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Modern power supply with a retro pc.

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First post, by Baoran

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Recently power supply of one of my retro PCs failed. I ordered a new seasonic focus+ 550W power supply to replace it. The power suply is modular and it seems to come with only one cable with molex connectors.
Would it be a problem to connect 200W worth of devices into that single cable with a molex splitter?
I have never actually thought about how much wattage a single cable can handle because before I have always been able to divide devices between multiple cables.

Reply 1 of 23, by elod

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You can check what is the AWG rating of the cable and from there you know the current.
Modular is nice, you could repurpose some cut off Molex cables and connect them to a modular cable you cut.

Basically you will not be able to pull 200W on a pair of cables. Not for long that is...

Reply 2 of 23, by Koltoroc

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not a cheap solution, but you can for some modular power supplies get aftermarket custom(ish) cables from cablemod.

https://store.cablemod.com/compatibility/

that link has a list of power supplies where they have compatible cables for. It's not cheap but a solution for your problem.

Reply 4 of 23, by cyclone3d

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You could use multiple splitters.. or you could get SATA to MOLEX adapters:
https://www.ebay.com/itm/Manhattan-6-SATA-15- … 77/192772021590

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Reply 5 of 23, by Baoran

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I did order few cheap chinese sata to molex adapters about a week ago, but it will be probably February before they come and that is why I asked what would be safe wattage in single cable so perhaps I could still use the system until then by not connecting some of the devices.

Reply 6 of 23, by SW-SSG

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How many devices are you planning to attach that would result in 200w draw, anyway? You'd need at least ten 7200RPM HDDs attached at once to even approach that, and even then they would pull that much current only at spin-up (e.g. less than 15 seconds).

Reply 7 of 23, by Baoran

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I might have overestimated the wattage I said to make sure. I was thinking that if you guys say it is ok to have 200W there, then I could be sure that I wouldn't have problems.
Basically I was about to connect two seagate barracuda 7200 rpm ide hard drives, 2 optical drives, 1.44Mb floppy drive and the molex connector that is in Geforce FX 5950 ultra all to a same cable.

Reply 8 of 23, by Baoran

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I could easily leave at least one of the optical drives disconnected if needed because I mostly left it there because I liked the way the drive looked like instead of real need for second optical drive.

Reply 9 of 23, by lost77

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It was quite common at one point to use a molex to 6-pin PCI-E power connector. They are rated for 75w. On the other hand people would usually warn you against doing that with a 8-pin connector (150w).

So maybe the limit is somewhere in between.

Considering the FX5950 Ultra has a TDP of 74 watt I would not want to run all that of a single molex cable. Maybe go with a less power hungry graphics card until you can find a fix.

Reply 10 of 23, by treeman

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I cut one of the sata power plugs on a modern psu and soldered on a molex connector from a old burner out psu I had. Its straight forward match up the 4 colours, they are in different order on the sata but as long as colours match its all the same. A 5th plug on sata is a 3.3V which molex doesn't use, leave it out.

Reply 11 of 23, by Baoran

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lost77 wrote:

It was quite common at one point to use a molex to 6-pin PCI-E power connector. They are rated for 75w. On the other hand people would usually warn you against doing that with a 8-pin connector (150w).

So maybe the limit is somewhere in between.

Considering the FX5950 Ultra has a TDP of 74 watt I would not want to run all that of a single molex cable. Maybe go with a less power hungry graphics card until you can find a fix.

That is true but some of those 74 watts should come from AGP instead of the molex, right?

Reply 13 of 23, by Baoran

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Nobody knows how much wattage one cable can handle exactly? I could take it down to one hard drive, one optical drive, floppy drive and fx 5950 ultra until I get adapters and leave one of the hard drives and one optical drive disconnected until then.

Reply 14 of 23, by HanJammer

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Baoran wrote:

Nobody knows how much wattage one cable can handle exactly? I could take it down to one hard drive, one optical drive, floppy drive and fx 5950 ultra until I get adapters and leave one of the hard drives and one optical drive disconnected until then.

https://www.powerstream.com/Wire_Size.htm

W = A * V (so A = W / V).

Most PSU cables are 18 or 20 AWG. But check yours (it should be described on the cable's insulation).

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Reply 15 of 23, by fitzpatr

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Realistically, you're probably fine. While not ideal, I doubt that you're the first person to string those all together.

Here is a chart showing Amperage and Wattage maximums for your set-up. The numbers for the GeForceFX 5950 Ultra are estimates, as I cannot find exact power draw specifications. I probably went more on the 5V rail than is actual.

18 AWG wire can handle ~16A for chassis wiring. and it's a Seasonic power supply, so everything will be of good quality.

I'd limit the Optical Drive to 1 just to be safe, but otherwise I think that you're fine.

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    Power Draw estimates for Baoran's MOLEX cable GeForce FX 5950 Ultra
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Reply 16 of 23, by Baoran

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I happened to find this from one of my boxes.

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I assume there would be no problem using it as second cable even if it isn't from a seasonic psu if the pinout matches the seasonic cable?
I think it is from antec TPQ-850 power supply. I just want to make sure I am not missing something, so that is why I want to make sure and ask about it here.

Reply 17 of 23, by cyclone3d

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Baoran wrote:
I happened to find this from one of my boxes. […]
Show full quote

I happened to find this from one of my boxes.

power1.jpg

I assume there would be no problem using it as second cable even if it isn't from a seasonic psu if the pinout matches the seasonic cable?
I think it is from antec TPQ-850 power supply. I just want to make sure I am not missing something, so that is why I want to make sure and ask about it here.

As long as the pinout is the same, it will be fine.

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Yamaha XG resource repository - updated November 27, 2018
Yamaha YMF7x4 Guide
AW744L II - YMF744 - AOpen Cobra Sound Card - Install SB-Link Header

Reply 18 of 23, by Baoran

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cyclone3d wrote:
Baoran wrote:
I happened to find this from one of my boxes. […]
Show full quote

I happened to find this from one of my boxes.

power1.jpg

I assume there would be no problem using it as second cable even if it isn't from a seasonic psu if the pinout matches the seasonic cable?
I think it is from antec TPQ-850 power supply. I just want to make sure I am not missing something, so that is why I want to make sure and ask about it here.

As long as the pinout is the same, it will be fine.

I went through the connectors in both Seasonic cable and this one twice using multimeter. Both have 2 same wires out of 6 missing and rest 4 wires go to the same pins in molex in both of the cables.

Reply 19 of 23, by SirNickity

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I would stick a meter in the business end of that donor cable to make sure everything is as you expect, though. There's no standard for the modular side of a PSU. Most manufacturers use Molex Mini-Fit Jr. plugs*, or similar, but the actual pinout is made up by the engineer designing that particular PSU.

My brother just called to ask for advice on a PC he's building this week. Apparently his modular PSU has a bunch of 8-pin sockets on the rear of the PSU that have identical plugs, but do different things. So, it should be technically possible to plug in a SATA power cable to the ATX 12V port on the PSU. Meh. What could go wrong? 😜

(* Note: Another option is just to make your own cables. Find the Mini-Fit Jr. plug that fits the modular sockets, buy some 4-pin Molex plugs, and DIY. FrozenCPU should have all the parts you need.)