Splicing PSU cables

JollysH1

JollysH1

JollysH1

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13 Mar 2020
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53
So I recently started sleeving my own PSU cables, and it's going ok so far, but I have a query, that I'm hoping someone knowledgeable can help me with.
On my 24 pin mboard connector, there are on occasion 2 wires into 1 pin! As I will probably only have a short amount of this cable visible, could I splice the two together earlier on? say 150mm from the mboard connector, and have just the one strand sleeved? or are the 2 wires carrying stuff that one wire couldn't handle? even for a short distance?
 
Those are sense wires for measuring voltage at connector.
They could be spliced into actual voltage wire earlier, but likely at slight expense of voltage regulation.
 
Interesting, is that info carried from mainboard to PSU or PSU to mainboard? Either way if they're both sharing a pin the signal to the PSU would be identical in both from the board, or combined from the PSU, to the board.

I think the upshot of it is, that one wire is capable of holding a combined signal, so splicing it pre plug, wouldn't be an issue? it would certainly look neater and cause less hassle with cable combs.

If anyone has any other thoughts, or has done something similar in the past, I'd love to hear.
 
Motherboard has nothing to do with that and they can't be combined while maintaining function.
That second wire is used by PSU for checking that voltage loss in wiring doesn't make actual voltage in motherboard's end drop too much when current increases.
If that joining point to actual current carrying wire is moved closer to PSU, its knowledge of voltage seen by motherboard becomes progressively worse.
 
Aha! I understand now, there's an "A" leg and a "B" leg! a loop in effect! So reporting back from half way, doesn't take into account losses incurred in the remaining part of the leg.
I dealt with similar scenarios when I was on the tools for a telecoms company, but obviously I was dealing with higher losses due to miles of cable rather than 60 cm, do you think the difference in reporting accuracy would be sufficient to make this a bad idea?
 
I really doubt the resistance of the cable would be drastic enough at those lengths to make a real world difference in the reading, also i'm sure it dosen't take into account the losses by the traces on the board itself which being smaller by nature would incur a larger resistance/vdrop penalty than a short run of decent wire. Perhaps using a awg of wire thicker than the loop wires would suffice? I'm talking mostly theory here and could be completely wrong and DC is a bit more finicky about losses but i'm doubting anything drastic would be the outcome. You a former openreach or BT tech too ? ;)
 
Justintime said:
DC is a bit more finicky about losses
Click to expand...
Actually it's AC which is cranky customer when frequency rises already because of "skin effect".
(current flowing only in outer section of conductor)
That must be taken into account in power line designs.

That might be actually one of the main reasons why it's harder to get high frequencies through long wiring than low frequency signals:
Conductor's effective resistance basically grows with frequency.
And "skin depth" (thickness in which current flows) for copper at 100kHz is 0.2mm and at 1MHz it's 0.065mm

https://en.wikipedia.org/wiki/Skin_...of_telephone_cable_as_a_function_of_frequency
 
@Justintime
Openreach, still with them but not down a hole anymore, kinda miss it! I'm pretty sure the tolerances in the wires are way over what they need to be anyway, but I'll look for some other solutions before getting the snips out. Thanks for your input by the way, much appreciated.
 
Fibre lad? :D I was copper only, trained in Yarnfield and Croydon and some hertfordshire exchange. Left because of too much parking tickets and stress, Central London is not the place to be for that job :o
 
Multiskill, trained in Harrogate, spent the last few years of my engineering career on UG only, Pair proves/diverts/jointing, SFI, that sort of thing. No parking issues! just plenty of hiking through forests and over the fields and moors of North Wales.
 
Wish i had that option. Was only fibre or copper stream and you had no choice. Wasn't there long enough for UG training and some guys in my exchange put in for it and were waiting years. I'm back doing electrics now and hating it as much as i did. Thinking of going back into my old field of IT in some school or something :(
 
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