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Comment by seanalltogether | Hacker News Reader

I'm genuinely curious whether new homes will start wiring lighting for DC to accommodate all these new LED bulbs? I just don't have a good sense whether its more efficient to transform AC to DC at a central hub in the home to distribute to all rooms, or more efficient to do it at the bulb itself.

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The Emerge Alliance[1] is an industry group that has been working on this issue, though they've started with a spec for datacenters (as stephen_g alludes to). I think the consensus is that it is definitely more efficient to convert to DC at a single point, but one located as physically close to the loads as is practical, because of the line losses mentioned. Definitely something that will make sense for commercial buildings/campuses and multi-unit residential, and single family homes are not too far behind, I think. I can picture homes sometime soon just being wired for AC in the kitchen/garage/utility rooms with a LV DC grid elsewhere. The lower safety requirements for low-voltage really open up possibilities for system design and integration in the built environment.

http://www.emergealliance.org/About/Vision.aspx

Line losses through the cables are usually a killer with really low voltage DC (like 5V or 12V), so I think that AC would be more efficient there.

But some datacentres are using 48V DC now and then just piping that through a switching regulators in the servers instead of going from AC to DC. That could be workable.

48V DC has been in multi-client data centres (Telehouse, TeleCity etc) for years. It's a standard voltage in telecoms kit. The data centre I was involved in building out back in 1999 got this as standard.

Interestingly, I'm looking to do exactly this in a new home (new to me, not newly constructed).

I'll soon be moving to a park home (a relatively-permanent mobile home) that is in need of a fair amount of renovation.

I'll be running all lighting, computers and the TV off 12v DV circuits powered by bank of vehicle batteries and where the batteries are charged from 12v solar panels.

Have you considered cabling loses? There is a reason power lines use very high voltages.

I've considered voltage drop over cable length only in as far as I'm aware that it occurs. I haven't tested the level of voltage drop.

I currently use 12v circuits in my camper van and haven't experienced any significant drop over cables about 3m in length. LED-based lighting and a 12v fridge operate as expected and the voltage at the point the power reaches these devices is very close to the voltage over the battery supplying the current.

I previously used 12v circuits in a narrowboat I used to own and didn't experience any drop over cables about 20m in length. This used halogen-based lighting and again the voltage at a lamp was very close to the voltage over the battery.

Just to be sure: You are aware that you have to measure the voltage drop under load? Even with rather thick wires, 20m should give you some noticable voltage drop with any non-minimal load.

Converting voltages is trivial with AC, how do you handle devices that require something other than 12v (lots of phones want 5, lots of laptops want 18) with a DC system?

I'll be fitting some 12v-based USB wall sockets, much like the type you can fit in a car. These can then provide power for phones.

Regarding computers, I've so far only considered my desktop. You can get ready made DC to DC ATX power supplies quite easily [1].

[1] http://www.mini-box.com/DC-DC

What sort of plugs and connectors are you going to use for this?

Could you be a little more specific?

Sure. For example I imagine you'll have some kind of 12v receptacle in the wall where you could plug in a computer or a lamp of some kind. Is there a standard for this type of thing?

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