VOGONS


Modern power supply with a retro pc.

Topic actions

First post, by Baoran

User metadata
Rank l33t
Rank
l33t

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

User metadata
Rank Member
Rank
Member

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

User metadata
Rank Member
Rank
Member

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 3 of 23, by Baoran

User metadata
Rank l33t
Rank
l33t

What would be the maximum safe wattage from single cable then?

Reply 5 of 23, by Baoran

User metadata
Rank l33t
Rank
l33t

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

User metadata
Rank Oldbie
Rank
Oldbie

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

User metadata
Rank l33t
Rank
l33t

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

User metadata
Rank l33t
Rank
l33t

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

User metadata
Rank Member
Rank
Member

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

User metadata
Rank Oldbie
Rank
Oldbie

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

User metadata
Rank l33t
Rank
l33t
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 12 of 23, by vvbee

User metadata
Rank Oldbie
Rank
Oldbie

Molex-sata adapters have a pretty bad record for starting fires. I wouldn't use random chinese adapters to convert the other way either.

Reply 13 of 23, by Baoran

User metadata
Rank l33t
Rank
l33t

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

User metadata
Rank Oldbie
Rank
Oldbie
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).

New items (October/November 2022) -> My Items for Sale
I8v8PGb.jpg

Reply 15 of 23, by fitzpatr

User metadata
Rank Member
Rank
Member

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.

MT-32 Old, CM-32L, CM-500, SC-55mkII, SC-88Pro, SC-D70, FB-01, MU2000EX
K6-III+/450/GA-5AX/G400 Max/Voodoo2 SLI/CT1750/MPU-401AT/Audigy 2ZS
486 Build

Reply 16 of 23, by Baoran

User metadata
Rank l33t
Rank
l33t

I happened to find this from one of my boxes.

The attachment power1.jpg is no longer available

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

User metadata
Rank l33t++
Rank
l33t++
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.

Yamaha modified setupds and drivers
Yamaha XG repository
YMF7x4 Guide
Aopen AW744L II SB-LINK

Reply 18 of 23, by Baoran

User metadata
Rank l33t
Rank
l33t
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

User metadata
Rank Oldbie
Rank
Oldbie

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.)