Custom cabling and simple questions

[PraxisPractical]

I'm looking into buying a new Silverstone DA1000. It's got a single 12v rail rated at 80A.

One thing I've always wanted to do was make my own modular cables for a PSU, at the exact specific lengths to reach from point A to point B, no more and no less.

One thing in particular I worry about is putting more than the typical 3 SATA connectors on one cable. I've got 6 SATA drives, and I'd like them to all be wired with just one cable, but is this safe? There's got to be a reason why the standard is only 3 connectors per cable. Is this just an average maximum case? I assume this is safer on a PSU with a single 12v rail rather than a PSU with multiple 12v rails, yes?

I would also like to power 5 or more fans from one cable, preferably using a single knob to control their speeds. Any idea's how I could go about doing this?

Similar to the harddrives and fans, I would also like to run two GPU's across a single cable. I don't yet have anything other than a single 8800gt, but in the future I would like to have 2 GTX 280's or better. Would it be safe for something so power intensive to run through a single cable, even if I have a single 12v rail?

I understand three questions are probably asking the same thing in different words. I just want to make 100% sure what I'd like to achieve isn't going to hurt my wallet because I failed to understand what I was doing.

Thanks for your help

 

[Kil4Thril]

You can do what you are asking, but you'll have to increase wire size to handle the amount of current you want to draw through each branch.

 

[Zero82z]

One thing in particular I worry about is putting more than the typical 3 SATA connectors on one cable. I've got 6 SATA drives, and I'd like them to all be wired with just one cable, but is this safe?

Yes, it's safe.

There's got to be a reason why the standard is only 3 connectors per cable. Is this just an average maximum case? I assume this is safer on a PSU with a single 12v rail rather than a PSU with multiple 12v rails, yes?

Presumably it's done simply because people may need cables going to different places, so putting all the connectors on one cable wouldn't be practical for a lot of people. It's easy to route two cables to the same location, but not so easy to route a single cable to two locations. And the amount of rails makes no difference.

I would also like to power 5 or more fans from one cable, preferably using a single knob to control their speeds. Any idea's how I could go about doing this?

Daisy-chain the fans, and connect them to a variable resistor with enough tolerance to withstand the amount of current that all the fans will be drawing. Basically, make your own fan controller.

Similar to the harddrives and fans, I would also like to run two GPU's across a single cable. I don't yet have anything other than a single 8800gt, but in the future I would like to have 2 GTX 280's or better. Would it be safe for something so power intensive to run through a single cable, even if I have a single 12v rail?

I'm not so sure about that, because the cable might not be broad enough to handle the current you'll be pulling. The PCI-E power spec allows for 75W max through a 6-pin connector and 150W through an 8-pin, which means that the three +12V wires that you'll be using need to be able to carry 37.5A of current collectively ([[150W+75W]*2]/12V = 37.5A). Look up a wire gauge table and see if the cables coming out of your PSU are capable of that.

To be honest though, I'm not a big fan of the idea of running two video cards off a single cable. If you can live with doing it with two cables, that would be my suggestion. You'll be fine with the other items since their power draw won't be nearly as high, but with GPUs you'll be pushing it.

 

[PraxisPractical]

I'm not so sure about that, because the cable might not be broad enough to handle the current you'll be pulling. The PCI-E power spec allows for 75W max through a 6-pin connector and 150W through an 8-pin, which means that the three +12V wires that you'll be using need to be able to carry 37.5A of current collectively ([[150W+75W]*2]/12V = 37.5A). Look up a wire gauge table and see if the cables coming out of your PSU are capable of that.

To be honest though, I'm not a big fan of the idea of running two video cards off a single cable. If you can live with doing it with two cables, that would be my suggestion. You'll be fine with the other items since their power draw won't be nearly as high, but with GPUs you'll be pushing it.

I see what you mean. For sake of safety, would it be wisest to just have two cables with one 8pin and one 6pin, or could I get away with a cable with two 8pins and a cable with two 6pins? It'd be the difference between 18.75A across each or 25A across one and 12.5 across the other. Common sense is trying to tell me the balanced 18.75A across two cables would be my best bet.

Thanks for your input.

 

[Zero82z]

Well, one way you'd be running 300W over one cable and 150W over the other, whereas if you balanced them you'd be carrying 225W on each cable. I'd probably do the latter just for the sake of symmetry . Either way would probably be fine though.

 

[PraxisPractical]

Thanks, that will have to be the route I take once I can pay for it. I'll be happy if I can just make all 6 drives span a single cable without extra cable getting in the way of everything else.

I'm planning to buy a new Lian Li P80 along with the PSU so I can't do any measurements until then unless I want to have two sets of cables for two different cases. The dual GPU's are a long ways away still...