pin ATX mobo connector on the second PSU is all that you need.

One word of caution about the two 600W PSUs that you have on a shelf at home.

Unless they have an 80+ rating, they were mostly likely designed for something like 600W max power, 400W continuous power and 65% efficiency. That would lead to a PSU rated to shed about 230W of heat when running at its continous power. Over a few years of use, the PSU efficiency will drop as the capacitors slowly cook and their internal structures and chemistry change. So today they may be down at 50% efficiency and the PSU that is delivering 400W to two graphics cards is now having to shed 400W of heat as well. That may be too much and it may only last a week or two.

Buying a new PSU will not only be a more reliable route. It will also pay for itself surprisingly quickly. Suppose that your total power drain is 700W for 3 GPUs and then the rest of the system. With a pair of tired old PSUs that will be a 1400W drain at the wall and $100 a month at 10c per kwh. Using an 80+ Silver PSU will get that bill below $60 a month and will pay for itself pretty quickly. It is worth noting that the efficiency argument does not mean that you should not consider multiple PSUs. Taking into account my local power prices and the price and availability of PSUs, the sweet spot for me is to buy as many 750W 80+ Silver PSUs as I need and run those.

[Takeshi_Kovacs]

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What about if you're not using risers? for mining LTC on multiple cards should I get some powered risers regardless if I need risers or not?
...

Then good luck keeping the cards cool. If you have three cards plugged directly into a mobo then the gaps between the cards will not be enough to allow the fans to move enough air to cool the cards when they are mining LTC.

[bo122081]

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What about if you're not using risers? for mining LTC on multiple cards should I get some powered risers regardless if I need risers or not?
...

Then good luck keeping the cards cool. If you have three cards plugged directly into a mobo then the gaps between the cards will not be enough to allow the fans to move enough air to cool the cards when they are mining LTC.

I would image that depends entirely on the mobo in question. But I will probably end up using risers. I'd just rather get as much info as possible.

[Zanatos666]

...
What about if you're not using risers? for mining LTC on multiple cards should I get some powered risers regardless if I need risers or not?
...

Then good luck keeping the cards cool. If you have three cards plugged directly into a mobo then the gaps between the cards will not be enough to allow the fans to move enough air to cool the cards when they are mining LTC.

I would image that depends entirely on the mobo in question. But I will probably end up using risers. I'd just rather get as much info as possible.

If you are mining LTC, you WILL need powered risers, regardless of MB and spacing.  LTC mining taxes your VRAM, where as BTC mining is GPU heavy.  Your GPU gets power from the PCI-E power connectors from your PSU, while your VRAM draws its power from the PCI-E bus on the MB.  If you are trying to draw PCI-E 16x power, overclocked power, out of a 1x slot, bye bye board.  Do any search around here for the numerous boards that have fried, caught fire, etc because of this.

[bo122081]

I won't be touching the 1x slots yet, the board I'm using has 4 16x slots. I'll be using risers with the 1x slots later to expand of course.

I have a feeling the powered risers are still recommended even in this case, though?

The 2 PSUs in question are a SolyTech SL-8600EPS which is 80%+ rated and a Thermaltake Toughpower W0103RU 600W, rated at 85%+.

I was also planning on testing the overall system with a kill-a-watt once it's put together.

[Zanatos666]

I won't be touching the 1x slots yet, the board I'm using has 4 16x slots. I'll be using risers with the 1x slots later to expand of course.

I have a feeling the powered risers are still recommended even in this case, though?

The 2 PSUs in question are a SolyTech SL-8600EPS which is 80%+ rated and a Thermaltake Toughpower W0103RU 600W, rated at 85%+.

I was also planning on testing the overall system with a kill-a-watt once it's put together.

Dont know if they are still needed, never done any 16x  to 16x extending, but its better to be safe than sorry, right?  Having them isnt going to hurt so might as well go the safe route.

[bo122081]

Dont know if they are still needed, never done any 16x  to 16x extending, but its better to be safe than sorry, right?  Having them isnt going to hurt so might as well go the safe route.

Yeah, no doubt.

Plus, since I'll likely be going egg-crate rather than using any of the cases I have lying around for heat-dispersion purposes (other than possibly retrofitting a big server case I have with a ton more fans??), risers would probably make that easier anyway.

I imagine that 1 900+W 80-90% PSU will still be vastly superior to 2x 600W 80-85% PSU, since the load will be a lot closer to optimal on the 1 PSU, rather than trying to somehow balance optimal load across two units?

I'll probably end up trying to sell off the 2 600Ws for a 900-1000W unit - if anyone's interested in a trade?

[Takeshi_Kovacs]

...
What about if you're not using risers? for mining LTC on multiple cards should I get some powered risers regardless if I need risers or not?
...

Then good luck keeping the cards cool. If you have three cards plugged directly into a mobo then the gaps between the cards will not be enough to allow the fans to move enough air to cool the cards when they are mining LTC.

I would image that depends entirely on the mobo in question. But I will probably end up using risers. I'd just rather get as much info as possible.

If you are mining LTC, you WILL need powered risers, regardless of MB and spacing.  LTC mining taxes your VRAM, where as BTC mining is GPU heavy.  Your GPU gets power from the PCI-E power connectors from your PSU, while your VRAM draws its power from the PCI-E bus on the MB.  If you are trying to draw PCI-E 16x power, overclocked power, out of a 1x slot, bye bye board.  Do any search around here for the numerous boards that have fried, caught fire, etc because of this.

Now that is very useful information. Thanks.

[darksoft]

If you have more than 3 cards then use the powered extensions, risers not needed. 1x and 16x extensions both work equally well. You can use the 1x to 16x extensions in 16x slots as well.

As for the dual PSUs use some thing like this:

http://www.add2psu.com/

which I am using right now with no issues, or this:

http://www.hashratestore.com/shop/cables/dual-power-supply-adapter-cable-24-pin-atx/

which I have not tried yet, but will soon and many others have sworn by it.