DC Power Standard for your home - Page 1
Forum section: electronics / general

author: Seekonk
author_rank: Super Contributor
timestamp: December 05, 2015, 05:12:56 pm
content: A few days ago NPR radio had a teaser about Edison may hve got it right about DC.http://www.npr.org/2015/12/02/458127706/planet-money-ad-versus-dc-power-gridI thought it might be about HV DC transmission on the grid allowing allowingtransmission of more power on existing transmision lines. No, it was about somelarge companies like GE trying to create a new standard for powering electronicsin the home. The claim was wall warts get hot and inefficient and besides theywant DC anyway. Good luck anyone making sense about what they were saying.The proposed solution was a super efficient converter per room. The effort isto create a standard socket and DC voltage that all future electronics would work off.Ignore the bad reporting, The push for this is probably the electric utility companiesthat are having to deal with rectified power supplies that only draw current at thepeaks of the cycle. LED lighting, entertainment electronics, even VFDs for air conditioning.Resitive type loads are disappearing. PFC chips in power supplies haven't made a dent inthis problem.For the future this is a pretty neat idea. My camp is 100% solar and I run my wall warts offthe raw 52V from the solar panels. Most of them do work at this reduced voltage and reducedpower output. The advantage is the 120V inverter only needs to be turned on when the fridgeor other device is needed. Think of every home having a single 250W panel powering all yourelectronic devices. Fits in with Ted Koppel's view of the grid being taken down for monthsfrom terrorist attacks. Grid tie looked like the future but the utilities are now pushing backand the politicians are working to kill your payback. A home DC power standard will be thefuture for the solar home. This could make a major dent in power use. My solar panels alwaysproduce 100% of their potential solar output. Any excess power goes to heating water.

author: kwass
author_rank: Frequent Contributor
timestamp: December 05, 2015, 05:45:48 pm
content: I think that it's about the Emerge Alliancehttp://www.emergealliance.org/which is primarily targeted to commercial buildings. The company they mention in the NPR interview, Nextek Power Systems, is looking to get into the residential aspect of this too. It's unclear if/when that will happen.The general idea is that in-building DC micro grids are more efficient to use for alternative DC generating power sources so that they're are fewer AC<-->DC conversion steps needed and battery storage is more readily achieved. Silly video on this:https://www.youtube.com/watch?v=2PkJOOA2v6o&feature=youtu.be

author: madires
author_rank: Super Contributor
timestamp: December 05, 2015, 06:04:41 pm
content: Quote from: Seekonk on December 05, 2015, 05:12:56 pmWhen you replace the wall warts with good buck converters you can reduce the power usage by about 50% since most cheap wall warts are quite lossy. I power all my network and telephone stuff by a central high efficiency 12V PSU and a few buck/boost/isolated flyback converters for the non 12V stuff. And for redundancy I can add a second PSU.

author: mtdoc
author_rank: Super Contributor
timestamp: December 05, 2015, 06:10:46 pm
content: The difficulty with broadly adopting this idea in the US for residential use is that electrical codes specify different requirements for DC wiring. Metal conduit enclosed wire runs, DC rate breakers, etc. That makes implementing this in existing homes very expensive.

author: rfeecs
author_rank: Frequent Contributor
timestamp: December 05, 2015, 06:18:49 pm
content: I heard that story on the radio on my drive to work yesterday morning.I was kind of shocked how much their engineer (named FUND) "dumbed down" the explanation:QuoteQuote

author: Seekonk
author_rank: Super Contributor
timestamp: December 05, 2015, 10:54:58 pm
content: I've read articles where they talk about silicone chips.I live half the time in two communities. One you could drive around for two days before seeing solar on a house. The other has solar on one in three homes. Fact is solar works and I enjoy being totally off grid. On my street one in five has a standby generator. Having you own DC power isn't off the wall thinking. Just takes a few big players to push it.

author: madires
author_rank: Super Contributor
timestamp: December 06, 2015, 12:13:39 pm
content: Quote from: Seekonk on December 05, 2015, 10:54:58 pmFor outdoor use, maybe?QuoteI've thought about adding a PV panel plus a buck converter (12V output) to my central DC power setup but a proper lightning protection and grounding isn't particularly inexpensive.

author: Chris Jones
author_rank: Regular Contributor
timestamp: December 07, 2015, 08:20:51 am
content: For Australians, an advantage in DC house wiring is that higher voltages (up to 120V) are allowed to be used before the work legally must be done by a person who has done a 4-year apprenticeship and paid for a government licence, rather than a mere street sweeper, amateur poet, chartered electrical engineer or busker etc. With AC, the limit is lower (50Vrms iirc).For example one could use 110VDC to wire a house without needing a licence, which would not require particularly fat cables as the RMS current would be much the same as for houses in the USA. I am not at all conviced that this would be safer than wiring one's own house for 240VAC, since DC switches are more prone to arcing. The disadvantage of 110VDC would be that for most appliances a DC-DC converter or DC-AC inverter would be needed. Filament lamps and resistive heating appliances from the USA might work, however the switches are unlikely to be safe when operating from 110VDC.

author: dexters_lab
author_rank: Unknown
timestamp: December 07, 2015, 09:10:14 pm
content: i had thoughts of something similar many years agomy thought would be to have a central power supply that would step the mains down to 24v DC and distribute it out to low power devices like chargers, lights, digital tv receiver boxes, that kind of thing. It would be smart so when you plug in the device it would request a certain power which the central supply can approve or deny depending on it's maximum loading, if it approves power can be applied to the local socket. I believe USB devices work like thisdevices would be enumerated like USB so you can have things like; a light can turn on/off on a timer from the central power controller but it wouldn't matter which socket it was plugged intoi decided it was a pointless system because it would require too many 3rd parties to commit to using it, it would be impossible to get it accepted

author: calexanian
author_rank: Super Contributor
timestamp: December 08, 2015, 06:19:31 am
content: Also do not forget about the galvanic effects. Yes they can be mitigated by periodic reversal of polarity, but that can surface harden and make the conductors brittle over time. DC is however used in some long run high tension line applications. The lines running down from Oregon to Los Angeles known as path 65 is an example.https://en.wikipedia.org/wiki/Pacific_DC_IntertieAs far as use in the house I see it being first applied to off grid buildings for obvious reasons first.

author: eugenenine
author_rank: Frequent Contributor
timestamp: December 08, 2015, 11:41:57 pm
content: A lot of the ham radio world will use anderson power poles as an unofficial standard. You can get wall plates with them already.

author: rdl
author_rank: Super Contributor
timestamp: December 09, 2015, 03:32:56 am
content: It's surprising that houses are still wired primarily with high voltage AC, since most of what get's plugged in the wall can't use it directly. Mains power throughout the house is becoming even less necessary with increasing usage of LED light bulbs and flat screen TVs.

author: rdl
author_rank: Super Contributor
timestamp: December 09, 2015, 04:23:12 am
content: Well, I did say "primarily". Obviously high power stuff like heating, AC, cooking, etc will still need mains power.

author: NiHaoMike
author_rank: Super Contributor
timestamp: December 09, 2015, 06:54:48 am
content: What about pulsed DC at 170V or 340V? The pulsing could be such that it would be simpler and more efficient than conversion to AC, yet solve the arcing problem with pure DC.

author: Zero999
author_rank: Super Contributor
timestamp: December 09, 2015, 11:09:29 am
content: Yes DC is safer than AC at the same voltage/current.It's the change in current with stimulates the nerves and disrupts the heart.Once I tried to shock myself with 70VDC. I couldn't feel a thing until I moistened my fingers with salt water and even then I only felt it when the current was interrupted.Pulsed DC would be more dangerous than steady DC, probably equivalent to the sum of the DC & AC components.

author: VK3DRB
author_rank: Super Contributor
timestamp: December 09, 2015, 11:23:35 am
content: Quote from: blueskull on December 09, 2015, 07:02:25 amWrong. 170VDC, without any current limiting can fry your flesh. And cause heart failure. Try at little as 20 milliamps though your flesh to become toast ("frying current"). Also DC makes muscle contraction constant, making it more difficult to disconnect one's self from the source, compared with AC.Even plugging together nineteen 9V batteries (a nominal 170V DC) in series may well kill you if you put a sweaty finger on each of the extreme end terminals.

author: Delta
author_rank: Super Contributor
timestamp: December 09, 2015, 01:40:46 pm
content: 170v DC will kill you as soon as look at you.Please tell me you don't work with anything greater than 5v!

author: dfmischler
author_rank: Frequent Contributor
timestamp: December 09, 2015, 02:54:24 pm
content: The DC power standard in use in my home and workplace is IEEE 802.3af (PoE). Haven't needed to upgrade to 802.3at (yet?).

author: Zero999
author_rank: Super Contributor
timestamp: December 09, 2015, 04:35:51 pm
content: 170VDC can kill but it's less likely to cause injury than 120VAC.

author: mtdoc
author_rank: Super Contributor
timestamp: December 09, 2015, 06:25:09 pm
content: Quote from: Hero999 on December 09, 2015, 04:35:51 pmI would say it differently. 120 VAC is more likely to kill you (by inducing a fatal cardiac arrhythmia) but 170 VDC is more likely to cause injury ( thermal tissue damage) but could also kill you.