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Rewiring home; DC network?

Added by haarts over 5 years ago

Hi all,

I recently purchased a home and it is a bad need of a full renovation. This includes the electricity/wiring. Now I’ve been toying with idea of putting in a (along side) DC network. More and more people seem to think this is a Good Idea. Currently most of my equipment is DC and putting 5/12V on the network seems easy enough. In the future I expect even more stuff to run on USB power/sockets (like the HP Chromebook 11). What do you think?

I, also, would like to measure power draw on all the sockets. The solution would ideally be cheap (Jeenode cheap) and build in the sockets (Jeenode micro?). I have scant idea how to do this and I’m looking for options, ideas, opinions (a Hall effect sensor seems a solution). Even commercial support/help I’d consider strongly.

Any views, suggestions, or wild ideas on how to make the most of this rare occasion (rewiring the entire house) would be greatly appreciated!

With kind regards,


Replies (4)

Rewiring home; DC network? - Added by martynj over 5 years ago

haarts, an interesting opportunity indeed. Some factors to bear in mind though. 
In general, the attached devices may well assume the Vbus follows the USB spec - meaning it is expected to be regulated around the nominal +5V.  Low distribution voltage implies considerable loss in the cables. For example, taking just 5W at one outlet requires ~1A to flow. For any practical size of cable, there will be some voltage drop, possibly taking the voltage available at the outlet below spec.

One solution is to push up the distributed voltage (that reduces the cable losses for the same wattage and conductor size) and make this match your DC storage value.  24V or even 48V nominal seems reasonable (keep it below 50V to avoid a lot of regulatory hassle).  Then at each outlet, buck convert the distributed DC to match the USB requestor. This gets around the regulation issue efficiently. There are chips emerging on the market (mostly from automotive applications) that do the USB device power ID properly and the DC-DC down conversion.

There are also some challenges with switching/fusing a DC distribution system. Standard A/C MCB’s don’t work as expected on DC.

RE: Rewiring home; DC network? - Added by haarts over 5 years ago

Thanks for the pointers. I hadn’t taken into account the loss in the cables and the voltage drop. The buck convertor solution seems the way forward indeed. What kind of Google words should I use to find these emerging chips?

As for the MCB; I need to look for a DC MCB then.

RE: Rewiring home; DC network? - Added by martynj over 5 years ago

haarts,

Maxim recently announced an example of a smart, automotive grade buck convertor, most of the major chip players have similar developments.
True DC MCB’s are unusual and expensive - if you chose carefully, some brands of domestic MCB’s do have DC ratings. The main parameter change is the maximum fault breaking current due to a DC arc sustaining after contact separation. You can design this issue out if the maximum fault current is limited externally. E.g. the source impedance of the supply may control the maximum flow as for solar panels but rarely for battery bank storage.

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