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Recently the DC cable from my AC/DC adapter to my laptop broke. I removed the broken section and it works again. Now the cable is too short for my taste and I would like to replace it. I heard from an electrician, that you should stick with the coaxial cable type (as it was used for the device, see picture below), saying something about the higher frequencies involved due to the switching-mode transformer. This is supported by the fact, that all major laptop producer seem to choose this kind of cabling.

DC coaxial power cable

So firstly I was wondering if that is true. After all, the output should be DC. Even if it contains spurious HF components, what would the coaxial cable help about it? Would using a "regular parallel cable" and a ferrite choke ring have the same effect?

Secondly I could not find any cable like this anywhere for sale¹. Do they have a special name under which they are sold?


¹ I was searching for "DC coaxial cable", "Laptop power coaxial cable", etc on DigiKey, ELV, eBay, Aliexpress, Reichelt and Conrad and found only either non-coaxial cables or RF-coaxial cables, but no high-current (4A) flexible DC coaxial cables.

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    \$\begingroup\$ The DC coming out of your adapter doesn't (or at least shouldn't) have any significant high-frequency components. \$\endgroup\$ – brhans Nov 1 '17 at 20:15
  • \$\begingroup\$ 4A is not high current in cable terms. A suitable lap screened coax shouldn't be hard to find. \$\endgroup\$ – Finbarr Nov 1 '17 at 20:20
  • \$\begingroup\$ @brhans That's what I would think/hope for. Why do most manufactures use coax cables or ferrite beads then? \$\endgroup\$ – 3244611user Nov 1 '17 at 20:28
  • \$\begingroup\$ @Finbarr High current only compared to HF coax cables. That's what I would have thought 2 hours ago, but I couldn't find any. I'm sorry, since this seems such a stupid and simple thing, but I really can't find anything, even after an hour of searching. \$\endgroup\$ – 3244611user Nov 1 '17 at 20:30
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    \$\begingroup\$ You're probably being far too specific with your search. Just look for single core screened cable or single core microphone cable. One reason manufacturers use cables like these is simply that they're nice and round. \$\endgroup\$ – Finbarr Nov 1 '17 at 20:39
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AC-DC adapters for laptop power supplies are of switching type. Therefore they do have some ripples, and the ripples can cause unwanted RF emissions. To mitigate this, manufacturers prefer to use "shielded" power cables, using coaxial cable construction. It is not a RF cable, but coaxial. I am not sure which particular cable they use, but as a good approximation you can look for "single-conductor cables" with "shielded" property, for example the Tensility cable (found via Digi-Key engine).

enter image description here

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  • \$\begingroup\$ I assume he would want a two conductor cable though, rather than two singles? \$\endgroup\$ – BeB00 Nov 1 '17 at 20:43
  • \$\begingroup\$ @BeB00, from what I can see from the cable datasheet, the shield has about the same current currying cross-section as the main conductor. Therefore you use the shield as ground return. \$\endgroup\$ – Ale..chenski Nov 1 '17 at 20:46
  • \$\begingroup\$ Thank you for your answer. So it is about emission and not about mitigating harm to the connected device? The cable you posted seems promising, but not designed for power transfer. E.g. the diameters of the shield phases summed up (60×𝜋×(0.12mm/2)²~0.68mm²) are only half the diameters of the conductor cables summed up (26×𝜋×(0.254mm/2)²~1.3mm²). \$\endgroup\$ – 3244611user Nov 1 '17 at 20:49
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    \$\begingroup\$ That cable will carry your 4A without any problems. You really are overthinking this. \$\endgroup\$ – Finbarr Nov 1 '17 at 21:01
  • \$\begingroup\$ @3244611user, a conductor with 0.68mm2 area has 60C-Ampacity between 7.5 and 10 A, en.wikipedia.org/wiki/American_wire_gauge \$\endgroup\$ – Ale..chenski Nov 1 '17 at 22:22

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