Stupid question of the week: power cables- to coil, or not to coil? - Page 1
Forum section: electronics / beginners

author: audiotubes
author_rank: Regular Contributor
timestamp: November 21, 2023, 09:48:02 pm
content: I seem to remember reading in the 1970s or 1980s that coiling power cords is a bad idea because they turn into 50/60 Hz radiators.Most of my gear runs off 2m / 6ft power cables because I had a long way to the sockets. I have a setup now with power strips on the bench. Is it ok to coil the power cords to control the mess, or should I buy short cords of minimum length?Thank you and sorry for my density.

author: Thunderer
author_rank: Regular Contributor
timestamp: November 21, 2023, 10:09:25 pm
content: For 2m / 6ft I would not mind about having it coiled, as long as the coil diameter is about 30cm/1ft (I mean should not be coiled on hand - in like 10cm / 4in diameter).The advice is surely for the 15m / 50ft power extensions, as lazy people would keep them coiled on the drum, and they would run hot and melt the PVC insulation eventually. Plus, it is one thing to run them at 15A (a power tool as a load), or to use them supply your 100W PSU or 25W class A amplifier.

author: themadhippy
author_rank: Super Contributor
timestamp: November 21, 2023, 10:27:33 pm
content: QuoteA slight myth,it has nothing to do with frequency,just plain old ohms law,the cable has a resistance and theres a current going through it so its going to heat up,if its coiled up the heat cant escape .Any magnetic field produced by the live and neutral conductors will equal and opposite to each other so cancels out

author: audiotubes
author_rank: Regular Contributor
timestamp: November 21, 2023, 10:32:21 pm
content: Thanks guys, this will save me a few euros and some time looking for short cords.I'll zip tie them all in loose loops and be done

author: DavidKo
author_rank: Frequent Contributor
timestamp: November 22, 2023, 08:14:46 am
content: Definitely check the cross section, common is 1.5mm^2. 2.5mm^2 will be better.

author: Siwastaja
author_rank: Super Contributor
timestamp: November 22, 2023, 09:35:23 am
content: Just don't coil when you have high power loads like power tools, heaters etc. because the cable could overheat. Otherwise than that, there is no difference.

author: audiotubes
author_rank: Regular Contributor
timestamp: November 22, 2023, 10:02:04 am
content: Yeah, I know. This is just for test gear and I wanted to make sure it wasn't going to create a 50 Hz broadcast system

author: radiolistener
author_rank: Super Contributor
timestamp: November 22, 2023, 10:22:20 am
content: Quote from: audiotubes on November 21, 2023, 09:48:02 pmNo it turns into RF choke filter and reduce RF interference injected into mains with switched mode power suppliesSince power cord has two wires with current flowing in opposite direction, they cancel electric and magnetic field from each other, so emission will be almost zero. With reactive load there is some phase shift, so some amount of energy may be radiated, but not much, because phase shift with home electronics is too small. For high power loads like heaters it's almost zero.So, in short, it's better to put cable into a coil, it will reduce high frequency emission which is present in mains from different parasite sources.For better filtering you can use mains filters which uses coil with core for better common mode current cancellation, something like this:If you're using radio receiver or transmitter, such filter is must have, because it reduces RF interference leakage through mains.

author: audiotubes
author_rank: Regular Contributor
timestamp: November 22, 2023, 12:40:28 pm
content: Thank you! That makes sense. Madhippy above said something similar but I didn't fully understand it at the time.RF chokes, for everyone

author: Siwastaja
author_rank: Super Contributor
timestamp: November 22, 2023, 12:54:28 pm
content: Realistically, any "filtration" effect you get from coiling up the wire is completely insignificant, but maybe you can just barely measure the effect given good enough test conditions.

author: shapirus
author_rank: Super Contributor
timestamp: November 22, 2023, 02:52:49 pm
content: Quote from: DavidKo on November 22, 2023, 08:14:46 am...and make sure that the actual cross section is not 50% of the claimed one, which is much less uncommon than we'd like.

author: radiolistener
author_rank: Super Contributor
timestamp: November 22, 2023, 03:18:32 pm
content: Quote from: Siwastaja on November 22, 2023, 12:54:28 pmfor 5-100 MHz even simple coil can give significant effect

author: Thunderer
author_rank: Regular Contributor
timestamp: November 24, 2023, 03:50:16 am
content: Quote from: radiolistener on November 22, 2023, 10:22:20 amAnd all be submerged in the finest snake oil, or some virgin tears... Sorry, I could not contain myself. On a more serious note, with all the electronic pollution, there is no way you can do much with any passive filter, and not the least with something of the size and type in your photo. Come back with some realistic measurements and I'll give some credit to your DIY filtering device. The hearing test is not acceptable, the ears cannot be calibrated, but they are highly susceptible to placebo.The OP did not say what is the load (application), maybe we went too far with our suggestions.PS: Stay strong against the occupiers!

author: ejeffrey
author_rank: Super Contributor
timestamp: November 24, 2023, 04:59:51 am
content: For a 2 meter cable it doesn't matter at all. Overheating is more of a problem for longer extension cords, for instance if you have a 15 meter cable could tightly and you only unwind 2 meters to plug in your heat gun. It's much worse if the cable is on a spool or enclosed.

author: radiolistener
author_rank: Super Contributor
timestamp: November 24, 2023, 06:04:07 am
content: Quote from: Thunderer on November 24, 2023, 03:50:16 amRF filter for mains is the very important thing for equipment with high sensitivity to RF interference, like radio receivers, spectrum analyzers, etc. It is also very important for powerful transmitters, in order to prevent RF leakage into mains, because it can break normal function of home electronics.The efficiency of coiled wire is not so good as a proper specialized RF filter, but still can help to reduce some amount of noise. This is because any wire coil is actually inductor which reduces AC current flow. Higher frequency == higher damping of AC current. For 10-20 MHz even 5-10 wire windings is enough in order to significantly block common mode AC current flow.

author: radiolistener
author_rank: Super Contributor
timestamp: November 24, 2023, 06:35:18 am
content: Quote from: audiotubes on November 21, 2023, 09:48:02 pmcoiling power cord is not effective radiator for 50/60 Hz, because coil size is much more smaller than wave length.The wavelength of 50/60 Hz is 5000-6000 kilometers, which is twice larger than the Moon size...You're needs to start worry about radiation when your power cord coil will be close the the Moon size...But if you're building so large power cord coil, then you will have serious issue with voltage drop on the wire and large heating loss...The main 50/60 Hz interference is happens due to capacitive coupling with mains wires, so power cord geometry doesn't matter... What is matters here is wire length (wire surface) and distance between wires and test point.

author: Siwastaja
author_rank: Super Contributor
timestamp: November 24, 2023, 07:04:06 am
content: Quote from: radiolistener on November 24, 2023, 06:04:07 amWhile this is true, to avoid misunderstandings, I might add this is always at the responsibility of the radio receiver / spectrum analyzer / trasmitter designer: such filtration (and they are the ones who know best) must be integrated within the device; this is actually mandated by law and you have to do compliance testing to prove it before you can sell or import the equipment.Of course, added external filters may be necessary when you have tighter requirements than those required by standards - but that would be quite specialized.