Sensibly Powering DC Technology? 90
splatnet asks: "Having upgraded my PC to a Mac Mini all my IT kit is now DC. The Mini, my flatscreen, external USB HDD, USB DVD writer, JBL speakers, ADSL/Wireless Router. I have practically the same amount of space taken up for transformers as I do computer equipment! Has anyone found/invented a way to power multiple DC devices (all with slightly different power requirements)? I'm thinking in terms of space/convenience/running costs etc." It would be neat if there was a DC power source that could be tuned to a specific voltage, as well as modular plugs to fit your various devices. Is there anything out there that comes close?
Froogle search: Universal Power Adapter (Score:3, Informative)
A Froogle search for Universal Power Adapter [google.com] found this: Coby CA-33 Universal 110-/220-Volt AC Power Adapter [buy.com], but it only supplies one voltage at a time.
It would be great if these were available to supply multiple voltages. A problem, however, would be that all devices powered would need to have the same ground, a condition that might not exist. Deciding whether all devices had the same ground might be tricky.
Power electronics can be tricky (Score:3, Informative)
Requirements (Score:4, Informative)
The requirements seem to be:
* 5 output ports;
* for each port (or via a central control panel) configuration for output voltage on that port, continuously variable from 2 VDC to 24 VDC;
* each port capable of 50 watts without significant voltage drop;
* a handful of accessory connectors / converters including 1 plug male -> 4 plugs female, big diameter plug to small plug, extension cables, etc.
* silent power supply if possible / air cooled, or very, very quiet fan
I'd think that a sealed design with a large external heat sink is best. I have a cat and the cat hair ends up all over things on the floor, which is the power bricks and one of my PC's, making cleaning a regular (once / 2 months) thing to lengthen lifespan / prevent overheating).
I don't care about weight too much. It should be well grounded.
Another wonderful idea is the ability of it to use as input a 12VDC car/marine-deep-cycle battery, so if the power goes, I can still use my accessories.
Re:Guitarists might have some ideas (Score:3, Informative)
Which is bugger all use for this situation, where everything wants its own different voltage, unfortunately.
Re:Requirements (Score:3, Informative)
The main power bus will be about 170VDC, since the power brick will presumably be AC powered.
However, for 2V a 50W supply is 25A - that takes BIG wire to carry, and special connectors.
Generally, devices don't require much more than 10A. However, they often do require up to 50W. Anyway, this should not be a problem.
See the power requirements - you are going to have a problem without forced air cooling, and if you want that to be quiet you have to have a fairly large device so that you can move lots of air slowly.
80% efficiency is unacceptable here. With decent quality components, you should be able to get up to about 95% efficiency out of a switching power supply, and perhaps even more. Besides, average power should be a lot less than 50W, more like 12W.
You also run into the possiblity of ground loops - you have one ground path from the computer to the gizmo, and one ground path from the gizmo to the power supply.
A shared ground is absolutely unacceptable in this application. This won't just cause noise, it will cause lots of smoke. All devices powered by a DC adapter assume they are running off of a transformer-type power brick, so they connect the grounds as they see fit. If the grounds are not isolated and you connect one device to another, chances are good their ground arrangements won't be compatible and you will short out something and fry one or both devices. I've personally seen two PlayStations get fried because they were connected to different phases of an AC line of an apparently miswired house and were connected together with a link cable. Apparently, the designers didn't think to isolate the console from ground in the power supply (although it could have been grounded through something else, like the TV).
A good solution would be to have an isolated switching supply (one that uses a transformer) for each output port. This will be almost impossible to do cheaply, though. I doubt such a device could be made for under $150, even with mass production in China.
Re:This could be done but probably shouldn't. (Score:3, Informative)
Generally, a voltage requirement like 14.1V means the peripheral will accept anything from 12V to 16V but they don't want you using a third-party adapter. Even switching adapters are usually off by half a volt or more, and regular transformer bricks are +/- 30% or more.
Also, you don't need heavy transformers to put out high currents. Read about switching power supplies sometime. With those, the transformer size depends mainly on switching frequency.
You do bring up a valid point. I think the main reason nobody makes such a device is because it's impossible to make idiot-proof. If someone doesn't set the voltage or polarity properly, they will be very pissed when they fry the device. When you have multiple outputs, this is extremely easy to do.
Re:I'm waiting for the day (Score:5, Informative)
You can't just step down DC power, that is one of the many reasons AC is ubiquitous when most electronics operate on DC.
Re:I'm waiting for the day (Score:3, Informative)
AC won't fry the living sh*t out of you like DC. You have a far better chance of living through an AC electrocution.
FALSE (Score:3, Informative)
Many ATX-type switchers use a flyback-style arrangement, where each of the voltages is obtained from a tapped transformer. Regulation is often performed by monitoring the voltage on one line, and if the loads on the other lines are within the design specifications of the supply then the other lines are guaranteed to be regulated if one is.
In any PC, it's pretty easy to guarantee that the loads are within specs, as the load ranges of a properly designed supply are quite wide. Unfortunately, it is basically impossible to maintain regulation in these designs if some of the lines have zero load, ESPECIALLY the line that is monitored.
Higher-end PC power supplies (Such as some of the top-end Thermaltake and Antec units) use independently controlled switching supplies for each output, and will run fine with zero load on some of their lines, but 90%+ of ATX supplies are not built this way because it's significantly more expensive.
If this doesn't make sense, I suggest reading up on switching power supply theory. For optimum operation, switching power supplies depend on there ALWAYS being current flowing through an inductor. Whether this happens is dependent on switching frequency, inductor size, and the value of the load resistance. The higher the load resistance is, the higher the inductor size and frequency needed to keep current always flowing in the correct direction. If an ideal (no resistive losses) power supply is operated within this region, its output voltage will always be a direct function of the input voltage and the ratio of on/off times of the switching element. If the load resistance is too high, this no longer holds true and the switching circuit is no longer regulated. In non-ideal circuits, resistive losses in the inductor and switching element will impose a maximum load in addition to minimum load.
If you add circuitry that monitors the output of the switching circuit and changes the switching waveform appropriately if it is out of tolerance, you can maintain regulation outside of the aforementioned regions of operation (specifically the low-load conditions), although efficiency will often suffer in these regimes. As I mentioned before, most PC power supplies do not implement this independently for each output simply because it is not necessary, in any situation the PS was designed for, regulation on one line will imply regulation on all lines because of the way the loads are balanced. But if you leave one line totally unloaded, regulation is no longer guaranteed.
Ham Radio suppliers carry these power supplies. (Score:4, Informative)
For example, I googled and the first entry under "ham radio supplies" was aesham.com, their catalog is downloadable as a PDF. On page 82, they have power supplies from Astron, Daiwa, Diamond, AIM, etc. Most of them only output a single voltage but are adjustable, however a few units have multiple voltage outputs. Many of these units have big geeky analog gauges on the front indicating the power draw, for extra nerd appeal.
A few pages later (pg 84) they have power distribution busses, for feeding multiple units from the same voltage. Just what you're looking for. And Hams are totally obsessed with clean power, so you can set up rigs with pure, clean power and no grounding problems.
Check out some other Amateur Radio suppliers and gaze through the catalogs, and stand in awe at true hardware geeks that have been doing this for about 3 times as long as computers have even existed. I learned more about electronics from Ham Radio catalogs than anywhere else.