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GeneralRe: USB for Power? Pin
Jörgen Andersson11-Feb-21 21:48
professionalJörgen Andersson11-Feb-21 21:48 
GeneralRe: USB for Power? Pin
Richard MacCutchan11-Feb-21 21:28
mveRichard MacCutchan11-Feb-21 21:28 
GeneralRe: USB for Power? Pin
James Curran11-Feb-21 23:28
James Curran11-Feb-21 23:28 
GeneralRe: USB for Power? Pin
glennPattonWork312-Feb-21 0:00
professionalglennPattonWork312-Feb-21 0:00 
GeneralRe: USB for Power? Pin
James Curran12-Feb-21 5:37
James Curran12-Feb-21 5:37 
GeneralRe: USB for Power? Pin
trønderen12-Feb-21 7:23
trønderen12-Feb-21 7:23 
GeneralRe: USB for Power? Pin
ElectronProgrammer12-Feb-21 7:53
ElectronProgrammer12-Feb-21 7:53 
GeneralRe: USB for Power? Pin
trønderen12-Feb-21 9:34
trønderen12-Feb-21 9:34 
Yes, it is possible to do it the wrong way. It is possible to do it the right way, too!
ElectronProgrammer wrote:
Electrocution voltage is smaller for DC than for AC, meaning that you can be electrocuted with a much smaller voltage (considering the same current).
Like 12VDC ...
I am surprised that you are at all allowed to sell 12VDC adapters, car batteries and PC power supplies delivering 12VDC! Smile | :)

If you set up a home 12VDC network, you will of course protect every single branch with fuses dimensioned for the expected load on that branch. Do you know what kind of current a lead-acid car battery can deliver? Compare that to the fuse protecting a LED strip. I honestly do not fear for my life, even if I am now installing a 12VDC network in my home.

Besides: In practical use, how would I get at that 12VDC to be electrocuted? Sockets, plugs and cables for 12VDC are as well insulated as for 230VAC. I won't be touching it. Only when installing new branches, new light fixtures, will I have direct access to the 12V. And why should I be less careful when doing this installation, compared to working with 230VAC?
Lower voltage implies:
1) higher current for the same power, which in turn implies:
1.a) thicker cabling
True, if we are talking about the same effect. But are we? A 12VDC network is not for feeding vacuum cleaners and dishwashers, but for LED lights, charging mobile phones and power feeding your external PC disk. Fifty watts of LED light on a single branch will brighten up your living room!

Look at the cabling for your 230VAC supply: A 1.5 sqmm is considered enough to carry 10A, or 2300 watts. Use the same cable with 12VDC: 120 watt is a lot for 12V based applications. At least in Norway, new houses are wired with 2.5 sqmm cables, handling 15-16A, or almost 200 watts if you use similar cabling for your 12VDC network.
1.b) greater heat losses because the current is continuous and the wires, besides heating more from the higher current, do not have time to cool down. In AC, the wires cool as the current goes toward zero in every cycle.
Fascinating idea: Giving the cables an opportunity to "cool down" every 10 milliseconds somehow makes it easier to dissipate the heat, when given the same resistance and total power loss. Honestly, I am somewhat sceptic to your theory.
c) more expensive protection circuitry since it is harder to detect anomalies. As an example, in DC you do not have phase nor frequency that can be used for detection. Nor can you rely on the return path, which is fixed at zero, unlike in AC where short-circuits can be detected on the return path when using circuit breakers (not fuses).
Do you have similar consideration for the cable between the 12VDC adapter plugged into the wall outlet and your external disk? We are talking about an extended version of that! The systems you are talking about are "grid related", of no relevance to, say, an active USB device powered from a solar battery bank.
1.d) more complex and expensive conversion systems
Whatever "conversion system" e.g. that USB hub has for providing 5VDC USB power from the 12VDC input is internal to the hub. And if the external power is provided by a 230-to-12VDC adapter plugged into the grid outlet, or provided by the 12VDC distribution system of my house, the task doesn't become more "complex and expensive".
2) since with DC there is no signal on the return path (negative wire) and the current is higher, there are higher EMI (electro-magnetic interference) whenever a device gets connected/disconnected/changes power drawn.
We are talking about devices drawing a handful of watts, at most - not of trans-ocean gigawatt cables, where your concerns are certainly valid. But not in a private home where you switch on a LED light of 5-10 watts!
there are wall sockets that have a transformer inside of them to convert the 230/110VAC to 5VDC
Sure, but during a blackout, you are blacked out. One major reason for a 12VDC home network is to prevent that. Also, you need to call an electrician to make any change to your setup.
If you are considering transmitting DC power from a central location throughout your house I advise against it, as you will be spending more money, both short term (cables through walls) and long term (power losses), and increase the risk of accidents (like fire from overheating cables).
The right way to do it includes - as you also say - doing it from a central point in your house, with a star of cables spreading from there. There probably won't be that many users per "star beam"; you need no monster cables! Obviously, you protect every cable with fuses well below the capacity of the cable, so that it will never overheat.

In my own setup, I have 4 sqmm four-armed star at each floor, with side branches to each specific lamp, fan or outlet using 2.5 sqmm cables. Calculate the power losses: In my house, the maximum cable distance from the center is 8 meters, typically half of which runs through 4 sqmm cable, half through 2.5 sqmm. To put it short: It won't cause you to throw out your old electrical heaters!
Some years ago, I had a colleague that had installed 12VDC distribution lines throughout is house to power a refrigerator, some tools and an "emergency system" (he didn't specified what that was) and had a fire precisely due to wires overheating.
To put it bluntly: So it wasn't done the right way. Even a low-voltage installation requires some knowledge of how to do it. Overheating due to incorrect dimensioning, and lack of overload protection with fuses, is just as bad with low-voltage installations as with 230VAC installations. Finding cases where unqualified 230VAC installations have caused fires is not difficult!

Another side is that you should know where 12VDC is a viable alternative. Anything involving motors is on the dubious side.
He ended having to pay a fine for 1) having an installation that did not comply with the law (in my country it is forbidden to have DC distribution in domestic buildings)Here (Norway), you can have a distribution net up to 200 watts, which covers a whole lot of the needs. It must be available for inspection, and wherever a cable goes though a wall, it must be in an a pipe of non-burning material (for all practical purposes: metal).

and 2) for not having protection systems on that circuit.
That is a cardinal sin! So it wasn't done right. Bottom line: Do it right!
DC distribution only makes sense for very high voltages (over 100KV) since losses in AC, at those voltages, become higher.
Sorry, I cannot agree. You cannot simply transfer the issues of gigawatt power lines into the home, and state that they apply equally in that context. If you insist on doing so, you will have to be prepared to explain how the same arguments count against 12VDC adapters. Or explain what makes the major difference between the AC adapter in the wall outlet, with a two meter cable, and the central 12VDC provision with an eight meter cable.

modified 12-Feb-21 16:39pm.

GeneralRe: USB for Power? Pin
ElectronProgrammer13-Feb-21 7:59
ElectronProgrammer13-Feb-21 7:59 
GeneralRe: USB for Power? Pin
trønderen13-Feb-21 12:54
trønderen13-Feb-21 12:54 
GeneralRe: USB for Power? Pin
ElectronProgrammer15-Feb-21 2:41
ElectronProgrammer15-Feb-21 2:41 
GeneralRe: USB for Power? Pin
trønderen15-Feb-21 4:20
trønderen15-Feb-21 4:20 
GeneralRe: USB for Power? Pin
glennPattonWork312-Feb-21 8:08
professionalglennPattonWork312-Feb-21 8:08 
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