PSU rewiring

gbellman

Trash Compacter
Original poster
Nov 7, 2019
50
9
First of all, few notes before my post:

1. I understand the risk of modding PSU, don't worry and please don't ask me to scrap the idea ?
2. Not opting for modularization as I think that the advantage is not much, you can only get rid of molex & fdd wire, probably another sata because the mobo, cpu, 2x PCIE wire are inevitable, and adding the connectors will significantly extend the PSU footprint. Instead of adding modular board, I think changing to soft silicone wire will be much better.

My question is, can we replace the wires from the PSU board? For example there are 30cm 4 yellow 4 black for CPU power, can we replace the 4 yellow (18awg) with only 1 wire (thicker, eg. 8awg), only split it to 4 wires 1 or 2 inches near to the connector?


Will that cause any problem? Assuming the wires are high quality, solder work is great. Will that idea work electrical wise? Need advice from electrician/engineer or whoever is experienced on this, thanks. ?
 

LegionDD

Cable Smoosher
Jan 6, 2020
12
10
Yes it is possible. The exact thickness for your wire depends on the current it has to pass (calculate voltage drop for a specific length of wire to see if it remains within specs at the expected power draw).
I've personally ditched the regular PSU for some of my builds by using just a 12V PSU + PicoPSU module. Taking 5V from the PicoPSU and 12V from the main power rail coming from the PSU for all the periphery. GPUs mostly need a lot of current at 12V, so you'll have to get the thickest wire for those (or run more than one set of wires again).

If your wires aren't thick enough (and remember, that depends on the thickness and length of the wire in question) you'll get brown outs; ie the voltage for a component drops below its minimum operating voltage and it shuts off - in case of a GPU that might crash your display driver or reset your entire system (don't ask how I know that).

Your biggest dangers then are the pinouts of your various plugs. Mess it up there and you can easily fry your system (doing something like putting 12V on a 5V line, or reversing power and ground).
 
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gbellman

Trash Compacter
Original poster
Nov 7, 2019
50
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1. Calculate voltage drop? Sorry idk how to do that ?, but my wire length will be max 20cm (gpu & cpu), max 15cm (mobo), less than 10cm (SATA). I bought 8awg soft silicone wire and found out that the stranded wire is almost 5mm diameter! So i bought solid copper wire with diameter 2.2 & 2.7mm, more than enough.

2. Nice! But it’s quite hard to find pico with 500w and above power, and the power brick also will be super huge.

3. Ya wrong pin out will be disastrous, I’ll be extremely careful with that, especially with unicolour wire.
 

LegionDD

Cable Smoosher
Jan 6, 2020
12
10
1. Calculate voltage drop? Sorry idk how to do that ?, but my wire length will be max 20cm (gpu & cpu), max 15cm (mobo), less than 10cm (SATA). I bought 8awg soft silicone wire and found out that the stranded wire is almost 5mm diameter! So i bought solid copper wire with diameter 2.2 & 2.7mm, more than enough.

2. Nice! But it’s quite hard to find pico with 500w and above power, and the power brick also will be super huge.

3. Ya wrong pin out will be disastrous, I’ll be extremely careful with that, especially with unicolour wire.

Well, about
1. You can use an online calculator (easy to google) to get the resistance of your wire, then you can use Ohms law to calculate the voltage drop (or google another calculator for that). Try this one for example

2. The point was you don't need a picoPSU with much wattage. All the power comes from your 12V line, which is passed to the mainboard through the 4 pin (or 6 or 8, depending on the mainboard) connector and the 24pin connector. The picoPSU does the same (hence why they're only rated for 12V input). All it does is generate the other, lower voltages the mainboard requires to function and those don't have to deliver a lot of power.
What I'd do is not use the included 4pin connector for the mainboard, as those wires are far too thin in most cases. Build your own with thicker wires and run it directly to the 12V supply.

3. When you've done this you can start thinking about the power supply equivalent of water cooling hardline metal tubing (because all you really need to run is a pair of 12V copper bus bars). ?
 

gbellman

Trash Compacter
Original poster
Nov 7, 2019
50
9
Well, about
1. You can use an online calculator (easy to google) to get the resistance of your wire, then you can use Ohms law to calculate the voltage drop (or google another calculator for that). Try this one for example

2. The point was you don't need a picoPSU with much wattage. All the power comes from your 12V line, which is passed to the mainboard through the 4 pin (or 6 or 8, depending on the mainboard) connector and the 24pin connector. The picoPSU does the same (hence why they're only rated for 12V input). All it does is generate the other, lower voltages the mainboard requires to function and those don't have to deliver a lot of power.
What I'd do is not use the included 4pin connector for the mainboard, as those wires are far too thin in most cases. Build your own with thicker wires and run it directly to the 12V supply.

3. When you've done this you can start thinking about the power supply equivalent of water cooling hardline metal tubing (because all you really need to run is a pair of 12V copper bus bars). ?

1. Ok thanks.

2. I never realized that, but anyway, now i'm using flex psu, which is small enough for my build ?

3. Maybe... but my wires' diameter won't be as big as the tubing and not as hard too, lol....
 

Kilrah

SFF Lingo Aficionado
Feb 20, 2017
128
112
You can but one large, rigid wire is actually often more annoying to deal with than multiple smaller ones sleeved together.
 
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LegionDD

Cable Smoosher
Jan 6, 2020
12
10
You can but one large, rigid wire is actually often more annoying to deal with than multiple smaller ones sleeved together.
True, but so is hardline water tubing. The appeal is in the potential for a clean and exceptionally tidy interior look. The more wires you have, the messier it looks, doubly so when wires are of the usual soft and jiggly type.
Imho when it comes to SFF, less is more (less wires = the more you can shrink the space), wouldn't you agree?
 

gbellman

Trash Compacter
Original poster
Nov 7, 2019
50
9
You can but one large, rigid wire is actually often more annoying to deal with than multiple smaller ones sleeved together.
Yes you’re right but 1 solid wire has higher max amp rating than stranded wire, to achieve the same rating it needs to get significantly thicker than single core solid wire, which is too much that you can’t insert it into the psu pcb board hole to get it soldered ?
 
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gbellman

Trash Compacter
Original poster
Nov 7, 2019
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True, but so is hardline water tubing. The appeal is in the potential for a clean and exceptionally tidy interior look. The more wires you have, the messier it looks, doubly so when wires are of the usual soft and jiggly type.
Imho when it comes to SFF, less is more (less wires = the more you can shrink the space), wouldn't you agree?
Ya agree that, every mm counts. And a 2++ mm wire is still relatively easy to manage compare to let’s say a 8 or 10mm metal pipe
 

gbellman

Trash Compacter
Original poster
Nov 7, 2019
50
9
Just to confirm again about the max amp carry by wires.

For example GPU is drawing 300W, minus the 75W by PCIE, meaning the 2x8P will be supplying the balance 225W: 225W/12V=18.75A, whereas the 18.75A will be divided amongst the 6 wires each of the 2x8P. Is that calculation correct? Because now I have 2 types of single core solid copper wires, copper diameter 2.7mm & 2.2mm. Just to make sure any one of it can support the amperage, as according to this page (https://www.engineeringtoolbox.com/amp/wire-gauges-d_419.html), a single core 2.6mm wire max amp is 52A, I'm planning to use 1x2.75mm wire for the 12v (same setup for the common ground) then branch out to 6 wires at the end for the GPU.
 
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LegionDD

Cable Smoosher
Jan 6, 2020
12
10
If 300W is the peak power draw, yes.
Considering I supplied a 3770K + GTX Titan with just two 2.5mm wires @1m length, I'd say you'll be fine supplying the GPU with one 2.75mm wire.
Just remember, if you run into instability with the GPU, the peak power draw might be too high and you need to add another wire.
Or if you actually want to run a longer wire, you might have to double it up.

Also keep in mind that connectors (and other type of connections, like screw terminals, etc) add some resitance on their own, so it's best to check the resistence of your entire run with a multimeter.
 

gbellman

Trash Compacter
Original poster
Nov 7, 2019
50
9
If 300W is the peak power draw, yes.
Considering I supplied a 3770K + GTX Titan with just two 2.5mm wires @1m length, I'd say you'll be fine supplying the GPU with one 2.75mm wire.
Just remember, if you run into instability with the GPU, the peak power draw might be too high and you need to add another wire.
Or if you actually want to run a longer wire, you might have to double it up.

Also keep in mind that connectors (and other type of connections, like screw terminals, etc) add some resitance on their own, so it's best to check the resistence of your entire run with a multimeter.

Thanks for the clarification, I just want to confirm so that I won't fry anything, lol....

My wire max length is not more than 32cm
I think currently there isn't any GPU drawing more than 300W natively, unless OC, which I do not plan to do.
 
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gbellman

Trash Compacter
Original poster
Nov 7, 2019
50
9
After running into this page (http://www.playtool.com/pages/psuconnectors/connectors.html#pciexpress6plus2), i can confirm that:

1. Mobo:
a. +3.3V (orange) 4 lines, max 24A
b. +5V (red) 5 lines, max 30A
c. +12V (yellow) 2 lines, max 12A

2. CPU:
a. +12V (yellow) 4 lines, max 28A

3. GPU:
a. +12V (yellow) 3 lines, max 4.2A for single 2+6P

4. SATA:
a. +3.3V (orange) 3 lines, max 4.5A
b. +5V (red) 3 lines, max 4.5A
c. +12V (yellow) 3 lines, max 4.5A

According to the info above, I decided to wire as below:

1. Mobo:
a. 2 x 2.75mm wires for GND (black), split to 4 each at the end
b. 1 x 2.75mm wire for +5V (red), split to 5 at the end
c. 1 x 2.75mm wire for +3.3V (orange), split to 4 at the end
d. 1 x 2.2mm wire for +12V (yellow), branching from CPU, split to 2 at the end

2. CPU:
a. 1 x 2.75mm wire for GND (black), branching to SATA, split to 4 at the end
b. 1 x 2.75mm wire for +12V (yellow), branching to Mobo, split to 4 at the end

3. GPU:
a. 1 x 2.75mm wire for GND (black), split to 6 at the end
b. 1 x 2.75mm wire for +12V (yellow), split to 6 at the end

4. SATA:
a. 1 x 2.2mm wire for GND (black), branching from CPU, split to 2 at the end
b. 1 x 2.2mm wire for +12V (yellow)
c. 1 x 2.2mm wire for +5V (red)

My wire max length is 32cm the most.

Anything I missed out? Feel free to comment ?
 
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LegionDD

Cable Smoosher
Jan 6, 2020
12
10
Looking fine, just that you could run far thinner wire for the 3.3V and 5V lines. Not much power will ever be drawn from them, especially if you're doing a run to an SSD or even HDD.
I usually don't use more than 0.15mm wire for SSDs for example.

Ofc, if you ever wanted to run only 12V wires, you could attach small voltage converters directly to things like SATA plugs, makes cable management easy.

Also it is unlikely that you'll fry anything (faulty wiring like hooking up a 12V line to a 3.3V input excluded), at most you'll get "brown outs" (ie the voltage drops below a threshold at which the computer can operate in a stable manner), which will cause flaky behavior (like the computer thinking someone suddenly pulled out a piece of hardware like say the GPU) and instant shutdowns.

I'd recommend making your wiring outside the case and testing the system open air, until you're certain there are no problems (use synthetic benchmarks, to stress the relevant components such as CPU and GPU).
 

gbellman

Trash Compacter
Original poster
Nov 7, 2019
50
9
Looking fine, just that you could run far thinner wire for the 3.3V and 5V lines. Not much power will ever be drawn from them, especially if you're doing a run to an SSD or even HDD.
I usually don't use more than 0.15mm wire for SSDs for example.

Ofc, if you ever wanted to run only 12V wires, you could attach small voltage converters directly to things like SATA plugs, makes cable management easy.

Also it is unlikely that you'll fry anything (faulty wiring like hooking up a 12V line to a 3.3V input excluded), at most you'll get "brown outs" (ie the voltage drops below a threshold at which the computer can operate in a stable manner), which will cause flaky behavior (like the computer thinking someone suddenly pulled out a piece of hardware like say the GPU) and instant shutdowns.

I'd recommend making your wiring outside the case and testing the system open air, until you're certain there are no problems (use synthetic benchmarks, to stress the relevant components such as CPU and GPU).

External diameter of 2.2 & 2.75 not much difference, so I'll go for 2.75 for both +3.3V & +5V, since I have it now and not wanting to add more wire of different size other than the 2 that I have, also rigid wire is easier to route and more minimal as now there are only 10 wires coming out from PSU.

Ya now my system is open, I have no time yet for my casing ?