The J-HACK M2426 is a super elegant solution to reducing the unnecessary wires, but seems be out of stock at the moment.
In the meantime, I am wondering if it is possible to make a "poor man's" version without any PCB just by wiring the minimally necessary pins in a standard 24-pin connector.
The idea would be to use this cable with an HDPLEX 250W GaN PSU as well as the standard 8-pin CPU EPS connector to supply +12V.
It was suggested this is possible with only 9 wires:
1x +12V
1x +3.3V
1x +5V
1x +5VSB
1x PS_ON
1x PWR_OK
3x Ground
(total 9 wires)
This thread indicates that some (not all) motherboards require -12V to boot (although apparently some can be fooled by ground), but I think it could be probably be omitted entirely. It seems the M2426 doesn't generate -12V.
The HDPLEX 250W GaN is rated to 10A on +5V and +3.3V and 5A on +5VSB, but my understanding is actual +5V and +3.3V draw is way lower in modern computers so I think a single wire for each of these should be OK. (Notably M2426 supports max 6A on these rails).
According to the molex spec, pins of a 24-pin PCB mount are rated to 5.5A to 8A depending on the wire gauge. So I think it would make sense to use thicker wire gauge for the higher current pins (Grounds, +12V, +3.3V, +5V, +5SB) and thinner gauge for PS_ON and PWR_OK.
I have a few questions:
In the meantime, I am wondering if it is possible to make a "poor man's" version without any PCB just by wiring the minimally necessary pins in a standard 24-pin connector.
The idea would be to use this cable with an HDPLEX 250W GaN PSU as well as the standard 8-pin CPU EPS connector to supply +12V.
It was suggested this is possible with only 9 wires:
1x +12V
1x +3.3V
1x +5V
1x +5VSB
1x PS_ON
1x PWR_OK
3x Ground
(total 9 wires)
This thread indicates that some (not all) motherboards require -12V to boot (although apparently some can be fooled by ground), but I think it could be probably be omitted entirely. It seems the M2426 doesn't generate -12V.
The HDPLEX 250W GaN is rated to 10A on +5V and +3.3V and 5A on +5VSB, but my understanding is actual +5V and +3.3V draw is way lower in modern computers so I think a single wire for each of these should be OK. (Notably M2426 supports max 6A on these rails).
According to the molex spec, pins of a 24-pin PCB mount are rated to 5.5A to 8A depending on the wire gauge. So I think it would make sense to use thicker wire gauge for the higher current pins (Grounds, +12V, +3.3V, +5V, +5SB) and thinner gauge for PS_ON and PWR_OK.
I have a few questions:
- Does the motherboard even require +12v from the 24-pin connector if an 8-pin CPU EPS is also used?
- If it does, I am somewhat concerned about a single wire for +12V into the 24-pin motherboard connector. Although apparently almost all draw for +12V actually comes from the EPS connector so it is fine?
- How many grounds would actually be required? It seems reasonable to have roughly the same number of ground pins as rails that draw any kind of current, but assuming the 8-pin EPS connector is used, should't there be relatively little current drawn from the 24-pin connector? If combined draw of the 24-pin is under say 5A, a single ground wire might suffice for all the rails?