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DC Power distribution - Nix the Transformers?

Cliff posted more than 9 years ago | from the we-call-'em-wall-warts dept.

Hardware Hacking 180

MailtoDelete asks: "I have most of my electronic gear plugged into a couple power strips hanging off a UPS. Most of these devices have big block-type transformers which, besides being bulky, are a bit of an eyesore. I have been trying to find a product out there somewhere that would allow me to have one central transformer that would distribute DC power at variable voltages, depending on what devices I wish to plug into it (think one AC input and 9 or so DC outputs individually adjustable). I found this device that resembles what I have in mind, but it does not have sufficient output for my router, switches, and various other devices. Is there a product on the market already that would do this? Can I build one with my marginally above average soldering and electrical schematic skills? Have any of you found a better way to eliminate these blocky plug-hogs?"

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Hardware Wars (4, Funny)

Jeremiah Cornelius (137) | more than 9 years ago | (#11817488)

"This is Reddy Kilowatt, reporting a dangerous, overloaded octopus connection in sector five!"

Re:Hardware Wars (4, Informative)

thegrassyknowl (762218) | more than 9 years ago | (#11817561)

Wasn't it Thomas Edison who tried to prove that Tesla's 3 phase AC power distribution was dangerous by electrocuting frogs with it and showing how they thrash about vioilently before they died?

*tongue firmly in cheek*
Perhaps DC power distribution is the best after all.

That said, you could easily build a device to power all those said gizmos. You'd really need a quite large multi-tap transformer with appropriate ratings, and a set of voltage regulators for the various voltages... 5, 6, 9, 12, 13.8, possibly a couple of adjustable ones for those pesky items that insist on odd voltages.

I had a similar (homebuilt) device with 6 outputs, all individually regulated.

This is a good excuse for a PIC-type project to set the ouput for each port... It could adjust the regulator to get the right voltage and also toggle relays for each port to get the right transformer tap (so as to avoid dissipating too much energy in the little regulators) for any given voltage.

Re:Hardware Wars (1)

snorklewacker (836663) | more than 9 years ago | (#11817636)

That said, you could easily build a device to power all those said gizmos. You'd really need a quite large multi-tap transformer with appropriate ratings, and a set of voltage regulators for the various voltages... 5, 6, 9, 12, 13.8, possibly a couple of adjustable ones for those pesky items that insist on odd voltages.

I believe such devices are called "power supplies". You can get hobby power supplies up to some pretty insane voltages with lots of different output voltages (and you can use voltage regulators and diodes for whatever's merely close). I don't think it's going to be terribly more convient to manage than a bunch of wall warts though.

Re:Hardware Wars (1)

sporktoast (246027) | more than 9 years ago | (#11817653)

Frogs. Sheep. Horses. Elephants. People.

Re:Hardware Wars (5, Interesting)

snorklewacker (836663) | more than 9 years ago | (#11817698)

Wasn't it Thomas Edison who tried to prove that Tesla's 3 phase AC power distribution was dangerous by electrocuting frogs with it and showing how they thrash about vioilently before they died?

Not Tesla, Westinghouse. The whole frog twitching thing was a sideshow trick when electricity was first discovered, and could be done with DC. Edison went all the way up to electrocuting horses, and advertised it could be done on people with "Westinghouse's Electric Chair". He thought people would be horrified. In the last bit of irony, several states loved it and actually ordered these things, using them for capital punishment for many decades afterward.

Edison may have been quite an inventor, but he was rather a ruthless man not above gross distortions and character assassination.

Re:Hardware Wars (4, Informative)

alienw (585907) | more than 9 years ago | (#11817777)

He was as much an inventor as Bill Gates is a programmer. Above all, he was a businessman. Most of "his" inventions were actually created by the people working for him.

Re:Hardware Wars (2, Funny)

bill_mcgonigle (4333) | more than 9 years ago | (#11820556)

He was as much an inventor as Bill Gates is a programmer.

Interesting analogy. I wonder if Bill Gates would electrocute a penguin to prove WIndows is more secure than Linux.

Re:Hardware Wars (1)

westlake (615356) | more than 9 years ago | (#11820981)

He was as much an inventor as Bill Gates is a programmer. Above all, he was a businessman. Most of "his" inventions were actually created by the people working for him.

Edison was born in 1847, by 1870, he had a national reputation for his work in telegraphy, and by 1879 he had been granted 170 patents. Edison's Patents 1868-1879 []

Re:Hardware Wars (2, Informative)

Grab (126025) | more than 9 years ago | (#11821808)

Alert - getting patents and getting a reputation for stuff your lab does do not mean you're so damn hot. In fact, it doesn't even mean you invented it - witness the *many* times Edison ripped stuff straight off other people. Nor does it mean the inventions are any damn good - Edison was quite happy to use publicity, lawsuits and outright lies to promote his stuff and crap on other people's stuff.

So a lot like Billy Gates and his organisation, in fact...


Re:Hardware Wars (1)

stevew (4845) | more than 9 years ago | (#11819622)

Nit Alert -

Tesla worked for Westinghouse

Re:Hardware Wars (1)

SteeldrivingJon (842919) | more than 9 years ago | (#11819834)

The frog twitching went way back, to Galvani, I believe, and inspired Mary Shelley's Frankenstein.

Edison went all the way up to electrocuting horses

He also did an elephant. []

Re:Hardware Wars (0)

Anonymous Coward | more than 9 years ago | (#11821798)

In retrospect, it's too bad Edison didn't win. Nowadays, DC devices are so much more common. Wouldn't it be great if we got 24V or something out of our wall and we could do away with all those stupid power bricks?

Why doesn't someone (with a lot of clout) come up with a DC standard? That way the OP could have some box installed in his electrical closet that produced DC to be distributed to special outlets, using a standard connector. We would soon see power bricks which output the same voltage using the same connector, so if you had the magic DC outlets, you could just toss the brick and plug your device straight into the wall.

Which is more unsightly? (0)

Anonymous Coward | more than 9 years ago | (#11817539)

5 or 10 transformers, or 5 or 10 plugs on every outlet, one for each voltage?

Marginally? (1, Insightful)

Anonymous Coward | more than 9 years ago | (#11817572)

If the true measure of your skills is "marginally above average" then the simpile answer is "No" However, if you actually have electrical design skills and have a good feeling for circuit protection, filtration etc. then you should already have built it.

Hobbyists should all die. (2, Troll)

b00m3rang (682108) | more than 9 years ago | (#11817684)

Instead of helping someone build the circuits they require and possibly learn something in the process, let's just remind them that they're only above average, and thus shouldn't even bother.

MOD UP! (0)

Anonymous Coward | more than 9 years ago | (#11818423)

Whew, finally somebody with some sense!

Re:Hobbyists should all die. (0)

Anonymous Coward | more than 9 years ago | (#11819024)

In this case, if he screws up, he fries whatever he plugs in... so, yes, essentially he shouldn't try until he has the requisite knowledge.

Re:Hobbyists should all die. (1)

b00m3rang (682108) | more than 9 years ago | (#11819118)

If the poster has above average soldering skills, I'm sure he can work a multimeter.

Power supply (2, Funny)

Anonymous Coward | more than 9 years ago | (#11817608)

The device you're looking for is a power supply -- they're not just for computers. Just get one that will put out enough amps for peak demand on all your devices, mount some molex connectors onto a board of some sort, color code them by their voltages, and stick the whole shebang in an old PC case.

Of course you'll have moved from a bunch of smaller blocky transformers to a large honking thing with a fan, you'll have to wire up your own cables. Watch that you don't overload it, or you let out the magic smoke and none of your devices have power (and you'll be ventilating your room of noxious fumes). And none of it will be portable. It's going to be loud with the fan, and don't skimp on that, or it's magic smoke again.

This is probably even more misguided than the guy who wanted a raised floor.

Re:Power supply (2, Insightful)

alienw (585907) | more than 9 years ago | (#11817861)

There is absolutely no reason a power supply has to be large or needs a fan. It's possible to make one the size of a notebook adapter.

Re:Power supply (1)

DrZaius (6588) | more than 9 years ago | (#11819040)

Like, say, a laptop AC Adapter?

Re:Power supply (1)

alienw (585907) | more than 9 years ago | (#11821002)

Well, yes, except with multiple outputs and more power.

Re:Power supply (0)

Anonymous Coward | more than 9 years ago | (#11817919)

the guy who wanted a raised floor

that sounds awefully interesting - considering all the recent dupes and "ask /." comments... now, where's that article...?

Re:Power supply (1)

stoborrobots (577882) | more than 9 years ago | (#11821118)

I guess that would be this one. []

HTH. Cheers.

Wireless power! (3, Funny)

hoggoth (414195) | more than 9 years ago | (#11817613)

Forget replacing wall warts with one very large wall wart.

Where is my wireless power?!

We wont be truly untethered until we have wireless power.

(Not entirely kidding. Is there any safe way to deliver wireless power? Or am I just asking to turn my house into a very large Microwave Oven?)

Re:Wireless power! (3, Funny)

Aparthy (7792) | more than 9 years ago | (#11817677)

How about batteries?

Re:Wireless power! (3, Funny)

hoggoth (414195) | more than 9 years ago | (#11817715)

Batteries? Great.
I already HAVE a battery for my server. It weighs 50 lbs and is as big as a shoe box. It's called a UPS and lasts less than 30 minutes.

I don't think that's the answer to everything electrical in my entire house.

The battery for the Fridge will be bigger than the fridge :-)

Re:Wireless power! (2, Insightful)

raider_red (156642) | more than 9 years ago | (#11817969)

We could probably set up a wireless power system, but you can forget about the "safe" part. You could also give up any hope of ever having children.

Re:Wireless power! (2, Informative)

fm6 (162816) | more than 9 years ago | (#11818062)

Already been tried! []

Re:Wireless power! (0)

Anonymous Coward | more than 9 years ago | (#11821029)

Entertaining read. Thanks for sharing that. I am convinced the Germans possess the ray. Funny!

Re:Wireless power! (1)

dotcher (761759) | more than 9 years ago | (#11818181)

This [] , perhaps?

(Yes, I know, it's very short range, but it's a step in the right direction, certainly.)

Re:Wireless power! (1)

LordEd (840443) | more than 9 years ago | (#11820566)

RFID tags work by receiving a sensing signal, stealing a small bit of that signal as power, then uses that power to transmit its own information back. This is over a short range, of course.

Now if you look in nature, there's a really good high-voltage wireless power transfer called lightning...

Re:Wireless power! (0)

Anonymous Coward | more than 9 years ago | (#11821819)

I've always wondered whether you could just put giant Tesla coils around your entire house. I've never done the calculation of just how big the magnetic field would have to be get decent amounts of power from reasonably sized coils in the products (and how much electricity it would take to keep those babies hot), but it seems like it could work. Maybe even with low enough fields that your hard drive would survive. (Of course, it's possible we'd need 1 T fields supported by superconducting wires and don't even come near the place with a piece of iron!)

No. (2, Interesting)

Short Circuit (52384) | more than 9 years ago | (#11817679)

Can I build one with my marginally above average soldering and electrical schematic skills? Have any of you found a better way to eliminate these blocky plug-hogs?

Sure, but you'd need a transformer with multiple sets of windings, one for each voltage you want to put out, and one for your line input... But you're not likely to find one that fits your exact needs.

Nevermind concerns about drawing too much current from your device, and failing gracefully.

Re:No. (2, Insightful)

alienw (585907) | more than 9 years ago | (#11817897)

You don't need a winding for every voltage. One winding with multiple taps should work just fine. As far as current draw: a circuit breaker or fuse on the primary will do the job.

Re:No. (1)

TFGeditor (737839) | more than 9 years ago | (#11818717)

I don't get all the talk about multiple windings/taps for each voltage. Why not one voltage (the highest required by the system) with oodles of current behind it, then simply regulate it down for each voltage. I think I remember that EIN max for an LM7805 (TO220 package) regulator is 12 volts or more. Just mount all your regulators on a big heatsink, regulate and filter from the common rail, and you're in business.

Re:No. (2, Informative)

Hank Reardon (534417) | more than 9 years ago | (#11819975)

Why not one voltage (the highest required by the system) with oodles of current behind it, then simply regulate it down for each voltage.

I seem to remember from my electronics courses, many years ago that the LM series of regulators work similarly to a resistor; they dissipate over-voltages as heat. Now, while you do need some overhead voltage for the regulator to function properly, too much and you'll fry the thing. The TO220 package also had a maximum current rating of somewhere in the neighborhood of 1.5 ampres with a 6-volt DC input last time I used one and the current rating went down the higher the input voltage.

Also, don't forget you just can't hook any DC power regulator right up to the transformer as a transformer is an AC device. You'll need to add a half-wave (bleah!) or full-wave rectifier and some filtering caps to feed your regulator with. Figure .7 to 1.5 volts of voltage drop across the rectifier, and I high voltage mark of 12 volts. The LM7812 will work with 13.8 volts on the input, but you'll probably want more like 15-18 volts. At this point you're talking dropping the voltage 10 to 13 volts with the LM7805. I'd be willing to bet the regulater would, at best, smell really bad while operating and, at worst, burst into flames under significant load.

I tried many times in my youth to make some regulated circuits for running various 12-volt equipment that required anywhere from 3 to 30 ampres of current. The high-current regulators were always incredibly expensive and the lower-current (read: affordable at Radio Shack) devices always ran out of smoke.

As other people have mentioned in the articles, it's just not something that anybody other than the Telecom industry uses. The equipment is expensive as all hell and, while it makes the UPS system more simple (think 48-volts right off of huge bank of lead-acid cells), effecient, high-current DC-to-DC regulators are typically out of reach of the low budget tinkerer.

Re:No. (1)

Bishop (4500) | more than 9 years ago | (#11820026)

Using voltage regulators as you suggest is very inefficient. For example if you have a device which draws 250mA at 2.5V you are burning 2.37watts (9.5V * .25A) just to supply 0.62watts. That sucks.

Re:No. (1)

alienw (585907) | more than 9 years ago | (#11820976)

You don't want to drop more voltage than you have to across the regulator. If you have 2 amps at 12V coming in, and 2 amps at 2V going out, you are losing 10 * 2 = 20W on that regulator. That's one HOT regulator. That will require a big heatsink and fan -- not to mention it's really inefficient.

Re:No. (1)

TFGeditor (737839) | more than 9 years ago | (#11821601)

The Ask Slashdotter is looking for convenience, not power efficiency.

And as to a previous poster's reference to rectifying/filtering, well, I took for granted that that was understood.

The original 7805 reference was a "jumping off place" for searching for suitable regulators. Newer versions come in a variety of packages, from tiny surface-mount to TO3 and larger packages. The big ones with a proper heatsink and mounting can dissipate a lot of heat, and the new designs are a lot more forgiving with large in/out voltage differentials. There are also adjustable output versions easily controllable with a potentiometer or switchable resistor network.

If you want to get fancy, you can go whole hog with a switching supply rather thana straight linear.

Either way, we're talking a power supply, not rocket surgery.

Re:No. (1)

PurpleFloyd (149812) | more than 9 years ago | (#11820979)

First, why would you need a multitap transformer to output different voltages? Simply set up a switch-mode power supply, like in a computer PSU: use a bridge circut, transformer and a couple of filter caps to get a few hundred DC volts, then use a transistor to pulse the output at a few hundred kilohertz. Output voltage equals duty cycle times input voltage; run it through a simple filter and you're done.

As for overcurrent protection, there's been a device around as long as mankind has harnessed electricity: the fuse. It's cheap, easy to find, fails gracefully (as long as going open-circut won't kill anyone) and easy to integrate into almost any device. If blowing fuses is a regular concern (why?), then use circut breakers instead.

Re:No. (1)

alienw (585907) | more than 9 years ago | (#11821117)

I take it you know very little about switching power supplies. Just so you know, they are rather complex and require a solid background in control theory, electromagnetics, and electronics to design and build. The EMI issues are challenging, and it's not a simple matter of applying a fixed duty cycle (since the voltage is proportional to the load).

Re:No. (1)

chthon (580889) | more than 9 years ago | (#11822044)

Yeah, and he should not forget the fire extinguisher as he tries to build such a thing.

Liberator (3, Interesting)

Zakir (849137) | more than 9 years ago | (#11817723)

This doesn't fit what you're looking for exactly, but it fill help the problem of having to plug wall worts into your power strip. It is basically a 12 inch extension cord that plugs into your power strip so that the transformer doesn't take more than one outlet up.
"Get full use of your power strips and UPS outlets with this premium power cable from Cables Unlimited! Just plug this cable between your bulky power adapter and any unused outlet and this revolutionary designed space saving cable acts as a 1' extension, giving you a little extra length to get into hard to reach places." SearchTool s/item-details.asp?EdpNo=392776&CatId=1284

Correct Link! (1)

Zakir (849137) | more than 9 years ago | (#11817879)

Here's the correct link.

Re:Liberator (1)

Profane MuthaFucka (574406) | more than 9 years ago | (#11817920)

If you live in Austin just go to Altex. 6 inches though, a better length for the purpose.

Re:Liberator (4, Informative)

Tintivilus (88810) | more than 9 years ago | (#11818065)

I'm actually kinda partial to Dr. Ferd's Wart Remover [] . It's only two-wire (how many grounded wall warts do you have?) and it has a nice big box on the outlet end so you can use a pad of double-sticky mounting tape to hold the mess together.

In places where I have a bunch of wall-warts hanging around, I like to use a Furman Pluglock [] power strip to keep then together and strapped down. I broke down and bought a couple of these when I got sick of having random things come unplugged in the pile of crap under/behind my desk, and they turned out to be a great buy. They're built like tanks, too.

Re:Liberator (3, Interesting)

MarkGriz (520778) | more than 9 years ago | (#11819185)

"I'm actually kinda partial to Dr. Ferd's Wart Remover"

Seems a bit overpriced at $6.99

The cheapest source for these I've come across is here [] $8.99 for a 5 pack.

They have tons of variations on this item too, including dual plugs, flat plugs (so you can put furniture up against them), etc.

Re:Liberator (1)

MindStalker (22827) | more than 9 years ago | (#11819888)

Wow, its actually called a "Wall Wart Remover" for some reason I'm slightly disturbed that "Wall Wart" has become official terminology.

Re:Liberator (1)

LazyBoy (128384) | more than 9 years ago | (#11818749)

Similar item here [] .

Your link. (3, Interesting)

Murphy Murph (833008) | more than 9 years ago | (#11817748)

The link you provided to the "ELK-PD9 Power Distribution Module" is telling.

Do you understand why devices such as that are used?

A power distribution module such as that is used to power devices like remote video cameras, remote security sensors, and other remote monitoring devices.

Key word being remote.

Devices such as these use structured wiring with data (video) and power coming in to the device over one cable bundle. This is done for ease of installation to the remote site, and because the security camera on your neighborhood Target store being 100 feet from the nearest power outlet makes a wall-wart is unfeasible not unsightly.

Re:Your link. (1)

Zakir (849137) | more than 9 years ago | (#11817855)

Sorry, I must have given the wrong link. Here's another link to it.

Re:Your link. (0)

Anonymous Coward | more than 9 years ago | (#11818200)

I'm sorry for the confusion - I was refering to "Mailtodelete", the asker of this Ask Slashdot question.

Why? (4, Insightful)

Guspaz (556486) | more than 9 years ago | (#11817750)

Why bother? If each device has it's own power brick, it's safer. If one fails, the others won't.

If you combine all of them into a single point of failure, you might reduce what you think is an "eye sore" but at the cost of a higher risk of failure.

Is making your setup less sturdy worth a cosmetic fix?

Re:Why? (2, Insightful)

voisine (153062) | more than 9 years ago | (#11817798)

never had a wall wort fail... ever. ac's gone out many times. I think the dc power supply is not the weak link in the chain unless you've got a battery backedup generator backed up ups at an earthquake/hurricane/tornado proof co-lo somewhere.

Re:Why? (3, Insightful)

Guspaz (556486) | more than 9 years ago | (#11818033)

All the more reason to continue using wall worts. You're moving from a simple wall wort to a much more complex system. One that is akin to a computer power supply. And I've had MANY computer power supplies fail.

Re:Why? (5, Informative)

voisine (153062) | more than 9 years ago | (#11818307)

Good point. I've had atx power supplies fail in spectacular fasion. Scared the crap out of me. I bought a used one and the local computer junk store, plugged it in, turned around, and then *KABLAM*. It was loud enough to make my ears ring. Then thick black acrid smoke started pouring out the back. I took it apart to investigate what the hell happened. It was a fairly large blown capacitor. I had no idea those could explode like that until after this little episode.

Re:Why? (3, Funny)

bluephone (200451) | more than 9 years ago | (#11820732)

Too much of the smoke escaped. Capacitors are smoke reserviors. It sounds like ther ewas a clog on the drain side of the capacitor, and the pressure of the smoke popped the capacitor. Since you say it was a used PSU, it could be that there was a build up of burnt electrons in it, and they clotted.

Re:Why? (1)

chthon (580889) | more than 9 years ago | (#11822050)

Mod this one Funny, :-)

Re:Why? (1)

alienw (585907) | more than 9 years ago | (#11817916)

The only reason a power supply might fail is if it is built using cheap, shoddy, or underrated components. A decently made power supply will work for decades without as much as a hiccup.

Re:Why? (1)

Guspaz (556486) | more than 9 years ago | (#11818053)

That depends how hard it has to work, and how much power filtering it has to do. My house has dirty power. I've had half a dozen power supplies fail in the period of a year or two. One of them was a high-end Antec TruePower Gold unit, which at the time of purchase was very close to the highest-end product sold (By an already "premium" PSU company).

On the other hand, I've never had a wall wort fail, not even the cheapest of them, made of the crapiest of components.

Re:Why? (1)

MindStalker (22827) | more than 9 years ago | (#11819859)

Though you do hear of the occasional recall due to potential to cause a fire.

Re:Why? (1)

GoRK (10018) | more than 9 years ago | (#11820724)

If you have AC that's so bad it destroys power supplies and you own your home, you should seriously consider some decent power conditioners. They cost a few hundred bucks but can seriously help your power on the whole house.

Re:Why? (1)

theLOUDroom (556455) | more than 9 years ago | (#11820440)

The only reason a power supply might fail is if it is built using cheap, shoddy, or underrated components. A decently made power supply will work for decades without as much as a hiccup.

Are where do you think most consumers place "Wall-wart quality" only their list when they go out to buy new widgets?
Rest assured that your wall warts (and line lumps) are a cheap as the manufacturer could get them from the third world. See the recent Dell recall for an example.

Decent components cost money. Derating components so they last longer costs more money.
I wouldn't count on the cheap electrolytic capacitors in your wall warts lasting for decades.

Re:Why? (1)

unitron (5733) | more than 9 years ago | (#11820639)

"I wouldn't count on the cheap electrolytic capacitors in your wall warts lasting for decades."

If it's an AC to AC wall wart, then it's probably nothing more than a step-down transformer. If it's AC to DC then they probably just added a diode or two. If you open up the piece of gear to be powered you'll probably find the filter caps (such as they are)in there (and maybe even a 7805-type regulator).

A non-home solution (2, Informative)

Yobgod Ababua (68687) | more than 9 years ago | (#11817801)

It's designed for large scale server rooms, and as such won't particularly adapt to what you want, but this does show that others have had the same thoughts and are applying them to various niches. They do also explain what they see as the benefits of this arrangement. []

Also... (2, Insightful)

Yobgod Ababua (68687) | more than 9 years ago | (#11817848) that I think about it, so could just obtain a hobbyist DC power supply of sufficient amperage and hook all your devices up to the appropriate voltages.

It's possible that a spare PC power supply might even suffice, but be careful that you get one that doesn't detect and auto-off when a motherboard isn't plugged in.

Lots of power supplies from somewhere like this:

Watch out for unexpected shorts! (2, Interesting)

RandomJoe (814420) | more than 9 years ago | (#11817857)

If you do this, be sure to check for unexpected shorts. A piece of equipment we install at work has a big warning to only use it with its own power supply. Of course, it's so much easier to tie it to the beefier supply running the other panels it associates with, so many techs do just that. And it works just fine. Until...

Turns out, due to some wierd design decision, the common pin for the serial port isn't really "common". If we plug into it with our laptops, and then plug the laptop into AC power (with ground pin intact on the PS) it shorts the power supply through the serial port, the laptop ground, back to the grounded power supply on the main panel. (This little panel "doesn't require" grounding - wonder why...)

So, if your devices all connect to each other in some way make sure this sort of loop doesn't occur. Especially if you use a single beefy supply - you might be in for fireworks!

Re:Watch out for unexpected shorts! (1)

squant0 (553256) | more than 9 years ago | (#11821161)

Ground loops are a pain. Thats why you need to have isolation transformers on the input of all devices.

Ever wonder why this type of situation doesn't happen in your home theater? Cause of isolation transformers.

As for the whole reason for this topic, I'd say stick with the individual AC-DC converters. They are quiet, small, put out very little heat, and work with your components. If you try to roll your own, you may learn some stuff, but you will most likely end up with a sub par item.

OMG... (2, Informative)

malejko (216594) | more than 9 years ago | (#11817904)

I swear reading most of these ask slashdot's are slowly killing me from the inside out.

If you're pissed that a block takes up like 3 ports on a surge protector, get a short extension cord like this: =CTLG&category_name=CTLG_009_001_003_000&product_i d=61-2755 [] , but if you want ONE DC converter with various voltages, you're just asking for trouble. An eyesore they may be, but they're quite safe for the most part and do their job properly.

Re:OMG... (1)

Slashdot Junky (265039) | more than 9 years ago | (#11818552)

I am using this to make better use of the outlets on my power strips. as p?T1=121+2550

-Slashdot Junky

Re:OMG... (1)

TFGeditor (737839) | more than 9 years ago | (#11818786)

The parent is NOT offtopic.

See you in MetaModeration.

PC Power Supply (1)

DavidYaw (447706) | more than 9 years ago | (#11818121)

Get a normal PC power supply. It's got output voltages at 5 and 12 volts, which should cover most of your equipment (a lot of stuff that has a 6 volt wall brick works fine on 5 volts). It's also got a 5 volt line that's always on, if you've got something that you don't want controlled by the switch.

Re:PC Power Supply (2)

WasteOfAmmo (526018) | more than 9 years ago | (#11818808)

The parent gave what I was going to suggest but I will take it a step further:

The PC power supply will give you the wattage/current you need to operate most if not all your DC devices. You will need to wire the power supply so that it will stay on without being hooked up to a motherboard. For ATX p/s' here [] is an article on how to do it.

That will give you +/- 5 VDC and +/- 12 VDC. To get the 9 VDC used by many devices you need to add some circuitry. Basically you want to use a voltage regulator to reduce the +12 VDC to 9 VDC. This can be done with as few as 1 part but adding a few more for safety is recommended. Here [] is a quick primer on the LM78XX series voltage regulators (your looking for a 7809, like this [] ) .

Regardless of what some posters say this does not have to be a big ugly noisy box. You will need some sort of case with ventilation for the ATX p/s and additional circuit. The fan in the ATX p/s should be enough to cool both the ATX p/s and the additional voltage regulators. If you use a bypass transistor to increase the current output of your voltage regulator or if you run the voltage regulator close to the max current you should attach them to a heat sink.

Also, from places like Digikey (or Jayco in AU) you can by barrel connectors (like the wallwarts have) to hook up so that you can plug/unplug your low voltage cables from your spiffy new box.

Overall this is a great first project to try so hop to it. Just make sure to post all the pictures and description of your project so we can /. your server. :-)

The above is not intended as a step by step howto instruction. It is intended as a starting point to research the correct way to construct your project. Tread carefully. You can also find lots of electronics sites that probably have the circuits you want and you can post to sci.electronics for help.


Re:PC Power Supply (1)

OdieWan (757584) | more than 9 years ago | (#11820786)

Another fact to keep in mind is that most PC power supplies (switching power supplies in general, actually) are unhappy running unloaded. A few k resistor from each of the rails to ground will be enough to keep it going, although I'd say this is an excellent chance to add some lights. Lights make everything better!

Re:PC Power Supply (1)

artemb (2016) | more than 9 years ago | (#11819474)

Keep in mind, though, that quite a few ATX power supplies will not work properly unless they are loaded. Usually they require that you draw few Amps on +5 or +3.3V lines. Without sufficient load output voltage may be not what you'd expect to see.

You can thank me later (0)

Anonymous Coward | more than 9 years ago | (#11818294)

Others have posted similar devices elsewhere in this thread, but as an AC mine will get buried. The one I list is cheaper than the rest and is available at a place many of us have actually heard of:

Micro Center 10" Power Cord []

Building it yourself might be fun (0)

Anonymous Coward | more than 9 years ago | (#11818780)

You're basically talking about a niche market application, which is not to say that it's unheard of, but if you did find it, it would be horrendously expensive.

Want to build one yourself? The easy way is to take apart a bunch of RadioShack universal wall warts, mount them in an enclosure, wire them up together with AC, add an AC plug, and do some cable management with the resulting output wires. Should take a couple of hours, and you wind up with a big box filled with tightly-packed transformers (watch out for ventilation).

Now, let's say you want to do it right. You'll need a single transformer to take the line voltage down to 32V, or 48V, a diode bridge, then some filtering caps (this is a basic, unregulated DC supply). From there, you will take this 32-48V rail, and use a variable switching converter on each output channel to bring the voltage down to the right level. If you need cleaner power, there are even circuits to take a variable switing converter, and use that to feed a variable linear converter for super clean power.

Some stock switching circuits are available in Linear Tech's Application note [] on switching regulator circuit collection. My favorite introduction to switching regs is Application Note 25 [] , Switching Regultors for Poets, bless Jim William's heart and drawing abilities.

Hope this helps

This wouldn't be too hard... (1)

Mike1024 (184871) | more than 9 years ago | (#11818829)

This would be entirely possible thanks to modern power electronics, if you really want to. Honestly I'm not sure it's worth the bother, but here you go:

Get a normal DC power supply that will supply the largest voltage you need and more current than you need. Or build one. Whatever.

Go to some electronics shop (If you're in the UK, Maplin [] are good) and get some Voltage Regulators [] . These are basically integrated circuits that can take in a wide range of voltages and output a fixed voltage.

Connect the voltage regulators' inputs to the output of the main power supply.

Connect the voltage regulators' outputs to your devices.

NOTE: Lots of external computer bits ask for unusual voltages. That might be a bother.

NOTE 2: There will be lots of books availiable on this topic. Look for 'Power Electronics' on Amazon - or in a local university's library (since textbooks are expensive). Don't get a book that's too old - some of this stuff is pretty recent technology.

NOTE 3: I am no expert. While I believe my design would work (and be pretty efficent), I can't promise anything.


Re:This wouldn't be too hard... (1)

klaasvakie (608359) | more than 9 years ago | (#11820656)

While you are correct about the regulators being able to ourput the desired voltage, they will not usually be able to provide enough current.
A normal LM7805 in a TO220 package can deliver 1 Amp with a heatsink (typically, check the datasheet for exact info).
That is only 5W. In some cases (external modem) you might be able to get away with it, but in others (ethernet hub) you might not.

You can't afford to do it right (2, Informative)

ikeleib (125180) | more than 9 years ago | (#11818934)

DC power distribution is used in telecomm applications. They use a 48V bus and use DC/DC converters to get the required voltages. The DC/DC converters are expensive, and the AC->48V converter is also expensive.

You could just get auto-adapters for all your crap and then use an AC->12V converter. However, I imagine that this is more work than it's worth.

Why not just do what everybody else does and get more outlet strips?

Re:You can't afford to do it right (1)

bill_mcgonigle (4333) | more than 9 years ago | (#11820581)

Why not just do what everybody else does and get more outlet strips?

Well his original goal was cosmetic, so he wants to do something different.

DC travels just fine over short distances. If I were him I'd just cut the ends off of the DC supplies, solder in a 10' length of wire, and put the wall-warts on the floor. Run all the lengths in a conduit up to the devices.

Then don't step on the rocker switch on the power strip. DAMHIKT.

Re:You can't afford to do it right (1)

chthon (580889) | more than 9 years ago | (#11822071)

Yes, and there is a reason why they use 48V.

I haven't seen it mentioned in the whole discussion, but a low voltage normally provides larger current.

One of the examples above mentioned 5W, 1A. If your cable is not thick enough or too long, you will have a serious voltage drop at the end of the line, unless you can sense the voltage there and feed it back to the regulator.

That is why 48V is used. It is not extremely dangerous (DC is more dangerous than AC because of elektrolytic effects on the blood) and the current through the wire will be less, which means a lower voltage drop, which means you can reach out farther.

Only in America (-1, Offtopic)

Anonymous Coward | more than 9 years ago | (#11819527)

Surely they have DC power distribution in Washington? (And I've heard of DC comics somewhere too...)

This could be the easiest/ cheapest way (1)

Immercenary_2000 (863998) | more than 9 years ago | (#11819855)

You already have all of these transformers in the original plugs right? Why not just find a suitable container to put a power strip or two in and have all of the transformers plugged into that? You could even change the connectors on the end of each transformer so that you could just build the jack into the box and just plug your device into this box that way it wouldn't be just a box with wires coming out of random holes.

Something to be said for -48vdc... (1)

mr. methane (593577) | more than 9 years ago | (#11820409)

I recently cleaned up my computer rats-nest at home and located no less than five wall-warts plugged in but with no equipment connected to them. Some I could remember; the old linksys router I bricked with a firmware idea, the DSL modem I replaced with cable a few months ago, and several others I just have no clue about. They join the existing crate full of cables in the garage.

Some accessory manufacturer will catch on and start building devices that don't each have a different shaped (linksys), voltage (belkin) or design (DELL!!!!) power brick, and they will clean up - moneywise, too.

Use the IC, dammit (1)

mnmn (145599) | more than 9 years ago | (#11820441)

ICs like this [] should step down 110V to 12V, and a bridge of diodes and eeny weeny capacitor should make it DC. I just dont see why would anyone need big coils. I've increasingly been seeing 3-pin ICs that are power regulators, some that can handle plenty of wattage with a heatsink, and are TINY. I fail to understand why manufacturers are still packaging the ugly adapter. My new voip device from linksys, a PAP2, is small sleek, and comes with a giant unslightly adapter. Its the stereotypical engineer thinking... input=12V and design the rest of the PCB from there. Marketing just looks away.

Re:Use the IC, dammit (2, Insightful)

robert bitchin' (765408) | more than 9 years ago | (#11820559)

The coils are there to provide electrical isolation. If they were left off then you'd be exposed to at least one side of the 120VAC in what may be a poorly isolated unit. The coils are large because electromagnetic inductive efficiency drops with the input frequency. Efficiency is the major reason why the switching frequency in PC switching power supplies are so high, most can get away with just using air cores rather than metallic cores.

The IC you mention is useful for completely isolated devices (no external connections) such as night lights.

Re:Use the IC, dammit (1)

unitron (5733) | more than 9 years ago | (#11820719)

Pulse width modulators have to be fed DC so the diode bridge and some of the filtering would have to come first. However, this would still result in a power supply without transformer isolation, a thoroughly dangerous situation from both a shock and fire hazard standpoint (and using the gear with this supply instead of the one supplied by the manufacturer or at least a similar replacement may lead to a denied insurance claim if you start a fire or electrocute somebody).

Re:Use the IC, dammit (2, Insightful)

LordEd (840443) | more than 9 years ago | (#11820752)

The problem is efficiency. You can drop 120V to 12V on this, but that means that the regulator has to burn up 108 V. If you're drawing 1A, then that's 108W being wasted just to step down the voltage, and 12W actually being used by the device (90% wasted).

However, a transformer can step down voltage with a very high efficiency (google says 80 - 90% efficient).

A stepped down signal of 12V and 1A means an input of 120V and 0.1A, plus loss due to resistance. With 90% efficiency, that means an input of about 13W for the same output as the regulator alone.

Of course, there will be some loss due to using a DC regulator after the transformer, but nowhere near the 108W lost above.

Re:Use the IC, dammit (1)

unitron (5733) | more than 9 years ago | (#11822138)

The Texas Instruments product the OP linked to is not a series pass regulator, it is a pulse width modulator, although he didn't seem to understand the proper use of it, either, as PWMs aren't designed for AC input.

Re:Use the IC, dammit (1)

alienw (585907) | more than 9 years ago | (#11821086)

You are smoking something. A linear regulator that converts 110V to 12V would be about 5% efficient. That means that it will run about as hot as a P4 when supplying any real load. Switching power supplies can get pretty small, but they are difficult projects even for an experienced electrical engineer.

Re:Use the IC, dammit (1)

unitron (5733) | more than 9 years ago | (#11822193)

As I point out elsewhere the TI device the OP linked to is a pulse width modulator, not a linear, i.e., series pass, regulator.

Re:Use the IC, dammit (1)

chthon (580889) | more than 9 years ago | (#11822087)

It has to do with safety and cost. These are most easily met by this setup.

Safety = human safety and equipment safety.

If you want to run 220V (110V) into expensive equipment, you have to design for it, which makes the equipment more expensive, and should something happen, your expensive equipment can get badly (completely) damaged. Ever wondered why PC power supplies are built in sturdy inox casings ?

Human safety is reached by providing an isolating transformer, and by stepping down the voltage to the equipment, you can design the equipment cheaper.

It is possible to shrink the transformer, but then you have to step up the AC frequency. For that you will need a complex circuit using thyristors (or MOSFETS) and an extra (small) transformer to power the thyristor (MOSFET) controlling circuit. This will bring up the cost again.

Make device transformers external, easy conversion (2, Interesting)

Eravnrekaree (467752) | more than 9 years ago | (#11820622)

As far as the things we plug into wall outlets, I think it would be very wise for all electric devices that uses a transformer to use an external transformer rather than build it directly into the device. this way, if you later switch to solar you can run the device directly off the DC from the solar panel, only perhaps having to adjust the voltage. DC is preferable with solar technology, which produces DC output, whenever possible, since an invertor to convert from DC to AC cuases you to lose energy and are somewhat innefficient. DC works best with short runs as well, such as from the panels into your house. AC for distribution was chosen since the voltages can be easily stepped down after high voltage runs, since high voltage carries better over long distances. It would be great if we could find clean, renewable, safe, practical, non-toxic energy sources, like improved solar, so we could get rid of AC and its EMF fields and all of those ugly high voltage power lines crossing the country.

Re:Make device transformers external, easy convers (2, Insightful)

alienw (585907) | more than 9 years ago | (#11821098)

Please, if you don't know anything, shut up. Converting from DC to AC is just as efficient as converting from DC to DC. Unless your solar cells happen to put out the exact voltage your device requires (they don't), you still need some kind of switching power supply. Whether it takes in or puts out DC or AC is almost completely irrelevant.

Re:Make device transformers external, easy convers (1)

Fritzed (634646) | more than 9 years ago | (#11821133)

I was going to mod you a troll, but since you're other posts in here are reasonable, you must honestly be missing the point.
I believe the original poster's point is that if the converter is built in, then you will end up having to convert the energy twice. If you use solar, and get DC current from it, then you could convert from DC to DC with acceptable power loss. However, if there is a converter built into the device, then you have to convert from DC to AC simply to power the device that will convert back from AC to a different voltage of DC. This means you had to convert twice and experience power loss twice.

-> Fritz

Easiest solution: (1)

NemosomeN (670035) | more than 9 years ago | (#11821039)

Mod a computer power supply. I got my 550 Watt power supply for $10 plus shipping, and it works great. (Was supposed to be free shipping, but with that good of a deal I wasn't going to bother with it).

furman? (0)

Anonymous Coward | more than 9 years ago | (#11821292)

I used to have a 1-rack space device that did just that... it was marketed for musicians to power rack gear. I think it was made by Furman, but I'm not sure.

At the risk of sounding like a moron (1)

OAB_X (818333) | more than 9 years ago | (#11821917)

Here is my 2c worth.

Buy a bunch of little extension chords (or shornten them yourself). You take your chord, plug one device in on either side of the end, and the other end into the wall/powerbar. You can now hide the worts in a big clump out of sight, and can also free up space in your power bars.

Basically, you want to just move the plug onto a smaller footprint, so, extend the plug a bit

|device|----wire----|wort|---minichord---|powerb ar |

hope that helps
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