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Author Topic: AC-DC Power  (Read 6368 times)

Mike Sokol

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Re: AC-DC Power
« Reply #10 on: August 05, 2014, 06:59:22 am »

We already have PoE standards now up to 30W with 802.3at and UPoE near or recently ratified.  Let's rally behind the standards UPoE is 60W that should be sufficient for lighting, PC's smaller LCD panels.
Any  PoE infrastructure would also allow device interconnectivity without hogging up with WiFI bandwidth. We're running out of RF space already, and the more appliances and gadgets that go "wireless" the more bandwidth issues we're going to have. We're seeing that already for situations using shared iPads and iPhones for control of small format digital mixers when used with Line6 digital mics. There's only so much spectrum to go around, and just like avoiding RF use for stationary mics, we should try to limit wireless connectivity for stationary gadgets, especially if they need to "plug in" for power anyways.  Have you ever tried to use your Bluetooth headset at a convention along with thousands of other Bluetooth users at the same time in the same space? 
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John Roberts {JR}

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Re: AC-DC Power
« Reply #11 on: August 05, 2014, 10:50:36 am »

I would not argue for 12 vdc either.  24 VDC would be more likely to become the standard-it is already the most universal voltage for industrial machine controls, found on machines made in the US, Britain, EU, China,Japan and Korea.  The AC voltages from these areas are all over the map-100, 110, 120, 200, 220, 230 and 240 are all used.

If other voltages are required, DC to DC converters are readily available, essentially switched mode powers supplies without the input rectifier section.   One reason AC distribution has been so common was the best way to change voltages was a transformer-not so much anymore.  The only real question is does it make sense to switch from AC to DC?

Other than the kitchen, major appliances and hair appliances how many rooms in a home really need something that couldn't be done with a power limited 24 VDC circuit?  What about the office?

This is the key technology difference between now and then... Transformers and AC distribution facilitated reasonably low tech and robust voltage shifting first up for transmission with less losses then down for use. Now we have high frequency switching regulators that can do the voltage shifting at higher frequency using smaller magnetics.

It isn't hard to imagine more DC distribution in homes and smart power conversion could probably work with whatever it gets, making it better for wind or solar power that varies all over the place.

That said I expect there to be a lot of inertia resisting wholesale change to DC, so DC power and AC power may coexist for some time, perhaps with bridges between the two system so either one could support the other as needed..

JR
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Cailen Waddell

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Re: AC-DC Power
« Reply #12 on: August 05, 2014, 11:19:47 am »


This is the key technology difference between now and then... Transformers and AC distribution facilitated reasonably low tech and robust voltage shifting first up for transmission with less losses then down for use. Now we have high frequency switching regulators that can do the voltage shifting at higher frequency using smaller magnetics.

It isn't hard to imagine more DC distribution in homes and smart power conversion could probably work with whatever it gets, making it better for wind or solar power that varies all over the place.

That said I expect there to be a lot of inertia resisting wholesale change to DC, so DC power and AC power may coexist for some time, perhaps with bridges between the two system so either one could support the other as needed..

JR

This is an interesting topic for me, my landscape lights are 12v LEDs, my undercounted lights in the kitchen, I'm about to put in some lights for our art in the living room....

I have considered a relay, deep cycle marine battery and central 12v pwm dimmer in my house...  Everything can run off of low voltage security wire.   When the power goes out - our lights will stay on.
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John Roberts {JR}

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Re: AC-DC Power
« Reply #13 on: August 05, 2014, 11:36:57 am »

This is an interesting topic for me, my landscape lights are 12v LEDs, my undercounted lights in the kitchen, I'm about to put in some lights for our art in the living room....

I have considered a relay, deep cycle marine battery and central 12v pwm dimmer in my house...  Everything can run off of low voltage security wire.   When the power goes out - our lights will stay on.

Just because it's only 12v do not treat it too casually, it can still start fires.

JR
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Scott Holtzman

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Re: AC-DC Power
« Reply #14 on: August 05, 2014, 12:15:36 pm »

Just because it's only 12v do not treat it too casually, it can still start fires.

JR

Amen, it also needs heavier wire to avoid voltage drop.   I am going to stay the PoE bandwagon.  It has current limiting, device negotiation etc.  Small DC-DC converts are pennies and very efficient.  Adding a PoE port to a device just for power would not be difficult.

It's already been pointed out that RF is a last resort if a wired connection is available.

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Scott AKA "Skyking" Holtzman

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Mike Sokol

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Re: AC-DC Power
« Reply #15 on: August 05, 2014, 02:04:45 pm »

It's already been pointed out that RF is a last resort if a wired connection is available.

Does anyone make a little 12-volt dimmer or on/off controller that can listen to IP control on a CAT-5 PoE cable? That way you could simply do home runs of CAT-5 to centrally located routers with PoE output. Run heavy wire to the PoE routers for the 12 volts, then standard CAT-5/6 cabling to power and control things such as under cabinet lighting, ceiling lights, in-wall speakers, security cameras, etc... Seems like a no-brainer to me since once you set up the local IP communication and a WAN link you could control anything you like with a smart phone from anywhere in the world.
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Steve M Smith

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Re: AC-DC Power
« Reply #16 on: August 05, 2014, 02:11:26 pm »

There could be a good case for a 24v or 48v supply for domestic lighting.  The current compact fluorescent bulbs are, in my opinion, just an interim technology until LEDs get better and/or more affordable.

The company I work for makes flexible flat panels with light guides and reflectors on them which are used for domestic and architectural lighting by this company: http://designledproducts.com/

There are some clever tricks you can do with LEDs to control the spread of light and I think that LEDs are the future of domestic lighting.  Having access to a suitable DC supply would certainly make a lot of sense compared with the other option of a small power supply for each light fixture.  It especially makes sense for the flat lighting panels I posted a link to as they would remain flat, requiring just a connection to the DC supply (switched, obviously!).


Steve.
« Last Edit: August 05, 2014, 02:15:18 pm by Steve M Smith »
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Scott Holtzman

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Re: AC-DC Power
« Reply #17 on: August 05, 2014, 02:37:05 pm »

Does anyone make a little 12-volt dimmer or on/off controller that can listen to IP control on a CAT-5 PoE cable? That way you could simply do home runs of CAT-5 to centrally located routers with PoE output. Run heavy wire to the PoE routers for the 12 volts, then standard CAT-5/6 cabling to power and control things such as under cabinet lighting, ceiling lights, in-wall speakers, security cameras, etc... Seems like a no-brainer to me since once you set up the local IP communication and a WAN link you could control anything you like with a smart phone from anywhere in the world.

PoE switches, especially a 24 port unit with a 600 or 1000 watt total capacity needs a -48vdc rail. 
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Scott AKA "Skyking" Holtzman

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Stephen Swaffer

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Re: AC-DC Power
« Reply #18 on: August 05, 2014, 09:40:21 pm »

Exhibit A: 12 VDC current limiter.

Seriously though, voltage drop is determined by current draw.  (Which is proportionately larger for lower voltage for the same watts than higher voltage).  We had some 24 VDC powered carts on rails where I used to work.  Someone had wired them with 2/0 weld cable because they were DC running off deep cycle batteries that looked like car batteries.  FLA for motors?  25 amps-easily handed by #10 AWG.  4 10 watt cans for a room is 40 watts or roughly 3.5 amps at 12 VDC which can use wire several sizes smaller than the minimum the NEC allows to be run for 120 VAC circuits.

Another plus to DC supply-DC dimming should be a lot less electrically noisy.  Mechanical DC switches are noisier and harder to design well-but solid state switching for DC is a natural.

But then, what would Mike do without ground loops and AC hum to chase down?
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Steve Swaffer

Mike Sokol

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Re: AC-DC Power
« Reply #19 on: August 05, 2014, 10:15:15 pm »

But then, what would Mike do without ground loops and AC hum to chase down?

What??? Say it's not so.... :o
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Mike Sokol
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Re: AC-DC Power
« Reply #19 on: August 05, 2014, 10:15:15 pm »


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