Why are AC/DC power cords heavier gauge on the AC side? - Page 1
Forum section: electronics / beginners

author: shaocaholica
author_rank: Newbie
timestamp: August 22, 2015, 10:25:07 pm
content: This is most common with modern laptops. You have somewhat standard IEC(?) cables on one end and sometimes a really thin cable on the DC end of the adapter but shouldn't the wattage be very similar on both ends? Why do I need to haul around heavier cabling on the AC side?Edit: Ok obviously AC and DC current behave differently but still there's a huge difference in the cabling. Is it because the AC end has to meet certain compliance code? Because for a <100W laptop you have AC cable ends that are rather for almost an order of magnitude more wattage.

author: Godzil
author_rank: Frequent Contributor
timestamp: August 22, 2015, 10:42:37 pm
content: I don't have the answer, but I here is my reasoning:- Cables on the AC side most of the time include earth; so you have 3 wire- Cable on the AC side are generally standard cable so the are rated for higher power than what the device really need- The cable on the AC side need to be safe, as even if the power consumed is near the same (in fact it's not true, as the power adapter have a certain efficiency, so the power on the intput side is slightly higher than the output side) if it break you will touch the main, and there will be no limitation.But on the output side, as the voltage (and current) are regulated and protected, even if you touche the inner wire there is no health risk

author: Balaur
author_rank: Unknown
timestamp: August 22, 2015, 10:48:09 pm
content: Many laptops utilize the three-pin C5/C6 connector. The cord contains three wires and it's double-insulated (wire insulation + sheath). That means a lot of PVC and a stiff, bulky cable.As for the actual diameter of the wires, mine has AWG 18, which is rather appropriate, not too excessive I think.But yes, I agree with you that beside the usual monstrosity of power cord contrasts heavily with today's rather delicate and compact power bricks.

author: Paul Moir
author_rank: Frequent Contributor
timestamp: August 23, 2015, 02:13:58 am
content: Because it doesn't have to do with wattage. If the wires in the power cord for some reason get shorted, it'll have to handle a lot of current until the breaker in you fuse panel trips. During this time, it should not catch fire and burn down your house.The output wires on the other hand are power limited by the SMPS. They can be shorted for much longer without catching fire.

author: singapol
author_rank: Frequent Contributor
timestamp: August 23, 2015, 03:11:11 am
content: Quote from: shaocaholica on August 22, 2015, 10:25:07 pmThis has to do with long established safety guidelines of the electrical power distribution industry. Especially in countries where houses are made of largely wooden structures.Surely youwould not like to burn down your own house let alone your neighbours?It's also because eg. in EU countries the wall sockets can supply 13 amperes so thickness of wires arespecified accordingly. What you do after it is rectified is your own business but if you are designing consumer or industrial equipment then safety is important for the viability of your business among otherfactors.

author: nitro2k01
author_rank: Frequent Contributor
timestamp: August 23, 2015, 03:25:14 am
content: As stated previously, double insulation, higher voltage rating, 3 wires including protective earth. The secondary side cable is also often made coaxial, which helps utilize the space in the cable.But also, the mains side cable needs to be overdimensioned so that it can trip the fuse/breaker in case of a dead short. Imagine if you had some crappy cable consisting of 4 strands of copper and you got a dead short in your power supply. Now, the cable may limit the current to below the rating of the fuse in the fusebox and act as a heater wire that starts a fire instead of blowing the fuse!

author: shaocaholica
author_rank: Newbie
timestamp: August 23, 2015, 03:51:02 am
content: Thanks all. I guess the design of AC mains power is the limiting factor. Seems like with today's smaller personal electronics it would be ideal to have negotiated DC power outlets at the wall but obviously not going to happen on a large scale. Maybe USB(next) might change that. You can still have normal AC mains power but DC-USB panel jacks with 100W+ USB(next gen) can be used without power bricks to power most portable devices up to large laptops. I say USB(next gen) because I don't think the USB-C connector is that great for a wall plug but its 100W rating is a step in the right direction.

author: amyk
author_rank: Super Contributor
timestamp: August 23, 2015, 01:17:11 pm
content: As mentioned above with IEC cables it's due to the standards that require wire which can handle the full mains current, even if the device itself doesn't use anywhere near as much - after all, someone could plug the cable into a higher power device.On the other hand, on devices with non-removable cables, you may see thinner gauges being used.

author: homebrew
author_rank: Frequent Contributor
timestamp: August 23, 2015, 01:42:13 pm
content: Quote from: amyk on August 23, 2015, 01:17:11 pm[Management meeting at some site, far, far away ...]Hmm, so there are production costs that could be shaved of by putting in less copper. We'll just make the insulation thicker! No one will ever notice ...And that's why I usually immediately toss these cables if hey are not from a GOOD NAMED brand. I once tore down one of these cables supplied with an external hard drive enclosure (even bought at a local store!). Made me skeptical that the plug was missing the usual labels and the cable felt unusually soft and wobbly. And guess what, a LOT less than even 0.25 mm^2.Bummer! I was actually surprised that it didn't instantly vaporize on the initial SMPS surge current when the capacitor is charged ...I didn't even bother to open the PSU -> Trashed ...

author: SeanB
author_rank: Super Contributor
timestamp: August 23, 2015, 01:58:31 pm
content: You have not met the IEC leads which appear to conform, with a 3 pin plug and a 3 pin IEC socket at the end, but where the conductors are a few strands of copper coated steel, and they put in a solid plastic core instead of the PE conductor....

author: madires
author_rank: Super Contributor
timestamp: August 23, 2015, 02:08:48 pm
content: Quote from: singapol on August 23, 2015, 03:11:11 amSchuko is up to 16A. Standard mains wiring in Gemany supports 16A and uses B16A automatic circuit breakers commonly. The "B" is the trigger characteristic and means that the breaker breaks the circuit at 80A (5x16A, worst case) short circuit current within a few ms. Therefore the wiring has to be dimensioned to support 80A short circuit current, i.e. the max. loop resistance must not exceed 230V / 80 A = 2.88 Ohms.

author: IanB
author_rank: Super Contributor
timestamp: August 23, 2015, 03:36:02 pm
content: My US power adapters (Dell or HP) tend to have 3 conductor zip cords on the mains side, which is somewhat flexible and easy to fold up although definitely thicker and stiffer than the DC cord. As noted by everyone above the cable is designed to be durable and robust to protect against damage given that it is carrying mains power.

author: Zero999
author_rank: Super Contributor
timestamp: August 23, 2015, 03:49:42 pm
content: Standards vary from country to country.Here in the UK, the minimum wire crosssectional area for mains cable is 0.5mm2for appliances with a 3A plug top fuse or less and is purely for mechanical strength.As mentioned above, IEC leads have three cores which makes them thicker. The wire also tends to be thicker (typically 0.75mm2) which is probably because they're designed for use in other countries which don't have fused plugs.

author: Towger
author_rank: Super Contributor
timestamp: August 23, 2015, 06:39:09 pm
content: Quote from: SeanB on August 23, 2015, 01:58:31 pmThey are the good ones. I got two a few week ago (Allieexpress) where they only used 2 core cable, not even an attempt at a 3rd core.But the items did come with DMX cables made from 3X0.75 cable mains cable.

author: Balaur
author_rank: Unknown
timestamp: August 23, 2015, 08:20:45 pm
content: Quote from: Towger on August 23, 2015, 06:39:09 pmThe worst I've seen yet was a energy saving device that cuts the TV power some time after powering off with the TV's remote. The idea was to remove the standby power completely.The device had a minuscule IR sensor that you were supposed to put in the path of the remote beam (while the device was plugged between the mains and the TV). However since the sensor could potentially be at a high potential, the cable between the device and the IR sensor was a rather robust three-wires, 0.75 sq. mm doubly insulated cord.